Do-it-yourself grinder speed controller repair

In detail: do-it-yourself repair of the grinder speed regulator from a real master for the site my.housecope.com.

Do-it-yourself grinder repair is a completely solvable task. The main thing is not to rush, to understand the structure, remember all the circumstances under which it broke down, determine what could have worn out during operation, make diagnostics and start repairing it.

Angle grinder (angle grinder) is called a grinder. The name of the instrument is due to the fact that it was produced by the Eltos-Bolgarka plant in Plovdiv. It is designed to perform work on grinding or trimming hard material:

Performs well sharpening of the tool.

The grinder in our time is a very necessary tool, so almost everyone has it.

There are grinding machines of different power: from 500 W to 2500, depending on the thickness of the wheel - from 115 mm to 230 mm. The most popular in the work are angle grinders with a power of 1.2 W, and the most used disc is 125 mm thick.

Every year the choice for this construction power tool is becoming wider, but the operating rules hardly change. And even if you always adhere to them, sooner or later there are malfunctions in the mechanism that you can try to fix with your own hands, collecting everything you need to repair the grinder.

Any grinder consists of the following parts:

rotor - a part of an electric motor that rotates during operation and is speed-controlled, also called an anchor;
collector - the place on the rotor where the control winding wires are located;
brushes - parts that serve as conductors of current from the cable to the collector winding;
reducer - a mechanism that acts as a drive from a rotating rotor to a rotating disk, consists of a spindle, a bearing, two gears (large and a shaft gear);
stator - the part of the electric motor in which the rotor operates;
grinder cooling impeller;
start button;
network cable with electric drive;
protection casing;
grinder body;
additional handle.

Video (click to play).

All these details can be divided into two parts:

How to disassemble a grinder? Not so difficult process. This does not require special knowledge, but everything must be done carefully and carefully. Each owner needs to know how to disassemble any working tool, because from time to time it needs to be cleaned internally from dirt and trapped dust, and its durability depends on it.

At the present time on the market, you can choose for yourself a different type of grinder, which differ in performance, size, quality. Manufacturers are also different. Whichever model of grinder you buy, everyone has the same assembly model.

Dismantling the grinder will require few tools, you just need a regular screwdriver or a reversible screwdriver with a ratchet mechanism.

Having prepared a screwdriver, you can start disassembling:

We unscrew the screws from the body and remove one side of the product.
Remove the nut that holds the disc, unscrew the bolts securing the protective casing.
We remove the brushes.
Disconnect the wires from the engine.
We unscrew the bolts that secure the gearbox inside, and very carefully remove it, and the rotor is also removed with it.
We unscrew the bolts that hold the stator and remove it.
We put the grinder back, put everything in place in the reverse order and fasten it.

When disassembling the grinder, it is important to remember the order in which the parts are removed in order to assemble them correctly.

In the event of a malfunction, first of all, it is necessary to exclude elementary breakdowns:

The grinder does not turn on. The angle grinder suddenly became faulty - it stopped turning on. In this case, you need to check the serviceability of the outlet, then the plug and the power cord, perhaps the drive simply does not work due to the fact that no current flows into the product.
The cable and plug are intact, but the drive does not work. You need to check the start button. It is easier to repair the grinder switch by purchasing a new button and replacing it. Since it rarely needs to be repaired - basically, the plastic rod of the switch breaks inside. If you want to experiment, you can disassemble it by numbering the contacts, and put everything back together in place so that after assembly does not happen a short circuit.
The above parts are intact and the angle grinder doesn't want to work - so it's time to check the brushes. Perhaps it's time to change them in the grinder. The brushes are constantly heated from work, so they wear out quickly and more often than other parts need to be replaced, and in pairs.

Having excluded all minor breakdowns, it is necessary to understand why the tool does not want to turn on, and how to repair it. Most likely, the malfunctions are serious and require additional knowledge. This happens if:

the body is deformed;
one of the bearings is seized;
the armature or stator does not work;
the teeth of the gear wheel of the reducer are broken or worn out;
the collector is out of order;
the sensor of the control electronics does not show signs of life.

If it is determined that a malfunction has occurred in the mechanical part of the grinder, then you need to pay attention to the condition of the large gear located on the shaft, and to the bushings. If the teeth are partially worn out or the shafts are wobbling, they must be replaced immediately.

