US5190019A. Interlock circuit for de-activating an engine. Google Patents
Publication number US5190019A US5190019A US07/757,178 US75717891A US5190019A US 5190019 A US5190019 A US 5190019A US 75717891 A US75717891 A US 75717891A US 5190019 A US5190019 A US 5190019A Authority US United States Prior art keywords magneto triac engine capacitor circuit Prior art date 1991-09-10 Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.) Expired. Lifetime Application number US07/757,178 Inventor Arthur J. Harvey Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.) Delta Systems Inc Original Assignee Delta Systems Inc Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.) 1991-09-10 Filing date 1991-09-10 Publication date 1993-03-02 1991-09-10 Application filed by Delta Systems Inc filed Critical Delta Systems Inc 1991-09-10 Priority to US07/757,178 priority Critical patent/US5190019A/en 1991-09-10 Assigned to DELTA SYSTEMS, INC. A CORP. OF OHIO reassignment DELTA SYSTEMS, INC. A CORP. OF OHIO ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: HARVEY, ARTHUR J. 1993-03-02 Application granted granted Critical 1993-03-02 Publication of US5190019A publication Critical patent/US5190019A/en 2011-09-10 Anticipated expiration legal-status Critical Status Expired. Lifetime legal-status Critical Current
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Classifications
- F — MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02 — COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02P — IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
- F02P11/00 — Safety means for electric spark ignition, not otherwise provided for
- F02P11/04 — Preventing unauthorised use of engines
- F — MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02 — COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02P — IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
- F02P11/00 — Safety means for electric spark ignition, not otherwise provided for
- F02P11/06 — Indicating unsafe conditions
Abstract
A safety circuit coupled to an ignition circuit and a magneto coil for disabling an engine that powers a riding lawn mower. The circuit includes a triac which is rendered conductive in response to a sensed unsafe condition. The triac turns on to short the magneto coil and prevent generation of a spark plug energization voltage. A capacitor coupled to the triac gate electrode charges in the event an unsafe condition is sensed and is prevented from charging when operating conditions are safe.
Description
The present invention concerns a safety control circuit for controlling the operation of a combustion engine having a magneto for energizing a spark plug and more particularly concerns a safety control circuit for use in controlling operation of a riding lawn mower.
U.S. Pat. No. 4,369,745 to Howard, which issued Jan. 25, 1983, concerns an interlock circuit for a motor vehicle that is powered by an internal combustion engine. The internal combustion engine is coupled to a magneto ignition system and includes circuitry for inhibiting starting of the engine under certain conditions. The interlock circuit is electrically connected to an ignition switch and three safety switches. One safety switch opens when the transmission to a traction drive is engaged, and a second safety switch opens when a power take-off from the engine is engaged. The disclosed and preferred use of the ignition interlock of the ‘745 patent is with a riding lawn mower having a third safety switch which opens whenever the operator gets off the lawn mower.
The switches prevent operation of the lawn mower solenoid starter in the event an unsafe condition is sensed. The engine is also disabled subsequent to starting of the engine if the seat becomes unoccupied and either the transmission or power take-off is engaged. If both the transmission and power take-off are disengaged, the operator can get off the seat and the engine will continue to run. The disclosure of the ‘745 patent to Howard is incorporated herein by reference.
FIGS. 1a and 1b depict prior art safety interlock systems commercially available from the assignee of the present invention. An SCR device coupled to an engine magneto coil short circuits the magneto coil under certain conditions. Once the engine is running, the SCR turns on to deactivate the engine if the seat switch is open and one or both the transmission and power take-off switches are also open. If the seat switch opens and both the transmission and the power take-off switch are closed, the engine continues to run since this switch configuration means both the transmission and power take-off are disengaged and in a safe operating condition.
The circuit depicted in FIG. 1a responds to negative pulses from the engine magneto. The circuit depicted in FIG. 1b responds to positive pulses from the engine magneto. Thus, two separate circuits, one for the FIG. 1a embodiment and the second for the FIG. 1b embodiment are required to accomplish the same safety control function for different ignition systems.
Marlin Electric of Milwaukee, Wis. produces a commercially available circuit for disabling an engine. The circuit includes a triac that is activated by a battery voltage which is coupled to a triac control electrode when an unsafe condition is sensed.
The present invention concerns a safety circuit for inhibiting operation of an engine having a spark plug that is energized by a magneto coil. The circuit includes a triac coupled to the magneto coil for shorting the magneto coil and thereby inhibiting engine operation. A circuit coupled to the triac activates the triac with a magneto generated signal at the triac gate when the engine is running and an unsafe condition is sensed. Once the triac is rendered conductive, the engine is quickly disabled. The use of a triac eliminates the requirement for two separate circuits to accomplish the same safety control function for different engine ignition circuits.
A safety circuit constructed in accordance with the present invention also avoids false sensing of an unsafe condition. The safety circuit utilizes switch contacts forming part of an ignition circuit that controls starting of the engine. If moisture condenses on these switch contacts, the engine may continue to run when, in fact, an unsafe condition exists. Use of a safety circuit constructed in accordance with the present invention makes false sensing of a safe condition much less likely.
FIG. 1a is a prior art circuit sold by the assignee of the invention for disabling a combustion engine;
FIG. 1b is a prior art circuit sold by the assignee of the invention for disabling a combustion engine;
FIG. 2 is a schematic diagram of a circuit constructed in accordance with one embodiment of the invention that disables an engine in response to a sensed condition;
Fastest Way to Check a Coil (Magneto) on Older Small Engines
FIG. 3 is an alternate embodiment of a circuit for disabling an engine in response to a sensed condition; and
FIG. 2 depicts an interlock or safety circuit 100 constructed in accordance with a preferred embodiment of the invention. The circuit 100 is supported within a metal housing 102 (FIG. 4) having an outwardly extending tab 104 which supports the housing. Three insulated wires 110, 112, 114 having conductors 110a, 112a, 114a are connected to the circuit 100 of FIG. 2 and exit a potting material 106 which encases the circuit 100. A fourth wire 116 carries a ground conductor that defines a ground voltage for the FIG. 2 circuit. The wires 110, 112, 114, 116 terminate at a connector 124 having contacts for engagement with a corresponding female connector (not shown). The corresponding female connector is electrically coupled to FIG. 2 circuit components external to the safety circuit 100 such as a starter solenoid, an engine magneto coil, and multiple safety switches described below.
A 12-volt battery 130 having a ground connection 132 energizes a starter solenoid coil 134 when the operator closes an ignition switch 136. Sufficient energization current (3 to 4 amperes) passes through the solenoid coil 134 only if three series-connected safety switches 150, 152, 154 are closed. A first switch 150 is coupled to a traction transmission which causes the wheels of the vehicle to rotate. In the preferred embodiment of the invention, the combustion engine is for a riding lawn mower. The transmission safety switch 150 is closed if the traction drive of the lawn mower is disengaged. A second safety switch 152 is coupled to a power take-off of the engine. This second safety switch 152 is closed if the mower blade is disengaged. The third switch 154 is a seat switch which is closed whenever the seat is occupied and opens in the event the operator leaves the lawn mower seat.
