[TR] Overdrive solenoid

[Randall]

> What did I do wrong?  My guess is this thing was drawing the 
> 15 amps all the time, instead of the brief moment to actuate.

There are several things that can happen.  One of the most commonly
overlooked is the "drop" when the solenoid is de-activated.  It only has a
limited range, and if the plunger drops too far, the solenoid won't pick it
back up again.  As you know, there is a contact in the top of the solenoid
that opens when the plunger reaches the upper end of it's travel, and
reduces the current from 15-20 amps down to 1 amp.
Some solenoid mounts have an adjustment for 'drop' (which may be missing or
misadjusted).  Others had only a rubber stop, which may have fallen out or
distorted until it lets the solenoid drop too far.  If you have the latter
type, I suggest you modify it to be adjustable.

Another possibility (since the TR lacks a cover over the lever arm) is that
grit or a small rock got into the solenoid and blocked the plunger from
opening the pull-in contacts.

Or, your solenoid may have simply been defective.  There's a little plastic
button that pushes against the contacts, and it seems that some of them are
made of thermoplastic that gets soft and distorts when it gets hot.  Or
maybe they just aren't hard enough to withstand the repeated pounding from
the plunger, I don't know.  But I've taken one out of a burned solenoid that
was simply too short to open the contacts.

My suggestion is to add a fuse to the OD solenoid circuit, sized so that it
will blow if the cutout contacts don't open quickly.  That won't fix the
problem obviously, but at least it will only cost you a 50 cent fuse instead
of a $150 solenoid to learn you have a problem.  I used a MDL 8 fuse (which
is an 8 amp slow-blow), just because I had a case of them on hand; but I
believe even a 5 amp (American) standard blow would work.  I also added a
diode across the relay contacts, which seems to make them last longer.

Randall