How to use arduino to control big DC motor by using thyristors.?

I have big DC motor what I want to control. It is making 1-2000 rpm and should use max 300V and 50A. At least I think it is so because there are no labels on the motor and almost no information about that working bench.

It is С1Е61А metal lathe using пто-м-230-50-у4 rectifier from 1977. Motori is from ПБСТ family should be Электродвигатель ....кВт ......... об ПБСТ43М ...... В IM1001 unfortunately I don't now exact parametsics. This lathe was produced for military use. There are some info about lather, rectifier and DC motor but no info to all of them together.

Rectifier is using tachogenerator to see motor RPMs, unfortunately tachogenerator is dead and can't repair. Everything in the rectifier box is working but I think it is nonsense to use arduino to make only tachogenerator info for the rectifier. There are to many parts what can die. Here (PDF) are technical sheet for the thyristors (unfortunately they are in Russian)

Backstory It was 1977 when Russians made this metal lathe. I bought it in spring, engine wasn't so powerful as I expected but I thought I can repair it. How hard can it be it is mechanical electronics. My knowledge in electronics isn't so good so I was looking person how know that old electronics. In some point I realised that I have friend who has big knowledge about that. After few days we discovered that someone had made some extra connections to fool rectifier and tachogenerator actually do not work. Unfortunately I haven't found new on, only used ones are in the market and with toes parts are too big risk that they aren’t working properly. So here I am, I think most efficient way to get engine works properly is to use arduino as a brain what are monitoring engine RPMs and giving commands to thyristors and ofcourse potentiometer for speed control.

Just for fun some pictures:

Russian technology is known for robustness, that's why it has been working for over 40 years now. But 300V 50A DC is no fun or hobby project, and even if an Arduino can control the speed of any DC motor, the hardware between Arduino and such a machine is a science of its own. I'd contact a machinery company for refurbishing that machine, or buy a new one. If you bought the machine recently, it was a very bad deal :-(

It is almost impossible to use a thyristor to control a DC motor. Once triggered a thyristor will stay on until the current or voltage is reduced to zero. Well to be strictly correct to a very low value given in the data sheet.

The only way I know how to do this is by discharging a large capacitor to oppose the current thus reducing the flow through the thyristor to a negative value and thus commutating the thyristor.

I have never seen this done with a very large current and I think motor speed control with this method is not possible.

I think you may have the component wrong and don’t mean a thyristor at all.

What you might mean is a power FET and applying a PWM signal to the gate.

With that kind of currents/voltages you may have to look for IGBTs, rather than MOSFETs. You will also want to look for someone that has actual experience and training in handling this kind of power (you're switching some 15 kW!), as 300V DC is lethal, and combined with 50A can give some interesting fireworks.

Looking at the PCB I see four big components with heat sinks - that must be the thyristors you mention. Is it possible that those thryistors are in bridge rectifier configuration? That would explain why you have four of them (in case of three phase power you'd need six). Now of course I'm not exactly familiar with old Russian technology, but I don't see anything that could be a bridge rectifier other than those four parts, and it would be the only sensible way to control a DC motor with thyristors, and actually quite sensible when it's powered by AC.

MOSFETs and IGBTs can be used in a similar manner, and with appropriate gate drivers can in turn be controlled by an Arduino. Reading the tachometer signal is of course quite easy to do with an Arduino.

I also guess that the thyristors form a controllable bridge rectifier.

DrDiettrich: I also guess that the thyristors form a controllable bridge rectifier.

How does that work then with DC?

Grumpy_Mike: How does that work then with DC?

OP mentioned the motor is a DC motor. They didn't mention how the power is provided to the whole assembly - I think it's quite safe to assume it's plugged in to mains AC power (with a plug that's a bit bigger than your normal household plugs, I'd wager), especially as OP does mention there's some kind of rectifier in the mix.

Here is wiring diagram, how it was made "mechanically" |500x338 Rectifier box itself are working but it does not see engine RPMs anymore. I was planning to use rectifier Diode Bridge on the rectifier.

Can you find out how rpm should be detected (optical...)? Perhaps it's easy to replace a defective part.

RPM are detected by using tachogenerator. unfortunately tachogenerator is dead and can't repair. Unfortunately I haven't found new one on sale, only used ones are in the market and with those parts there are too big risk that they aren't working properly.

It is almost impossible to use a thyristor to control a DC motor.

Thyristors are de-facto standard for DC motor variable speed control because just like the OP’s drive, it has an AC supply.

The drive can probably be converted to use armature voltage feedback rather than a tacho, most drives provide this ability.

I do not see a tacho in the diagram provided, is it connected to points 46 and 66 on the schematic?

My bad in my last post, that is only Rectifier wiring diagram. Unfortunately I don't have full diagram.

Here are diagram how is tachogenerator related to rectifier. |500x270

Is the RPM settings pot working?

Yes pot is ok, everything except tachogenerator is working.
In the tachogenerator rotor there are too many failed connections (there are 93 wire and commutator connections and 49 are broken), it does not produce any power.
With my friend we tested all other component, they are working(how long, who knows, they are from 1977 and older)

What voltage and what signal pattern did the tachogenerator deliver to the motor when it was working?

Here is something what I need. But I need potentiometer where I set motor RPM and RPM sensor. Can I use car engine crankshaft sensor and drigere wheel? Do I have to use transformers TR1 and TR2 can't I use p-fets to control tyristors?


Can you tell us your electronics, programming, arduino, hardware experience?

Thanks.. Tom.. :)

What voltage and what signal pattern did the tachogenerator deliver to the motor when it was working?

Voltage should be 0 to 70+ linear rise.


Can you tell us your electronics, programming, arduino, hardware experience?

Thanks… Tom… :slight_smile:

Unfortunately my knowledge in electronics, programming, arduino, hardware isn’t good.
I have friend who knows a lot of on DC, has give me lot of good advice.
And another friend who will help me on arduino and programming, he has some experience in programming and arduino.

Here is diagram what I can use from old Rectifier box. I know that all of it is working as it have to and are perfect to the motor. |317x500

So all I need is to control it ;)