From: "David Roden (Akron OH USA)" <roden ald net>
To: elec-trak cosmos5 phy tufts edu
Subject: Re: (ET) Using 4QD controllers
Date: Thu, 05 Jun 2003 12:26:36 -0400
On 5 Jun 2003 at 10:46, john briese wrote:
> I am not sure I understood this correctly. Is he saying that by using
the
> brake circut this controller will have reverse?
No, he's saying the brake drive helps power the ET field. Reverse is a
different issue.
With a wound field, separately excited motor (ETs are actually compound
motors, but the shunt field is dominant), you MUST power up the field
before
applying power to the armature. This isn't a concern for a series motor,
where the field is permanently wired in series with the armature; or for a
permanent magnet motor, which has a field 24 hours a day.
I believe the 4QD controllers, which are actually designed for permant
magnet motors, are based on a wheelchair controller design (someone correct
me if I'm wrong). So apparently they have a circuit which can be used to
apply a brake when the power is off. It releases the brake right before
applying power to the armature, and sets it when the motor is fully stopped
-
this is exactly the behavior you want for the motor's field, too. So you
can use the brake drive to properly power a separately excited wound field
for the motor. (BTW, permanent magnet motors were used in the E8 and E10
tractors.)
Note though that the brake drive will NOT provide field weakening as used
on
the E20 and I5.
About reversing. 4QDs come in at least two "flavors," 2-quadrant and 4-
quadrant.
The 2-quadrant controllers have electronics to drive the motor in only one
direction. You can reverse them by externally reversing the field or
armature connections (but not both) with a relay or contactor.
The 4-quadrant controllers have a double power stage. One stage drives the
motor forward, the other drives it backward. No external reversing
contactors or relays are needed to get reverse.
To understand what quadrants have to do with it, think of a joystick
control
with 4 quadrants -- front left, front right, rear right, rear left. If you
remove the rear right and rear left quadrants, you can go only forward;
hence "2 quadrant control." Make sense?
David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea 36vdc
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