For all these switches 150, 152, 154 to be closed, the operator must be seated on the seat and both the lawn mower transmission and blade are disengaged. In the event any of these switches are open, a low impedance path to ground through these switches from one end of the starter solenoid 134 is removed.
As seen in FIG. 2, the solenoid coil 134 is also coupled to ground through the parallel combination of a resistor 160, diode 162, and capacitor 164 that form part of the safety circuit 100. The resistance 160 is in series with the low (approximately 4 ohm) resistance of the starter solenoid 134. Closure of the ignition switch 136 with one of the switches 150, 152, 154 open will cause current to flow through the series combination of the starter solenoid coil 134 and the resistor 160, but of a magnitude much less than the 3 to 4 amps needed to actuate the starter.
Once the combustion engine is running, the circuit 100 monitors the continued status of the switches 150, 152, 154. In the event an unsafe operating condition is sensed, the engine is deactivated by shorting an engine magneto primary coil thereby inhibiting voltage from reaching the spark plug. Once the magneto primary coil is shorted, the engine stops and cannot be restarted until all three switches 150, 152, 154 are again closed corresponding to a safe condition. One example of an unsafe condition is the situation where the operator leaves the seat of the lawn mower and either the transmission or the power take-off is engaged. If the operator leaves the seat, but both the power take-off and transmission are disengaged, however, the engine continues to run.
The circuit 100 includes a triac 170 coupled in parallel to a primary coil of the engine magneto. The magneto also includes a transformer secondary inductively coupled to the primary that transmits large voltages (approximately 20 kilovolts) to the spark plug each time current through the magneto primary is disrupted. U.S. Pat. No. 4,270,509 to Tharman discloses a typical small engine magneto system for use with a lawn mower and is incorporated herein by reference. If the triac 170 has been rendered conductive, the time varying signal imposed across the primary is shunted to ground through the conducting triac. Without sufficient spark voltage, the spark plug does not ignite combustibles in the combustion chamber and the engine stops.
The triac 170 is rendered conductive whenever the voltage at a control or gate electrode 172 increases to a point where the triac 170 turns on. The gate electrode of the triac 170 can be activated with either a positive or negative voltage with respect to the triac ground connection. Three different switch configurations must be examined:
Magneto generated pulses coupled to the safety circuit 100 by the conductor 114a are transmitted through the parallel combination of a resistor 174 and a capacitor 176 and charge a capacitor 180 connected to the gate 172. This turns on the triac 170 and provides a low impedance path through the triac for pulses applied to the magneto primary to inhibit generation of spark plug energizing voltages.
Magneto generated pulses transmitted by the conductor 114a pass through the capacitor 176 and resistor 174, but do not charge the capacitor 180. Instead, these signals pass through the closed safety switches 150, 152 to the parallel combination of the resistor 160, and capacitor 164 which presents a low impedance path to ground for the magneto pulses. The triac 170 remains non-conductive and a sufficient voltage is induced in the magneto secondary to maintain engine operation. The path to ground through the capacitor 176 and resistor 174 presents significantly more impedance than the conducting triac so that the magneto primary is still adequately energized and de-energized by the magneto signals.
Magneto signals which could charge the capacitor 180 instead pass through the switch 154 to ground. The triac 170 remains non-conductive and therefore a sufficient voltage is induced in the magneto secondary to maintain engine operation. So long as the seat switch is closed, the operator is assumed to be seated on the seat and the engine continues to run regardless of the state of the switches 150, 152.
Turning to FIG. 3, this figure shows an alternate design of a safety circuit 200 coupled to an ignition circuit such as an ignition circuit for use with a riding lawn mower. In this figure, certain components of the ignition circuit and the safety circuit 200 function the same as components of FIG. 2. These components are identified with the same reference characters as FIG. 2 but with a differentiating prime (‘) appended to the reference character. By way of example, the battery 130’ of FIG. 3 performs a function similar to the battery 130 of FIG. 2. The circuit 200 is supported within a larger housing (not shown) having eight wires entering the potting material.
The FIG. 3 embodiment of the ignition circuit has a switch contact 210 which operates in parallel with the lawn mower blade safety switch 152′. A solenoid coil 212 is energized if the switch contact 210 is closed and the seat safety switch 154′ is also closed. Energization of the solenoid coil 212 causes a clutch to engage, transmitting power to the lawn mower blade. A light bulb 214 electrically coupled in parallel to the solenoid coil 212 is also energized when the switch 210 contact closes.
The circuit 200 also includes a driver circuit 220 for energizing a seat light 222 whenever the seat is occupied. The driver circuit 220 includes two transistors 230, 232 for activating the seat light 222. The transistor 232 is turned on to energize the seat light 222. A base input 234 to this transistor 232 is pulled low when the transistor 230 conducts so that when the transistor 230 conducts, the seat light 222 is extinguished.
The transistor 230 has a base input 236 coupled to a capacitor 238 which normally charges to a level sufficient to turn on the transistor 230. When a discharge path for the capacitor 238 is maintained through the seat switch 154′, however, the capacitor 238 discharges and turns off the transistor 230, causing the transistor 232 to turn on and activate the light 222. When the seat switch 154′ opens in response to the operator leaving the lawn mower seat, the capacitor 238 charges to turn on the transistor 230, turning off the transistor 232 and extinguishing the light 222.
A diode 250 is coupled between the positive side of the seat switch 154′ and the coil 212 for actuating the lawn mower blade clutch. When the switch contact 210 closes, current passes through the coil 212 to actuate the lawn mower blade. When the switch 210 opens in the normal course of lawn mower operation, a back emf is induced in the coil 210 which causes current to flow in the light 214. The diode 250 provides a current dissipation path in parallel with the light 214. Stated in another way, instead of all the current from the coil flowing through the light 214, it flows through the diode 250 and is dissipated in the form of heat in the coil 212, thus avoiding burning out the light 214.
The FIG. 3 circuit also includes a zener diode 260. The zener diode breaks down to conduct high-voltage (approximately 300 volts) pulses from the engine magneto to the gate electrode 172′ of the triac 170′. The zener diode 260 does not break down, however, due to the battery voltage applied across a voltage divider of a 2.2K ohm resistor 262 that forms part of the drive circuit 220 and the 220 ohm resistor 160′ coupled to ground through the two safety switches 150′ and 152′.
Experience with the FIG. 1b circuit (prior art) has shown that it is susceptible to false sensing of a safe condition. Recall that with this system one safe condition is when the blade switch and transmission switch are closed and pulses from the engine magneto that might turn on the SCR pass to ground through a 150 ohm resistor. If the seat switch is shorted by water, the resistance of the water is approximately 300 ohms. This path to ground may allow the engine to continue to run even though the seat switch is open (a possible unsafe condition).