The most common breakdowns

Grinder malfunctions happen quite often. Everyone who works with this tool knows about this. What goes wrong most often?

Just one awkward pressing of the spindle lock button while the disc is rotating will break it. It can sometimes be broken if used to remove a jammed disc. To prevent this from happening, you need to use an open-end wrench inserted into the special holes near the place where the disc is attached.

It mainly occurs when a jam occurs. If a rumble is heard in the gearbox, this is a symptom of just such a malfunction. When more than one tooth is broken at the gear, the grinder will not be able to cut the required material.

In order for the tool to continue working, it is necessary to change the gears, and everything, and even the bevel wheel. Before going to the store for spare parts, remember the manufacturer's firm, the model and the power of the product.

This type of breakdown happens with angle grinders, which work in places where there is a lot of dust, and when they are given rest, they are left on the ground. Dust that gets inside will damage the winding. Large loads, especially for a small power grinder, turn into a motor breakdown.

If the grinder is used for cutting materials that create a lot of dust, then it is recommended to cover the ventilation holes with something.

The weakest link, and not only among the grinders, are the bearings. A high speed will quickly wear out the mechanism. The good news is that changing the bearing is easy. Replacing a sprinkled bearing at a grinder must be done in time so that a breakdown does not happen that cannot be fixed.

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This breakdown is easy to determine when the angle grinder has turned on, but the disc revolutions are too intense and differ from normal operation, which means that there is a turn circuit in the stator on the winding. Stator breakdown is considered the most serious, and special skills are required to eliminate it. When you have doubts about yourself, it is better to turn to professionals so that you do not have to buy a new instrument later.

If the decision to fix it yourself is made, it begins with cutting off the frontal parts of the winding, all the remnants are removed.The next step is to make a new winding according to the template. It must be identical in the number of turns, with the same density, and made of wire of the same thickness as the previous one.

LBM, the power of which is less than 1100 W, are usually equipped with spur gears. They are located on the stator. Bulgarians with more power have helical gears. Each of the options has a conical shape, the rod of the grinder's gearbox crosses with the stator shaft at an angle.

Repair of the grinder gearbox mainly consists of replacing the gears. If the disc gear breaks, it is difficult to replace it because it is very firmly fixed. It is easy to disassemble the gearbox:

you need to unscrew the nut from its side;
gently take the rotor body in a vice and knock out the gearbox housing with light blows;
change the position of the clamped rotor and knock out the bearing through a wooden board;
unscrew the gear from the shaft.

The speed regulator is not present on all models of grinders. When the angle grinder is used for cutting, it is, in principle, not needed, but if grinding is carried out, it is simply necessary. If suddenly it stopped working, then, most likely, the board burned out, which must be removed and bought the same in a power tool store for further replacement.

Self-repair of the grinder is not always feasible. If suddenly something does not work out or everything is not clear, it is better to contact the service center.

Before it completely breaks down, the angle grinder signals the beginning of a malfunction.

Pay attention to the work of your assistant: you should be alerted if:

the brushes began to spark too much;
the grinder is heated during work;
the motor hums inside the case when the tool is turned on;
the vibration of the body has become much greater during work;
the grinder's gearbox is bursting inside;
you hear the sound of a creak of bearings during spin-up or periodic wedging when the rotor shaft rotates;
The angle grinder has smoked, or an uncharacteristic burning smell emanates from it.

In order not to buy a new grinder, you need to be careful about the operation of the tool. In case of any deviations from the usual work, start troubleshooting, determine the cause and repair the power tool.

The service life of the grinder directly depends on the owner's care for it. Each instrument needs good care, then it will work properly for a long time.

Any grinder will warm up during operation, but in order to postpone the repair of angle grinders for a long time, you must adhere to some rules in the work:

Do not overload the tool to avoid overheating and smoke.
Do not put pressure on it while working.
Timely clean and lubricate the necessary parts inside the case.
If malfunctions are noticeable, discontinue operation and inspect for malfunctions.
Replace wearing parts in a timely manner.
If the grinder smokes, immediately stop working and do not turn it on again.
Do not use the tool when processing wood-type material.
Hold the grinder firmly during work so as not to drop or damage.

