[Vwdiesel] Auxiliary Battery

Roger Brown r.c.brown at ieee.org
Mon Apr 21 09:23:46 EDT 2003

Sandy Cameron wrote:
> At 11:32 PM 4/20/03 -0400, you wrote:
> >The only concern I have is trying to keep both batteries charged. I think
> charging them simultaneously is out of the question due to the stress put on
> the alternator. I dont want to upgrade the alternator.
> >
> Most of the diesel pickups, like the chevy suburban, the ford powerstroke,
> etc, use dual batteries, and they just connect them in parallel. (I don't
> like parallel batteries unless they are identical in type and age).
> The alternator is a self-limiting device, which is why they do not use
> current regulators like the old generators used to. It's not the problem.
> Parallel dual batteries are OK in vehicles used daily, as long as they are
> the same age (preferably from the same batch) , the same type, and replaced
> together. In most solar electricity system, batteries are usually connected
> together series-parallel to achieve the power levels required.
> ***
> Hey Hagar, how about the batteries in those old diesel electric submarines
> (Like Canada just bought) , were they series-parallel??
> ***
> Just make sure your wiring is in good shape and properly fused, and parallel
> the 2 negative ground cables to the same LARGE bolt on the engine block near
> the starter.
> The only item likely to suffer is the starter itself because of all the
> extra amps it can suck, if the engine is stiff.
> There is no substitute for a light weight synthetic oil, new heavy battery
> cables, (the stock ones suck) and an absolutely perfect glow plug system for
> reliable winter starts. Begin there.

In my 4x4, I run two identical batteries, purchased at the same time to ensure as close a match as possible.  However, I still
run an isolating solenoid that separates the batteries unless the slenoid is energized.  The main issue with hard wired parallel
batteries is that they can self-discharge each other will sitting if there is a slight voltage difference between them.  By
having them separated they can't discharge each other while sitting.  And ditto on the heavier cables, I use 1/0 weldign cable
for mine, power and ground connections.  Welding shops have very good prices on the heavier cables like this if you need any


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