Returning to FIG. 2, it is seen that magneto pulses transmitted to the circuit 100 by the conductor 114a pass through a parallel resistor 174 and capacitor 176. The impedance to these magneto generated pulses is both resistive and capacitive. The combination of the parallel resistor 174 and capacitor 176 and a seat switch 154 shorted by water has a relatively low resistive impedance, but still has a high enough capacitive impedance to allow charging of the capacitor 180 and activation of the triac 170. Experience with the circuit 100 has shown that for some magneto circuits, the resistor 174 can be entirely eliminated and only the capacitor 176 used as a path for magneto pulses that activate the triac 170.
Two embodiments of the invention have been described with a degree of particularity. It is the intent that the invention encompass all alterations and modifications from these embodiments falling within the spirit or scope of the appended claims.
How to Test A Lawn Mower.Briggs And Stratton Coil Magneto With a multimeter #easy
Claims ( 11 )
A safety circuit for inhibiting operation of an engine having a spark plug energized by a magneto coil comprising:
a) a triac coupled to a magneto coil for diverting magneto generated pulses applied to said magneto coil away from said magneto coil and thereby inhibiting engine operation; and
b) disabling circuitry for coupling a triac activation voltage to a gate electrode of the triac in response to a sensed condition; said disabling circuitry including a first circuit portion for coupling the magneto generated pulses to the triac gate electrode and rendering said triac conductive to prevent the magneto coil from energizing the spark plug and a second circuit portion for routing magneto generated pulses away from the triac gate electrode to ground, thereby inhibiting triac conduction when a safe operating condition is sensed.
The safety circuit of claim 1 wherein the first circuit portion comprises a first capacitor for transmitting magneto generated pulses and a second capacitor coupled to the gate electrode of the triac that charges to the triac activation voltage as the first capacitor transmits the magneto generated pulses.
The safety circuit of claim 1 wherein the engine provides motive power to a vehicle having a seat and further wherein the second circuit portion routes magneto generated pulses through a safety switch that is closed when an operator is seated on the seat.
The safety circuit of claim 1 wherein the engine provides motive power to a vehicle having a power take-off and further wherein the second circuit portion routes magneto generated pulses through a safety switch that is closed when the portion take-off is disengaged.
The safety circuit of claim 1 wherein the engine provides motive power to a vehicle having a transmission and further wherein the second circuit portion routes magneto generated pulses through a safety switch that is closed when the transmission is disengaged.
The safety circuit of claim 1 where the second circuit portion of said disabling circuitry comprises a parallel combination of a resistor and a capacitor that is coupled to the gate electrode of the triac through an external safety circuit.
The safety circuit of claim 6 additionally comprising means for coupling the parallel combination of the resistor and capacitor to a starter solenoid to inhibit starting of the engine by limiting current through the starter solenoid.
A method of sensing an unsafe condition and de-activating an engine having a magneto energized spark plug comprising the steps of:
b) routing magneto generated pulses to a capacitor coupled to a triac control electrode to charge the capacitor and activate the triac in the event an unsafe condition is sensed; and
c) preventing the magneto generated pulses from charging the capacitor during normal engine operation.
The method of claim 8 where the preventing step is accomplished by routing the magneto generated pulses away from the capacitor through safety switches which open in the event an unsafe condition is sensed.
A safety circuit for inhibiting operation of an engine having a spark plug energized by a magneto coil comprising:
a) a triac coupled to a magneto coil for diverting magneto generated signals applied to said magneto coil away from said magneto coil and thereby inhibiting engine operation; and
b) disabling circuitry for coupling a triac activation voltage to a gate electrode of the triac in response to a sensed condition; said disabling circuitry including a first circuit portion for coupling the magneto generated signals to the triac gate electrode and rendering said triac conductive to prevent the magneto coil from energizing the spark plug and a second circuit portion for routing the magneto generated signals away from the triac gate electrode to a reference potential, thereby inhibiting triac condition when a safe operating condition is sensed.
A safety circuit for inhibiting operation of an engine having a spark plug energized by a magneto coil comprising:
a) a triac coupled to a magneto coil for diverting magneto generated pulses applied to said magneto coil away from said magneto coil and thereby inhibiting engine operation; and
b) disabling circuitry for coupling a triac activation voltage to a gate electrode of the triac in response to a sensed condition; said disabling circuitry including a gate electrode capacitor coupled to the gate electrode of said triac which charges to the triac activation voltage to render the triac conductive to prevent the magneto coil from energizing the spark plug and a capacitor for transmitting magneto generated pulses to the gate electrode capacitor absent closure of a safety switch that provides a low impedance path to ground for the magneto pulses during safe operating conditions.
US07/757,178 1991-09-10 1991-09-10 Interlock circuit for de-activating an engine Expired. Lifetime US5190019A ( en )
Priority Applications (1)
| US07/757,178 US5190019A ( en ) | 1991-09-10 | 1991-09-10 | Interlock circuit for de-activating an engine |
Applications Claiming Priority (1)
| US07/757,178 US5190019A ( en ) | 1991-09-10 | 1991-09-10 | Interlock circuit for de-activating an engine |
Family Applications (1)
| US07/757,178 Expired. Lifetime US5190019A ( en ) | 1991-09-10 | 1991-09-10 | Interlock circuit for de-activating an engine |
Cited By (19)
| US5424502A ( en ) | 1993-07-27 | 1995-06-13 | Delta Systems, Inc. | Quick-install seat switch |
| US5551866A ( en ) | 1994-08-29 | 1996-09-03 | Josephs; Harold | Safety system and fuel cap for inhibiting operation of an apparatus during refueling |
| US5564375A ( en ) | 1995-05-15 | 1996-10-15 | Wacker Corporation | Start circuit with anti-restart circuitry |
| US5664550A ( en ) | 1995-08-04 | 1997-09-09 | Hitachi, Ltd. | Ignition system of internal combustion engine |
