Soft starter for power tools with their own hands

Models for 600 W angle grinder

For 600 W power tools, starter motors with triacs are used, the overload capacity of which does not exceed 10 A. It’s also worth noting that there are many devices with overrides. They are protected and not afraid of high temperatures. The minimum frequency for 600-watt grinders is 30 Hz. In this case, the resistance depends on the installed triode. If it is used of the linear type, the above parameter does not exceed 50 ohms.

If we talk about duplex triodes, the resistance at high speeds can reach up to 80 ohms. Very rare models have stabilizers that operate from comparators. They are most often mounted directly on modules. Some modifications are made with wired transistors. They have a minimum frequency starting at 5 Hz. They are afraid of overload, but are able to maintain high speeds at 220 V.

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How to make a soft start for power tools with their own hands

If you buy a cheap angle grinder, it will probably lack the soft start option. During start, especially powerful angle grinder, you can feel all the “charm” jerk, which produces an angle grinder when you turn on. With a soft starter, the power tool will begin to do its job in a comfortable environment for the user. Undoubtedly, the angle grinder with such an option is more expensive. However, it is possible to install a soft starter on the angle grinder yourself. This solves the problems of cost savings and facilitates further operation. a device made by hand is easier to repair in case of failure.

Principle of operation

During start-up of the electric motor of collector type, there is a significant short-term increase in current consumption, which causes the premature failure of electric tools and its delivery for repair. There is wear and tear on the electrical parts (7 times the current) and mechanical parts (abrupt start). For soft starters, soft starters must be used. These devices must meet the basic requirements:

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 that look similar to KRRQD.

But they are based on a slightly different principle and should be installed after the START button, in the tool itself. 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.

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

Without the button, such a device would be permanently energized to 220V, which is not acceptable.

In the two-wire unit, there is no such a thing, because 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.

One more point. 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.

Controlling part

Let’s consider the work of the control part of the SPM wiring diagram.

The important element here is the start and stop circuit input terminals. There are two types of control circuit. 2-wire and 3-wire. Type of control selectable by the user via control panel.

Two-wire control circuit

The diagram shows a locking key (switch) K. When its contacts are closed, the SPM starts, when they are open, the soft stop process begins.

The “Instant Stop” contact should normally be closed. It shows the emergency circuit, e.g. “Emergency stop” button, or limit switches for opening safety guards. As soon as this circuit is broken, the soft starter stops the engine accidentally.

If the tool is not equipped with a speed regulator, then it does not need one. An angle grinder, for example, is always used at full speed, otherwise it becomes dangerous. Why would a power tool need a soft starter? There are many reasons for this, because a sharp start of the motor of the same grinder or electric grinder causes:

  • Burnout of brushes and rotor blades;
  • current shock in the power grid;
  • An attempt by the tool to escape from the hand, which is not safe;
  • Strong starting shock of gears against each other, causing their rapid wear.

With a soft start there will be no current or mechanical shock. The motor of the power tool will start smoothly and reach its maximum speed.

A BPP with a variable speed drive

Here is another variant of self-made carrying with BPP and speed regulator. The following diagram shows the power tool’s smooth-running performance at rated speed. The acceleration time to the declared speed depends directly on the capacitance of the used capacitor C3. Variable resistor R2 of group A is used for speed regulation.

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Schematic diagram of a soft starter with speed regulator

It is possible to install a soft starter directly into the handle of the power tool, but this is a more complex upgrade and, as already mentioned, it can lead to forfeiture of the right to warranty repair. The optimal option to assemble a soft starter with a speed regulator. is to use a junction box. This scheme uses a triac TS122-25-5, but you can install almost any device with a voltage class not less than four and a current of at least 1.5-2 ratings.

Carrier with a soft starter and speed regulator

Thyristor soft starter for asynchronous electric motor. Assemble your own hands.

It is well known that not every tool is equipped with such soft start circuits. They mostly come in expensive models of well-known brands Bosch, Hilti, DeWALT. And both in the mains and in the battery range.

A power tool without such a device has a lot of disadvantages:

    gears bump against each other and trigger more quickly

When working with an end saw that has a PP, the disk will not stray from the prepared cutting point. Which is important for non-professional carpenters.

If you have a cottage or house in the initial stage of construction is not yet electricity and you use a generator, then sooner or later you will realize that without PSU (soft starter) with a sharp initial currents, the generator will not last long. Therefore, such a thing is able to save not only tools, but also emergency power supplies.

Of course it is possible to build BPP inside the angle grinder or slicer, but not everybody wants to dismantle equipment and get into the guts.

In addition to all that, opening a new case will cause a loss of warranty. So the best use for the KRRQD12A is the external connection.

Only keep in mind, it is suitable for collector motors. For asynchronous, you need a frequency converter with different principles of regulation.

This box is designed for a current of 12 Amps.

What is characteristic, the dimensions are the same, but the price difference is a couple of tens.

It would seem better to take it, but for a standard 16A socket, the first option is more profitable. There will be no desire to connect a more powerful load and thereby to burn all the contacts.

Masters certainly build similar circuits and their own hands, based on thyristors BTA 12-600 or others, capacitors, a diistor and a couple of small resistors. You can find a lot of examples of schemes on the Internet.

But for the average tool user, it’s much easier to buy it all in a ready-made compact case. You can order a similar unit from here.

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Soft starter for power tools

It’s common knowledge that not every tool is equipped with such soft starter circuits. They usually come in expensive models of famous brands like Bosch, Hilti, DeWALT. And both in the power line, as well as in the battery line.

A power tool without such a device has a lot of disadvantages:

  • gears hitting each other and triggering faster
  • Dangerous jerking start that lifts the tool out of your hands and increases the risk of injury

When you work with a coping saw, the blade will not run off the prepared cutting point. Which is not unimportant for non-professional carpenters.

If you have a cottage or house in the initial stage of construction is not yet electricity and you use a generator, then sooner or later you will realize that without PSU (soft starter) with a sharp initial currents, the generator will not last long. That’s why such a thing can save not only tools, but also emergency power supplies.

Soft starter power tool

It is possible of course to build BPP inside the angle grinder or crosscut saw, but not everybody wants to disassemble equipment and rummage in the guts.

Plus, on top of everything else, opening a new case entails the loss of warranty. Therefore, the best application for the KRRQD12A is an external connection.

Just keep in mind, it is suitable for collector engines. For asynchronous machines you need a frequency converter with different control principles.

This box is designed for 12 Amps.

Characteristically, they have the same dimensions and the price difference of a couple of dozen.

It would seem better to buy it, but for a standard 16A socket, the first option is more profitable. There will be no desire to connect a more powerful load and thereby scorch all the contacts.

Masters certainly build similar circuits with their own hands, based on thyristors BTA 12-600 or others, capacitors, a diistor and a couple of small resistors. You can find a lot of sample circuits on the internet.

But for the average tool user, it’s much easier to buy it all in a ready-made compact case. You can order a similar unit from here.

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