Acceptable Motor Temperature??

[ASJ]

I have recently replaced the old (but not original) motor in my Viceroy TDS 1/1 GBL with:
TEC motors TCC 802-4,
Single phase
0.75Kw (1H.P.)
4 pole (1400 RPM)
Capacitor start, Capacitor Run.
I noticed recently when changing the belt positions (for the first time since installing the motor) that the motor seemed very hot, almost too hot to touch, so I hooked up a thermometer to monitor the temperature, and found that it was running at around 75 C and rising, so after about another 5 mins, when it reached 80C I switched it off to cool down for a while. By this point it had been running for about 45 mins to 1 hour of "typical" use.
Now, I appreciate that these motors don't like to be switched on and off a lot due to the high start up currents, but this is kind of un-avoidable owing to the necessity to clear swarf and take occasional measurements. Also there is practically no ventilation in the enclosed motor cabinet of the viceroy lathe, which doesn't help, but I cant recall the old motor ever getting this hot, and I don't think either the original 3 phase, or old single phase even had a cooling fan (the new one does).
So I was just wondering what other peoples experiences were regarding heat build up, Particularly from modern retro-fit motors.

I don't really want to, but I have pretty much resigned myself to the fact that I am going to have to butcher some ventilation holes into the lathe cabinet

[Pete.]

Doesn't sound right. I have stop/started my lathe probably two dozen times in an hour without the motor suffering.

I don't think that putting holes in the cabinet will help at all. It's not like the door seals or anything there's plenty of placed for air to get in. I would get in touch with the supplier and get a replacement.

[DavidB]

If you can check that the motor fan is actually going round with the motor, I've seen it a few times over the years where the fans have come loose and were just slipping on the end of the shaft and not providing cooling. IIRC the plastic fans had a moulded collet type affair to fit around the shaft with a metal collar around that to close the collet and it had come loose allowing the fan to slip, an easy fix by just tapping the collar back in place to hold the fan tightly again. Some motors also just have a push on cover for the fan and that can get knocked against the fan jamming it and stopping it turning.

[ASJ]

The fan is going round as the temperature actually comes down initially when you start the motor, before it begins to climb again. If you stop the motor the temperature rises faster presumably due to the lack of air flow from the fan as the heat in the windings transfers to the casing where my thermocouple is located. Regarding ventilation, opening the door to let the hot air out definitely helped so I think it would benefit from a few extra holes somewhere. I think a phone call to the manufacturer may help to confirm what is normal.
Cheers.

[ASJ]

Update,
I spoke to the Technical guru at TEC Motors and in short my situation is normal but not ideal!
Apparently single phase motors draw the same amount of current regardless of the load put upon them so it will heat up just as much under no load as it does under full load, and will continue to do so until it melts (great sales pitch!)
The trick is to try to keep the case temperature below 75C by whatever means possible! You learn something new every day!
So to conclude, there is nothing wrong with my motor its just the way they are I need to improve the airflow / cooling some how

On a side note, non of this is an issue with 3 phase, so the ideal solution, according to Mr TEC is to fit a 3 phase motor with single phase inverter. So glad I had the lathe rewired for single phase to suit this new motor.


So for anyone considering converting to single phase, take heed of this, keep your 3 phase, and invest in a phase inverter instead!

Thanks

[Pete.]

If what he said is true why aren't there melted single phase motors on lathes all over the country? I had a single phase motor on my viceroy it never got more than warm even after multiple stop-starts. Have one on my mill it doesn't either.

That 'tech' is spinning you a yarn to cover up the fact that they sell crappy quality motors I think.

[LesT]

Hi,

"Apparently single phase motors draw the same amount of current regardless of the load put upon them so it will heat up just as much under no load as it does under full load, and will continue to do so until it melts "

Thats rubbish, if that was the case a thermal overload unit, a P&B golds type relay would never work.

Motors have two kinds of impedance, there is the resistance of the motor copper coils itself, added to the electrical impedance due to the induction of the windings.
Thats why there is a current inrush when a motor starts. The current then falls away as the motor speeds up. The Impedance however depends on the supply voltage and frequency,( thats why 60 Hz motors buzz badly on 50 Hz). If there is insufficient induction in the motor it will be unable to impede the current flow and it will get hotter and hotter just like a one bar fire.

I would check the supply voltage for a start, is it high for some reason ?. As you are unlikely to be able to tap change to bring the voltage down, it might be the best idea is to just get another motor. ( Strangely if the voltage is low the current will rise as well, but you will have the same problem re tap changing as well)

I wondered if someone had changed the capacitor to a larger one on the start/run winding, but if its the one supplied by the manufacturer that would seem a long shot.

"So for anyone considering converting to single phase, take heed of this, keep your 3 phase, and invest in a phase inverter instead"

Thats what I have BTW.

Regards,

Les.T.

[ASJ]

I get what you're saying Pete, my the old motor was single phase as is my mill and I can't say they ever got this warm but then again I've never paid that much attention to it before now. I did however replace the old motor because the insulation had crumbled away from the wires!
I guess the guy is covering his back side a bit, and being conservative with his safety factors. The insulation is rated to 155C, presumably for a reason, and from what I've read the General rule of thumb is that if the max rating is exceeded then the life span of the motor will be reduced by roughly half for every 10C above the rated value, so you would have to run it at 165 C for thousands of hours before it actually fails. I doubt my lathe has done that many hours in its entire life.
In fairness the motor was cheap, I paid £90 brand new, so I suppose there has to be some compromise somewhere. If I'd paid more I'm sure it would be quieter, cooler, run smoother, but its horses for courses.
That said, there is definitely some mileage in extra ventilation. Tonight I ran the same job with the motor cabinet door open (don't report me to the elf and safety police) and it never rose Above 60C so I'm sure I can make it work. Anyway, ill be glad of all this heat come winter
Cheers!

[ASJ]

Hi,

If there is insufficient induction in the motor it will be unable to impede the current flow and it will get hotter and hotter just like a one bar fire.

I wondered if someone had changed the capacitor to a larger one on the start/run winding, but if its the one supplied by the manufacturer that would seem a long shot.


Regards,

Les.T.

Hi Les,
Thank you for your informed reply, i just have a few questions, more for my own curiosity than anything else,
1) What would cause there to be "insufficient induction"?
2) If everything was operating correctly, under constant load, should the temperature of the motor stabilise and then remain constant for the duration? I would expect changes in the load would affect the temperature accordingly?
3) Re. your comment on the capacitor, could this be faulty / defective, i.e. poor quality, out of tolerance?

FYI this is the name plate of the motor, don't know if it gives any clues!

IMG_1697.JPG (193.12 KiB) Viewed 12934 times

Thanks again!

[LesT]

Hi Alex,

1) Where there is a chance that a motor could be stalled in service a type of motor called an "impedance protected " motor is used. This just has a greater amount of iron in its construction so that the core does not become saturated magnetically, even when the motor is not turning. The little synchron motors found in CH spring return zone valves are like this. They just run open until they stall, when the power goes off they run closed. Mining belt conveyor motors used to be like this as well, but are now protected electronically I think.

2) Yes, load changes affect the motor temperature. Traction motors often have separate blowers to cool them when under heavy load. Sometimes the wrong kind of snow blocks up the cooling passages.

3) Yes, the wrong/faulty capacitor can cause a problem or prevent the motor from starting at all.
One thing you could check is that the speed switch is working properly, if it was jammed it could keep the start capacitor in circuit, this would not be good and might produce overheating symptoms.

I'm not a motor expert but google is your friend, there is a lot of information available.

Regards,

Les.T.