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This sounds like a dumb question to me, but what the heck. Is there any reason why I can't just put a large potentiometer in series with the batteries and the motor and use that as my throttle to control the power output?
Not a dumb question. Sure, you could do it. The potentiometer would need to be about ten times the size of your motor. And it would waste half of the battery energy needed for every acceleration. And at any speed less than full speed, it would waste considerable amounts of power.

Good news, it could double as a cabin heater :) If there was any room left for a cabin on the vehicle after finding a place to mount such a large pot. See if you can even find a 25 kW pot.




This is a 7 kW pot. You'd need like 3 or 4 of these. It weighs something like 150 pounds.

Other than that, good idea :eek:

major
 

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That's a bit drastic. Let's not scare the poor guy to death!
Just having a bit of fun and trying to make a point :) But the big pot is about what he'd need for an EV car.

The adjustable resistor in series with the motor is called a "rheostat" (not a potentiometer). At this power level, it is generally built with a number of fixed resistors, selected in by a big rotary switch.
Yep, but most buy a potentiometer and just use two terminals for rheostat applications. Even the PB-6 is this way. And the rotary switch with resistors approach would be on the same order of size as that giant pot with the same loss problem.

And sure, you can build EVs with resistor speed controls, or battery switching, but it is unlikely the outcome will be suitable for highway capable car performance.

Regards,

major
 
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