Adhering to the listed simple recommendations and rules in working with a tool called a grinder, you can extend its life longer than provided for by the warranty period.

All budget options for angle grinders have several disadvantages. First, there is no soft start system. This is a very important option. Surely all of you plugged this powerful power tool into the mains, and when starting up, you watched the incandescence of a light bulb, which is also connected to this mains, drop.

This phenomenon occurs due to the fact that powerful electric motors at the moment of starting consume huge currents, due to which the mains voltage sags. This can damage the tool itself, especially those made in China with unreliable windings that could one day burn out during start-up.

That is, the soft start system will protect both the network and the tool. In addition, at the moment the tool is launched, a powerful kickback or push occurs, and in the case of a soft start system, this, of course, will not happen.

Secondly, there is no speed regulator, which will allow the tool to work for a long time without loading it.

The diagram below is from an industrial design:

It is introduced by the manufacturer into expensive devices.

You can connect not only a grinder to the circuit, but, in principle, any devices - a drill, milling and turning machines. But taking into account the fact that the collector motor must be in the tool.

This will not work with induction motors. A frequency converter is needed there.

So, you need to make a printed circuit board and start assembling.

You can download the board at the following link, which is at the bottom of the article.

A dual operational amplifier LM358 is used as a regulating element, which, using a transistor VT1, controls a power triac.

So, the power link in this circuit is a powerful BTA20-600 triac.

There was no such triac in the store and I had to buy a BTA28. It is slightly more powerful than the one according to the scheme. In general, for motors with a power of up to 1 kW, you can use any triac with a voltage of at least 600 V and a current of 10-12 A. But it is better to have some margin and take 20 A triacs, they still cost a penny.

During operation, the triac will heat up, so a heat sink must be installed on it.

So that there are no questions about the fact that the motor, when starting, can consume currents that significantly exceed the maximum current of the triac, and the latter can simply burn out, remember that the circuit has a soft start, and starting currents can be disregarded.

Surely everyone is familiar with the phenomenon of self-induction. This effect is observed when the circuit to which the inductive load is connected is opened.

It's the same with this scheme. When the power supply to the motor is abruptly cut off, the self-induction current from it can burn the triac. And the snubber circuit dampens self-induction.

The resistor in this circuit has a resistance of 47 to 68 ohms, and a power of 1 to 2 watts. Film capacitor for 400 V. In this version, self-induction as a side effect.

Resistor R2 provides current damping for the low voltage control circuit.

The circuit itself is to some extent both a load and a stabilizing link. Due to this, after the resistor, it is possible not to stabilize the power supply. Although the network has the same circuits with an additional zener diode, it makes no sense to use it, since the voltage at the power supply pins of the operational amplifier is within normal limits.

Possible replacement options for low-power transistors can be seen in the following picture:

The PCB that was mentioned earlier is only a board for the soft starter and does not have components to adjust the speed. This is done on purpose, since in any case, the regulator must be brought out using wires.

The regulator is tuned using a 100 kΩ multiturn trimmer.

And the main adjustment is already using the resistor R5. It should be said that a scheme of this kind will not allow adjustment from zero, only from 30 to 100%.

If a more powerful regulator is needed, then it can be assembled according to the following scheme:

This circuit allows you to adjust the power almost from zero, but for the "grinder" it makes no sense.

First, the circuit must be checked for operability by connecting a 40-60 W 220 V light bulb as a load.

If everything is in order, then after disconnecting from the network, you immediately need to check the triac by touch - it must be cold.

Further, the board is connected to the "grinder" and the launch is carried out.

If everything works fine - the grinder starts up smoothly and the speed is regulated - then it's time to start testing under load.

I would like to use the grinder as a cutter, for cleaning, grinding, etc. anything. But here's the problem, these are very high revs. I have two grinders, alas, without speed control. Of course, you can buy another third, with speed control, but I don't see much sense in this.

And using a cup-type attachment with brass-plated wire is generally dangerous. Bo1x it is designed for revolutions up to 5000-6500 rpm. the grinder has a default of 12000 rpm. As a result, the metal wires from the brush scatter, striking everything around with their wire. An unpleasant sensation, and just plain dangerous.

