[ausev] question about Geo Metro conversion

[Nick Viera]

Hi Lisa and all,

Lisa Korf wrote:
> It's a 15 kilowatt DC shunt motor.  Literature says
> "This motor is rated at 15 kw , 4000-8000 RPM ,and 400
> amps continuous."

What physical size is this motor? The 15kW (20 HP) continuous power 
rating sounds about right for a typical EV-sized DC motor, but the 
8000RPM speed limit and "400 amps continuous" sound questionably high.

> My Honda conversion will have an Alltrax pulse width
> modulation controller rated at 72 volts, but the
> literature from Wilderness EV says "This controller is
> rated at 24-72 volts DC and 450 amps. The motor is
> capable of running at up to 144 volts DC."  I'm not
> sure what that last part's about.  Does that mean I
> could go up to 144 volts and be okay?  Doubtful...  

No. This means that the motor is designed to operate at up to 144 volts, 
but the Alltrax controller is designed for use with a 72 volt nominal 
set of batteries. A 72 volt set of Lead Acid batteries will operate in a 
range of about 63 volts (1.75 volts per cell) minimum under load to 93 
volts (2.6 volts per cell) maximum during an equalization charge. Thus 
this controller probably isn't designed to withstand more than about 100 
volts peak (check with the manufacturer to be sure!).

The point in all this is that your *controller* is your limiting factor. 
Even at it's peak it can only deliver about 1/2 the power that the motor 
is capable of producing (assuming you follow the recommended motor 
ratings). Though, in reality, most EV-sized brushed DC motors can 
sustain up to about 170 volts and 1000+ Amps maximum, which is around 
170kW or 227HP max. Of course, this would only be for a short while 
because they'll be dissipating a lot of heat at these power levels!!!

> What are the safety risks riding around with that much
> battery potential?  I originally settled on the 72
> volts for safety reasons. 

Well then it's irrelevant to this discussion because you *can't* safely 
use more than 72 volts (nominal) worth of batteries with this 
controller! :-)

Hope that helps,

-- 
-Nick
1988 Jeep Cherokee 4x4 EV
http://Go.DriveEV.com/
http://www.ACEAA.org/
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