GP car (green porsche)

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Tom Thomson
Posts: 64
Joined: Fri Aug 31, 2007 12:48 am

GP car (green porsche)

Postby Tom Thomson » Thu Aug 07, 2008 11:29 pm

The E-Porsche hit the road today and under it's own power this time. It is readily apparent that motor temperature will be my limiting factor. Ambient here is lo 80's and even with the hood off the thermocouple showed 350 F at one point. Lifting on the throttle and/or downshifting quickly brings it back to 250 - 300. What motor temps are you folks running?
tommyt

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qdos
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Postby qdos » Fri Aug 08, 2008 12:07 am

Yaaaay She runs!!! :D

We're British and we use sensible Centigrade so I'm affraid you'rre going to get completely different temperatures from us here. Plus of course being British the temperature generally mid summer isn't much over 25C so our ambient conditions are more reasonable here plus in the winter we don't go much down past 10C very often But it's often rather wet LOL

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Jeremy
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Postby Jeremy » Fri Aug 08, 2008 6:17 am

350 deg F is around 177deg C which is seriously hot, even with your ambient temperature of around 27 deg C, which isn't far off our UK Summer temperature.

It's quite likely that a decent fan directed into the motor cooling vents (in the right direction, so that it aids the motor fan) will bring the temperature down a great deal. The fan ideally needs to be a fairly high pressure type, ducted so that it both draws air from outside and directs it through the motor effectively.

You can either leave the fan on all the time, or hook it up so that it turns on when the motor gets hot.

The alternative is to look at changing (or adapting) the motor to liquid cooling, but that will be loads more hassle I would think.

Jeremy

MalcolmB
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Postby MalcolmB » Fri Aug 08, 2008 7:09 am

Congratulations Tom!

Like Jeremy says, it sounds like you could do with some cooling on that motor. Most decent EV motors have insulation with a class H rating, for which the recommended temperature limit is 180C or 350F http://tristate.apogee.net/mnd/mfnrins.asp

Again, as Jeremy says, something like a heater blower fan ducted into the brush end of the motor to aid cooling would help a lot. Keeping the motor cool also lowers winding resistance which in turn improves efficiency.

Just out of curiosity, what motor and transmission are you using?

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EVguru
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Postby EVguru » Fri Aug 08, 2008 8:23 am

I see from another thread, you're running an 84 volt system.

I'd say this is 90% of your overheating problem. You are simply pulling too many amps through the motor at too low an rpm. For a car as heavy as a 924 you want at least 120 volt and let the motor rev! Unless the motor has no internal fan, fitting an external blower is just a crutch for a system that's not designed right. Of course you may just be driving in too high a gear, LET THAT MOTOR REV!

If you got to 350F case temperature, the motor is damaged. If you got to 350 field winding temperature, the motor is still probably damaged. Class H insulation is rated for 350F PEAK and you are measuring the average winding temperature, there's bound to be a hot spot in there. The motor may still be Ok, but its life expenctancy and reliability will be lower now.

The best place to measure temperature in a motor is probably the brushes, they're the first thing to heat up and the commutator is the first thing to get damaged. Drilling a hole in the back of one of the brushes and inserting an electrically insulated sensor is not too difficult.
Paul

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Tom Thomson
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Joined: Fri Aug 31, 2007 12:48 am

GP car

Postby Tom Thomson » Sat Aug 09, 2008 1:27 am

The transmision in the Porsche is the stock unit, a 5 speed transaxle and the motor is a D&D ES15A-6 which is a 6.7" (sorry qdos - 170mm) series wound. Yes yes - I know that it's too small but for my purposes it'll do. The temp readings come from a thermocouple which is indeed buried in one of the brushes. As it's tucked away in the driveshaft tunnel the motor will be hard to cool but I have more things to try such as a windage tray under the motor, waiting for cooler weather etc. Complicating things is the fact that the controller tends to heat at part throttle while the motor heats at full. It's all fun though and the most fun of all is parking in front of the coffee shop with the hood off.
tommyt


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