Soft starter for power tools with their own hands

Soft starters with three wires

By the way be careful, there are similar devices, but with three wires. For example XS-12/D3.

Or other models similar in appearance to KRRQD.

But they are made on a slightly different principle and should be installed after the START button in the tool. The voltage to it should be applied only at the moment of closing the start button of the angle grinder and immediately disappear after its release.

Phase goes to pin A, and zero to pin C. Then the phase control output wire goes to the motor (this is just the third wire).

Without pushbutton, such a device will be constantly under voltage of 220V, which is not allowed.

In two-wire unit, there is no such a thing, since it is connected in the gap circuit, and the voltage (potential difference) is applied to it only during start-up and operation of the tool.

Another point is the so-called electric brake or brake winding on angle grinders. It may not work with a 3-wire external controller, but it will work with a 2-wire model.

Where to buy the starter for angle grinder 2 kW and other

Companies that are collected in a separate section, offer a soft starter for angle grinders of various types. In addition, the visitors of our site have the opportunity to buy angle grinders with soft start function, which are in demand category of power tools and implemented by many suppliers, some of which are presented here.

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How to connect, installation

For the users of lathes who do not have electrical installation skills it is possible to buy a separately sold soft starter unit. It will only be necessary to install it correctly. There are two variants of starter location. inside the body of angle grinder and outside, if it is impossible.

Hand Tools VS Power Tools. Are Hand Tools still Relevant in 2020?

In the following video the author placed one of the purchased blocks inside the angle grinder with a small modification of the angle grinder body. Two wires of the starter unit are connected according to the following scheme: one wire to the contact of the switch, the other to the stator winding of the electric drive.

In another video the author also managed to place the purchased unit inside the angle grinder. But the connection scheme he chose another. in the gap of the network. It is not important to take into account where to connect “zero” and where to connect “phase”.

Features and durability

In manual power tools, such as: angle grinder (angle grinder), circular saw, electric screwdriver, drill. use collector motors with series excitation. They can be operated with DC or AC current.

They are generally powered by a 230 V 50 Hz mains supply. In the past, a 380 volt power supply was used for professional tools. Now, with the increasing power of single-phase consumers (offices and residential sector), 220 V professional power tools have appeared.

Collector motors have a high torque and starting torque, are compact, and can be easily manufactured for higher voltages. The torque is the decisive factor. With a low machine weight, it is just right for hand-held power tools. But these electric motors have disadvantages and weaknesses. One of these weak points is the brush knot.

Pressed graphite brushes with fillers rub against the copper plates of the collector and suffer mechanical wear and electrical erosion. It causes more sparking and increases the fire and explosion hazard of the power tool. The ingress of mineral dust accelerates wear. Although ventilators are designed to blow air outward, dust and cement can easily get inside. During downtime, if the tool is misplaced, dust can easily get inside. In practice, it’s a constant occurrence.

soft, starter, power, tools

Motor brushes made of pressed graphite

Another disadvantage of power tools is frequent gearbox failures. It occurs precisely because of the high starting torque. An advantage is often a disadvantage. If a gearbox breaks, you have to replace the tool; they are not usually repairable. Unfortunately, the industry, in its desire to reduce production costs, does it at the expense of quality. If you want to use a good power tool, you have to pay a lot of money.

The last drawback can be effectively dealt with by soft starter. Many manufacturers do, but they don’t always pay enough attention to it. Not all tools have good speed controllers.

How to make a starter block for power tools

There are quite a few variants of self-equipment of the angle grinder with a soft starter. Some of them are presented in the author’s video.

Start-up unit based on LM358 chip

In the following video the author shares his experience of making a soft starter board based on a schematic taken from the Internet, on the LM358 chip. The author made the case for the circuit board from a shampoo box, which shows the rich imagination of amateur craftsmen. The author did not just blindly copy the circuit from the internet, but modified it, changing characteristics of some of its elements: transistors, diodes, resistors. The radiator for cooling semiconductor devices was taken from a tape recorder. In order to place the soft starter block inside the body of the angle grinder and not in the case of the offered variant, a board of a smaller size was developed.

One of the options for the layout of the home-built starter unit

As an initial variant the author of the following video chose the assembly with the LM358 chip known on the internet.As the assembled starter block did not fit inside the body of the angle grinder, the author “packed” inside only a triac with a radiator, because of the good cooling conditions from the angle grinder’s fan wheel. The rest of the block together with the chip was mounted on the angle grinder body.

Using an iron as an additional load to reduce the angle grinder’s rpm

This method is not specifically related to the topic of soft-start angle grinder. However, to understand the principle of operation of an electronic device, the dimmer, which is used to adjust the power (or the number of revolutions) of angle grinder is quite acceptable. In the following video the iron takes some power from the angle grinder, thereby reducing its speed.

How to adjust the dimmer in the angle grinder to adjust the speed

In the following video the author finalized the trigger (made it spring-loaded) in order to use the possibilities of commercially available dimmer to adjust the angle grinder RPM. After turning the angle grinder on, moving the button sets the desired RPM. The dimmer locks the mode and is set when you turn it on again.

