PDA

View Full Version : Electric Motor Running Temp ?????



JoeLee
10-08-2013, 12:17 PM
I've been wondering about the operating temp of the hydraulic pump motor on my KO surface grinder for quite some time.
I think it runs pretty hot but not sure if it's normal or not. It's a 220 volt 3 phase motor, I think it's 1/3 HP, made by GE.
I run it off a VFD. All the motor does is run the hydraulic pump for the table, in my opinion it's a bit undersized for the job but I didn't design the machine. After about 20 - 30 min. of running the motor will reach about 158 degrees. It varies a few degrees across the housing but that is the hottest point I've indicated. The ends, sides or bearing housing what ever you want to call them run at about 90 degrees, not bad. The motor tags does say 40c amb.
Any thoughts?????

JL.........................

CalM
10-08-2013, 12:21 PM
I've been wondering about the operating temp of the hydraulic pump motor on my KO surface grinder for quite some time.
I think it runs pretty hot but not sure if it's normal or not. It's a 220 volt 3 phase motor, I think it's 1/3 HP, made by GE.
I run it off a VFD. All the motor does is run the hydraulic pump for the table, in my opinion it's a bit undersized for the job but I didn't design the machine. After about 20 - 30 min. of running the motor will reach about 158 degrees. It varies a few degrees across the housing but that is the hottest point I've indicated. The ends, sides or bearing housing what ever you want to call them run at about 90 degrees, not bad. The motor tags does say 40c amb.
Any thoughts?????

JL.........................


The 40C figure is temperature RAISE over ambient.

Add 40 C to your room temp of say 20C you have 60 C That is too hot to put your hand on for more than a moment

Clean the motor case or put a small fan to blow air over the motor if it troubles you. I bet the insulation in the motor is good for MUCH higher temps than that.

I start to worry when motors start to smell hot ;-)

ps the motor bearings are held in "End Bells"

JoeLee
10-08-2013, 12:28 PM
OK, thanks, when I checked the temp in C it read as 70. Still sounds like 10 higher than it should be. Shop temp or amb. is about 67 deg F.

End bells................ that's what I was thinking of.

JL..............................

CalM
10-08-2013, 12:29 PM
Are you running the VFD at 60hz (or name plate freq)

John Stevenson
10-08-2013, 02:53 PM
THIS is a hot motor :p

http://www.stevenson-engineers.co.uk/files/motor1.jpg

JoeLee
10-08-2013, 03:23 PM
Are you running the VFD at 60hz (or name plate freq)

Yes I am........... The grinder motor runs cool.

John, that's a real hot motor. I would wrap coils around it and preheat your hot water.

JL..................

Cuttings
10-08-2013, 05:01 PM
I had the same concern about the motor on my mill a while back so I did some research and measured the operating temperature.
It turned out that it felt quite hot but was well within the normal operating temp. for that motor.
I just had another look at the info.
Surface temperature of continuously operating general purpose electric motor will easily be 80C (176F) and can be as high as 100 (212F)
Depending on the temperature rating of the insulation on the windings they can go even higher.

lane
10-08-2013, 06:22 PM
I also have a KOLee 7-18 and it runs about the same
like you worried about it at first but dont any more been working for 40 + years now. it is a 1960 something model and mine is 110 volt 3/4 HP on pump and 110 volt 1 HP on spindle . Some times I run with the door to the HYG.open. But dont think it helps just more noise.

Doozer
10-08-2013, 08:04 PM
I understand that most motors are rated to run hot to the touch and be OK.
I don't like it though. If I had a hot one on a machine I use long enough to
get that hot, I would put a 4" computer fan on it. Not necessary, but I
sleep better.

--Doozer

J Tiers
10-08-2013, 08:23 PM
Cooler is always better. ALL organic-based insulation, varnish, paper, plastic, whatever..... it all degrades with heat. Eventually it will actually char, despite never being nearly hot enough to char quickly.

That said, even basic motors are rated at a max temp of 115C inside. That likely equates to about 95 to 100C on the exterior, which is a temp you would *notice* if you touched it. The usual "hot spot" allowance is 10C from measurable exterior to inside hot spot, and the measurable exterior is essentially anything you can see from outside (even the outside of windings).

