Motor Heat... while we're on the topic of motors

69_knives

69_knives

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Nov 20, 2008
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I finally got around to doing some actual knife grinding today with the grinder I built and I noticed that the motor case was quite hot.

I am aware that the TEFC design uses the motor case to draw heat out of the windings and the external fan cools it but it was surprising just how hot the motor was to touch.

Should I be concerned? I didn't take any temp readings but I think a few more degrees and my finger might have sizzled.

Oh, it's AC, 2HP, 115V...
 
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Make sure the cooling fan is not blocked with dust, spider webs, etc. Make sure that the air can circulate around it well. Possibly,there may be too much side tension on the shaft, causing more friction than desirer ( not likely the cause). Make sure the motor spins freely with no belt or load ( it should spin for a long while when the power is shut off). If it does not spin freely, it may need bushings or have other issues.
All that said, some motors run hot, but should not be hot enough to feel like they will burn you.
Stacy
 
I've been wondering the same thing - I have a new Leeson 2HP (the "red one"), and it gets a lot warmer than I expected.
 
If running them 115 volts it will run a little hot. Run them 220 and you have less heat, 1/2 the use of electricity and your motor life will be longer. Make sure you have the correct thickness wire (#12) and a switch that is strong enough for a solid contact.
 
I'm using a link belt and the motors weight for tension so I think I will take a link out and reduce the leverage advantage and see if that makes a difference.

I spun the motor in the store before I bought it and it spun freely. One thing I noticed when I got it home in the quiet garage is that there is a drag that can be heard. When the motor is running it is not there but when shut off and slows to a certain RPM, it kicks in and stops the motor so I think it is some sort of brake. The next time I was at the store I spun another identical and listened closely and could hear it on that one too.

I will check the fan as well just to make sure it is OK.
 
DanGraves said:
If running them 115 volts it will run a little hot. Run them 220 and you have less heat, 1/2 the use of electricity and your motor life will be longer. Make sure you have the correct thickness wire (#12) and a switch that is strong enough for a solid contact.
Click to expand...

Unfortunately, theres no 220 in the garage and I rent, so I can't do much about that.

Wire and switch are up to par.

I guess I could put a little auxiliary fan on it to help the situation.
 
I'm doing 220V with #12 wire and a 30A switch.

DanGraves said:
If running them 115 volts it will run a little hot. Run them 220 and you have less heat, 1/2 the use of electricity and your motor life will be longer. Make sure you have the correct thickness wire (#12) and a switch that is strong enough for a solid contact.
Click to expand...
 
Turn on grinder apply some load and have an assistant measure the voltage at the wall socket with a multimeter. It may run just fine at 115V, but if the voltage drop gets down much below 110volts then the motor will definitely heat up. If its say 105 volts then there is not enough juice coming into the shop.


If this is the problem, then the wiring to the garage is not able to handle the load and motor burnout over time will occurr.

The only choice then is to get a wiring upgrade or move to a better shop set up, or go down to a smaller motor.

Another thing, you may also want to apply an amp probe to the grinder to find out what its current draw is. If it is exceding the load on the nameplate, then there may be a developing problem in the motor itself.
 
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Bufford has some good info there . A amp reading and voltage drop reading will tell you everything . Also on the motor name plate there should be a motor heat rating
 
Yes, voltage drop iws a problem with overheating.
The noise on startup and shut down with the motor ( at the lower RPM) is the centrifugal starter. It should sound like that.
Stacy
 
Ok, I checked the voltage at the outlet and the line voltage is 124V, with the grinder running, no load it drops to 122, and with a simulated "grinding a knife" load it drops another half a volt to 121.5; so I don't think that is a problem.

I took a couple of leaves out of the link belt and aligned the motor pulley a bit better so we'll see if that makes any difference.

Heat rating is 40C ambient temp, it gets close to that for a few days in summer but never over that... yet. :)

I'll try to remember to bring home a clamp meter from work in the next few days and check the amperage.
 
I had the same problem found out the belt was slipping when grinding. I tightened everything up (v belts) and works fine now.
 
Thanks for that link!

I feel at least a little better. I'm going to go with the motor being really efficient at it's heat dissipation from the windings. It is a class F motor with a 1.15 SF. I will keep an eye on it though and give it breaks; I got readings off the case of 88°C after grinding a 3/16" x 5" x 1-1/4", 1095, full hollow grind blade start to finish up to 120 grit.
 
patriqq said:
I've been wondering the same thing - I have a new Leeson 2HP (the "red one"), and it gets a lot warmer than I expected.
Click to expand...

I have the same one and it does get warm.
 
88C is about 190F!!! That is way too hot for safety and for the motor.

I think it will cook itself if run at that heat for long. The motor gurus here might have some tables. I would only give it short runs and long rests until you get it figured out.

Is the motor brand new? Have you verified that the fan is working? I'd take the end cover off and have a look to see that all is well at the fan end ( should be three screws). It is possible the fan set screw is not tight.

Stacy
 
According to the charts , class F insulation can withstand temps of 155 degree C . Now thats getting hot
 
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