Re: (ET) ok, not the fusible link

[David C Robie <mycroftxx1 juno com>]

ANSWERS WITHIN

On Tue, 1 Aug 2006 18:09:10 -0400 (EDT) Michael S Briggs
<msbriggs alberti unh edu> writes:
> 
> Dave,
>       What do you mean by an open? An open circuit (which to me 
> means no 
> current would flow, 
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Righto !  no current flow.  Another way of stating it, across an open
circuit in any complete circuit which includes a power supply, you will
find full power supply voltage.
   Across a 'patially open' circuit  (a high resistance) you will find
full power supply voltage
Across a closed circuit (such as closed relay contacts) you will find no
voltage.
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so you'd have no field, so the motor shouldn't 
> turn at 
> all). 
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It will but erratically, lo power, and in a random direction.  The field
still will have it's tiny residual magnetism and some induced too even
though no 'strong' electromagnetism.  Not enough for the poor thing to
even determine which way to go. 
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The belt doesn't seem to be doing diddly when I try to go 
> forward. 
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Not even a slight movement?  A slight one, 1/32"  would be enough to
prove 'open field' 
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> It definitely seems like I'm getting armature current but no field 
> current 
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Why not try 'downstairs' under the tractor first - at the motor's field
terminals? Sometime this is a plug and spcket sometimes it's a pair of
female terms on the motor,  males on the wires, and sometimes it's small
bolt on terms.  They used all kinds seemingly willy nilly.
With the field actuated the voltage there should be at or real near
battery voltage
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> in forward. Hm, I suppose if the relay fails such that all the pins 
> are 
> connected, the current would just bypass the field coil entirely.... 
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If it did that you would have heard a powerful explosion with perhaps an
issue of blood.

Only modes of relay failure;
*   open coil
*   top contact not making at rest
*   bottom contact not making when actuated
*   one of the contacts fused together, or not breaking due to being
bent.
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> I 
> need to get the pinouts of the relay figured out (see the email I 
> just 
> sent the list - the diagram in the service manual shows 6 pins on 
> the 
> relay, but it has 8).
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8 pins are normal.  2 coil, and 2 DPDT (3 ea) switches.  The diagram does
not show unused pins. It's a waste of ink.
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Dave
Weymouth MA




> 
> Mike
> 
> -- 
> 
> --------------------------------------------------------------
> Michael S. Briggs
> UNH Physics Department
> (603) 862-2828
> ---------------------------------------------------------------
> 
> On Mon, 31 Jul 2006, David C Robie wrote:
> 
> > If the field opens up the motor don't know which way it's gonna go 
> no
> > matter what polarity is on the armature and it will go there 
> weakly, at
> > random, and sometimes not go at all.  Put the tranny in neutral 
> and watch
> > the belt.  If it does what's described above there's an open in 
> the field
> > somewhere.
> >
> > Dave
> > Weymouth MA
> >
> >
> > On Mon, 31 Jul 2006 21:37:19 -0400 (EDT) Michael S Briggs
> > <msbriggs alberti unh edu> writes:
> >>
> >>
> >> On Mon, 31 Jul 2006, David C Robie wrote:
> >>
> >>> BE SURE that all connections under the tractor to the motor
> >> especially
> >>> the little wires are oK.  You could've hooked something, a 
> branch
> >> etc
> >>
> >> I'll check 'em. Since it's working in reverse though, shouldn't 
> that
> >> mean
> >> all those connections are fine? My understanding from the 
> schematics
> >> is
> >> that the forward/reverse relay reverses the direction of the 
> field
> >> (ok,
> >> reverses the direction of the current that makes the field) to 
> swap
> >> from
> >> forward to reverse, but the same connections on the motor itself 
> are
> >> used.
> >> No? If that's the way it works, it seems like the connections at 
> the
> >> motor
> >> should be fine. I think.
> >>
> >>>   If it twer me would check the RTN contacts  and open the
> >> kickplate,
> >>
> >> Which are the RTN (Return to Neutral, I think?) contacts?
> >>
> >>> put some WD better yet a good breakfree on all the big relay
> >> terminals
> >>> then tighten em.
> >>
> >> I assume the kickplate is the plate just in front of where you 
> sit?
> >> :) If
> >> so, I've become somewhat familiar with things down there as I've
> >> poked
> >> around. I've sprayed the connections with De-Oxit, but haven't
> >> loosened
> >> and retightened all the connections.
> >>
> >>> A bad connection at the 3 big terminals on the armature resistor
> >> guard on
> >>> front would cause this too.  Breakfree em and tighten em.
> >>
> >> Armature resistor guard? Do you mean the connections to R1 and R2 
> on
> >> the
> >> "screen" above the charger?
> >>
> >> Thanks,
> >> Mike
> >>
> >
>