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CaptainKlapton
23 December 2014, 2039
So financial uncertainty is keeping me in the planning stage on my build... So I will continue to obsess over every detail, but bear with me.
I would like to run a heat sink to make sure it stays cool enough (ambient temperatures in a Tennessee summer are often above 95F). Before I went and slapped a sink on it though, I wanted to get a better idea of what I was working with.
I took as close a look as I could at my AC-20 over the summer and measured as many aspects as I could without taking it apart. One of the things I noticed was that the stator is not circular as the 18gauge sheet metal jacket makes it appear. From what I can tell, the stator is shaped like so:
6229
The flat areas are ~2.3" long before curving to fit the curvature of the circle made by the jacket.
This means that a heat sink clamped on the sheet metal is relying on the heat conductivity of air and a ~0.05" piece of steel to conduct from over the majority of the area. How much area? Well if I worked it out right, the surface area of the stator is 68.3% higher than the area of the sheet metal case. So now I am wondering if it would be worth it to go ahead and cut the sheet metal off and make the aluminum heat sink conform to the stator. That would eliminate a thermal junction (between the sheet metal and the stator) as well as increase the contact area by over 68%.

I know ARC-EV ran this motor with a sink clamped onto the sheet metal and the motor never overheated, so I doubt that it is really necessary to do, but the cooler the better in my opinion.

Thoughts?
Here are a few views of a quick CAD model: 6230 6231

Hugues
23 December 2014, 2322
Hi,

I'm also trying to find ways to cool my AC-20.

I'm not entirely sure I understand which part of the jacket you want to cut away. Could you make a drawing of the stator and jacket with that part away ? How would you keep the structural integrity of the motor ? And if your idea is correct, you're planning to machine that heat sink to match that odd shape ?

CaptainKlapton
24 December 2014, 1145
Hi Hugues,
The part I am thinking of removing is the sheet metal case that is between the two end bells. You can see a weld along the bottom part of the case where the two ends of the sheet are joined. Here is a cut away of the case:
6263 6264 6265

The end bells are attached with the 4 bolts you can see the heads of on the encoder end:
6266 6267

It looks like the sheet metal is acting like a spacer for the end bells, but that isn't a big deal. So long as the heat sink is the same width, it will be the same in terms of spacing and probably stronger in terms of structure.

And yes, I would machine the heat sink to match the odd shape of the stator, that would give the most benefit.

Hugues
24 December 2014, 1219
ok clear, if you are going to replace the role of the jacket by your heatsink, i better understand what you want to do now.

Interesting to know there is some air gap between jacket and stator, did not expect that.

Thanks for the nice CAD.

Myself I will try to force air through the inlet with a 12v blower. Last summer the motor was reaching max temp only when i was stopping after a long climb (no more ventilation when motor stopped). So i believe i will be able to keep my motor below critical temp if i force air into it when at rest.

Keep us posted.

Electro Flyers
24 December 2014, 1744
Interesting to know there is some air gap between jacket and stator, did not expect that.


I referred to these chord areas(defined by flat spots on the stator laminations inside the circular sheet metal housing) when you were asking about motor cooling on another thread. I'm sorry I wasn't better able to explain them to you. If they are as big as indicated on the AC-20 by CK, forcing air through the inside of the motor may be sufficient to cool it. A fan that moves air axially over the outside of the motor as well the inside, would be the best.

Athlon
24 December 2014, 1941
Last summer the motor was reaching max temp only when i was stopping after a long climb (no more ventilation when motor stopped). So i believe i will be able to keep my motor below critical temp if i force air into it when at rest.

this is a HUGE problem , it menas that the thermal sensor is NOT int the hot spot of the motor.
Thermal sensor MUST be in the hottest spot of the motor , right in the point where the critical temperature will be reached fist.
When the thermal sensor is in the right position when you stop the motor temperature will always decrease because the sensor is in the hottest spot and the rest of the motor is for sure at a lower temperature , so when you stop temperature can only go down.

If you recorded any increase of temperature when the motor is not powered it means that somewhere in your motor there is a point hotter than the point of the thermal sensor and if not blowed away the heat it moves from the hot point to the rest of the motor heating it up.

Stevo
24 December 2014, 2255
It looks like there is enough room in there to run some copper or aluminum tubing, then run oil or water through to a radiator via electric pump. Is that possible?

CaptainKlapton
25 December 2014, 1024
It would be possible to do that. But the end bells would probably need to be modified as well to get the full length of the tube in contact with the stator, though I suppose you could use a sharp right angle. I may look into liquid cooling later, but if I can get by with passive air initially it will make for a much simpler initial installation with one less system to trouble shoot.

podolefsky
25 December 2014, 1104
this is a HUGE problem , it menas that the thermal sensor is NOT int the hot spot of the motor.
Thermal sensor MUST be in the hottest spot of the motor , right in the point where the critical temperature will be reached fist.
When the thermal sensor is in the right position when you stop the motor temperature will always decrease because the sensor is in the hottest spot and the rest of the motor is for sure at a lower temperature , so when you stop temperature can only go down.

If you recorded any increase of temperature when the motor is not powered it means that somewhere in your motor there is a point hotter than the point of the thermal sensor and if not blowed away the heat it moves from the hot point to the rest of the motor heating it up.

HPEVS systems begin to cut back at 145C and kill power completely at 160C. The motor insulation is rated to 180C, so they have designed in a safety margin.

Really, you shouldn't be anywhere near that temperature if the motor is properly sized for the application.

It would be ideal to have the temp sensor at the hottest spot, but that might not be feasible. Especially if the hottest spot is inside the windings. The temp sensor is going to be on the surface where the temperature is lower.