3 phase Motor maintenance

[Ttrees]

Howdy folks
Was using my bandsaw recently for processing my reclaimed wood ...
In an attempt to cut behind the putty on a lot of stock I have, I inevitably cut into some, and my new blade
lost its set on one side and I ended up fighting with the saw trying to cut the rest of this waste off the rest
Upon turning my saw on again my Huanyang VFD seems to have failed as its showing a "DL" error code.
That means short at output

Lesson learned, Don't put strain on a motor with a VFD !!
Should have tried sorting the blade straight away, regardless of the time involved making a tooth setter
or whatever.

Anyway I stripped the VFD apart....again and found nothing wrong with it.
No smell or melted anything.
I have read up on this, and apparently the spindles that come with these can burn up also.

This prompted me to take the motor terminal cover apart and have a look.
It smells slightly burnt, but no sign of melted anything.

I then tried the VFD on another motor, and lastly the tablesaw motor I have running,
and this DL error shows up on all of them.
So the VFD needs work ....

What I am concerned about is the ABB motor on my bandsaw
I have not connected the good Huanyang up to it yet because, I thought it might need maintenance work.
I only have a multimeter and resistance testing requires a Ohmmeter or a megohmmeter from what I gather.

I must admit, I never took the casing of this motor apart to inspect anything, but it looked really clean from the outside.I think I would have smelled the terminals if it was like this before.
No smell from anywhere else, yet ... Its still on the machine, I have not disassembled it.

What procedure should be done next ?
Buy a cheap megohmmeter or Ohmmeter from China ?
I've seen on YT people using motor varnish on the coils
Should this be done ?

I cannot find good info online for my situation
Any help very much appreciated
Thanks
Tom

 

[wallace]

Since you mention VFD I take it we are talking 3 phase motors. I have taken loads of 3 phase motors to bits and they are simple things. If the motor turns freely and it looks ok give it a try. I've had a few motors re wound because of faults in the windings. They usually hum loudly and the motor shaft goes back and forth. I have a nice motor guy local to me who is happy to test my motors with a mega tester.

 

[Alexam]

When you cut into waste wood and particularly putty, you could easily be hitting tacks or nails, which is likely to ruin any blade. By ruining the blade teeth set, you cannot expect any good results, but if the bandsaw is being used to cut up rough suff, then the poor blade can only do what it can. I hope you have a few spare blades available, preferably Tuffsaw.

I cannot comment on the Huanyang VFD, as I have never used one and not likely to but it sounds a bit 'iffy'. Perhaps others may be able to help.
Good luck.
Malcolm

 

[Ttrees]

Thanks Wallace
It is a three phase motor, I should have mentioned that, I'll try to alter the title a bit.

I am concerned because I read that its not a good idea to run it if the insulation could be compromised.
I will be trying to fix the VFD first anyway.
Presumably the IGBT's are toast or maybe the zener diodes
I would like to know if these can be tested with a multimeter ...

I have seen megohmmeters on eBay for just over 4 pounds,
I might have to get one, as I read 3 phase motors are difficult to do an insulation resistance test on.

Why do folks varnish motors then ?
Presumably the varnish is insulating the windings.
I can only presume this has deteriorated since theirs a smell coming from the terminals.
What else could be done for maintenance ?


Alexam, Malcom
I have a metal detector wand for this job, and it works very well
Indeed, I need to reset these teeth
Was very happy with this 1.3TPI ripper till the inevitable occurred

Tom

 

[dzj]

A three phase motor has 3 separate coils. Best to disconnect the six leads in the electrical connection box.
Check the resistance of each coil. An Ohmmeter should be used as it's low resistance, probably not greater than 100 Ohms.
There are also other things to look out for, here's a site that explains it well:
http://www.pcbheaven.com/userpages/chec ... _ac_motor/

 

[Ttrees]

Hello again
Dzj
I had visited that page before but read it again there...
I will be checking each terminal for infinite resistance, and hopefully I will get this reading, apart from the other end
of the coil that is....
and the reading of this coil/pair of terminals should give the same factor as the other two coils hopefully.
I take it this is everything that is done with a basic insulation resistance test.