| US5715800A ( en ) | 1995-11-10 | 1998-02-10 | Vdo Adolf Schindling Ag | Load adjustment device for an internal combustion engine, in particular, of a motor vehicle |
| US5775482A ( en ) | 1996-05-08 | 1998-07-07 | Delta Systems, Inc. | Snap-in mount for plunger switch |
| US5829421A ( en ) | 1997-06-27 | 1998-11-03 | R. E. Phelon Co., Inc. | Discharge ignition apparatus for internal combustion engine having shut-off feature |
| US5855199A ( en ) | 1997-06-25 | 1999-01-05 | R.E. Phelon Co., Inc. | Discharge ignition apparatus for internal combustion engine having shut-off feature |
| US5878709A ( en ) | 1997-08-19 | 1999-03-09 | Walbro Corporation | Ignition switch having a positive off and automatic on |
| US6109010A ( en ) | 1998-10-06 | 2000-08-29 | The Toro Company | Mowing vehicle control system |
| US6207910B1 ( en ) | 1999-07-06 | 2001-03-27 | Delta Systems, Inc. | Low profile, double pole safety switch and connector assembly |
| US6457545B1 ( en ) | 2000-06-05 | 2002-10-01 | Delta Systems, Inc. | Hall effect seat switch |
| US20040124026A1 ( en ) | 2002-11-06 | 2004-07-01 | Tracey Walters | Mow-in reverse control |
| US20040201288A1 ( en ) | 2003-04-10 | 2004-10-14 | Delta Systems, Inc. | Switch mounting assembly |
| US20080022971A1 ( en ) | 2006-07-31 | 2008-01-31 | Delta Systems, Inc. | Ignition circuit |
| US20100183447A1 ( en ) | 2009-01-20 | 2010-07-22 | Peter Moskun | Digital over speed circuit |
| US7991028B1 ( en ) | 2010-03-17 | 2011-08-02 | Thomas Bruno | Tunable solid state laser system |
| DE102010034613A1 ( en ) | 2010-08-18 | 2012-02-23 | Robert Bosch Gmbh | Agricultural working machine e.g. tractor, has sensor which is mounted in driver’s seat for sensing occupancy state of driver’s seat, and draft control unit which is automatically switched off, when driver’s seat is not occupied |
| US8323153B2 ( en ) | 2010-04-16 | 2012-12-04 | Deere Company | Interlock circuit for utility vehicle park brake |
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| US3884203A ( en ) | 1973-04-23 | 1975-05-20 | Arnie L Cliffgard | Engine RPM control system |
| US4369745A ( en ) | 1978-12-15 | 1983-01-25 | Delta Systems, Inc. | Safety interlock for machine and engine with magneto ignition |
| US4392474A ( en ) | 1980-04-25 | 1983-07-12 | Licentia Patent-Verwaltungs-Gmbh | Electronic ignition system |
| US4385617A ( en ) | 1980-08-25 | 1983-05-31 | Oppama Kogyo Kabushiki Kaisha | Over-rotation preventing device for internal combustion engines |
| US4565179A ( en ) | 1983-07-07 | 1986-01-21 | Aktiebolaget Svenska Elektromagneter | Apparatus in magneto ignition systems for providing time-separated sequences for charging and triggering in co-phased charging and triggering voltage sequences, including inhibition of the ignition sequence in such apparatus |
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Cited By (24)
| US5424502A ( en ) | 1993-07-27 | 1995-06-13 | Delta Systems, Inc. | Quick-install seat switch |
| US5548888A ( en ) | 1993-07-27 | 1996-08-27 | Delta Systems, Inc. | Method of securing a quick-install seat switch |
| US5551866A ( en ) | 1994-08-29 | 1996-09-03 | Josephs; Harold | Safety system and fuel cap for inhibiting operation of an apparatus during refueling |
| US5564375A ( en ) | 1995-05-15 | 1996-10-15 | Wacker Corporation | Start circuit with anti-restart circuitry |
| US5664550A ( en ) | 1995-08-04 | 1997-09-09 | Hitachi, Ltd. | Ignition system of internal combustion engine |
| US5715800A ( en ) | 1995-11-10 | 1998-02-10 | Vdo Adolf Schindling Ag | Load adjustment device for an internal combustion engine, in particular, of a motor vehicle |
| US5775482A ( en ) | 1996-05-08 | 1998-07-07 | Delta Systems, Inc. | Snap-in mount for plunger switch |
| US5855199A ( en ) | 1997-06-25 | 1999-01-05 | R.E. Phelon Co., Inc. | Discharge ignition apparatus for internal combustion engine having shut-off feature |
| US5829421A ( en ) | 1997-06-27 | 1998-11-03 | R. E. Phelon Co., Inc. | Discharge ignition apparatus for internal combustion engine having shut-off feature |
| US5878709A ( en ) | 1997-08-19 | 1999-03-09 | Walbro Corporation | Ignition switch having a positive off and automatic on |
| US6109010A ( en ) | 1998-10-06 | 2000-08-29 | The Toro Company | Mowing vehicle control system |
| US6207910B1 ( en ) | 1999-07-06 | 2001-03-27 | Delta Systems, Inc. | Low profile, double pole safety switch and connector assembly |
| US6457545B1 ( en ) | 2000-06-05 | 2002-10-01 | Delta Systems, Inc. | Hall effect seat switch |
| US6648092B2 ( en ) | 2000-06-05 | 2003-11-18 | Delta Systems, Inc. | Hall effect seat switch |
| US20040124026A1 ( en ) | 2002-11-06 | 2004-07-01 | Tracey Walters | Mow-in reverse control |
| US7126237B2 ( en ) | 2002-11-06 | 2006-10-24 | Husqvarna Outdoor Products Inc. | Mow-in reverse control |
| US20040201288A1 ( en ) | 2003-04-10 | 2004-10-14 | Delta Systems, Inc. | Switch mounting assembly |
| US7168519B2 ( en ) | 2003-04-10 | 2007-01-30 | Delta Systems, Inc. | Switch mounting assembly |
| US20080022971A1 ( en ) | 2006-07-31 | 2008-01-31 | Delta Systems, Inc. | Ignition circuit |
| US7520264B2 ( en ) | 2006-07-31 | 2009-04-21 | Delta Systems, Inc. | Ignition circuit |
| US20100183447A1 ( en ) | 2009-01-20 | 2010-07-22 | Peter Moskun | Digital over speed circuit |
| US7991028B1 ( en ) | 2010-03-17 | 2011-08-02 | Thomas Bruno | Tunable solid state laser system |
| US8323153B2 ( en ) | 2010-04-16 | 2012-12-04 | Deere Company | Interlock circuit for utility vehicle park brake |
| DE102010034613A1 ( en ) | 2010-08-18 | 2012-02-23 | Robert Bosch Gmbh | Agricultural working machine e.g. tractor, has sensor which is mounted in driver’s seat for sensing occupancy state of driver’s seat, and draft control unit which is automatically switched off, when driver’s seat is not occupied |
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Magneto Voltage Value: How to Use a Voltmeter
Figure 3: The moon-shaped pole pieces inside the magneto body and the plates on the ends of the armature core are visible.
What does your magneto voltage tell you? Learn how to use a voltmeter to accurately measure a low-tension rotary magneto’s condition.
It is common practice to try to determine the health of a low-tension rotary magneto by putting a voltmeter on the magneto and spinning it up. Typical readings range from 5v to 12v. What does the value of that magneto voltage tell you? The short answer is — nothing. It turns out that your voltmeter does not tell the truth.
Let’s say the reading was 10v. If 10v will run an engine, why not just hook a 12v battery and a resistor to the igniter and forget the magneto? Also, when the engine is running, the igniter is closed (shorted) for all but a brief period of time, so the actual running magneto voltage is 0v. Those thoughts alone should raise some questions. Let’s try to understand those issues and find a way for how to use a voltmeter to accurately measure a magneto’s condition.
