RE: (ET) RE: Alltrax DCX300 availability - Field current

["Markus Lorch" <mlorch vt edu>]

Rod,

the E20 has also a compound wound motor with a small
series field (I think this was discussed as being the
reason why reverse doesn't do additional field weakening,
as the field in reverse is already weakened through
the series field)

At 36V I think my field draws about 4A. 

One curiosity that I don't understand is why, on the 
E20 BA and CC, they used an H bridge of 4 mechanically 
interlocked heavy-duty contactors to reverse direction 
via the armature when they could've achieved the same 
with a single dpdt relay reversing the field.

I noticed today that the RTN (return to neutral) lockout
on my E20 only works when switching from forward to 
reverse, but not when from reverse to forward. Thus
I can see a serious current spike (maybe thats what
welded Chris' contactors as well) if I am switching
without letting off the throttle. I am not sure 
how it should be working. 
 
Markus

> -----Original Message-----
> From: Rod Hower [mailto:rodhower ameritech net] 
> Sent: Dienstag, 25. Januar 2005 22:07
> To: Markus Lorch; elec-trak cosmos phy tufts edu
> Subject: RE: (ET) RE: Alltrax DCX300 availability - Field current
> 
> 
> What does the ET shunt field draw (or more
> specifically how much field current flows in the
> E15?).
> My E15 has a compound wound motor and from a control
> design point is not as difficult to prevent blow ups
> compared to a full sepex motor.  The biggest problem
> with a motor like this is what happens during a
> reverse command.  If you don't let the field current
> decay before reversing, the armature current can be
> quite high, even with a compound motor, I wonder if
> this was the problem?  For background info I designed
> a compound wound control for a Caterpillar forklift
> back in the early 90's.  If I didn't allow sufficient
> time for the shunt field to decay there was a huge
> current spike.
> It would be interesting to hear what problems caused
> control failures in the Alltrax.
> Rod
> 
> --- Markus Lorch <mlorch vt edu> wrote:
> 
> > 
> > 
> > > 
> > > >From what I understand, the ET model has
> > additional current sensing 
> > > circuitry for the field controller.  The ET's
> > motor wants a 
> > > much lower field 
> > > current than a typical separately excited field
> > golf car 
> > > motor, something like 
> > > one-tenth.
> > 
> > Yes, I think I was wrong and they had to make some
> > (minor, but
> > manual) hardware modifications. Plus they also
> > developed a different field 
> > map which Steve R. posted to the list a while ago.
> > So the ET version is
> > basically a customized, low-volume product.
> > 
> > I have gotten info on the (inexpensive) SPX
> > controllers that "look like"
> > the DCP controllers we would need from Jeff @
> > Alltrax. It turns out these
> > were DCP controllers that had a problem with a bad
> > component in the field
> > control circuit and thus were converted by Alltrax
> > to standard controllers 
> > for series wound or PM motors. 
> > 
> > Markus
> > 
> > 
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