How do we best achieve increased battery charging capacity?

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How do we best achieve increased battery charging capacity?

Postby TheAussies » Fri Jul 30, 2010 1:44 pm

G'day Arild
We have a question for you please:
Can we successfully use a second Xantrex inverter/charger, in parallel to our present 3Kw/140A unit, to double our battery charge rate?
Our boat uses a lot of battery power because it's all electric, a large household refrigerator being the big drain.
We presently have four Lifeline 8D AGM house batteries, soon to be renewed, and perhaps increased to six Lifeline 8D AGM batteries.
We also have a single generator battery, and the two engine start batteries, all Optima AGMs.
Our generator is a 17Kw Onan, with two x 70A 110V outputs.
We also have a 12V 40A Sentry battery charger, which limits output to about 13.2V, then it cuts out.
Currently we charge our batteries with both the Sentry and the Xantrex battery chargers together.
When we first start the charge the Sentry cuts in immediately and the Xantrex follows via a timer, so we get around 180A.
However before long the Sentry charger stops and we are limited to 140A ex the Xantrex charger.
Before long we find ourselves running our 17Kw generator, with 140A capacity, inefficiently with a power draw of only 10A to 20A.
Our battery bank can clearly handle a much higher charge rate.
If we buy a second Xantrex inverter/charger, perhaps another 3Kw/140A unit then we could carry that as a spare.
We hope to do some long voyages, perhaps to Alaska and the Mediterranean, so carrying a spare inverter/charger makes some sense.
We are happy with the 3Kw 110V output so we'd not connect the 110V output of the spare inverter charger.
But we could hook up the battery charge side of that second inverter/charger.
That we could easily do, via a separate 110V input supply, with it's own breaker.
We could run jumpers from the present inverter/charger's 12V connections to the spare inverter/charger.
Both those wires are presently short 0000 cables, running through a 350A fuse.
It seems to us that arrangement would give up to two x 140A (plus the Sentry's 40A) so 320A charging capacity.
Very soon that would drop to 280A, as the Sentry dropped out, then during the acceptance charge stage it would drop back to 140A.
At that point we could turn off the second (spare) inverter/charger.
Hopefully that would halve our batteries charge time, using our generator more efficiently.
Do you think this proposed arrangement would work satisfactorily and significantly increase our battery charge rate?
Can you advise a better way to achieve a much higher battery charge rate than we can presently get?
Thanks from Pauline and Rodney
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Re: How do we best achieve increased battery charging capacity?

Postby trawlerguy » Wed Oct 06, 2010 11:16 am

Why no answers/response to this post???
"The winner of a Rat Race is always a Rat, the only thing I can think to do about that--is to haul up the anchor." - Ken Gill – “It’s Blowin’ Up A Hooly”
MV "MARIAH" Gwynn's Island,62

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Re: How do we best achieve increased battery charging capacity?

Postby elnav » Thu Oct 07, 2010 11:46 am

If you have 3 stage chargers you can parallel them during the bulk stage. Once absorption stage is reached one of the chargers will react first and cut back at some point. This point is not easy to predetermine but you can note it by observation. At that point only one charger is sufficient. In most cases the same charger will cut out first each charge cycle.
When doing this I have heard many people see less than maximum charge current . The reasons are many.
The internal resistance of the battery limits maximum charge current. The recharging was started when battery was nowher near depleted. Some people take an ultra cautious approach and start recharging when battery is only depleted by 30%. There is not enough absorption ability in the battery at that point to permit a high charge current.
People have the mistaken impression a battery is just like a water tank and you can feed it faster by simply adding more pumping capacity.
When you double the charging capacity you do not necessarily see double the charge current. In most cases iconnecting a second charger in parallel will increases charge current during bulk stage. In order to see a high charge rate you need to deplete the battery bank to about 75% - 80%
Arild Jensen
Custom electrical design for cruising boats
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