We measure voltage as a difference between two points. One of those points is a reference, often a stake driven in the ground, aptly called ground. Generally, we make the block on our engine the reference, or ground. When we say the magneto voltage is 10v, we are saying its voltage is 10v higher than the engine block voltage. But as the bird sitting on the 50kv power line would tell you, voltage by itself isn’t worth much. A single turn of wire will deliver several hundred volts to an igniter — but no spark. Shuffling across the carpet on a dry day will provide several thousand volts. Rather than thinking of voltage as the answer to all our problems, think of it as a facilitator that will enable things to happen.
A few hundred volts across your igniter is enough voltage for an electron to jump across the open points of your igniter. It takes about 70v per 0.001-inch of gap for the arc to start. If the voltage is consumed and disappears when that electron jumps, you won’t have combustion. There must be enough voltage to drive enough electrons (the current is measured in Amps) across the points’ gap to create a hot spark channel for combustion. The simultaneous delivery of voltage and current is power (measured in Watts). You may have a 75Watt heating blanket (120v using 0.63A of current) that will keep you nice and warm long term. It won’t do much if a fuse blows the instant you turn on the blanket.
Here is where it gets tough. For the magneto, it isn’t enough to deliver voltage (a few 100v) and current (1/2 Amp or so) to create a hot spark channel. It must do so long enough to cause combustion, about 0.002 of a second. Voltage plus current plus time is energy measured as Watts per seconds (kWh by your utility company) or Joules over in the physics department. We need to know if the magneto is capable of delivering enough energy to cause combustion. Almost any magneto can deliver the voltage and current, but doing so long enough to create combustion is the stumbling block for most weak magnetos. You’re probably thinking, “there’s no way I can to measure voltage, current, and time simultaneously.” It is hoped that you understand energy is the key and voltage is just one component.
Rotary low-tension magneto ignition
These magnetos are simply dressed-up battery and coil systems. The magneto steals energy from the flywheel and converts it to electrical energy thus replacing the battery. The magneto armature windings act as the coil for the battery and coil ignition as well as the windings for the generator action.
Figure 1a is a simplified schematic during the first half of rotation. When the igniter is closed, the generator action (represented here as a battery) pushes current through the coil and its wire resistance (often around 5 Ohm) through the igniter to ground. During the second half of the magneto’s rotation, the generated voltage pulls current out of ground, through the igniter, and through the coil resistance (see Figure 1b). The voltage and current alternate in and out of the magneto. That’s what we call AC or alternating current.
Figure 2 is key to understanding the low-tension magneto. Anytime current is flowing in a coil, the coil develops a magnetic field around itself. That field is pure energy. You can’t feel it or see it, but it’s real. Just as real as the energy in a spinning flywheel.
The physics department has given us an easy way to measure the stored magnetic energy, although we can’t touch or feel it.
L is the coil’s inductance, a measure of how much the coil acts like a coil. It is determined by the number of wire turns, core material that the coil is wound around (air, steel, etc.), length and diameter of the coil, and other physical terms. Once the armature coil is wound, L doesn’t change. A magneto model will have the same L value over the years of manufacturing. The L value is around 0.1 for many magnetos. I is the current in Amps and is squared. Current-squared means that the energy goes up rapidly with current. The energy goes up four times if the current, I, is doubled.
Physical analogy
Let’s use a rope to pull a 50-pound rock up a rafter (the magneto is building current in the armature coil). It is storing energy while the rock hangs there. This is called potential energy; you can’t see or feel the magneto’s magnetic field energy. When the rope breaks (igniter trips), the rock won’t sit there storing energy (the coil is not going to continue storing energy). Energy is always conserved. It might move or change form, but it will not evaporate. The rock’s potential energy is converted to damage on the ground (magnetic energy is converted to a spark).
Measuring magneto voltage
Using the energy equation: If the current is zero, the stored energy in the armature coil is zero; if there is current in the armature coil, there is stored energy. The magneto acts as a battery and coil for half a rotation of the magneto and pushes current through the coil building energy in the coil’s magnetic field. Suddenly, the igniter trips and the points pop open creating an open circuit. The coil looks at that and says, “They want the current to be zero and my energy to be zero.” The coil must dump all the stored energy, but the open points are blocking its only path. The only way out is to jump the igniter and dissipate the energy as heat in a spark. The coil will find a way to dump its stored energy, hopefully across the igniter rather than a spark across the mica washers, or other undesired places.
How does the coil do that? The amount of energy is the product of voltage, current, and time. The time goes down if the required voltage goes up. The coil takes that low-voltage, high-current energy it has collected over a long period of time (1/2 of an armature rotation) and trades time for voltage and dumps its energy as high-voltage high-current for a very short time. The energy in your spark is the energy stored in the armature coil the moment the igniter trips. Period. There is no voltage in that equation, only current. Want a hotter spark? Store more energy in the armature coil. Increase the current at the time the igniter trips to store more energy and get a hotter spark. Measure short-circuit AC current to measure the health of a magneto.
How to use a voltmeter to measure magneto voltage per early magneto manuals
When magnetos were being developed in the late 1800s and early 1900s, the only meters capable of measuring AC were voltmeters. AC current meters, AC power meters, and scopes were developed later. Using a voltmeter is easy: Stick one lead on the point of interest and the other lead on the engine block. Measuring current is a bit more complicated. The meter must be inserted inline. To make matters worse, many inexpensive multimeters will not measure AC current.
The L value would double and the spark would be twice as hot if we were to double the number of wire turns in the armature coil, but the armature would grow to twice its size. The spark would be 4X hotter if we found a way to raise the current from 1 Amp to 2 Amps. The early magneto developers looked at the energy equation and realized only one thing was important: get the most voltage possible to drive the most current possible at the exact time the igniter trips. Any time the igniter is not tripping, voltage and current are irrelevant. The irrelevant periods of time can be sacrificed to enable maximum voltage (and maximum current) when the igniter trips. Early engineers added moon-shaped pieces of steel (pole pieces) inside the magneto body, rounded plates on the end of the armature core, and shaped the magnets like horseshoes (see Figure 3). Those design changes created a severely distorted voltage wave form that pushes the current to a peak just as the igniter trips. Figure 4 is the voltage developed by the magneto in Figure 3. That is the voltage you are trying to measure when you hang a voltmeter on a magneto and spin it up.
Time moves from left to right while voltage is up and down in a scope trace. In Figure 4, 0v is a horizontal line across the middle of the screen, the vertical is 20v per box. As time progresses, the armature is rotating clockwise and we move along the scope trace to the right. In Figure 4, the key in the armature shaft is at the 6 o’clock position starting at the left negative peak at.55V. As we move in time toward the right, the armature rotates and, by 7 o’clock, the voltage has abruptly risen to near zero and stays there until near 11 o’clock where it rapidly shoots up to 60v (12 o’clock) when the igniter trips. By 1 o’clock, the voltage is down near 0v again and hangs around that value until near 5 o’clock. Remember, the only time that counts is the 11 o’clock to 1 o’clock value during which the igniter trips, if timed properly. The relevant region represents less than 10 percent of the total time. No meter in your arsenal can read the voltage at this time. Voltmeters are all designed to read a smooth looking sinusoidal wave form, similar to Figure 5.