JoeLee
10-08-2013, 09:59 PM
Cooler is always better. ALL organic-based insulation, varnish, paper, plastic, whatever..... it all degrades with heat. Eventually it will actually char, despite never being nearly hot enough to char quickly.

That said, even basic motors are rated at a max temp of 115C inside. That likely equates to about 95 to 100C on the exterior, which is a temp you would *notice* if you touched it. The usual "hot spot" allowance is 10C from measurable exterior to inside hot spot, and the measurable exterior is essentially anything you can see from outside (even the outside of windings).

Well that's good to know, kind of reassuring. The KO S-718 grinder is mid 60's as lane mentioned, only mine is the 3 phase version with 1/3 HP for the hydraulics, lane said his is 3/4 HP single phase and he mentioned it runs hot also. I won't worry about as it's been running since the 60's.

JL......................

Doozer
10-08-2013, 10:10 PM
Do the motor bearing have grease fittings?
I seen many a motors with the end bells
slap ass full of nasty grease. That would
not allow air flow and make it run hot for
sure. Might maybe take it apart and clean
the insides out with mineral spirits, being
so many years that old.

--Doozer

EVguru
10-09-2013, 04:48 AM
Try lowering the carrier frequency on your VFD.

JoeLee
10-09-2013, 08:17 AM
The motor has oil caps, it doesn't have ball bearings either and everything is clean.

If I lower the VFD freq. the motor just runs slower. Since it's designed for 60 Hz. I thought it would be best to run it at that freq. Running the motor slower would probably cause it to run even hotter as I feel that 1/3 HP is undersized for the job.

JL.........................

J Tiers
10-09-2013, 08:25 AM
The "carrier" isn't the set output frequency, it is the PWM frequency. Usually you can choose from a series such as 4 kHz, 8 kHz, or 16 kHz.... some use other sets of frequencies.

It does NOT AFFECT the motor speed. It usually does not affect motor heating as much as it does VFD heating, but it could make a difference.

projectnut
10-09-2013, 09:10 AM
Here's a quote from the operators manual for my Sanford Surface Grinder:

CAUTION HOT MOTOR

"Using your hand to test the running temperature of a motor can be a very painful experience.

NORMAL BODY TEMPERATURE 98.6*F

THRESHOLD OF PAIN CAUSED BY HEAT 120*F

AVERAGE TEMPERATURE OF HOT TAP WATER 140*F

AVERAGE TEMPERATURE OF HOT COFFEE 180*F

NORMAL OPERATING TEMPERATURE OF A
FULLY LOADED ELECTRIC MOTOR OPEN
TYPE 70* AMBIENT TEMPERATURE 174*F

YOU CANNOT WASH YOUR HANDS IN 140*F HOT WATER.
YOU CANNOT STIR A FRESH CUP OF COFFEE WITH YOUR FINGER
YOU CANNOT PLACE YOUR HAND ON A MOTOR THAT IS OPERATING PROPERLY WITHOUT BURNING YOUR HAND"

JoeLee
10-09-2013, 09:37 PM
The "carrier" isn't the set output frequency, it is the PWM frequency. Usually you can choose from a series such as 4 kHz, 8 kHz, or 16 kHz.... some use other sets of frequencies.

It does NOT AFFECT the motor speed. It usually does not affect motor heating as much as it does VFD heating, but it could make a difference.

Now you have me wondering........... I have a Yaskawa VFD, not sure of the moder V7 something I think. I can vary the freq. with the little knob on the main panel and the display changes. Max setting was set up for 60 Hz. I can dial it down and the speed drops. I always thought that was the freq. Now I'll have to do some research from what your telling me. These things are a pain to program.

JL........................

JoeLee
10-17-2013, 11:12 AM
The "carrier" isn't the set output frequency, it is the PWM frequency. Usually you can choose from a series such as 4 kHz, 8 kHz, or 16 kHz.... some use other sets of frequencies.

