Wayne & Bob:
Yes, I agree, it is possible to connect batteries in parallel, and it is
often done. For example, in our Nuclear Power plants, we use lead-acid
batteries in the emergency back-up power supplies. These are connected in a
series/parallel arrangement to provide 250 volts, with a HUGE current
capacity. One big difference, though - they are monitored on a daily basis,
and are located in a room with a sophisticated fire detection/protection
system.
The truck applications mentioned - are these the standard 18 wheelers we see
on the highway, or, are the the massive trucks used around mining and similar
applications? I wonder what kind of precautions and maintainence instructions
come with them? I hope they are not on the 18 wheelers, because I know what
poor mainaintence some of them get!
It's also true that we parallel batteries every time we jumper a car. Have
you ever wondered, though, why you get a spark when you make the connections?
If the voltage of the batteries were the same, there would be no spark. The
fact that there is a spark proves that one battery has a lower voltage than
the other. As long as there is a difference in voltage, there will be a
current draw from the higher voltage battery to the lower voltage one. The
larger the difference, of course, the larger the current draw. An internal
short, for example, on one cell in an otherwise good battery will give a 2
volt difference. With a 0.01 ohm cable resistance, you are talking 200 amps!
The power dissipated is 400 watts. If the bulk of the cable resistance is
confined to the relatively small area of a connection, the temperature can
get quite hot! (Think about a match. A match is hot enough to set a house on
fire, yet the power output is too small to heat the house - much less than
400 watts. All the energy in the match is concentrated in a small area). When
you jump start, you remove the cable very quickly. What happens when the
current is allowed to flow, say, overnight?
I may be wrong. Maybe there isn't as much potential for fire as I think, but
why take the chance. What are you gaining? If your car needs the extra power
of the dual batteries, something is wrong with your car (unless you have a
Mega-watt sound system, or live in someplace like the Artic).
Dan (call me paranoid) Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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