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car batteries in parellel

D

Dan

Jan 1, 1970
0
I have a project car with a high torque starter and the battery is one of
the sealed omni-positional batteries. I was going to put a regular wet-cell
battery in parellel with it for backup and was wondering if there would be a
problem. I can't imagine what problems there could be as long as they are
both 12v other than the fact that one may have more cranking power.

dansteely2001 at yahoo dot com
 
T

Tim Wescott

Jan 1, 1970
0
Dan said:
I have a project car with a high torque starter and the battery is one of
the sealed omni-positional batteries. I was going to put a regular wet-cell
battery in parellel with it for backup and was wondering if there would be a
problem. I can't imagine what problems there could be as long as they are
both 12v other than the fact that one may have more cranking power.

dansteely2001 at yahoo dot com

Paralleling batteries is usually not a good idea if you do it for any
length of time, because the batteries can get unbalanced over multiple
charge/discharge cycles until eventually you have a dead battery in
parallel with a good one. Paralleling individual cells works very well,
but you can't do that here.

For race and aviation applications it is common to have a booster
battery on a cart and a fairly small battery on board. This saves space
and weight at the cost of having to maintain the booster cart. It
doesn't cause the charge/discharge problems because the two batteries
are charged separately.

If you must parallel them consider using two identical batteries. This
will at least minimize the effect. Better would be to just get a
humongous battery that can handle your starter's current.

Is it a geared starter? Have you considered selling and getting a
geared starter? You should be able to get plenty of torque from one of
them with significantly less current draw than a direct-drive.
 
B

Bill Darden

Jan 1, 1970
0
Hi Dan,

I agree with Tim's conclusion that you should not parallel wet and
VRLA batteries, but respectfully disagree with his reasoning. Wet and
VRLA lead-acid batteries have different discharge and charging
charactistics due to different plate chemistries. Up to four identical
batteries and be paralleled to produce more capacity. For more
information on battery types, please see Section 7 of the Car and Deep
Cycle Battery FAQ on www.batteryfaq.org.

Kindest regards,

BiLL......
 
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