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Old 15-08-2012, 12:31   #1
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Alternate House Battery While on Shore Power ?

Hello,

I am looking for opinions regarding the use of deep-cell batteries while on shore power (with the battery charger working).

I have heard that it is potentially damaging to the deep cycle batteries to use them while connected to shore power for your 12V loads. (Because the battery charger is supplying most of the current, the drain on the house battery bank will be very small.)

Does anyone have an opinion on installing an auxiliary 12V automotive style (thin-plate) battery for use while connected to shore power?

Since they are relatively inexpensive, I thought it may be a worthwhile addition to save wear on the deep-cycle house bank (6V 'golf-cart' lead-acid batteries wired in series-parallel).


Thanks,

Robb
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Old 15-08-2012, 13:21   #2
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Re: Alternate house battery while on shore power?

I had a friend who did just that. He runs his fridge and built in a relay so when he turns his main DC switch to OFF to the relay switches his battery charger to just a small auto battery to run the fridge when he's away from the boat. A little complicated for me, since I am of the school that if you are not on your boat it shouldn't be plugged in. Your boat, your choice.

PS - In the long run, the bigger the house bank, the longer the same amount of lead will last, so adding a small battery may not make sense. All depends on how long you're planning to do so. If irregularly, it isn't worth it IMHO. Long term, maybe.
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Old 15-08-2012, 13:35   #3
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Re: Alternate house battery while on shore power?

Stop worrying. So long as you have a good regulated battery charging source....shorepower or solar or wind or whatever....your deep cycle batteries will be just fine.

In order to prolong their life, however, it will be good to use a sufficiently high float voltage to stave off the almost inevitable sulfation, and it will be good to equalize them (controlled gassing) periodically to help knock off the PbSO4 crystals from the plates and stir up the electrolyte to avoid stratification.

Even at dockside, it's possible to "exercise" your batteries, and that's a good thing. For example, turn off the charger for a day or two or three and run everything from the batteries. Then, charge 'em up and you're good to go.

My six year old T-104's still test like new, and they're mostly on shorepower 24/7.

Bill
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Old 15-08-2012, 15:21   #4
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Re: Alternate House Battery While on Shore Power ?

For clarification, I'm considering the situation when cruising and dockside, not unattended. Charger is a Xantrex TrueCharge 20+, which has an equalize mode. Sounds like I don't need to worry, and the money and space would be better spent on an additional pair of 6V. Thanks.
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Old 17-08-2012, 10:51   #5
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Re: Alternate House Battery While on Shore Power ?

See the article I wrote at Hints and Projects

Any battery being maintained by a charger (smart or not) will be sitting at exactly the same state of charge 99.99% of the time so each time you flush a toilet or run a pump you are cyclying at the same place on the plates. Over an extended period the electrodes will get spongy just at that spot and you can end up with diminished capacity.

Perodic discharging well below that float point will remove and replace that area of electrode stress so long as you remember to do it. However since you don't need a $1,000 battery bank standing by when on shore power I strongly suggest the action described in that article.
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