Increasing inductance slows down the ramp up of current, so adding inductance 
to a motor with too low inductance helps to get better current limit, 
especially on controllers with low switching speed where a single step will 
cause so big current change that it can damage the controller.This is entirely 
different from the addition of a physical loop of wire, even though that also 
adds inductance, because a physical distance between the two wires or even a 
wire running without the "return" current running right next to it, will act as 
antenna, spewing the switching noise into the air and possibly disrupting the 
operation of sensitive circuits in the controller but certainly killing your 
radio reception and possibly someone else's which is illegal.
The addition of inductance is what i have done on my previous EV truck which 
had a low speed EV100 controller and a large 11 inch motor. I could fit 3 loops 
of the motor cable through a large microwave transformer core. But i kept the 
motor cables close together.
Do not add resistance in the motor loop, as that only increases losses.Hope 
this clarifies.Cor


Sent from my T-Mobile 4G LTE Device
-------- Original message --------From: EVDL Administrator via EV 
<ev@lists.evdl.org> Date: 12/17/17  9:13 AM  (GMT-08:00) To: Electric Vehicle 
Discussion List <ev@lists.evdl.org> Cc: EVDL Administrator <evp...@drmm.net> 
Subject: Re: [EVDL] DC controller common terminal 
Cor, Paul, thanks for the replies!  I forgot about the freeewheeling 
diode(s).

So I'll connect it the way the manual says.

Still ...

I recall some discussion years ago about fixed frequency 15kHz+ Curtis 
controllers having trouble with current limiting on large, low inductance 
motors.  It caused the combination to have jerky starts, or worse.  The way 
Lee Hart explained it was that the low resistance meant that the current 
didn't have time to decay enough when the chopping transistors were off 
(because it was a very short time), so the current just kept rising insead 
of being properly limited.

If that were the crucial factor here, I would think that extra resistance in 
the motor loop would HELP.  But obviously not, because we're always advised 
to keep the motor leads as short as possible.

I hate to sound dense (even though I am), but while I can understand that 
connecting the motor lead at the contactor (or other point ahead of the 
controller common terminal) could change the way the controller "sees" the 
motor, I still don't fully understand what specific problems that might 
cause.  Maybe the earlier discussion about motor loop impedance / resistance 
isn't relevant here?

Thanks again!

David Roden - Akron, Ohio, USA
EVDL Administrator

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