Your voltmeter will be happily reading 5v to 15v in the irrelevant region when it gets hit with a short 60v ping. The ping is too short, timewise, to register. Basically, you are left reading the voltage in the irrelevant region and ignoring the voltage in the relevant region. To make matters worse, most voltmeters are designed to read voltages with a frequency above 50Hz (cycles per second). The 600rpm you may have spinning the magneto is 10Hz, well below your meter’s range. Your voltmeter doesn’t have a prayer and can’t read both the wave form and frequency. The voltage wave form of Figure 4 was read on the four meters shown in Figure 6. All four meters have been shown to be accurate on their intended sinusoidal voltages. The meters range from relatively inexpensive to a professional grade meter on the right. The readings were 5.9v, 8.6v, 5.7v and 8.2v. Had I told you I read four magnetos with voltages of 5.9V, 8.6V, 5.7V and 8.2V, you would likely have told me to send the 5.7V and 5.9V units to the shop, but the other two would be OK. The lesson there is, if you don’t like the reading you get, try a different meter. But keep in mind, any reading is pretty meaningless.
The current you are interested in that develops from this distorted voltage is rather well behaved, nearly sinusoidal and readable with an AC Amp meter. At 600rpm, the magneto in Figure 3 produced 1.0 Amp peaks (shown in Figure 7). If the igniter is timed properly and trips at one of those peaks, a healthy, high energy spark will be delivered.
Looking again at Figure 7, if your magneto and igniter are not timed properly, things can quickly go bad. If you have your igniter tripping at exactly where your engine manufacturer suggests, maybe 20 degrees B.T.D.C., the magneto must also be timed correctly. If the magneto is as little as one gear tooth too late or early, the current at the time of igniter trip can be 1/2 the peak current producing a spark 1/4 as hot.
The takeaways here are: The energy in your spark is the energy being stored in the armature coil when the igniter trips and that energy is dependent on the coil current. The only meaningful measure of the magnetos condition is to measure its AC output current. Measuring an armature output voltage does have some value — if the voltage is zero, the magneto is dead; if the voltage is not zero, the magneto is not dead. Not dead, however, could mean it needs intensive care or it could mean it’s capable of running a marathon.
The voltage waveform in Figure 4 came from the John Deere magneto in Figure 3. As a comparison, the output of an IHC Type R is shown in Figure 8a, a Sumpter No. 12 in Figure 8b, and a Webster (springs removed and spun up) in Figure 8c.
You are interested in the peak current, always trying to have the igniter trip at the very top of the wave in Figure 7. The current spends only a short time at the peak. Your meter will give you the R.M.S. (root mean square) value that represents how much the current could get done (over all time). Your reading will always be around 0.7 times the peak. So, what should the AC current be for a good magneto? I cannot speak for all, but in the magnetos I have measured (Iowa Dairy, John Deere, Associated, IHC, Sumpter, Webster, etc.) a reading of 0.5 Amp and above on your AC current meter is a good magneto, when turning 300rpm or higher.
Addendum
As pointed out above (due to meter short comings), reading the output voltage of a magneto while spinning it up provides no useful information on the health of the magneto. The output of the magneto is short pulses of voltage, in the range of 70v to 100v, that are too narrow for any meter to read. Additionally the frequency is well below what is readable by standard meters. The 5v to 12v typical meter reading is simply the meter’s “stab in the dark” at a voltage it cannot read. It was pointed out that different meters will likely give varying results. Also stated, the energy in your spark is determined by the current in the coil at the time the igniter trips, not the voltage you are trying to measure.
Fortunately, coil action converts these narrow voltage pulses to a nice AC coil current. The function of the voltage, that your meter cannot read, is to get the current rolling in the coil. The useful measure of a low-tension magneto’s health is its AC short circuit current (see Figure 1). Although the output varies across magneto brands, 0.7A is typically a good magneto. Most magnetos that produce only 0.5A or less are likely in trouble.
But, as pointed out in the previous article, many low-cost analog meters don’t have an AC current setting. Fortunately, any analog AC voltmeter can be converted to an AC current meter by simply adding a resistor (see Figure 2).
First, short the output of the magneto through a 1 Ohm resistor. When the resistor is in place, connect the AC volt meter across it. Figure 3 is a completed set up.
By Ohms Law, the voltage across the resistor will be exactly the AC current in Amps. When the magneto is spun up, at least 500rpm, a 0.75v voltage reading (for example) means the magneto is putting out 0.75A. This test should be conducted using an analog meter. A digital meter is often bothered by the low frequency. The resistor should have a power rating of at least 1 Watt and is readily available on Amazon and eBay.
Above addendum originally published as “Addendum to Voltage Value” in the June/July 2023 issue of Gas Engine Magazine.
Dr. David Cave is a regular contributor to Gas Engine Magazine and can be reached at jdengines@cox.net.
Originally published as “Voltage value” in the February/March issue of Gas Engine Magazine.
Mower Won’t Start No Spark (This Is Why)
Pulling and pulling and nothing, a mower without spark, is useless. In this post, we’ll cover all the most common ignition system failures.
Mower won’t start any spark? Common reasons a lawnmower has no spark include:
None of these tests are difficult, and twenty minutes from now, you’ll know why your mower has no spark.This post will have you covered, but if you need video help diagnosing no spark or help to fit a new coil, check out “Mower won’t start video.”
Checking Lawnmower Spark
Since you’ve checked the spark already, I’m guessing you know the procedure. However, it’s worth pointing out, getting this test wrong can lead to misdiagnosing and replacing the ignition coil or other parts unnecessarily.
Spark testing is, as you know, a simple test, you won’t need any special tools here, but a spark testing tool does make the job easier and totally foolproof.
If you need video help, check out the mower “Mower spark test video,” where I cover the whole process.
Tools needed
For these tests, you’ll need a plug spanner, insulated pliers, screwdrivers, and a spark plug is useful. You’ll also need a helper, as we’re not using a spark testing tool. It can be difficult to crank over the engine and, at the same time, check for spark. With all the tools gathered and a helper on hand, we’ll get right to it.
Spark Testing
As we’ll have a helper cranking over the engine, that means the blade will be spinning, and even though the engine’s not running, it can still remove body parts, so, you know!
You must use insulated pliers (plastic/rubber-handled pliers) to hold the plug as the voltages produced are enough to give you a jolt, which isn’t pleasant.
Tools – Plug spanner, insulated pliers, and a spark plug will be needed.