Seeing a block on Ali that allows you to reduce the speed, I bought such a block. Got it, plug it in, it works. Indeed, the rpm has decreased, to the point where the destruction of the brushes does not occur. I will not say that it is possible to reduce these revolutions to zero, but practically at the very minimum, it is halved.

First I tried to put the block in the grinder itself. It didn't work out. There was too little room in the grinder's case. Therefore, I had to make an external block with regulation. But that's not even a bad thing, as it can be used for many purposes.

I made it in the case of an external, two-socket box, I used one part of the bark for the adjustment unit, and the second socket, where the angle grinder is connected. To do this, the very block with sockets had to be sequestered. Yes, so as to leave the fastening for the screw holding the socket housing.
Then I cut out a plate with a hole for an adjustment resistor from a white soap dish.
Since the resistor was originally soldered to the board, in order to place it as intended, it had to be removed from the board by connecting it to the board with wires.

I posted and secured everything. I glued the socket and fastened it with small screws. Now this whole structure looks like a regular extension cord. However, when setting the maximum current, it can be used in this way.

The grinder, being the most demanded tool in the house, is subject to considerable stress and intensive use. Because of this, after some time, it happens that when the engine is started, jerks, a burning smell and other malfunctions appear, suggesting that the angle grinder (angle grinder) has broken down. But do not immediately carry the device for repair or buy a new one. Most faults in this device can be rectified by yourself.

Over the long years of the existence of such a tool as angle grinder, its appearance, as well as its internal structure, have practically not changed. To repair a grinder with your own hands, you need to know the structure of its mechanical part, as well as electrical.

If you look at the figure below, you can see what parts the angle grinder consists of.

Wheel for adjusting the spindle speed of the unit.
An electric motor consisting of a rotor and a stator.
Start button. Sometimes a soft start system is connected to it.
High impact plastic housing.
Spindle lock button (used when changing tools).
Safety clutch. Protects the motor from overload when the tool is jammed.
Protective cover. Covers the tool and protects the user from escaping particles of the processed material, and also prevents injury to a person when a tool is destroyed, such as an abrasive disc.
Tool clamping nut. It can be unscrewed using a special key that comes with the power tool. There are also quick-locking nuts that can be unscrewed without a wrench.
The gearbox housing and the gearbox itself. Consists of a block of gears that transmit rotational movements from the rotor to the spindle with the tool.

The picture below shows electric diagram of the grinder.

The electrical part of the angle grinder has the following elements:

electric cable with a plug for connecting to the mains;
start button;
stator;
electric brushes (carbon or graphite);
collector;
anchor (rotor).

The following figure shows grinder connection diagram, namely its engine.

All components of an electric motor perform specific functions.

Rotor - this is the shaft on which the coils and the collector are located. The rotor, rotating in the magnetic field of the stator, transmits the rotational motion to the angle grinder.
Collector... It is the part of the rotor to which all control cables are connected. Electrical signals from the control unit to the engine pass through the manifold. It is to the collector that the electric brushes are connected.
Electric brushes. Their main task is to transfer electric current from the power cable to the collector.
Stator. It is a coil with a certain number of turns. The task of the stator is to create a magnetic field, which, interacting with the armature, sets the latter in motion.

According to statistics, most cases of failure of angle grinders are associated with the electrical part of the apparatus. Some breakdowns may be minor, which allows you to repair the grinder yourself. But, for example, if the motor windings burn out, only a specialist can repair the angle grinder.

The reasons that the angle grinder does not turn on may be the following:

defective electrical plug;
defective electrical cable;
the start button has broken;
broken contact between the power cable and the button;
breakage of the contact wire of the electric brush;
strong wear of the electric brushes;
failure of the rotor or stator windings.

Then there are more serious malfunctions, respectively, and repair requires certain knowledge and skills.

- breakage or licking of the gear teeth of the gearbox;
- jamming of bearings;
- failure of the armature or stator;
- failure of the control electronics;
- failure of the collector;
- deformation of the body;

When determining the mechanical defects of the grinder, more attention should be paid to the condition of the plonitarka (large gear), shank (gear on the shaft) and bushings. Uneven wear of the teeth or wobbling of the shafts indicates immediate replacement of the worn parts.

