Rob,
I'm assuming you want to increase the available current, which
means you'd connect the batteries in parallel. If you connect
in series, you'll double the voltage and let ALL the smoke out.
Really, there's no reason to do this and nothing to be gained.
The starter is going to pull a certain amount of current (200-300amps)
for a split second when it starts to rotate, then the current draw
will drop as the inductive impedance builds in the windings.
The starter will not pull more current than this (unless you have
a short in the windings, and it'll overheat quickly and probably
not work anyway). As long as your battery is rated and capable of
producing 200-300 amps ("cold cranking amperage"), the starter
will only pull that amount regardless of how much is available.
You gain nothing (unless you're trying to power a 1,200-watt stereo
with the engine off).
If you're really concerned about the starter's cranking ability
maybe you should consider a high torque starter conversion.
bs
--
***************************************************************
Bob Spidell San Jose, CA bspidell@comcast.net
'67 Austin-Healey 3000 '56 Austin-Healey 100M
***************************************************************
-------------- Original message ----------------------
From: bj8healey@juno.com
> Hello listers, I have a question.
> I want to hook up two 12 volt batteries to give extra cranking power to
> my BJ8. I want to end up with the equivalent of a large 12 volt battery
> without frying my electrical system. There are two ways I can think of to
> do it but I am not sure which one, if either is correct.
>
> I could connect the positive cable from my car to the positive terminal
> of one battery. Then connect the negative cable from my car to the
> negative terminal of the OTHER battery. To complete the circuit I would
> then run a cable from the unused positive terminal on one battery to the
> unused negative terminal on the OTHER battery. I think this would suit
> the purpose, but not remembering my college electrical physics I don't
> want to chance it without some expert advice from you folks. The car is
> now a negative ground if that plays into this.
>
> The other way to do it, which I think is not the correct way, is to cable
> the two batteries together -- positive to positive and negative to
> negative then attach the car cables as usual, positive cable to a
> positive terminal and the negative cable to a negative terminal. I don't
> guess it matters which terminal goes to which battery as long as the
> polarity is correct. But I think this would create 24 volts and be a
> disaster.
>
> I don't know if either, neither or both of these methods would give me
> the desired results. As stated before, my electrical knowledge leaves a
> lot to be desired.
>
> Any advice would be sincerely appreciated.
>
> Rob Fromm
> bj8healey@juno.com
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