VFD testing operation question?

[Mr Fixit]

Hi Group,

I have the opportunity to buy a 3hp VFD for a good price and was wanting to test it before I buy it. Can you apply power and run it without a load and see the output with a digital meter or do you have to have a motor load to see it run?

Hope to get it today if I can confirm this question.

TX
Mr fixit for the family
Chris

[J Tiers]

You can.

You do not really need a meter, you can verify that the output frequency changes and it does not fault out. Nothing WRONG with a meter, but it will probably read a different voltage than it would with a motor on it.

3HP usually does not have a "load prover", so generally will not look for a load. At 5 HP, it is pretty common. If it has one, it will show a "no load" fault, and you will not know anything.

What brand?

Old models may be peculiar.....

[Noitoen]

You will have to change the parameters to avoid "output phase loss" error.

[The Artful Bodger]

I would not connect it to anything except a motor supplied/borrowed from the vendor. Connect anything else and it does not work you run the risk of being accused of having 'broken' it.

[Doc Nickel]

I would not connect it to anything except a motor supplied/borrowed from the vendor. Connect anything else and it does not work you run the risk of being accused of having 'broken' it.

-This.

I believe most VFDs won't even cycle/start without a motor connected, but even if they did- or your forced it to- I'm given to understand that's not good for the capacitors.

Doc.

[Mr Fixit]

Hi Guys,

I got it after all, but was not able to test it because the fella had moved from his home to an apartment and he didn't have 240v accessible. It is a older Micropaq N2 Series which when you look at the model/serial label it says TECO on it, so I think I might have done good. $125.00 for a 3ph 3 HP VFD. No smoke smell and all looks good on the inside when I cracked the case open. I'll be able to test it sometime this week, dinner is soon and then I have to be at work early this week. 😴

TX
Mr fixit for the family
Chris

[J Tiers]

-This.

I believe most VFDs won't even cycle/start without a motor connected, but even if they did- or your forced it to- I'm given to understand that's not good for the capacitors.

Doc.

Most all decent modern VFDs in the low HP range have no problem with running open circuit. Some, usually at 5 HP and above, but sometimes lower, DO have a "load prover" on them, and will not work with no load.

A meter on the output will not be a problem, although the meter may not read right, and some meters may not like the signal.

The "load prover" is usually more for protecting the motor and less for the VFD itself. A few much older VFDs may not like no load, but modern ones have no issues.

We would always check a VFD for operating with no load if there was any question of what section of the system had the problem. A bad VFD (shorted device) will fail that test, and will throw a code. If it did not at no load, but did when connected, we'd check the wiring and motor.