Spark test tools
Step 1 – Remove the spark plug wire by twisting and pulling, then using the plug tool, remove the spark plug.
Step 2 – Reattach the spark plug wire to the plug. Using your insulated pliers, hold the plug threads firmly against the metal of the engine. This is known as grounding. If the plug doesn’t make good contact with the metal of the engine, you won’t get a spark.
Step 3 – While you watch for spark, have the helper hold the bail lever as normal and yank on the pull cord.
If you have no spark, swap out the plug and test again.
If you still have no spark, it is most likely a failed coil, but best to check the on/off switch assembly first.
Common Spark Plug Faults
A healthy spark plug is essential for reliability, power, and smooth running. Plugs have a tough job. They carry high voltages and live at the heart of the engine where it’s hottest.
Making matters worse for the plug is its location – right out front of the engine. So getting shoved into fences and trees is all part of a spark plug’s life, and you thought you had it hard!These are the most common spark plug faults:
- Wrong plug type
- Dirty plug
- Bad plug gap
- Cracked spark plug insulator
Wrong Plug Type
Plugs areas you know are graded; each engine will have a particular plug code. So even though a plug fits, it doesn’t mean it’s correct. Plugs are graded by heat. The plug should get hot enough to burn off contaminants but not so hot that it pre-ignites. Wrong plug types can cause all types of problems, from hard starting, rough running, hot start failures, etc.
Plug type – Check your plug type with your mower engine maker.
An incorrect plug type will lead to intermittent problems.
Dirty Plug
Self-explanatory, it’s a plug that’s contaminated by too much gas (flooding), carbon, or oil. All of these will prevent the plug from doing its job. Flooding may be caused for a few reasons – blocked air filter, faulty choke, overuse of choke, tipping mower over on its carburetor side, and carburetor fault. Check out the video “How to fix a flooded engine.”
Carbon build-up in the engine is a normal condition. Fuel type, oil type, maintenance, and plug type all affect how quickly it builds.
Oil on the plug is also common. It’s caused by too much oil, blocked crankcase breather, head gasket fault, engine wear, and wrong plug type. Check out the video “How to clean a plug.”
Bad Plug Gap
A spark plug function is obviously to create a spark, and it can only do this if the electrode gap is correct. The coil has been designed to create a sufficient spark to jump a pre-determined spark plug gap.
- No gap, means no spark
- Gap too small means poor running or no start
- Gap too big means no start and risks damaging the coil
A plug gap tool is used to set the spark plugs gap. The electrode is manipulated to the correct size by simply bending it with pliers. Check out the video “How to gap a plug.”
Plug gap – The gap is important. Too small or too big can lead to no starts or poor running.
Cracked Plug Insulator
Self-explanatory too. The insulator is the white ceramic material of the plug’s body, and as said earlier, plugs are at risk of being damaged by bumping into obstacles. If the insulator breaks or cracks, the plug stops working.
Common Spark Plug Wire Faults
A spark plug wire has a few particular problems that affect them, depending on a few variables, like how and where they’re stored.
The common faults I see again and again include:
Loose Terminal
Caused by our old friends, the trees, shrubs, and fences. The plug wire terminal that clips to the spark plug becomes loose, and that can cause no starts, poor running, and intermittent starting/running.The fix here is simple, squeeze the terminal body using pliers to tighten it.
A loose terminal will cause the engine to misfire or not start at all. The quick fix here is to squeeze the terminal until it fits snugly on the plug.
Faulty Terminal
Because this cap was loose, it created arching, which burnt the metal of the terminal cap.
Faulty terminal connector – It’s different but related to a loose connector. A loose connector will often turn into a faulty one as the spark starts to jump inside the terminal, burning it or setting up conditions for corrosion to take hold.
The outcome is the same, no spark or poor running. A replacement terminal can be purchased and fitted to solve this issue.
Damaged Plug Wire
Plug wire rubbing off the engine cover can cause the insulation to wear and the coil to ground. But more often than not, a damaged plug wire means rodents. Mice love wiring insulation, and unfortunately, our furry friends have cost us a coil.
Sure, you can wrap them with insulation tape, but it’s only a quick fix. The long-term repair is to replace.
Damaged wire – Mice love to chew on the wiring insulation.
Common Stop/StartAssembly Faults
Most mower owners are familiar with the bail lever at the handlebars, which must be held to start the mower. Most mowers will use this type of stop/start system; other manufacturers may incorporate the stop/start function with the throttle lever. But apart from this difference, all other components will be very similar.
The main components of the stop/start assembly include:
- Bail/throttle lever
- Cable
- Flywheel brake assembly
- Stop/start switch
- Coil control wire
Bail / Throttle Lever
Common faults here include disconnected, out of adjustment, or broken levers.
Cable
The cables break and stretch, so it’s not uncommon for the bail lever to work, but because the cable has stretched, it doesn’t move the brake assembly to the start position.
Stop / start cable
Flywheel Brake Assembly
Common faults here include cable out of adjustment, meaning the bail lever doesn’t pull the brake to the off position.
Flywheel assembly
Stop/Start Switch
This is the on/off switch. It’s fitted at the flywheel brake assembly. When the bail lever pulls the assembly, it pushes on the switch removing the ground connection to the coil. This allows the mower to start.
On /off switch
Coil control – Here’s a different mower coil control switch. It’s a very simple connection; the contact points must separate before the coil and plug will create a spark.
The Coil (also known as Armature)
The control wire is connected from the stop/start switch on the flywheel brake assembly to the coil, which is fitted to the engine. The coil and plug won’t produce a spark so long as the control wire is connected to the ground (Metal of the engine).
A common fault is the chafing of the control wire on the engine (shorting to the ground); this effect is the same as releasing the bail lever – turns the engine off.
Check coil control wire for chafing, especially anywhere the wiring turns sharply around the engine.
Coil control wire – Coil control is a single wire with a push-on connection. Often they’ll come loose, and when they do, the mower won’t turn off.
Common Coil Faults
Coils generally work, or they don’t. Occasionally, you’ll get a coil that works when it’s cold and stops when the engine heats up. Coils are solid-state units – they can’t be repaired. Testing a coil and fitting a new one is easy; I wrote a whole post about it right here “Push mower hard to start when hot”.
Or check out the video here; it covers spark checking, diagnosing, and replacing the coil. If you need to replace the coil, check out the great deals on the Amazon link below.
Coils – Lawnmower coils give lots of problems; I replace tons of them.
Related Questions
Can a spark plug have a bad spark? Spark plugs wear out. A spark plug should be changed once every year at the start of the new season. You can check the spark plug for spark by removing it, connecting the plug wire, grounding it off the engine, and turning over the engine.
Hey, I’m John, and I’m a Red Seal Qualified Service Technician with over twenty-five years experience.
I’ve worked on all types of mechanical equipment, from cars to grass machinery, and this site is where I share fluff-free hacks, tips, and insider know-how.
