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Hot Motor

Posted: Mon Oct 20, 2008 12:10 am
by Tom Thomson
My Porsche (924) conversion has suddenly begun to run hot. Several days ago, on a level stretch of road where I have in the past observed 300F, I noticed the motor showing 400F. Suitably alarmed, I backed off and within seconds had the temperature back down to 350F. Since then I have watched the temp guage more than the road and have had to adjust my driving to the temp. I thought that perhaps a plastic bag or piece of paper had wrapped around the motor but it is clean. I am not flogging the car; this happens at 40 mph, 80V, 110A with an ambient of 60F. I am reading a type J thermocouple imbedded in one of the brushes. I have an 84V system, a 6.7" D&D motor and an Alltrax controller. I have made no changes to the car but obviously something has changed. Any ideas?
ps before someone wastes a lot of keystrokes talking about how I don't have enough voltage, enough motor etc etc let me repeat that it worked fine one day and did not the next.

Posted: Mon Oct 20, 2008 10:38 am
by Nigel P.A. Smith
Hi tommyt,

Seems like worn or sticky brushes are the first thing to check, but I'm not an
expert! :?

I would like to know how fast your conversion will go and distance as I just
bought a new set of Trojan T105 batteries for my converted Rover but at
72 volts I am not getting up to 35mph :( maybe the controller currant can
be tweaked, it has 3 adjustments but I'm not sure about doing it! Any
advice welcome, probably new controller and more volts! Thanks Nigel

Electric Rover
maybe slow but I'm not fuming 8)

Posted: Mon Oct 20, 2008 3:36 pm
by mattcarr
What sort of range are you getting with the new batteries in it? Does your conversion still have the gear box in it? as 35mph is pretty slow for a top end speed.

Posted: Mon Oct 20, 2008 6:08 pm
by Nigel P.A. Smith
Hi mattcarr,

Yes it still has gearbox and clutch but slowly getting the range; have to find
roads that aren't to long and steep, previous owner said he got over 20
miles, for details see "FOR SALE Rover 414 on ebay"

Regards Nigel

Posted: Mon Oct 20, 2008 11:16 pm
by Tom Thomson
The Porsche will top out at abt 60 mph or 95km/hr in 5th. It might go faster but at that speed it was pulling over 300A which caused the motor to heat quickly. Do you have volt and amp gages in the Rover? Are you running out of hp or motor rpm?
ps Once upon a time I had a 2000TC - what a nice car!

Posted: Wed Oct 22, 2008 9:33 am
by Nigel P.A. Smith
Hi Tommyt,

Did you modify the brushes yourself "I am reading a type J thermocouple
embedded in one of the brushes." and when were they put in?

I have no gauges but the Curtis state of charge indicator, I think HP is the
problem but motor is rated at 1700rpm, so probably limited by both.

I have been looking at controllers; both Kelly and Alltrax 72 volts say they
operate at 8-84volts, so maybe I could add 12volts without changing the
controller? :? Is that a bad idea?

Thanks Nigel

Electric Rover
maybe slow but I'm not fuming 8)

Posted: Wed Oct 22, 2008 2:14 pm
by nino500
I think you'll find that the curtis controller will be happy enough at 84 volts as well. The last time I read their specs I seem to remember the overvoltage being set at 90 volts. might be a bit too close on a full charge, mind you. What's your pack voltage after charging?


Posted: Thu Oct 23, 2008 3:41 pm
by Nigel P.A. Smith
72 volts from batteries but 82 from the controller terminals when turned on!?
And 55volts turned off!
Tommyt still got your hot motor?


Posted: Thu Oct 23, 2008 6:34 pm
by nino500
Interesting, I would have thought a new set of batts would hold at about 12.7 volts each when charged, so you should be getting about 76.2v or so. Are you sure your charger is working properly?

Is it an industrial type charger which switches into float mode when it's finished? What's the pack voltage when on float charge?

I wonder if you have any resistance in the battery connections.

Still if you add one more batt you should be on about 89v at rest when charged so there's a possibility that the controller will register overvoltage and switch off but you can always try before lashing out on new kit.

You'd need to change your charging setup anyway if you went up to 84v, so if your charger is a problem you'd solve that one on the way as well.


Posted: Thu Oct 23, 2008 6:39 pm
by nino500
Yes, sorry we wandered off the point there.

I don't have any ideas on the motor problem but a bit of lateral thinking brings me to the brakes and transmission. Anything sticking, rubbing or binding in there? wheel bearings even?