[TR] Overdrive Solenoids aftermarket

[Randall]

> Thank you, Randall.  Maybe that's the problem.  I had added a modern two

> prong mini 10 amp fuse.  Don't remember why, but I thought the amp was in

> the 3 to 5 range, but that must not be for pull in.  I'll try switching to

> a slo-blo fuse at 8 amp too and see what happens.

 

No point, IMO.  From your description, I do think you have a problem.  Might
be an internal short in the "holding" coil (which should draw only about 1
amp), but my guess is that the pull-in contacts are not opening for some
reason, or are closing back up again when things get hot.

 

Just so we're on the same page, the A-type solenoid has two windings
internally.  When the relay first closes, current passes through both
windings, producing a big strong jolt of magnetism to move the solenoid
plunger.  Once the plunger has reached the end of it's travel (against the
inside of the housing), it is supposed to press on a small button that
pushes open the contacts under the housing outside, and cuts the current
through the high current "pull-in" coil.  This should happen very quickly,
normally too fast to blow a 10 amp fuse.  The pull-in coil draws somewhere
around 15-20 amps, while the holding coil is only about 1 amp.

 

Here's a photo where you can kind of see the black button under the contact
lever.  https://goo.gl/W5Q23V

(Ignore the diode, it was a mistake.)

 

I only used the MDL-8 fuse because I had a box of them on hand (scrounged
from the trash when a previous employer shut down a production line).  Your
10 amp mini fuse should work just fine.

 

Anything that blocks the solenoid plunger from rising all the way can cause
the fuse to blow.  In my case, it appeared to be a bit of gravel that found
its way inside and jammed the plunger.  But misadjustment of the linkage can
do it too, or even losing the stop that controls how far the plunger can
drop out of the solenoid.  (On some A-types, there is supposed to be a
little rubber bumper mounted on the stop arm.  Mine was missing, so I
replaced it with a bolt.

http://s258.photobucket.com/user/TR3driver/media/A-type%20OD/DSCF0055.jpg.ht
ml

 

Randall

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