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

["RJ Kanary" <rjkanary nauticom net>]

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.

       The answer is quite simple. Look at all the reports of reversing 
relay failures. Repeated ones. The field reversing control systems just 
don't respond too well to operator error, regardless of how inadvertent it 
may be.
       The armature reversing scheme, while more expensive, has proven to 
have the edge in reliability.
At least that is my observation over the past twenty five or so years.
       GE eventually simplified the scheme, using two four terminal 
armature contactors, with the same rate of reliability.
     Bill Gunn even marketed an update kit, to retrofit the older models at 
a considerable cost savings.