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Subject: Re: TWL: Electrical issues
From: Arild Jensen (elnav@XXX.XXX)
Date: Wed Mar 27 2002 - 08:49:13 EST
Garrett wrote:
> First, your plan, in my view, is a good one. Second, I doubt very much
> that the differences in the batteries are significant in terms of
> charging.
REPLY
Sorry Garrett but here I feel obliged to jump in.
When you wire several batteries in parallel there is no isolation
between them. Consequently any differences in the batteries will
result in unequal amounts of charge current going to each.
For this reason, Jim's idea of having one bank of "old" batteries and
one bank of new batteries is less likely to produce problems than
mixing one old battery in with the two new batteries.
Having said that I would like to remind people of the desulfator
devices such as PulseTech. See archives for past list discussion
in detail.
I would like to describe an experience I had recently.
The genset did not seem to be charging its own battery and it
would not start on just the one battery. It required using the
Selector switch on BOTH to get it going.
All the batteries in the boat had been equipped with PulseTech
devices more than a year ago.
The cranking problem turned out to be cables corroded inside the
insulation. Now to check if the genset was actually charging the
mechanic tried to draw down the single Group 27 battery by
shutting off the fuel and cranking the motor extensively.
After many tries, the cables got very hot. However the battery
would not drop below 12.57 V open circuit and 11.2V under full
cranking load which included the glow plugs.
Normally I would have expected that size battery to be somewhat
depleted after ten or so minutes of cranking a diesel engine.
The PulseTech device seems to have contributed to the ability of
the battery to perform very well, as good as new in fact.
If some other factor was responsible I do not know what it would
be. I do know that the battery had not been charged for two weeks
prior to this starting attempt.
This latest example reinforces my impression that these devices
are a good thing to fit to large battery banks where long life and
total reliability is critical.
Cheers
Arild
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