It does NOT AFFECT the motor speed. It usually does not affect motor heating as much as it does VFD heating, but it could make a difference.

I changed the carrier freq. of the drive. The first thing I noticed upon powering up is the motor made a real high pitched whining noise. So I set it back to the factory default.

JL....................

Noitoen
10-17-2013, 11:37 AM
Set the carrier frequency to the lowest and configure the drive to V/F curve, set the correct data on the motor's plate on the correct drive menu and some drives have a "power save" mode that can be switched off. This sometimes runs the motor at a higher current.

Last if everything fails and if the motor is a little "underpowered" for the job, you can "release" a little load on the motor by removing it's cooling fan and replacing it by an external motor/fan unit.

MaxHeadRoom
10-17-2013, 11:59 AM
I think it runs pretty hot but not sure if it's normal or not. It's a 220 volt 3 phase motor, I think it's 1/3 HP, made by GE.

JL.........................


Many times Hydraulic pumps run continuously loaded which can heat the motor and the Oil up pretty fast.
If the pump is running constantly and the use is frequent, if it is not necessary to maintain pump pressure at all times, a unload valve saves alot of heat and wear and tear on the pump etc.
The unload is activated any time a function is called for immediately restoring pressure.
Max.


Max.

EVguru
10-17-2013, 12:00 PM
I changed the carrier freq. of the drive. The first thing I noticed upon powering up is the motor made a real high pitched whining noise.

You just lowered the frequency of the noise into your hearing range, it was there all along.

Did it make any difference to the heating?

If it did, then it indicates rather lossy Iron in the laminations (or cheap thick laminations). If that's the case, the motor will never really be happy on a VFD. I'd run it till dies, then source a better motor.

JoeLee
10-18-2013, 11:11 AM
I ended up changing the carrier freq. back to the factory default which eliminated the high pitched whine and it also seems to run with less vibration at that setting. I also changed another setting to open loop vector mode which I was told should make the motor run cooler. We'll see about that.

JL................

Forrest Addy
10-18-2013, 01:42 PM
Efficient goal directed trouble shooting starts with gathering data. I suggest you check your VFD parameter settings. It may be the VFD thinks your motor is bigger than it relly is and consequently pumps a few too many Amps into it.

Right now you have no real data except the motor runs hot. Start with the motor Amps. Check the motor's nameplate for rated full load amps. Then poke the panel buttons so the panel display shows the motor amps. A typical idle current for a small induction motor is about 40% of full load Amps. Most idle hydraulic systems place little load on the pump motor so it's idle current won't be much higher than a motor running with no mechanical load. BUT: that's for motors running from plain vanilla three phase juice from the power line. Get a parameter wrong and a VFD can be made to fry the motor it's supposed to protect.

VFD's are a whole other world. They put out synthesized three phase as a series of timed pulses switched from rectifed DC it makes from the line voltage. The Volts, Amps, and frequency constantly change with load in response to the VFD's programming. The motor averages the pulses so it behaves like it's running from three phase magically adjusted a zillion times a minute. The gadget is pretty smart but it can't look beyond its programming and parameter settings.

Many VFD's have economiser programming that reduces the motor voltage. Motor current paradoxically rises and power factor shifts from about 35% to roughly 80%. This leads to greater electrical efficiency but it also heats the motor. This economiser setting is derived from the VFD parameters relating to name plate motor current. The same parameters are not consistantly identified, maker to maker. Look in your VFD's manual with an open mind.

Double check the VFD's panel display with an actual analog tong ammeter. I still don't quite trust a digital meter to honestly display true RMS when sensing a VFD's sine coded PWM output to an induction motor - but then I'm a Luddite in these matters.

Also take motor Amp readings with the table in motion on a longish stroke. The VFD's display may not change much but table reversals should show as a distinct bump on the analog tong meter.

Page through the parameter settings and note those affecting the motor current. It may be the VFD is set up for 60 Hz and the motor is 50 Hz. That's probably not it but it's illustrative of what to look for. Once you have the data, your insight will lead you to a solution. Without the data you're stabbing in the dark.