At 01:43 PM 5/17/2002, Alistair Bell wrote:
>1. the starter itself as designed is pretty much a dead short, i.e. it draws
>a lot (technical term "butt-load") of current .
>I think the power rating for the diesel starter is 2.3kW or is it (1.7kW?),
>that equals a current draw (at 10V) of 170 to 230 amps. The contacts in the
>solenoid are pretty well taking as much as the battery can give! Plus the
>contacts close when solenoid is tested (minus internal spring) and have very
>low/no resistance.

This is a quibble, but any decent 12v battery will give you over a thousand
amps into a dead short.  Briefly.  Before it either runs down or throws
acid all over the joint.  200 amps at ten volts means an effective total
resistance in the circuit of a whole twentieth of an ohm, including the
"back-EMF" that the starter generates as it spins (the stall current of the
starter will be much higher than the running current).  0.05 ohms doesn't
sound like much, but it's quite a bit in this particular scheme of things.

That's why we disconnect the negative lead first, so that when we're
undoing the positive and the wrench touches the chassis -- nothing happens,
instead of instant welding machine.

david

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"