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Old 05-10-2010, 06:49 PM   #9 (permalink)
Electric Porsche
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Many thanks for the expert comments! Here are answers/questions:

I have an old 11 inch Kostov sepex. I bought it from Randy at Canadian Electric Vehicles Ltd. . I believe he upgraded the wiring, so there is a chance my field wiring is different than the original Kostov wiring. My field is 1.0 Ohm of resistance. He also upgraded the bearings and wrapped it (fiberglass? carbon fiber? not sure).

Given your 160 C to 220 C numbers, I think my motor is running much cooler than I realized even though it felt hot to the touch (I'd guess it was around 70 C).

48 V is just testing for short times, I'm going to much higher voltage. The car has not done serious hills or high speeds, and typically testing has been at 50 to 150 Amps.

Thanks for confirming the 144V spec voltage. What I'm not sure was clearly communicated, or maybe I'm not clear on your comments: I'd think you'd want to run the armature at 144 V, but you'd typically be running the field at much less than 144 V -- true or not? How long could I run the field on 144V? This page for the newer 11 inch shows field currents of around 6 to 12 Amps: , so that hints to me to the field is getting much less than 120V.

Thanks for the temperature numbers, I'll start using my IR thermometer instead of my hand. What would you recommend for monitoring temperature? I could do an IR measurement of the brushes... or measure the difference in temperature of intake air vs. exhausted air... It seems if one just monitored the motor case temperature it would be too late by the time one detected overheat.

In addition to keeping the stock fan and generally running higher rpm, I am also adding an external blower.

Originally Posted by Plamenator View Post
I cannot quite remember which sepex you got but the reasons it is hot are:

1) Your motor is rated for triple the voltage you are using. Being at 48V means ventilation is not 3 times worse - it is 4-5 times worse as it varies exponentially with rpm. It is not a coincidence that we put a lower voltage spec on our motors...
2) Your motor is wound for much higher voltage. Operating as low as 24-48V results in lower efficiency which produces more heat.
3) Class H insulation allows the coils to get to 160-220C which feels quite hot even on the outside case. Even 60C feels quite hot to touch.
4) Running a sepex motor at 1/3 the voltage does not allow you to overload properly - your armature will witness increased amps, while the field will barely increase its amps. This is very bad for commutation and heats up the comm.

Why do you use 48V anyway?!?
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