So next thing is the polarization test as explained by Chris Kitcher in this video..
https://www.youtube.com/watch?v=FUjZwMMoltQ

If these readings show to be under tolerance is it then when I buy some motor varnish
Or is it shop for a new motor ...
I get the feeling my motor could be sound but needs this maintenance.

On the plus side I checked out the 2HP motor from the Magic tablesaw and it works
No humming or (centrifugal wobbling I'm guessing from your comment Wallace?) on the shaft...
I opened this one up and the rotor did smell a wee bit also.
I still have not took the bandsaw motor apart though.

I guess this is what I'm looking for ???
Cheapest Megohmeters I can find ....
http://www.ebay.co.uk/itm/Electric-Digi ... 2439196507
Or
http://www.ebay.co.uk/itm/2017-A830L-Ha ... SwjwlXA4be
Here is a piccy of the first one

I guess my multimeter is not suitable for the application
Thanks for the advice folks
Tom

 

[wallace]

3 phase motors are really basic things and not much to go wrong. If theirs a fault in the windings theirs not much you can do to diy fix unless its really close to the wires coming out of the windings. If it was a rotor failure then it would be really obvious. Damp can affect old motors. I have never heard of varnishing as a maintenance procedure. The only maintenance I do is blow them out and regrease once a year maybe.

 

[Ttrees]

Thanks Wallace
I just guessed the varnish was to do with the insulation.
I'm presuming I melted some of it, since there is a light smell from the terminals.

I wonder then, What is the point of doing an insulation test, if you can't do any maintenance work ?
Judging by what I've read its cheaper to just buy a new motor.....
Is it strictly for motors that are a custom job and not easy to source/very expensive compared to a rewind ?
Cheers
Tom

 

[dzj]

"I take it this is everything that is done with a basic insulation resistance test."

Check for coil to ground contact also.

As for varnish, I've only seen it done in the rewinding shops. They also use a type of oven
for heating the varnish. I haven't heard of people doing this at home.

 

[Ttrees]

Check for coil to ground contact also.

As for varnish, I've only seen it done in the rewinding shops. They also use a type of oven
for heating the varnish. I haven't heard of people doing this at home.

Oh yeah, forgot to mention that
Starting to think this is not done .
I should probably have asked a more constructive question.
I'll have another shot at it

If the insulation is deemed below tolerance by the professionals, do they varnish it, or is it something else they do?
I take it a rewind is when it past this point ...
Or is it a rewind and then the varnish is applied, and this is the only time varnish is applied to a motor.

Could it hurt to try ?
Like a loss of power or something else ?
I know I've asked a lot of questions here, Ill try to be more sensible in future
Thanks again
Tom

 

[Sawdust Sam]

To test each winding to earth, an insulation resistance test you really need a megger test instrument, a multimeter is unlikely to identify a break down in insulation unless it's a dead short.

You should also test each winding with a multimeter, each winding should an almost identical resistance. There's no requirement to disconnect the windings to do any of these tests.

You'll need to determine if the motor is configured as a star or delta motor in order to determine how to test the 3 windings with your multimeter.

I wouldn't worry about a polarisation index check, as long as the mugger test is above say 10 megohms it's all good. A PI test is just an insulation resistance test carried out for longer and readings taken at certain times during the test, dividing these numbers gives a ratio which must be greater than 1. It's only usually done on very big machines or if the IR test is low.

 

[Ttrees]

Thanks Sam
Advice heeded on the multimeter.
Does this black instrument shown above qualify as a megger to you, or is it the swinging type that is more suitable.
Like this type of one
Tom

 

[Sawdust Sam]

Thanks Sam
Advice heeded on the multimeter.
Does this black instrument shown above qualify as a megger to you, or is it the swinging type that is more suitable.
Like this type of one
Tom

Can't Quite make that out too well, cheap enough here though

https://www.amazon.co.uk/Digital-Insula ... rds=megger

 

[Ttrees]

Hello again
I've been searching for these insulation resistance testers again, and I thought that black one was the same as this yellow one.
Is this suitable ??
BM500A 1000V Digital Insulation Resistance Tester Meter Megohmmeter Megger 1999M
£12.49 freepost.
I may try and find it cheaper if its suitable
Thanks
Tom