The reason that the screwdriver has stopped working is often excessive wear on the brushes of its electric motor. It is not difficult to fix such a malfunction, but a minimum knowledge of the DC motor is necessary. Let’s start by defining what brushes are.
Brushes
Electric motor brushes are contacts through which current is supplied to the rotor windings. Since the rotor is designed for rotation, the current in its windings cannot be supplied through a stationary wire connection. To do this, use the collector-brush unit (KShCHU). The collector consists of copper plates fixed on an isolated section of the armature shaft. The outputs of the rotor windings are connected to them. Brushes are mounted close to the collector. When the rotor rotates, they slide along the collector plates. Current flows through the sliding contacts in the armature windings. The alternating magnetic field arising from this is the force that rotates the rotor.
Knowing how the assembly that feeds the windings of the armature works, it is easy to guess that its parts must wear out. The rotor is difficult to manufacture and expensive. Therefore, to protect it from wear and tear collector, material for making brushes intentionally choose less resistant to abrasion. Otherwise, it would be necessary to replace not the brushes, but the anchor. Another necessary property of brushes should be good electrical conductivity. Best of all, these conditions correspond to a mixture of copper powder with graphite. Electric motors with lower power or higher than that of a screwdriver, operating voltage can be equipped with graphite brushes. And graphite is not suitable for a screwdriver motor with a low operating voltage and high currents because of the electric resistance too large for it.
Diagnostics
Do not rush to disassemble the screwdriver when the cartridge does not rotate when you press the start button. Start with a simple one. replace the battery with a known good and fully charged one. If no changes occur, remove the battery, turn the screws out of the housing and disassemble it. Using a multimeter, measure the resistance between the brushes. If the wear is not higher than permissible, they will have good contact with the manifold, and the device will show resistance close to 0. If the readings are more like a broken circuit than short circuit, tap the brush holders with a screwdriver handle and turn the motor rotor by hand several times. A constant tester will indicate that contact has not recovered and the instrument needs repair. Making such a check easier than disassembling a motor, especially not serviced. It should be noted that the symptoms of breakage of the armature windings and brush wear are the same. But the breakage of the windings is an extremely rare event, wear is much more common.
Video: How to Change Brushes On a Makita Screwdriver
Replacement
On a serviced engine, everything is simple
- Disassemble the case
- Take out the worn out kit
- Put a new one
- Assemble the housing
The maintenance-free motor is characterized by rolling the rear ends of the holders. Often the lid, on the inside of which they are located, inserted into the case, is fastened by rolling. The process is a bit more complicated here.
- With pliers, bend the flare holding the cover
- On the perimeter of the cover and body, mark 3 points equally spaced from each other
- Take out the cover
- Using solder grease, solder and a powerful soldering iron, irradiate the target points
- After cutting stranded wiring, replace worn brushes with new ones.
- Solder to the wiring holders coming from them. Then, in order not to break the copper. graphite contacts when installing the cover, alternately drown them in the holders and secure each in this position with a thread, tying it with a bow
- Leaving the ends of the threads outside, install the cover into the case
- Restore contact in the control panel by untying and stretching the threads
- Solder the cover to the motor housing
About labor
Repairing a screwdriver with a serviced engine can be done relatively quickly. You can not say about the restoration of a device that cannot be repaired. Think about it, maybe, in the time necessary for repair, you can earn by what you are good at doing, an amount sufficient to buy a new one. After all, you should not learn something to do it just 1 time.