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Discussion Starter #1
I'm trying to model the performance of an electric car. When I look up the
performance specs for electric motors, the manufacturers always list power,
torque, etc., down to a particular rpm (i.e., 2,000 rpm), but never down to
zero. I know that electric motors produce their maximum torque at zero rpm.
Clutches in IC cars are designed to handle power being dumped to them at
just a few hundred rpm. Does the controller deal with this issue? For
purposes of calculating acceleration, how should I approximate the torque
between zero and 2,000 rpm? Just be conservative and consider the torque to
be flat in that range, using the torque value at 2,000 rpm?



Thanks,



Alan K. Gideon





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Discussion Starter #2
Hi Alan,

The performance specs given by the motor manufacturer
are usually at a rated voltage. And, typically, at
that rated voltage, the specs at stall (or zero RPM)
would be beyond the recommended operating range. That
is, at full voltage stall (zero RPM), the current
would likely be over a thousand amperes, maybe several
thousand. That is why controllers have a current
limit.

So, you need to include the controller in your model.
The current limit should give you the maximum for
motor torque, needed for gradability and acceleration
calculations.

Hopefully some others can point you to an informative
web site. I am cramped for time and on a stange
computer in a Holiday Inn lobby.

Good luck,

Jeff M



--- Alan Gideon <[email protected]> wrote:

> I'm trying to model the performance of an electric
> car. When I look up the
> performance specs for electric motors, the
> manufacturers always list power,
> torque, etc., down to a particular rpm (i.e., 2,000
> rpm), but never down to
> zero. I know that electric motors produce their
> maximum torque at zero rpm.
> Clutches in IC cars are designed to handle power
> being dumped to them at
> just a few hundred rpm. Does the controller deal
> with this issue? For
> purposes of calculating acceleration, how should I
> approximate the torque
> between zero and 2,000 rpm? Just be conservative
> and consider the torque to
> be flat in that range, using the torque value at
> 2,000 rpm?
>
>
>
> Thanks,
>
>
>
> Alan K. Gideon




____________________________________________________________________________________
Pinpoint customers who are looking for what you sell.
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Discussion Starter #3
A cople points that might help you out:

Stalling is not really an issue with electric motors, so you don't need to
slip the clutch (unless you have an unusual setup). In fact, for most
conversions, you don't /want/ to slip the clutch.
Put it in gear, let up off the clutch and /then/ apply power.

Second point, assuming a series wound motor, the torque is directly
related to the current. If, for example, you have a controller with a 500
amps current limit, then all you have to do is look up 500 amps anywhere
on the chart. The torque at 500 amps (with a series motor) will be the
same regardless of RPM or applied voltage.
So once you know how much torque the motor produces at your controllers
current limit, then you know how much torque the motor will produce at
stall (when fed by that controller)

At really big current levels the torque to current curve flattens out and
become almost linear. So if you have a controller that can handle say
1,000 amps, but your chart only goes to 500 amps, then you can estimate
the torque at 1,000 amps as being about twice what it is at 500 amps.

HTH. Cheers.

> I'm trying to model the performance of an electric car. When I look up
> the
> performance specs for electric motors, the manufacturers always list
> power,
> torque, etc., down to a particular rpm (i.e., 2,000 rpm), but never down
> to
> zero. I know that electric motors produce their maximum torque at zero
> rpm.
> Clutches in IC cars are designed to handle power being dumped to them at
> just a few hundred rpm. Does the controller deal with this issue? For
> purposes of calculating acceleration, how should I approximate the torque
> between zero and 2,000 rpm? Just be conservative and consider the torque
> to
> be flat in that range, using the torque value at 2,000 rpm?
>
>
>
> Thanks,
>
>
>
> Alan K. Gideon
>
>
>
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


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