Motor Heat

kojo

Tonight I went riding with three other people on my cart through some trails and a little sand all flatland. Probably went about 1.5-2 miles before turning around. When we did stop for about 30 min. I checked motor heat with a meter I bought from HD and temp. was 167 degrees. So I was pleased. Half way back out I noticed volt meter was dropping slightly. Came out, hit the highway and came home. I could tell it lost a little speed but wasn't REAL slow. When we got home I waited about an hour and checked voltage on each batt. and was around 75% to maybe 80%, but then checked motor temp. and it was 212 degreesQuestion is as batteries get weaker on a ride does motor temp. go up. And also is this temp. too hot. Thanks for any input.

BGW

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scottyb

212 is about as hot as you want to see it. To answer your question, the motor will draw more amperage the lower the pack voltage is for a given task. The simple equation is volts plus amps = (x amount of) power If you take away some of the voltage then more amps have to be consumed to equal the X amount of power required. The more amperage you consume the hotter the motor will run.

kojo

Thanks ScottyB, I was kinda hoping that was the case. At least now I'm not real worried, kind of, but not as much because I thought something was about to injure my wallet. I've noticed you are one of the go-to-guys on this forum, and I personally am grateful for that. Thanks again buddy.

JohnnieB

Let me take what Scotty said a step further.

Like he said, it takes the same power to move the cart as the voltage drops, so the Amps increase. V x A = Watts, which is a linear relationship.

However, the formula for the amount of heat generated is A^2 x R = Watts, which is an exponential relationship.
In other words, if the Amps double, the heat generated is quadrupled and if the Amps triple, the heat generated increases by a factor of 9.

Of course, it is only the Amps that are not converted into motion by the motor that are converted into heat, so figuring out how much motor heat increase is to be expected for each volt the battery pack drops, gets fairly complex to say the least.

FWIW: D&D told me 115°C (239°F) was the Max case temperature I should take my motor to. That is the rule of thumb for non-ventilated motors with Class H insulation on the windings.

High motor temperatures have a cumulative effect, so the cooler your motor runs, the longer the winding's insulation lasts.

Volt_Ampere

JohnnyB you are dead on. Motor heat (mostly due to armature resistance) will go as the square of the current so motor heat goes up rapidly as the battery voltage drops given that you are running the cart at the same speed. 212 degrees seems very hot to me for normal riding though.

scottyb

It's not normal riding. He said 4 people riding a lifted cart in sand and highway for 3 miles.
Normal duty for this motor is 2 people 300 yds on a golf course (on stock tires). The load increase will cause the motor to draw additional amperage, I would expect temps to increase significantly

JohnnieB

He said he had 4 souls on-board while driving on some trails and a little sand, but didn't mention if that was normal loading and terrain or not.

If that is normal loading and terrain, upping the pack voltage would help the motor run cooler.

I am flatland challenged in my geographic area, so it isn't unusual for my motor to go over 200°F. When I was running a DCX400 and a stock PDS motor on 36V, I saw 235° a couple times and when I went to 42V, 225° was the highest I saw. With the DCX500 and the D&D motor, 220° is the highest I've seen and that was pushing it hard with about 600 pounds of people and cargo on-board. Of course, I use regen braking, which adds to the motor heat.

remac

JohnnieB - What do you use to measure the motor temp?

JohnnieB

I cleaned a spot next the the Field winding bolt, put a dollop of thermal grease on it and put the thermocouple in the grease.
The foam rubber is adhesive backed weather stripping and held in place with a big Ty-wrap.

I use the same setup on my D&D motor, but the DMM pictured, shuts off after about 15 minutes, so I use one that stays on forever in the Min/Max mode when I want to check the max temp reached while out and about.

IIRC, that thermocouple reads spot on at 200°F with the DMM pictured and about 2° high on the other DMM, but both are well within the ballpark.

I clip the DMM to the side of the basket, so I can glance at it over my shoulder.

Attached Images

	Thermocouple attached to DMM.jpg (913.8 KB, 0 views)
	Thermocouple on motor.jpg (911.9 KB, 0 views)

kojo

I want to thank you guys for the useful info. you've given me. Usually it's only me and the wife going through those same trails but, had a couple more this time which I knew was going to be alot more drag on it. Actually, I want to bump up voltage to 48v, from what I've read on here, that's the way to go. But I'm gonna have to wait till after the 1st of the year before thinking about that. Getting back, I thought 212 was getting hot because I couldn't hold my hand on it for long. I'm sure glad I bought that temp. meter. I've liked the sound of going to 48v w/ 36v motor, more power + more range = happiness , in my opinion. I'm learning more on this forum than if I worked at two cart shops. Again guys thanks for all your helpful info.