Re: (ET) e-15 eats reverse relays

["Christopher Zach" <czach computer org>]

Well, if I recall correctly, the E15 reverses the direction of current in
the stator field when you go to reverse. The E20 reverses the contactors
that flow power to the armature.

When you toss an E20 into reverse, the relay basically only has to switch
the current for two contactors. Not much at all. The contactors take the
surge from the armature, but they are really big, so this is not too much 
of
a problem.

On the E15 though, going through to reverse while the motor is going 
forward
will set up a significant amount of current which will fry the very small
pads on the relay.

My guess is they went to the E15 method of reversal (stator vs. armature)
because it's cheaper. Going this way removes four contactors from the
circuit (each direction requires two contactors). The "right" way to do it
would be to put a stronger relay in there, or a solenoid, however if this
were done my quess would be that the back-current would blow up the field
weakening logic pretty quickly.

Chris




----- Original Message -----
From: "Pieter Litchfield" <plitch attglobal net>
To: "Discussion list Electrac tractor" <elec-trak cosmos phy tufts edu>
Sent: Friday, June 07, 2002 8:24 PM
Subject: (ET) e-15 eats reverse relays


> Gang:
>
> My e-15 w/bucket loader has a nasty habit of eating the reverse relay - 
> it
> welds or fries the contacts while in reverse, or when switching from
reverse
> to forward modes.  Over the past several years it has eaten 3 or 4.
>
> I am now using the improved Bill Gunn relay, and while definitely
stronger,
> the tractor's demon is stronger still.
>
> I had assumed that perhaps the motor of a rolling  tractor acts as a
> generator and that shifting too quickly from reverse to forward might
allow
> the motor to weld contacts (or something).  I do notice a spark when the
> rely breaks contacts with the reverse contacts if I shift it without the
> motor coming to a standstill, even with the tractor in neutral.  No spark
> seems to occur when the motor is completely stopped.  However, this could
> just be coincidental with something else - like a component that looses a
> charge over a short time.
>
> I do have the complete "homeowner's repair manual", but I ain't no
engineer,
> so I look at the pretty pictures of wires and remain more or less
clueless.
>
> I'll ask Bill when I order more relays, but does anyone else want to
venture
> a suggestion as to why I eat relays?
>
> Thanks!
>
>
>