1
\$\begingroup\$

I've been given a bench grinder (rated for 150W @ 230V), which uses a (psc motor?), just an induction motor with start/run capacitor/winding (it has no centrifugal switch whatsoever).

I always wanted to use an atmega to make a 3 phase inverter for motor control, but the high voltages and currents involved at mains have always set me back.

So I thought that being useless as a grinder, because it bogs down as you try to sharpen anything (besides that I already have one three times as powerful), I could try rewinding it for 12 volts three-phase and use a pc power-supply to play around with it.

That way I'd save the mains-filtering and rectification part of the inverter, and yet have 5 volt supply for the micro out of the box.

However, been looking for a while on the internet and found nothing related, so just wanted to ask, would it be worth the effort?

I still have to count motor's number of poles to check it can be three-phase, but the fact nobody has ever done this before leads me to ask.

Cheers!

\$\endgroup\$
  • 1
    \$\begingroup\$ Way too broad but I like your ambition! \$\endgroup\$ – winny Feb 26 '18 at 16:09
  • \$\begingroup\$ About the only benefit is educational. As Charles says, the only physical issue is slots. You have two coils at the moment, start and run using non-salient poles. You need an even multiple (2-poles/phase) of 3 slots to convert your stator to three-phase. That should be easy to determine. \$\endgroup\$ – StainlessSteelRat Feb 26 '18 at 17:07
2
\$\begingroup\$

Whether or not it is worth the effort mostly depends on how much education or enjoyment you gain from the project. It is certainly not something that will provide something useful for less than you would have to pay to buy it as a new motor and variable frequency drive (VFD or inverter).

If the motor has a compatible number of slots, it can certainly be rewound for three-phase power. Winding it for 12 volts may be quite a bit more difficult than 60 volts or 30 volts. At 12 volts, the wire will be quite a bit larger and one turn difference in the number of wires in a slot will will be more significant.

You probably can not get very far with a project like this without good reference material.

Most questions about how to do it will be way too broad for this forum.

Re Comments:

Winding the motor for three-phase should provide a motor with performance comparable to a motor designed to be a three-phase motor. Winding for a lower voltage will be similar, but the internal voltage drops in the motor will increase significance as the voltage is reduced. VFD operation always faces that problem. At higher frequencies, constant V/Hz provides good performance, but but the V/Hz needs to be increased to compensate for internal voltage drops at low frequencies.

The DC power supply can be very simple. All that is needed is a transformer, rectifier and capacitor plus a system to limit the capacitor charging current.

\$\endgroup\$
  • \$\begingroup\$ For unloaded demonstration purposes, it may be possible to run the motor severely under-voltage. I've seen a 208-volt or so motor run from a 24v or 30v DC bench supply feeding an experimental VFD. So maybe the motor can be wound for as low a voltage as physically practical, and then undervolted. \$\endgroup\$ – Chris Stratton Feb 26 '18 at 19:17
  • \$\begingroup\$ Thanks guys. I have to say I'm a bit versed on the driver part, and I got all the components needed for it since long ago. If I'd need to buy a 30 or higher volts power supply, then I could live with that. My question is more if the motor (taking for granted here it can be wound as a three-phase one) would behave the same as if driving a proper one at 230V. Thus I'm trying to use this as a test-bench. I'm sure you'll understand Charles, that buying a motor and a vfd is not what I'm after here. \$\endgroup\$ – user1476851 Feb 26 '18 at 20:20
  • \$\begingroup\$ Revised answer per comments. \$\endgroup\$ – Charles Cowie Feb 26 '18 at 20:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.