Induction motor problem (help wanted)

[NickWelford]

Thanks for showing us the dialogue and not keeping it in PM's - although I have nothing to add, it is interesting, and might well help me in the future.

 

[9fingers]

Hi Jon,

The other imported TS user has a different setup from yours Jon.
Firstly it is nearer 2 hp but also a 120v motor and is run from a transformer so I don't think we can conclude much by comparing them.

hth

Bob

 

[jonny boy]

Hello Bob,
I have just read Brians messages and yes, it's a contractor saw by the sound of it with a 115v motor, so he has to run it on a transformer.
We do however have some good news (fingers crossed) I,ve spoken to an engineer today at work and he needs me to take the motor out so he can check it all with the proper equipment but he did say that the overload dial in the starter sounds a little low at under 12 amps. Because of this, when I got home from work today, i've turned the dial up to 14amps and tried again, this time with a stopwatch in tow. I started the saw and let it run for 10 mins to get it warmed up an stopped it. Then run it for another 10 mins just for good measure and stopped it again. Then I started it again and this time let it run without stopping it. I got fed up just standing and looking at it after over 15 mins so I turned it off and it never tripped at all. It just looks like you may have been right and could have sussed it. I'm going to use it all day this Sunday and really put it to the test and hopefully it's fixed.
cheers,
jon.

 

[jonny boy]

One thing I forgot to add though, the motor was really hot, almost too hot to touch, and this is something that I hope won't cause me any future problems.
Q. How hot can an induction motor get before it fails?

jon.

 

[9fingers]

The answer is 'it depends'
European motor ratings are specified by IEC85. Your motor will be specified by a US similar standard.

IEC 85 class F which many industrial motors are made to meet allow a winding temparature rise of 105 degrees centigrade at an ambient temperature of 40 degree C max.
So this is a maximum of 145 degrees C inside. Externally this will be quite a bit cooler but well over boiling point of water.
If you can still touch your motor, then it is possibly up to 55 degrees -( I usually reckon 60 C as too hot to keep my hand on)
So I don't think you have much to worry about.

Also in normal use the saw will only run for a few minutes at a time before a break.

HTH

Bob

 

[jonny boy]

Yes, there's no way i'll need to run the saw for 15mins un-interupted under normal usage. The motor got hotter than it's been before, but I could keep my hand on it without getting burnt. Is it because it's a 60hz motor? Is there absolutely nothing I can do about that?

jon.

 

[9fingers]

Part of the heating could well be due to the supply frequency but the rest is perfectly natural and due to motor losses.
No need to try and do anything about it.

Bob

 

[jonny boy]

Thanks for your help again Bob, what with the 16 amp connection trouble I had previously and now the motor trouble, I wouldn't have got it sorted without your help.
cheers,
jonathan.

 

[9fingers]

My Pleasure Jon!

Only too happy to help. Hope you enjoy making sawdust with your TS

Bob