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(ET) field weakening with series-wound motors
- Subject: (ET) field weakening with series-wound motors
- From: "Max Hall" <maxo iname com>
- Date: Sun, 31 Mar 2002 21:51:34 -0500
- References: <3.0.6.32.20020330190202.0087cc40@mail.vt.edu> <001501c1d84f$70a0ffe0$157ffea9@paulscomputer> <00f501c1d8cd$d99991a0$0e00a8c0@earthlink.net> <000901c1d91f$49c5d500$157ffea9@paulscomputer>
- Sender: owner-elec-trak cosmos phy tufts edu
Paul, all,
Minding that we're close to the border of relevant... (some of the ETs use
series wound, no?!)
> Wow! Do you mean I can just shunt the field winding on my series-wound
golf
> cart and get some extra speed?
Yessir. It's not much, but can be a help. I was running a 36v (nominal)
series motor with its differential and axle with a 72v traction pack last
summer. No trouble from that alone. Add to that that I did this field shunt
trick. No trouble then, either. And interestingly, no unusual heat. (Since
there was no trouble, I haven't looked at the commutator. Just in the
interest of disclosure.) Shouldn't have been, really. Same upper current
limit, though twice the EMF.
> What are the rules? I'm guessing that you would only do this in a
> low-torque application such as when already travelling at top speed. Any
> limits on how long you can run it this way? Is there any penalty to the
> life of the motor? Anything else I should know?
Someone on this list may offer up some horror stories or sober wisdom, but
I
have done this on three different EVs all with golf cart series-wound
motors, and it's always worked without trouble. It should, really... the
overall current goes up a bit, yes, but the current through the field is
less when the shunt is engaged. The current through the brushes is higher,
though, and I suppose that's a concern. But my use of it was always, as you
say, for lower torque times.... when you're already chugging along. I would
be drawing something like 100A before engaging this "overdrive," and 120A
or
so after; nothing like the 275A through the motor when accelerating up
hills.
> Thanks for the idea,
'welcome, but it's not new with me. I first got it from my father-in-law, a
cagey electrical theoretician for sure.
I look forward to hearing other thoughts on it from the veterans in ET
land,
ever mindful of topic, topic and topic.
-Maxo