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Re: Simple Controller

Lee Hart wrote:
>> My EV is a Renault LeCar, with an ADC L91 6.7" motor and Curtis 1231C
>> controller, turned down to 400 amps max...

Dan Frederiksen wrote:
> I have pondered if a 6.7" or two would be more lean in some way than
> bigger [motors].

This 2400 lbs car has a relatively small 750 lbs battery pack. The 6.7"
motor has a 1-hour rating of about 12 hp. It actually takes more like 15
hp to move this car at 70 mph. So, I couldn't drive at 70 mph for more
than 30-40 minutes before the motor overheated. But this doesn't matter,
because the lightweight pack can't supply that much power for even 30
minutes.

Bigger motors don't deliver more horsepower -- that's determined by the
controller (and sometimes the batteries). But a bigger motor lets you
get the same horsepower for longer before it overheats.

> I had gotten the impression that Curtis based cars faded out about
> freeway speeds because of the relatively low voltage. Is the 6.7" less
> hungry in some way or do all 1231 small cars go 65mph+?

The controller is fully "on" at freeway speeds, so it isn't limiting
things. The batteries are in effect connected directly to the motor, and
the current the motor draws is controlled only by pack voltage and motor
RPM. To go faster, you shift to a higher gear, to make the motor turn
slower, and so draw more current, and so make more horsepower. Seems
backwards to ICE drivers; but that's how it's done with a series motor!

>> Things get exponentially more complicated, not linear. I.e. going
>> from 500a to 1000a is more than twice the cost.

> I know you are using exponentially loosely here but how do you mean
> it gets harder? Matching transistors?

Just that as you go up in current and voltage, you cross various
plateaus and thresholds. You transition from mass produced commodity
parts to specialized low-production parts. Normal PC board techniques
give way to buss bars. Normal heatsinks become special water-cooled
ones. IC drivers get replaced with discrete transistor drivers.

> I noticed you agreed with me on a few issues contrary to a detractor.
> I hope that will save me from some of their balking.

No; you will save (or condemn) yourself, based on what you say and do. :)

I try to pay attention to *what* people say, rather than *who* said it.
I read posts without looking at who said it. So, I will respond to well
reasoned posts even from people I might otherwise vigorously disagree
with on many other topics.

We need more experts ("this is true because of these facts"), and fewer
authorities ("This is true because I say so").
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
 
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