And the best part. it’s free!
What Makes a Lawn Mower Coil Go Bad? ( How You Can Prevent This)
It’s very likely that you’ll need to swap out your lawn mower ignition coil at some point during its lifespan. This is a pretty normal replacement that has to be done for all types of lawn mowers, whether it’s a push mower or a ride-on mower. But if you find that your lawn mower ignition coil keeps going bad, then this definitely isn’t normal. So, let’s look at what causes multiple ignition coils to fail and what you can do to prevent it.
What Causes Repeated Ignition Coil Failure? (The Short Answer)
The most common causes of repeated ignition coil failure are engine overheating, defective coil components such as spark plugs and cables, using incorrect parts, and poor maintenance methods. Any one of these causes, or a combination of multiple causes, can lead to your lawn mower coil failing.
What Makes a Lawn Mower Coil Go Bad (6 Possible Causes)
A lawn mower coil is made up of an iron core and copper winding tucked neatly inside the lawn mower’s ignition coil. Every time the magnet attached to the flywheel passes the coil, there is a complex reaction between the iron core, the copper winding, and the magnet that produces an electrical charge. As soon as conditions for this reaction change to less than ideal, the coil suffers. So, let’s take a look at what causes an ignition coil to go bad.
Overheating of the Engine Coil
During the reaction inside the coil, a fair amount of heat is generated on the copper windings. To make sure the windings can cope with the heat, the copper winding is insulated to make sure that the single wire of the winding never touches itself. Now, this insulation is rated to cope with the reaction heat and the heat of the engine. Consequently, the insulation is not rated to take the added heat of an overheating engine.
So, if your lawn mower is low on oil or has a problem with cooling, then it’s probably overheating The result is the insulation loses its integrity, and the copper winding arcs back on itself. The final result is a change in the amount of charge created and the time of release. These changes lead to a burned out ignition coil.
Over Gapped Spark Plug
The charge that is created in the coil needs a method to discharge itself so that it can continue to process and make more charge safely. This is where the spark plug steps in. The spark plug on your lawn mower is basically a grounding point that this charge is attracted to.
So, once the charge gets to the end of the spark plug, it needs to arc over the gap. Now, if the gap is too big and the sparkplug is over-gapped, the arc can’t happen. This makes the coil think that more current is needed, so it increases the charge. Unfortunately, the coil isn’t designed to do this. The result is the coil produces more current and more heat. The one thing that the coil can’t handle is extra heat. So, if your spark plug is over-gapped, your coil is going to quickly burn out.
Faulty or Damaged Spark Plug
Other than over-gapping the spark plug, you might have a bad spark plug that needs changing. A bad spark plug is going to have the same effect as a poorly gapped spark plug. The coil is going to overheat because it is not able to discharge. The result is another burned out coil.
Incorrect Spark Plug
Yep, I’m afraid we’re still talking about spark plugs, but this is the last one. If you’re sitting there wondering, “why does my ignition coil keep burning out” it could be because you’re using the wrong spark plug.
Well, you’ll find that you can buy a spark plug that both fits into your lawn mower and that connects to the ignition cable/spark plug cable. But just because it fits doesn’t mean it’s the right one.
What happens if you use the wrong spark plug? Well, inside the spark plug is an electrode that the current reaches before it arcs to the ground. This electrode is designed with a specific resistance. So, if you have the wrong spark plug, the charge can’t pass the electrode. A wrong spark plug is the same as an over-gapped plug and a faulty plug. Once again, the coil produces more charge, more heat and burns itself out.
Damaged Ignition Cable/Spark Plug Cable
The reaction between the protons and the neutrons inside the coil produces an electron, the charge. This electron charge needs somewhere to go, so it heads for the spark plug. Time for the spark plug cable to step in.
Now, some years back, you would buy a coil and cable separately, but nowadays, they come as one item. Before, it was possible to get the wrong combination and mess up your coil. Fortunately, you don’t need to worry about a mix-up these days.
However, you do need to be aware of cable damage. Just like the overheating problems a spark plug can cause, a cable can do the same. If the cable is damaged or broken, the charge will back up in the coil and form the same heat damage.
Poor Practices
Let me ask you a question. Do you think it’s a good idea to test a spark plug that is attached to your lawn mower without it being grounded? Definitely not. Most of us, at some point, have removed the spark plug from the mower and pulled the starter cord to see if it’s working ok.
Well, if you pull the cord and the spark plug isn’t grounded to the mower’s engine, the coil begins to overheat. This is just the same as a bad spark plug or a broken cable. The charge has nowhere to go.
Signs a Lawn Mower Coil is Going Bad
When figuring out what makes a lawn mower coil go bad, you’ll probably be seeing a few symptoms with your lawn mower before the coil burns out. If you notice these symptoms quickly enough, you might be able to avoid another coil replacement. Here’s what to look out for.
Is There Anything You Can Do If Your Mower’s Ignition Coil Keeps Going Bad?
Now that we have been through what makes a lawn mower coil go bad. Let’s have a look at a few things that will help you avoid another replacement. Here are some tips to help keep the coil protected.
Check the Engine Oil Level
A common cause of a lawn mower engine overheating is low oil. A lack of oil in the engine causes the metal parts to rub together and generate excessive heat. I suggest that every time you fill the gas tap, you check the oil level.
Carry Out Regular Oil Changes
As oil is used and heated, it starts to lose its cooling and lubricating abilities. This results in overheating and potential coil damage. I suggest working out an oil change schedule and make sure that you are changing your lawn mower oil often enough.
Clean Out the Air Vane Guard
When I finish using my lawn mower, I always make a point of cleaning off all the grass. I also make sure to clean out the flywheel. Located on top of the flywheel is a fan that cools the engine. It is super important to keep this clean so that the engine can cool efficiently.
Gap the Spark Plug
Gapping a spark plug is a job that a lot of people skip. I’m guessing this is because it’s not always easy to understand why it’s important. But once you know what makes a lawn mower coil go bad, I’m pretty sure you will not skip it again. So, the simple solution is to get a spark plug gapping tool and gap your plug regularly (here’s a post that explains how to gap a mower spark plug).
Double Check the Spark Plug Specification
If you look in your lawn mower manual, you’ll find out what size spark plug your mower needs. If you can’t find it, you can look online or check with your local mower store.
Using the Mower’s Off Switch
Within the electrical circuit of your lawn mower, there is a bypass for the coil. This basically grounds the coil in a different direction than the spark plug. So, if you are doing repairs on your lawn mower that require the flywheel or engine to turn, make sure the lawn mower is switched off. Disconnecting the spark plug will stop the mower from starting, but it won’t protect the coil.
About Tom Greene
I’ve always had a keen interest in lawn care as long as I can remember. Friends used to call me the lawn mower guru (hence the site name), but I’m anything but. I just enjoy cutting my lawn and spending time outdoors. I also love the well-deserved doughnuts and coffee afterward!
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