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I’m working on a project where I want to run a 3-phase induction motor (see picture for specifics) using a VFD (Variable Frequency Drive). The VFD I have is a cheap Chinese one (the “T13-750w-12-H”), but I’ve seen others have success with it.

However, when starting the VFD, the motor does spin, but with a slight hum and vibration, and it gets super hot after a few minutes running it at only around 10 Hz. Now I know that these are symptoms of a lost phase, but I’ve tried actually disconnecting a whole phase and that is MUCH more aggressive. I’ve also checked the voltage across each phase as its running and it looks fine in terms of evenness of voltage (at least to my untrained eye). Running the motor slowly (as low as a single Hz) you can even see how the rotor almost stops rotating for a split second every 6th of a turn or so.

The VFD is configured correctly, I’ve tried every setting I can find that’s relevant.

I’m starting to think it might be the VFD that is faulty.

Does anyone have any ideas?

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    \$\begingroup\$ Picture didn’t make it - can you edit your question and try again? \$\endgroup\$
    – Bryan
    Jan 22, 2023 at 0:01
  • \$\begingroup\$ Check each phase, you might have a weak one. \$\endgroup\$
    – Gil
    Jan 22, 2023 at 2:21
  • \$\begingroup\$ There seem to many settings that may be relevant.|| Delta connected? || Spec sheet here with manual links nvcnc.net/t13-400w-12-h-t13-750w-12h.html \$\endgroup\$
    – Russell McMahon
    Jan 22, 2023 at 5:34
  • \$\begingroup\$ One thing to consider is that if you are using this with single phase input, the bus link capacitors may not be fully capable of holding a steady voltage with sufficient ripple filtering to run smoothly. However, at low speeds the V/f algorithm should place less demand at low speed. But at a low PWM duty cycle slight variations of pulse width may cause less stability. Maybe try changing carrier frequency. And also select simple V/f mode rather than FOC or other complex algorithms. \$\endgroup\$
    – PStechPaul
    Jan 22, 2023 at 6:56

2 Answers 2

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Running a motor at 10 Hz can cause serious heating, unless it is rated for VFD use and has an internal fan for cooling at low RPM. You might also be able to add an external fan or blower if you really need to run it so slow. It also may be unstable without a load like a flywheel. Hopefully you can supply images of the VFD and the motor, and any faceplate data or link to manuals. There are also many settings for the VFD that might help, but you will need a manual for that.

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Thanks very much for the comments and answers. It turns out that the VFD was overcompensating voltage at low frequencies (pushing almost 90V per phase already at 5hz...). After trying most settings on the VFD, I found that setting the compensation to the lowest possible value (10V) seems to have solved the problem. Now its pulling a much more reasonable ~36V per phase at about 10hz which seems to be what its rated for.

The documentation of the T13-750w-12-H has the wrong limits for the different settings as well, so had to trial and error each setting to find the real min/max.

Sorry about the pic not coming through, will make sure it does next time.

If anyone comes across a similar problem, happy to share more details!

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