> From:         Herbert Graf[SMTP:mailinglist@FARCITE.NET]
> Sent:         Wednesday, December 03, 2003 4:53 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [EE:] Voltage measurement

>> >         Unfortunately the problem with just this is that the lowest
>> >"engine on"
>> >voltage may be below the maximum "engine off" voltage when you
>> consider all
>> >conditions. For example, on a really cold day the "engine
>> running" voltage
>> >might be below the "engine off with fully charged battery" voltage. TTYL
>> >
>>
>> I would find that surprising, but I'll grant that it's possible.
>>
>> Measure the current.  It will flow one way as an indicator of engine
>> start-up, and the other way until the battery is re-charged from the
>> effort...

>         Hmm, now that's a good idea, only problem I can see if you'd have to build
> your shunt such that it could pass the hundred or more amps needed during
> starting, without suffering a large drop. TTYL

Not so. If you look at most "hot" terminal battery cables, you will see that
they are made of two conductors.The thicker cable goes directly to the
starter motor, and the thinner one powers the rest of the car. Measuring the
current in the thicker cable would not only be difficult, but it would also be
pointless.

John Power

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