DANMAS@aol.com wrote:
>
> In a message dated 97-07-03 19:56:35 EDT, wkube@iadfw.net (Wayne Kube)
> writes:
>
> > But, if you're *really*
> > serious about more cranking power, put 2 twelve volts in parallel. You
> > still end up with 12 volts, but the amperage will be doubled. Just make
> > sure the batteries are identical for proper charging.
>
> Wayne:
>
> This is an invitation for disaster! I agree with you, that as long as both
> batteries are identical, everything is OK, and you have twice the charging
> current. But what happens when one battery goes bad (and sooner or later, one
> will)? The good battery will now act as a battery charger to the bad battery.
> With nothing but the internal resistance of the battery to limit current,
> there is a real probability of a melt down.
>
> As for the use of parallel batteries in trucks, are you sure they don't use
> some type of isolation scheme, such as the use of rectifiers, to prevent
> this? I would be interested in learning more about this.
>
> Dan Masters,
> Alcoa, TN
Dan and all -
I have seen numerous trucks, tractors, and large Caterpillar heavy
equipment all with parallel batteries and no type of isolation. The
batteries are hard wired with heavy guage battery cables, positive to
positive and negative to negative. The use of diode isolation that you
are referring to is used in motor homes and other specialty vehicles
that use an auxillary battery to power other systems. The diodes allow
both batteries to charge off the alternator, but the load on the aux
battery will never drain the main vehicle battery, so there is always
power to start the engine.
Interstate Batteries say it's ok to connect them in parallel. Go to
their website at
http://www.interstatebatteries.com/currentfall/techtalk.html for more
information. It says, in part:
(quote on)
We often have to work with multiple batteries to achieve desired power
demand requirements. The batteries may be placed in:
• series to achieve a higher voltage
• parallel for increased current, or
• a series/parallel combination.
Whichever method is used, you need balanced power to gain the highest
efficiency.
Let's look at some examples. Batteries connected in any of the three
type systems work the most effectively when they have the same CCA,
Reserve Capacity and life expectation. When this balance is attained,
all of the batteries (with connections in good working order) operate
equally to supply the necessary load capabilities.
(quote off)
There are also some examples of systems connected this way. In my
opinion, if the manufacturers say it's OK, then the potential for
disaster must be pretty low, as they wouldn't want to get into a product
liability lawsuit.
YMMV
Wayne (that's my story, and I'm sticking with it!) Kube
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