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Discussion Starter #1
Does anyone know what the relationship of the pot reading and the current
out of the controller? Is it linear? For example, the pot is set at 1k
ohms, and 100 amps is delivered to the motor. The pot is at halfway, at
2.5k ohms, and the current is 250 amps. The full 5k ohms, and 500 amps. Is
this correct?

Then the question comes, as another way to limit the current. Can I
parallel a resistor that would limit the resistance of the pot. Say I don't
want more than 100 amps, so I put a 1k ohm resistor in parallel. Would this
work? If so, what would the power of the resistor need to be? Quarter
watt? Half?

And lastly, if the current to the motor is 100 amps, is that what I am
pulling from the batteries?

I appreciate any suggestions.

Brian
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70 Posts
Discussion Starter #2
> Does anyone know what the relationship of the pot reading and the current
> out of the controller? Is it linear? For example, the pot is set at 1k
> ohms, and 100 amps is delivered to the motor. The pot is at halfway, at
> 2.5k ohms, and the current is 250 amps. The full 5k ohms, and 500 amps.
> Is
> this correct?

No, if we're talking about the throttle pot, then it's a PWM percentage duty
damand, which is equivilent to a voltage demand. The current is dependant on
the load curve of the motor; maximum at stall and minimum at no load. The
current at stall could in theory be thousands of amps if full voltage was
applied, so the controller limits its PWM duty (output voltage). There are
controllers that operate in current mode, the Brusa permenant magnet
controllers for example. The Curtis is a current limited voltage controller.

> Then the question comes, as another way to limit the current. Can I
> parallel a resistor that would limit the resistance of the pot. Say I
> don't
> want more than 100 amps, so I put a 1k ohm resistor in parallel. Would
> this
> work? If so, what would the power of the resistor need to be? Quarter
> watt? Half?

You can use this technique to limit the duty cycle and it's a useful trick
to do so for reversing, making full throttle in reverse give you say 20mph
max.

>
> And lastly, if the current to the motor is 100 amps, is that what I am
> pulling from the batteries?

If the controller is at 100% PWM duty cycle, then 100 amps. If it was at 50%
duty cycle, then 50 amps.

Paul Compton
www.evguru.co.uk
www.sciroccoev.co.uk
www.bvs.org.uk
www.morini-mania.co.uk
www.compton.vispa.com/the_named
----- Original Message -----
From: "Brian Staffanson" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Wednesday, October 10, 2007 8:22 PM
Subject: [EVDL] Curtis1231 questions


>
> I appreciate any suggestions.
>
> Brian
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