Smooth start of an angle grinder on accessible parts

People who often use power tools sometimes encounter the following problem: the engine of a grinder, circular saw, planer or other equipment starts very abruptly. Such a sharp start is fraught with many troubles: firstly, there is a high starting current, which does not have the best effect on the wiring, secondly, a sharp start of the engine quickly wears out the mechanical parts of the tool, thirdly, ease of use decreases when starting the grinder you have to hold it tightly, it tries to break free from your hands. Expensive models already have a built-in soft start system that easily copes with all these troubles. But what to do if this system does not exist? There is a way out - to assemble a soft start circuit yourself. In addition, it can be used with incandescent light bulbs, because most often they burn out at the moment they are turned on. A soft start will significantly reduce the chances of a light bulb burning out quickly.

Scheme

On the Internet you can often find a soft start circuit built on a rather rare domestic microcircuit K1182PM1R, which is not always easy to get now.That is why I propose an equally effective circuit for assembly, the key link of which is the available TL072 microcircuit; you can also use LM358 instead of it. The time it takes for the engine to reach full speed is set by capacitor C1. The larger its capacity, the more time it will take to overclock; the best option is 2.2 µF. Capacitors C1 and C2 must be designed for a voltage of at least 50 volts. Capacitor C5 - at least 400 volts. Resistor R11 will dissipate a decent amount of heat, so its power should be at least 1 Watt. Any low-power transistors can be used in the circuit, T1, T2, T4 have an n-p-n structure, you can use BC457 or domestic KT3102, T4 has a p-n-p structure, BC557 or KT3107 are suitable in its place. T5 - any semistor suitable for power and voltage, for example, BTA12 or TS-122.

Making a soft start

The circuit is assembled on a printed circuit board measuring 45 x 35 mm, the board is laid out as compactly as possible so that it can be built inside the body of a tool that requires a soft start. It is better to solder the power wires directly into the board, but if the load power is small, then you can install terminal blocks, as I did. The board is made using the LUT method, photographs of the process are presented below.

Download the board:
plavnyy-pusk-bolgarki.zip [20.96 Kb] (downloads: 2285)

It is advisable to tin the tracks before soldering the parts, this will improve their conductivity. The microcircuit can be installed in the socket, then it can be easily removed from the board. First, resistors, diodes, small capacitors are sealed, and only then the largest components.After completing the assembly of the board, it is necessary to check it for correct installation, ring the tracks, and wash off the remaining flux.

First launch and tests

After the board is completely ready, you can check its functionality. First of all, you need to find a low-power light bulb of 5-10 watts and connect it to the board through a 220-volt network. Those. the board and the light bulb are connected to the network in series, and the OUT output remains unconnected. If nothing is burned on the board and the light does not light up, you can connect the circuit directly to the network. The same low-power bulb can be connected to the OUT output for testing. When connected, it should smoothly gain brightness to maximum. If the circuit works properly, you can connect more powerful electrical appliances. During prolonged operation, the semistor may become slightly warm - there is nothing to worry about. If there is free space, it would not hurt to install it on the radiator.

Dangerous mains voltage is present on the board during operation, so precautions must be taken. Under no circumstances should you touch the board parts while it is connected to the network. Before turning on, make sure that the board is securely fastened and that no metal objects that can cause a short circuit will fall on it. For reliability, it is recommended to fill the board with varnish or epoxy resin, then even moisture will not harm it. Happy build!

Watch the video of work

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Comments (11)
  1. Richard
    #1 Richard Guests 21 June 2018 15:59
    0
    And how much hazel grouse will such a scheme cost if you order it?
  2. Valery I.
    #2 Valery I. Guests 21 June 2018 21:17
    0
    Maybe it's a triac?
  3. Rybochka
    #3 Rybochka Guests 22 June 2018 19:35
    2
    didn't see any difference
  4. Vovan
    #4 Vovan Guests 26 June 2018 22:47
    0
    Everything is much simpler! Buy yourself a “modern” grinder! All previous problems will “dissolve” into non-existence!
    1. Guest Andrey
      #5 Guest Andrey Guests 2 July 2018 13:55
      5
      We bought a Makita instead of the deceased Devault... What other “modern” angle grinder do you know that doesn’t have a sharp start? If you don't know how to work with your hands, take the flag into your hands - make purchases!
  5. Michael
    #6 Michael Guests 12 July 2018 12:38
    1
    What about the radiator for the seven-stor?
  6. Guest Sergey
    #7 Guest Sergey Guests 21 January 2019 20:57
    1
    Tell me. Is your device constantly connected to the network, and the load, as in the diagram, is in series with the triac and is turned on by a standard switch?
  7. glblba
    #8 glblba Guests 13 April 2019 14:59
    1
    It only works when plugged directly into a socket; it does not work from the standard button of the instrument. The resistance is 20 kOhm.
  8. Guest vladimir
    #9 Guest vladimir Guests 9 May 2019 19:39
    5
    Error ! Transistor T4 is installed incorrectly. The pin of triac G is connected to pin E of transistor T4, according to the diagram it must be connected to pin C of transistor T4 (see diagram)
    Change it when installing in a mirror!
  9. Guest Victor
    #10 Guest Victor Guests June 23, 2019 11:59
    5
    I am very confused by the absence of a bias resistor on the T4 base. The circuit was ripped off from some source and everyone has the same thing. By the way, there is a video from YouTube of the launch of an angle grinder where the circuit is completely different. It’s not good, my friend, to sell it in vain.
  10. Guest Sergey
    #11 Guest Sergey Guests 14 October 2019 19:25
    0
    on the diagram bc547, bc557, and which ones are on the board?