Breaking out the spindle lock button.
The reason is just one careless movement, namely pressing (deliberate or accidental) on the button when the disc is spinning. Sometimes breakdowns occur due to attempts to remove a jammed disc using a button. Many grinders have slots on the spindle where the disc is attached specifically for a regular open-end wrench, look at your grinder, most likely you have one too. So, it is better to use them and an open-end wrench than a disc lock button.

Chipped gear teeth.
Usually they arise due to jamming (in such a situation, tool breakage is not the worst thing that can happen). A rumble in the gearbox is a sign of a malfunction. If the gear has lost two or three teeth, then the tool will not be able to cut.
In this case, it is necessary to change the gears by a pair and the gear itself and the bevel wheel. When you go to the store for gears, do not forget to write down the name of your grinder and its power.

Failure of the electric motor.
This often happens with tools that work in dust and which are forced to rest in the sand or on the ground: the sucked-in dust grinds off the winding. However, you can ditch the motor without dust - by strong overloads, especially if the tool is low-power. Therefore, in small Bulgarians, not only the anchor, but also the stator often burns out. Small grinders also have a breakdown of the electronic speed control unit. If you use a grinder to cut very dusty materials, in particular slate, a stocking put on in place of the ventilation slots in the housing helps a lot to protect the tool.

Bearings.
Another sore spot of the Bulgarians (as well as other twisting power tools). Few machines stand out with strong immunities against dust, and high rpm suggests rapid wear. In general, bearings are not the worst failure, they are easy to change. However, it is important to make a replacement on time, otherwise there is a greater likelihood of a more serious breakdown, the repair of which is comparable to a purchase.

Stator
If, when turned on, the disk starts to gain speed and accelerates too much, there is definitely a turn circuit on the stator winding. Stator repair is one of the most serious breakdowns and requires appropriate skills.If you are not confident in your abilities, then it is more expedient to entrust it to professionals or use the services of a repair shop.

We start repairing the grinder's stator by cutting off the frontal parts of the winding, the remnants of which we take out. Next, we make a new winding using a template sandwiched between two large plates on an axis, which can be inserted into an electric drill. The main thing is to achieve an identical number of turns, made with the proper density and withstand the thickness of the wire. We insert two coils into the stator housing, we draw conclusions from the same winding wire, insulating with flexible tubes of the appropriate diameter.

Reducer
In models with a power of up to 1100 W, spur gears are usually used, mounted on an anchor, but grinders with a higher power, for example, 1500 W, require helical gear wheels. Both options are tapered, since the axis of the gearbox stem intersects with the armature shaft, and transmission is possible only by angular engagement of the teeth.
As a rule, repairing the grinder's gearbox consists only in replacing the gears. If a disk gear wheel breaks down, then it will be very difficult to remove it for replacement, this unit is best fixed in the gearbox.

Speed regulator
Almost all modern models of drills, jigsaws, screwdrivers have a speed controller. But not all grinders (grinders) are equipped with such a mechanism. In principle, a regulator is not needed for cutting metal with a cut-off stone, but for grinding it simply cannot be replaced. The proposed scheme of a home-made regulator is very simple and reliable. There are not many parts and they are not expensive. If you already have a grinder without a standard speed governor, then you can easily improve it.

Can be assembled separately in a box with a power outlet and used as a carrier with a power regulator. Or you can immediately assemble the regulator in the grinder body and remove the resistor handle.

The power tool must not be allowed to operate under load for a long time at significantly reduced speeds (this can be determined by ear) in comparison with idle speed, and even more so, clamping (blocking) of the tool must not be allowed, otherwise it will burn out within a few seconds.

Do not turn off the power tool immediately after operating at reduced speed. To prevent local overheating, it needs to run for some time (more than 1 minute).

It is important to strictly observe the intervals for changing (adding) the lubricant and its quantity specified in the operating instructions.

Video (click to play).

Prevention consists in complete or partial disassembly of the tool, cleaning, lubrication and replacement (if necessary) of some parts.
Timely replacement of relatively cheap parts that wear out quickly will preserve more expensive durable components, which ultimately will lead to savings in tool operation, eliminate premature repairs and significantly extend the life of the tool.