# Simple way to test a motor?



## adeyo (Jun 6, 2012)

I am considering buying a motor off of craigslist. I just want to know if there's a way to test the motor when I arrived to inspect it?


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## subcooledheatpump (Mar 5, 2012)

AC? DC?

If it's an AC motor, 3 phase or single phase all you need to do is hook it up to your mains supply. 

If it is 3 phase, connect the line to two of the 3 phases. On the third phase, connect one lead of an AC rated capacitor. The other lead of the capacitor goes on phase one or two. 

If it's a DC motor, I've always heard you can check them from a 12v battery, but just remember to cut the power before they spin too fast


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## Ziggythewiz (May 16, 2010)

If it's series wound DC you can spin it on 12V. I think most just do a visual inspection for weight, name plate ratings, shaft, and commutator conditions (for forklifts and such).

What kind of motor are you looking at?


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## adeyo (Jun 6, 2012)

3 phase ac. I'm inexperienced...could one of you elaborate on that process in stupid man terms?


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## major (Apr 4, 2008)

adeyo said:


> 3 phase ac. I'm inexperienced...could one of you elaborate on that process in stupid man terms?


To test the AC motor, hook it up to your inverter and power supply and run it up to speed.


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## adeyo (Jun 6, 2012)

Well, I don't have an inverter or power supply. I just was going to drive an hour to go pick up the potential motor and I wanted to test it if possible. Didn't know if there was a way to test it on site.


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## major (Apr 4, 2008)

adeyo said:


> Well, I don't have an inverter or power supply. I just was going to drive an hour to go pick up the potential motor and I wanted to test it if possible. Didn't know if there was a way to test it on site.


Do you have any idea what you'd be getting?


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## mizlplix (May 1, 2011)

The only quick/dirty field tests are continuity and Ohm through the motor.

But It just tells you that it has continuity and relatively the same resistance thru the stator coils.

Spin by hand for roughness or noises.

Visual for grease/bearing leaks, discoloration.

Cheap price is not everything. Ask Ivansgarage....LOL

Try to get an inverter duty motor if possible. Select your motor size then get one 1/3rd bigger. (just my observations and experiences to back this up)

Miz


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## Ivansgarage (Sep 3, 2011)

For once Miz is right, check all 3 leads for Ohms, lead 1-2 1-3 2-3 they should be real close, allso
check each lead to ground (case) should be zero ohms. You really need to figure out what controller
ie. voltage you are going to run. (curtis controller) motor needs to be wound for 70-80 volts rms and
100-150 amps continuois.. Any off the self 3 phase motor is only going to be able too handle ie.. 10-20 hp 30-40 amps. Have you seen what inverters put out? So in conclusion any 3 phase of the self
motor is not going to handle ev use..

Last ? how many people have you seen, or heard of useing a 3 phase
of the self motor?


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## major (Apr 4, 2008)

Ivansgarage said:


> ..... allso
> check each lead to ground (case) should be zero ohms....


Ivan,

.....should be infinite Ohms, not zero.

But I agree with what I think you're trying to tell adeyo. That is that he is biting off more than he can chew. Some of the members have been seemingly encouraging him to go AC. That is a bad idea for a first timer unless he has a lot of experience with AC drives or a dad who is in the business.

For a first time conversion, go DC, or buy an AC kit.

major


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## PStechPaul (May 1, 2012)

It is possible to test a motor on single phase by spinning it manually. You can even run a 240V motor on 120V - just barely - but enough to check for major problems. I have also run my 3 phase motor using a capacitor and inductor to get phase shift, and possibly just a motor run capacitor of about 100uF or so to the third winding may be enough.

But you can get a VFD fairly cheap, and they will usually run on single phase although often at reduced power. You'll need a controller anyway, so might as well get one before getting the motor. The controller can usually be programmed to work with just about any motor. You can probably use a small VFD to test a motor up to 10x its rating just to spin it under no load for testing.

Also, the ohmmeter frame leakage test is not really sufficient. You should do a Hipot or insulation resistance test at 1250 VDC for 240V motors and 2500 VDC for 480V motors. Connect all three leads together to avoid inductive transients and measure from them to the frame. Be sure to reuce the voltage back to zero before removing the tester. The windings have a lot of capacitance and can hold the voltage for quite a while.

It is best to use something like this:
http://www.ebay.com/itm/5-KV-DC-HIG...222?pt=LH_DefaultDomain_0&hash=item25744d3676

Something like these are OK, although they only go to 1000V:
http://www.ebay.com/itm/Digital-Meg...595?pt=LH_DefaultDomain_2&hash=item4606d29483
http://www.ebay.com/itm/BM500A-1000...lectrical_Equipment_Tools&hash=item337168534c

A "poor man's" tester would be to plug the motor into a GFCI outlet and see if it trips.


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## Ace_bridger (Nov 22, 2011)

If your spinning up a DC motor on 12V (or more) I would suggest using a contactor to switch the supply...if you just jam the wires onto a battery you risk arcing and damaging the battery terminal and/or any terminal on the motor wires.

I tested mine on 12V and got nothing so tested on 24V and off it went. Sticking bush?


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## McRat (Jul 10, 2012)

Ace_bridger said:


> If your spinning up a DC motor on 12V (or more) I would suggest using a contactor to switch the supply...if you just jam the wires onto a battery you risk arcing and damaging the battery terminal and/or any terminal on the motor wires.
> 
> I tested mine on 12V and got nothing so tested on 24V and off it went. Sticking bush?


I saw the same thing on a motor I knew for a fact was in good shape. In my case, there weren't enough amps to start the motion. When I gave it more power, it jumped off the bench instantly.

Note to self: Always bolt motor down prior to testing.


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## adeyo (Jun 6, 2012)

Lol. I'll remember that. Thank you guys for the tips. Really helpful for me.


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