Advantages of the soft start angle grinder

Bosch GWS 17-150 CI Professional 0 angle grinder.601.798.0R6 with soft start. Photo by VseInstrumenty.Manual

angle grinders with the soft start option are characterized by the absence of the following disadvantages that are present in power tools without this function.

  • Brush collector sets are subject to more sparking, which burns out the lamellas on the collector.
  • Brushes also wear out more quickly for the same reason.
  • Stator and rotor windings are damaged far more frequently due to the higher starting current.
  • The mains network reacts to the inrush current with a possible triggering of the circuit breaker. However, if operation is performed from, for example, an alternator, it may fail.
  • The mechanical part of the angle grinder in the form of bevel gears and support bearings, experiencing increased loads, has a risk of premature failure.
  • An increased jerk force when starting an angle grinder (especially high-power) can wrest it from your hands, and in some circumstances cause injury.

Do you need soft start for power tools?

Given the above advantages of a soft starter angle grinder is inevitably necessary. However, small household angle grinders belong to the category, where the low price is one of the priority parameters. Therefore it does not always make sense to equip them with start unit, increasing their selling price. Such inexpensive angle grinders are used mainly for works where professional skill is not required.

Choosing the scheme

There are many schemes of soft starters, we will try to choose something suitable and most affordable for us.

On discrete elements

The regulator, which scheme is shown below, is assembled on the symmetric thyristor (triac) KU208G and allows you to perform a soft start of power tools up to 2 kW.

Immediately after applying voltage to the circuit (tumbler SA1) Capacitor C1 is discharged, triac VS1 is closed and motor M does not rotate. Then the capacitor is gradually charged through the diode VD1 and the resistor R2, the triac begins to open, but with a long delay from the start of the half-wave of line voltage. A small initial voltage is applied to the motor and it starts at minimum rpm.

as the capacitor charges, the triac delay decreases, the voltage across the motor increases, and therefore the speed increases. As soon as the capacitor is fully charged the symmetric thyristor will open at the beginning of each half-wave, supplying full line voltage to the motor, and the motor will come into full speed.

The soft start time can be adjusted by adjusting the capacity of the capacitor C1. With the specified ratings (500 uF) the tool will reach the operating mode in about 2-3 seconds after switching on.

Important! If the power of the power tool is more than 500 W the symmetrical thyristor should be mounted on the heatsink.

On chip and triac

This circuit is based on a domestic universal microcircuit KR1182PM1. It can be used to build a soft starter as well as a voltage regulator. In the circuit shown below, the microcircuit is included in the soft-start mode.

Since the chip has a relatively small output power. up to 150W, it is equipped with a powerful output switch, which acts as a symmetrical thyristor TC122-20-10, sustaining a current up to 20A. Time of the engine operation depends on the capacitance of the capacitor C1. Such a circuit can operate without a heatsink for loads up to 1 kW.

Useful at! If necessary the TC122-20-10 triac can be replaced with KU208G, but the power of the device will fall by half.

Integral regulator

The discrete element circuit is simple enough and does not have any missing elements, but it is too bulky and must be placed in a separate enclosure, especially if the power tool is powerful and a heatsink is needed. It is much more convenient to use ready-made integrated soft starters. The most convenient variant is the KRRQD20A.

The compact integrated soft starter (IS) is designed for currents up to 20A and can switch powers up to 4kW. The module has 2 pins and is connected in the gap of one of the power wires of the tool. If you equip it with an extension cord (many people call it a “porterhouse” for some reason), then the power tool, connected through it, will smoothly start when the trigger is pushed.

You can clearly see in the photo that the module is designed for installation on a radiator, but if the power of the power tool does not exceed 1 kW, then the radiator is not needed.

Important! There are similar modules with the same function, but with three outputs. They are not suitable for our purposes, since they are not simply switched on in the break of the supply wire, but supply voltage to the motor via a separate mowing line.

The connection diagram is printed directly on the body of the device and it is obvious that it can be used only by installing it after the switch in the power tool itself. Also not bad variant, but firstly, the power strip is more universal solution (you can connect any tool or even a lamp), and secondly, disassembling the tool, we lose warranty service.

The simplest diagram of a soft starter for use in an extension cord

Soft starter block with speed regulator for power tools, made on the basis of thyristor KU202, is popular due to its simple performance. No special skills are needed to build and connect it, and the components can be purchased at any hardware store or on the market. BPP consists of diode bridge, variable resistor to adjust voltage and thyristor tuning circuit.

Schematic diagram of PSU with speed regulator

Due to the fact that this BPP circuit requires a small number of parts and its size is quite compact, it can be built into both the handle of the power tool and the body of the extension cord socket. The principle of operation of the soft starter is to adjust the rotor speed of the power tool by limiting the power in manual mode. This scheme is intended for use with power tools with power up to 1,5 kW. For BPP to work with a more powerful tool, you need to replace the thyristor with a more powerful device. You must also take into account that the control circuit will be different from the original one.

Soft starter

The design features of some tools, such as an angle grinder, entail a high impact on the motor of the device of dynamic loads. To eliminate the uneven loads on the electric device and its components is recommended to acquire or make their own hands soft starter (PSA).

Appearance of soft starter SPP 7-22 on 12V