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The mention of reversing relays reminded me that I should
mention something about reversing. Sorry, this goes on a
bit...
There are one-, two-, and four- quadrant solid-state
controllers. The one's can only supply voltage of one polarity, the two's
can supply voltage of one polarity and do regenerative braking, and the four's
can supply voltage of both polarities (i.e., reverse the armature current and
therefore rotation) as well as do regen braking.
When I bought the 4QD controller for mine I was under the
impression that the motor was fully compound wound, i.e., that the series
winding made up a significant part of the magnetic field. I therefore
further assumed that I couldn't/shouldn't reverse the armature current to
reverse the motor and that I'd have to reverse the shunt field like is normally
done on an E12. I therefore bought a two-quadrant controller. I plan
to use a "parking brake" output from the controller, which goes active when
armature current goes to zero, to enable/disable switching of the reversing
relay.
From later discussions on this board, however, I've learned
that the motor is really more of a shunt-wound motor and that the series winding
is just a "compensating" winding that weakens the magnetic field a little as
load (current) on the motor increases to maintain speed. This leaves me
with the feeling that I should have used a four-quadrant controller and just
left the shunt field always fully energized in the "forward" direction, which
would have gotten me out of the messy reversing relay circuitry.
A nice feature of both what I intend to do messily or what a four-quadrant
controller would do cleanly is that because of the built-in current limiting
there'll be no harm in throwing the lever from full forward to full reverse; in
either case the controller will limit currents to safe values and do the
transition smoothly...Bob
>>> "Pieter Litchfield" <plitch attglobal net> 7/23/2002 4:06:44 PM >>> As the owner of the E-15 with
bucket loader that loves to eat relays, my suggestion would be that whatever
controller is designed, be sure it can withstand the abuse hard use will heap on
it. For example, my tendency to rapidly shift from reverse to forward
while using the bucket has had dire consequences for my relays. A better
design could improve on this behavior, or at least prevent the idiot behind the
wheel from making the quick shift ( a timer or charge-up delay
circuit?)
As a gross observation, my E-12 while not as elegant
a control design seems far more robust than the E-15. At least I
haven't cooked relays there yet. But this does suggest that a prime
characteristic of a power control system for an E-15 ought to be "robust-ness"
and "fault tolerance."
-----Original Message-----
From: owner-elec-trak cosmos phy tufts edu [mailto:owner-elec-trak cosmos phy tufts edu]On Behalf Of Bob Murcek Sent: Tuesday, July 23, 2002 2:11 PM To: elec-trak cosmos phy tufts edu; ssawtelle fcc net Subject: Re: (ET) Solid state controls
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