----- Original Message -----
From: "Lisa" <jeepcj8@home.com>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Sunday, November 19, 2000 11:28 PM
Subject: [MV] 24v Coil ohms test
> Hi all,
> Just had to replace a bad coil in the M37. Using an
> ohmmeter, the bad coil showed 0.000, the replacement coil
> borrowed from another distributor showed 0.402. Does anyone
> know the proper range for a good coil? This one works, but I
> would like to be able to test the ones I come across at swap
> meets.
>
I know nothing of M37s, however, surely something wrong here. I've never
seen a 24V coil either as the norm is to use a 12V one with ballast
resistors allowing a useful boost on start-up.
0.402 ohms is not sensible since with a running engine and therefore
charging battery some 28V + can be expected as a supply and this would
result in a primary coil current of some 69.65 Amps, this can't be correct.
Either the measuring instrument is way off or more likely perhaps the
measurement has been done with the coil in-circuit which would mean the
measurement includes all the parallel circuits of the vehicle. One or other
primary lead must be disconnected to effect a correct reading.
Maybe a typo also, 4.02 ohms is entirely believable and typical of a
so-called 12V "sports coil", all examples of RR B Range Mil (gas) engines
from fours in Champs through the sixes in Ferrets to the eights in
Saracen/Saladin/Stalwart/432 have 12V coils of 4 ohm nominally and 4 ohm
ballast resistor (in reality a pair of 8 ohm devices in parallel).
Richard
Southampton - England
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