Check 3 phase motor

[Bsmith]

Yesterday I bought a 3 phase motor from the local scrap yard. All looks good, rotates fine and not had much, if any, use to my way of thinking.
I hope to use it on a lathe via a vfd.
Is there some way I can check that it is in working order with a multimeter or some other way?

 

[minimutly]

You need. 500V megger with an ohms scale. Measure the end to end winding resistance and windings to Earth with the megger.
Funniest test I ever did - motor ok to Earth but all windings open circuit. Turned out the apprentice who was attaching plant labels drilled through the casing and windings - then denied it!

 

[Turbo]

You can test run it from a single phase supply by using a capacitor to create a dummy 3rd leg. Plenty of info online on how to do it.

 

[daleyd]

As said a megger is the usual way of testing, if you don’t have one then a multimeter set to resistance will give you an indication of it’s ok - set to resistance measure between the three phases and they should all read a few ohms, but importantly they should all read the same.

Then measure between each phase and the earth point or the metal motor housing, and it should read infinity, or at the very least some value in the M ohms range.

Using a multimeter isn’t as good as a megger because it’s measuring resistance using a very low internally generated voltage, as opposed to a megger which generates the same (or more) high voltages as the motor is going to see when it’s running, but it will give you a good indication of if it’s at least somewhere near.

 

[Hopefuldave]

That's currently linked for 240v, and as said a *run* capacitor between one powered phase and the loose phase should see it spin up, don't use a start capacitor (for more than a few seconds) unless you enjoy chaff flares going off in your shed and the ensuing clean-up. Don't ask.

 

[minimutly]

For winding resistance you need ohms (0 to 10 or less). For insulation test (to Earth) you need 500V megohms range.

 

[Bsmith]

Thanks all, best I have is a multimeter, I'll go over the windings ends with it.
Maybe buy a megger or try to find someone who has one, no rush, we will see.
Thanks again

 

[Pete.]

I think TBH going by what I see in the pics I would expect that motor to be perfectly servicable.

 

[brightspark]

as above looks mint

 

[Bsmith]

I think TBH going by what I see in the pics I would expect that motor to be perfectly servicable.

I agree judging by apperance Pete. It's just that I pulled it out of a skip and who ever put it in did it no favours.

 

[Erie Fred]

Thanks all, best I have is a multimeter, I'll go over the windings ends with it.
Maybe buy a megger or try to find someone who has one, no rush, we will see.
Thanks again

what I have done, when checking with the ohm meter, is then give the shaft a simple spin.
You should see the numbers move.

 

[brightspark]

I agree judging by apperance Pete. It's just that I pulled it out of a skip and who ever put it in did it no favours.

as long as shaft isnt bent or the fan isnt catching or full of water it will be fine .theres plenty of 3 phase motors get chucked and changed to single phase

 

[Bsmith]

as long as shaft isnt bent or the fan isnt catching or full of water it will be fine .theres plenty of 3 phase motors get chucked and changed to single phase

Ok thanks bs, I got another while the going was good, it has a few broken cooling fins and the fan hits the cowling but I recon it will be ok with a bit of panel beating.

 

[Guineafowl]

Thanks all, best I have is a multimeter, I'll go over the windings ends with it.
Maybe buy a megger or try to find someone who has one, no rush, we will see.
Thanks again

Yes, just separate the U V W windings, check resistance is the same, check they’re not shorted together or to earth. On a test run you could then check current to each one is the same.

 

[Bsmith]

I got another while the going was good, it has a few broken cooling fins and the fan hits the cowling but I recon it will be ok with a bit of panel beating.

The other salvaged motor.
I'm sure I can batter the cowling into a condition that will be good enough but could I rebuild the fins with fibreglass or something similar or do I not need to bother.

 

[6ply]

Ok thanks bs, I got another while the going was good, it has a few broken cooling fins and the fan hits the cowling but I recon it will be ok with a bit of panel beating.

You can buy replacement fans cheaply on AliExpress if you don't mind the wait.

 

[Bsmith]

You can buy replacement fans cheaply on AliExpress if you don't mind the wait.

The fan itself is ok, it's the cooling fins on the motor case I wonder about?

 

[sparkysy]

That'll polish out!
Seriously though take it off and use a round dolly or a piece of rounded hardwood and most of that should come out enough not to impede the fan blades.
Or make a new one!

 

[Bsmith]

Ally air flow fins/channels that are broken on the motor case. Is the damage negligible?

 

[Hopefuldave]

Ally air flow fins/channels that are broken on the motor case. Is the damage negligible?

Will you be running it at max load / current in a sweltering equipment room for hours or days on end? If not... yeah, it'll be fine, if you're that bothered about cosmetics you could build the fins back up (TIG on bits of ally plate?). The motor on my bandsaw (a 7x12 with the dead original single-phase swapped for a bigger 3-phase - Hotrod Bandsaw!) is missing the fan cowling and a few chunks of fin (it WAS out of a skip...), the motor casing's never got even warm to the touch...