Is my motor toast?

[dawesy]

So as some of you know I'm restoring a churchill lathe.
The motor was missing its data plate so I was unsure what size it was.
After calling a few motor refurbishers it was thought that it was less than 2.2kw ( the overload trip in the original DOL starter was set at just under 2A).
It was wired in star but fortunately the star connection was easy to get at. Reworded it in delta and got a 2.2kw inverter.
I've connected it up and although it runs it runs very slowly and can easily be stopped by hand. If I increase the hz above 50 the spindle slows although the pitch of the motor goes up. Are the windings of the motor screwed? I was unable to test before purchase but was told by the seller that it worked fine ( yeah that old chestnut)
Any help would be appreciated.
I don't mind getting another motor but want to make sure it's not some thing simple first.

[Swarfing]

Swap one of the three legs over and try again. it may run in reverse but don’t worry can just swap the first with last wire to correct that if it happens.

[BillTodd]

does it smell burnt?  check the resistance of each of the phases (they should match)

Or could you have one of the delta phases reveresed?

bill

[dawesy]

Not really. It's a little crispy inside ( if it's the original from the lathe, that's 1930's)
I separated the wires into 3 coil pairs then connected these up according to a delta diagram a1 connects to c2. B1 to a2, c1 to b2 with the bridges going from a1 to a2 etc. I did try it with the coils reversed ie a1 to b2, b1 to c2 and c1 to a2 but the effect was the same. The motor makes no smells or unusual noises in operation, just the spindle turns very slowly.

[awemawson]

DC resistance check needed. First separate the coils and check they are not leaking to earth by checking on a high resistance range to the case. Then check that there is no leakage between the coils. Then on a low ohms range check the three coils and record their resistance, they should be very close - you'll need a digital meter for this. Then check the phasing of the coils. Do this by putting the meter on a low DC voltage range, connect across one coil and slowly turn the motor by hand. The residual magnetism in the rotor will generate a small voltage and each coil should produce the same alternating +ve and -ve sequence. If one does the reverse it's ends are muddled.

Andrew

[lordedmond]

 Sound like its two phasing

break open that meter and test it  do not be to concerned as to the resistance value at this stage but they must be the same plus or minus a knats

Stuart

[mgnbuk]

If you have not got a rating plate, what values did you put in the drive parameters for the motor characteristics ?

It is usual to have to set full load current & number of poles initially to configure the drive to suit the motor.

Nigel B.

[dawesy]

thanks for the replys guys.
so following some of your advice i have done the following
checked individual coil resistance all were 4.3ohm
checked the coil phasing one appeared to be backward, not sure if i did it right but i set the shaft with keyway facing up and connected the meter to one coil rotated clockwise, meter went -, +, -,+then back to - at the start point. then did the same for the rest
tested between case and coils nothing unless the meter was on the 20M setting. i then got a value of 20 which then started to decay.
checked the inverter settings. current is set at the inverter max (11) the poles setting was at 4 so i changed this to 2 (judging by the pulley ratio and the fact that the gearing plate specs 500 shaft speed, the motor is a 2 pole)
so i have come to the conclusion that the motor is destined for scrap
think ill try a brand new 3hp 3ph motor and see how we go from there. at least ill have a motor plate that i can use to make sure the inverter settings are correct.
thanks for your help guys

[BillTodd]

the reistances seem in the right ballpark .  I'd doulble check the phasing before scrapping that motor if i were you..

[dawesy]

to be fair ive tried various combinations of connection and all have the same or worse effect, the motor spins slowly at 50hz, but has no torque and the rotation speed drops off to 0 as the frequency is increased. or it barely spins at all

[awemawson]

Have you got another motor to prove that it is not the inverter that is toast?

Andrew

[dawesy]

Unfortunately not. Got a motor coming from machinemart so we'll soon know. This motor was originally 415v star wired and on top of that I never saw it in use so have no way of confirming if it was good before conversion.
Is there a way of checking the phasing?

[Pete W.]

SNIP
checked the inverter settings. current is set at the inverter max (11) the poles setting was at 4 so i changed this to 2 (judging by the pulley ratio and the fact that the gearing plate specs 500 shaft speed, the motor is a 2 pole)
SNIP

Hi there, Dawesy,

Please could you clarify what I've quoted above?  If 500 is referring to the actual motor shaft speed on a 50 Hz supply, the number of poles would be 12!!          

[dawesy]

Sorry the 500 rpm is the lathe input shaft not the motor, sorry just re-read my post and it was a little confusing.

[BillTodd]

what is the motor current reading on the vfd ? no current output means vfd fault, given the resistance readings.

what switching frequency is the vfd set to ? usually this  can be 4/8/16khz etc. and can cause resonances that give odd results.

are you sure that the vfd is set to 50hz not 500 or 5 ? (btdt:)) anything way out of range could give odd results.

maybe worth reseting the vfd to its default setting and working through the params' carefully

[lordedmond]

easy way to test that motor is to break part the winding chose one and connect up to 230 Vac 50 hz   turn on and spin the shaft if it goes round is it Ok ?
if yes do the same for the other two then at least you will know if it will motor

but as Bill intimates reset the VFD and make sure the base frequency is set to 50 hz

at Least is still got the magic smoke in so no need for a refill 
Stuart

[dawesy]

Guys you are awesome.
Originally when I set up the vfd I was struggling with the chinglish in the manual. So I went online to check the values for the pd's, checked what they were set at ( not the motor ones as I had to guess those) the ones in the vfd matched what I found. However just been to check the base frequency and it was set to 400hz! Reset to 50hz and the motor is running sweet. Just gotta cancel the machinemart order now ( made late so it won't have gone out but I'll call tomorrow )
Very happy bunny
Thanks again to all who have helped, your what make this community great

[Pete W.]

Hi there, Dawesy,

That's a good result, I'm pleased for you.                   

[dawesy]

Yeah I'm well chuffed. Hopefully my lathe tools will be here soon and I can start playing 

[awemawson]

Excellent result 

With the resistance readings you got I'd have been surprised if it was the motor unless something very odd had happened to the armature squirrel cage.

Andrew

[dsquire]

To All

This outcome is what makes me proud and happy to be a part of MadModder Forum. One person has a problem and people from near and far pool their colective knowledge to solve the problem and save a bunch of $$ and keep a few more pounds out of the scrap bin.

Excellent job by all concerned. 

Cheers 

Don