Re: (ET) e-15 eats reverse relays

["Christopher Zach" <czach computer org>]

Well, then perhaps one of the solutions is to get a DPDT contactor and have
the relay points toss the contactor points. Take the strain off the relays
(which after all should just switch little bits of current).

Chris

----- Original Message -----
From: "Pieter Litchfield" <plitch attglobal net>
To: "Discussion list Electrac tractor" <elec-trak cosmos phy tufts edu>;
"Christopher Zach" <czach computer org>
Sent: Saturday, June 08, 2002 7:52 AM
Subject: RE: (ET) e-15 eats reverse relays


> As I mentioned in another post, your observation about the current flow
> seems borne out by my experience - unless I allow the motor to come to a
> complete standstill (even in neutral), I can see quite an arc on the
reverse
> relay points.  I can read enough of a schematic to confirm that you are
> correct in your recollection of e-15 technology; the reversing relay does
> indeed reverse the field.
>
> Of course my problem is heightened by use - a loader spends a lot of time
> reversing direction compared to a trac used to just mow the lawn, 
> allowing
> lots of opportunity to burn those relay points.
>
> Many thanks for your reply.
> Pieter
>
> -----Original Message-----
> From: owner-elec-trak cosmos phy tufts edu
> [mailto:owner-elec-trak cosmos phy tufts edu]On Behalf Of Christopher
> Zach
> Sent: Friday, June 07, 2002 10:50 PM
> To: Pieter Litchfield; Discussion list Electrac tractor
> Subject: Re: (ET) e-15 eats reverse relays
>
>
> 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!
> >
> >
> >
>
>
>