Motor heat

Helirich

Today I took my wife and granddaughter for a ride. (48v PDS, 500 XCT, 12 hp) We drove for about 15 miles at speeds between 5 and 20 mph. (A few short stops) When I got home, the motor was hot enough to fry an egg.

It never smoked or give any indication of a problem. I've had it hot like this before when I ran it all out for a couple miles. (25-27 mph) But this was much more leisurely.

I was wondering if you guys feel your motor after a naighberhood tour. Although it wouldn't boil water, mine was way to hot to hold my hand on.
Is this normal?

I've heard the 275 degree inside limit. I got to believe it had to be close based on what I felt.

BGW

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JohnnieB

The "275 degree inside limit" isn't one I'm familiar with. What class insulation is it for and where/how is it measured.

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SepEx motor's can get mighty hot when operated at low RPM and at high RPM, especially if the field mapping is bumping into or exceeding the motor manufacturer's max recommend field weakening limits to increase the RPM reachable at the voltage applied.

Like most cart motors, my motor doesn't have temperature sensors embedded in the windings, so I try to stay below 239°F case temperature, which is too hot to touch and will boil water.

The thing to remember about max temperature recommendations is that they are more of a goal than a limit since the result of exceeding them is shorter motor life rather than instant failure. In very general terms, increasing a motor's operating temperature by 18°F (10°C) above the rerecorded max, halves its life expectancy, while operating it 18°F below the max recommended temperature doubles its life expectancy.

Volt_Ampere

It's a lot hotter inside than outside. If the outside is too hot to touch, it's too hot IMO. I fried my stock motor and replaced it with a D&D. That motor runs much cooler. I put a temperature probe on it and I never see more than about 120 F on the case near the terminals. That is the hottest part on the outside of the motor. The stuff that gets damaged by heat is way inside. When you get it too hot you will smell the damaged insulation smell.

Helirich

I guess I'm getting senile. I thought it was you who told me that. But I looked back through the threads and all I could find is the 239 number. I did pour water on mine when I got home and it didn't boil. This brings up another question. Am I being stupid to squirt water on the motor when I get it hot? If it got too hot, is the damage allready done or is cooling it down fast helping? Am I just making matters worse by introducing corrosion?

I have the correct field map now. So that shouldn't be the problem. My large, 7 psi "torque sucking" tires are not helping. But everybody loves the ride on my cart.

I would agree, it must be hotter inside. That's why I'm worried. I've not smelled any smoke yet. On your motor, you are saying that if you drive 10-15 miles at 16 mph, it won't get hot?

My motor came from a cart that sat in the guys yard for a year or more. Do you think that would cause any problem? It has a sheet metal cover over the brush section. Do you sappose its full of bugs? Would that cause any problems? (Except a fire, maybe, LOL) I guess I should take a look. I wish I had when the body was off. Is there any recommended maintance (other than if it needs brushes)

Does anyone use "heat tape" on there motor? I'm talking about the tape that changes colors at different temperatures. I think I'm going to get some.

JohnnieB

I keep forgetting if I am senile or not.

The "damage" is already done, so cooling motor down with water probably doesn't help much, but other than the helping the terminals and cables corrode faster, it probably doesn't hurt either.

The case temperature in an indirect measurement of the winding temperature, so it is derated considerably from the 180°C (356°F) max recommended for Class-H insulated wires.

That max temperature number is a bit ambiguous since is assumes the motor is operating in a 40°C (104°F) environment, plus there is a 15°C (59°F) fudge factor for hot spots in the windings. The actual recommended temperature rise is 125°C (257°F). See attached charts.

The correct field map doesn't necessarily mean the motor will run cool.
For example, the max field weakening recommended by D&D for my motor at 100A or less armature current is 3A, but the Alltrax field map for it reduces the field current to about 1A when at high RPM with less than 100A armature current. The net result is that my motor runs hot and won't last as long as it would if I was running it cooler. If I get 10 years out of it instead of 20 years, I'll be happy.

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Since your motor sat for a year or more, I'd replace the shaft bearings when the brushes are replaced. The lubrication may have seeped out or thickened and flat spots might have developed. If possible, I'd use a hybrid (Ceramic balls - Steel race) bearing.

Attached Images

	Motor Insulation.jpg (16.7 KB, 0 views)
	Max Temp.jpg (64.1 KB, 0 views)

scottyb

The temp probes I installed on one of my PDS test cart with D&D mootr revealed the highest temperature was 5 - 10 minutes after I parked it so external cooling may be useful, if actually needed, because my infrared temp gun and probes agreed the motor case was 150º +/- and I could not hold my hand on it.
I conclude the 'too hot to touch" test is way too subjective and in accurate to submit as evidence - use of a thermal detection device is best.

Volt_Ampere

Bad brushes can make the commutator heat up more than normal and that can damage it. These motors do not do a good job of cooling. Heat has to dissipate through the case. The armature gets way hotter than the outer case temperature.

Clemsoncartguy

Why don't they make fins into the case?

skipsmith521

What you need to cool the motor is a new flux capacitor that has injection cooling.

Just make sure you don't cool it too fast or you may travel back in time.

Sent from my Nexus 6 using Tapatalk

Helirich

I've wondered about rough brushes/commutator making heat. But I would think the cart would not preform well if they were all grooved up.

I've always heard 140 is as hot as you can hold your hand on. I agree that is subjective. But mine was way hotter than that.