starter solenoid

["Ed & Marsha Prytherch" <mred2u@domain.elided>]

Bob:
Are you sure about the dual windings?
I have measured peak and steady state current and they are about the same -
4.5 amps.
A diode will sink the voltage spike to ground, if it is a concern, but I
doubt that it would harm another solenoid, since that solenoid will have
insulation designed to withstand it's own voltage spikes.
Ed Prytherch

>I'm not so sure that you're a dummy.  The starter solenoid "pulls in" via
its "pull in" winding that is grounded through the starter windings.  When
the solenoid "pulls in", a copper disk applies 12 V directly to the
starter.  With the key to "start", but just before pulling in, because the
starter's resistance is so low compared to the pull-in winding of the
solenoid, most of the voltage drop was across the pull-in winding.  But
once pulled in, the starter winding is at 12 volts--and so is the
"grounded" end of the pull-in winding.  So the pull-in winding has no
voltage across it (12 volts on both ends) and does nothing (otherwise it
would get hot and consume a lot of current).  Meanwhile, the weaker "hold"
winding of the solenoid is wired conventionally--one side grounded, other
to solenoid 12 V terminal, so it keeps holding.  Connecting your cold start
solenoid across the starter winding means that it will share in sinking the
"pull in" solenoid current to ground, which is probably OK.  However, when
the key is released from the start position, any inductive "kick back" from
the starter windings will flow to ground not only through the two starter
solenoid windings in series (if I've got that right) but also through your
cold start solenoid.  Here, I'm not sure whether or not there's a potential
problem.  I suspect you weren't sure either, which is why you used a
separate relay.

By the way, earlier in this thread it was stated that the starter solenoid
consumes far less current than the cold-start.  That seems very strange to
me--a starter relay, yes, but most starter solenoids consume many amps
until "pulled in".  I'm too lazy to measure mine, though.
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