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post #1 of 8 Old 03-26-2007 Thread Starter
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Undersized charger question

I'm charging our 675Ah house bank with a 20amp A/C charger. The manufacturer says that the charger is only designed for systems up to 400Ah. So I'm assuming that the only down side to using the undersized charger (truecharge 20) is that it'll take longer to charge the batteries. Is there any other consequences to using it for a larger than recommended system?
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post #2 of 8 Old 03-26-2007
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I'm thinking that you would not be getting the full 20 amps to each cell with the smaller charger. I wouldn't foresee that being a problem to the batteries. It would probably run the charger at the higher amp setting for a fair amount longer, and whether that is deliterious to the charger I don't know either. Might be something to anonymously ask the manufacturer.

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post #3 of 8 Old 03-26-2007
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AFAIK it will work just fine.

If you are running a 675Ah bank down to 50%, it will need some 400Ah put back into it to recharge it fully, because of charging inefficiency. If your charger doesn't overheat running 20 hours straight under full load, and you don't mind leaving the charger running "all day and night" to recharge...Yeah, it should work.

On the bright side, the charger is SO underpowered compared to the battery bank, that you can probably leave it running 'forever' without ever cooking the batteries--assuming it is putting out the right voltage.
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post #4 of 8 Old 03-26-2007
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Originally Posted by hellosailor
On the bright side, the charger is SO underpowered compared to the battery bank, that you can probably leave it running 'forever' without ever cooking the batteries--assuming it is putting out the right voltage.
That was my theory running my 10 amp Guest most of the time I was off the boat. It would run for a day before getting to float stage with my two 1100 CCA deep cycles.

I will rethink this policy when I get my new inverter charger aboard, because I have a West Marine 3-stage 20 amp charger now doing two Seavolt 6 VDC ganged together, with a little Xantrex echo charger keeping the 12 VDC start battery happy. The new inverter could take 100 amps in...I can only get 60 amps via two cables! But it's nice to know I could charge my batteries while running power tools and vacuum cleaners on the boat without tripping the AC panels.
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Glorious weekend that it was here, I think everyone had spring fever and like groundhogs you could see all the heads popping out of cabin hatches at the boatyard, eventually followed by extension cords and chargers, or dead batteries.

That time of year, FINALLY!
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post #6 of 8 Old 04-07-2007
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In my opinion there is one problem.

In the early bulk charging phase (battery deep discharge) you can see consequence: the overheat of your charger. The current will be quite large - bigger than charger efficiency.

Most of modern chargers has the thermal protection so your charger should make self-turning off and after temperature drop down he should to begin charging again. The practical result is the increase of charging time. The solution is mounting additional cooling fan for the charger.
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post #7 of 8 Old 04-07-2007
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Quote:
Originally Posted by hellosailor
Glorious weekend that it was here, I think everyone had spring fever and like groundhogs you could see all the heads popping out of cabin hatches at the boatyard, eventually followed by extension cords and chargers, or dead batteries.

That time of year, FINALLY!
Not quite that time of year... supposed to have some more snow inbound...

But, I did plug in the charger and have topped off the house and starting banks.

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post #8 of 8 Old 04-07-2007
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Newport41,

If you're talking only about charging your batteries at dockside only (where, presumably, the time required to bring them to a full charge isn't critical), then the size of the charger isn't a huge concern.

However, what is a concern is the prevention of sulfation of the plates through proper staged charging (bulk, acceptance, float) and, for flooded batteries, periodic equalization (bringing the voltage up to about 15.5 volts for several hours). Some battery chargers have an equalization capability.

The good news is that for relatively little money you can buy a top-notch battery charger which is sized properly for your battery bank. The Iota chargers are very robust, well designed, and relatively inexpensive. They come in several sizes, up to 90A. They use PWM (pulse width modulation) technology and with the IQ-4 smart charge option ($35) will keep your batteries happy and fully charged.

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