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Discussion Starter #1
Hi,

Since I have a 400A 2kHz ye-ol Curtis that battery amps are limited (noticed
50A starting). I decided to try an additional choke in series with the
motor but inside the bypass contactor loop. Since T=L/R with the motor
inductance at 150uh and 58 milli-ohms, the time constant to pulse by pulse
current limit is quick thus limiting the duty cycle on start to 2.5ms. By
doubling the inductance or adding a 150uH choke, the start pulse width would
then be limited to 5ms. So I took a uWave oven transformer, angle ground
off the I bar on the E core and removed the coild and magnetic shunt. I
then put 6 turns of #2 welding wire on and MIG welded the I back on the E
for a 72uH choke measured. I then started the car again from a dead stop
and noticed 80A instead of 50 battery amps and it moved quicker into
operating range. I'll get another dead uWave and add another choke for a
total of 150uH. So if you have acceleration problems and you're duty cycle
limiting on start, try a choke or 2.

Best Regards,
Mark

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Registered
Joined
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70 Posts
Discussion Starter #2
Hi Mark,

You run a by-pass? Not many do, that I am aware of.
This is with the MTC motor, right?

Anyway, regarding additional motor inductance. Yea,
sometimes these high speed motors would be called
rotating short circuits by those involved in control.
Increased PWM frequency helps. Adding inductance to
the motor circuit with chokes, inductors or reactors
or whatever you call them is a fix when you're stuck
with existing components. From the get-go, it would
have been better to put the additional steel and
copper (used in the choke) into the motor. A bigger,
higher inductance motor motor makes more sense than
external inductance. But working with what you have,
nice way to raise the average current when the peak
current is limiting.

You know, the MTC motor was designed with a little
heavier field just to get the inductance up to where
it's at. This makes it a good candidate for field
weakening. Once you're in by-pass, you can switch in
a field diverter resistor and increase motor speed.
You'd want to use some smarts so that the control
never attempts to chop with the field weakened. A 19
milliOhm diverter resistor is good for the MTC. Would
give you another 500 RPM or so.

Also, how did you get the inductance of the motor?
You know that value is current dependent. Probably
doesn't make a big difference in what you're doing.
Which BTW, I love to see. Keep playing and let us
know results.

Jeff


--- Mark Hanson <[email protected]> wrote:

> Hi,
>
> Since I have a 400A 2kHz ye-ol Curtis that battery
> amps are limited (noticed
> 50A starting). I decided to try an additional choke
> in series with the
> motor but inside the bypass contactor loop. Since
> T=L/R with the motor
> inductance at 150uh and 58 milli-ohms, the time
> constant to pulse by pulse
> current limit is quick thus limiting the duty cycle
> on start to 2.5ms. By
> doubling the inductance or adding a 150uH choke, the
> start pulse width would
> then be limited to 5ms. So I took a uWave oven
> transformer, angle ground
> off the I bar on the E core and removed the coild
> and magnetic shunt. I
> then put 6 turns of #2 welding wire on and MIG
> welded the I back on the E
> for a 72uH choke measured. I then started the car
> again from a dead stop
> and noticed 80A instead of 50 battery amps and it
> moved quicker into
> operating range. I'll get another dead uWave and
> add another choke for a
> total of 150uH. So if you have acceleration
> problems and you're duty cycle
> limiting on start, try a choke or 2.
>
> Best Regards,
> Mark
>
>



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