Join Date: Aug 2006
Location: Arlington, VA
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Re: Solar Battery Charging
Yes, you could do that, but it's not the optimum solution.
AGM and flooded battery charging profiles are almost identical, so no problem there.
However, in the (somewhat unlikely but not impossible) event that a short developed in either battery bank, or a load was inadvertently left on (bilge pump continuous running?) you could flatten both banks.
A better solution is to use a voltage follower device like the Xantrex EchoCharge or the Balmar DuoCharge to keep the starting battery topped off.
These devices work by sensing a charging voltage on the house batteries and, when it is present, drawing off enough current to just top off and maintain the start battery. All automatic. No switches required. You don't have to remember to switch anything.
In your situation, the EchoCharge would be appropriate. It costs about $140 and is very easy to install. Mine has worked 24/7 for the past nine years, and I've installed a bunch of them on client's boats....all without issue so far as I know.
IMHO, these devices are better than "combiners" because there are no mechanical relays to go bad and they allow regulated current to flow in only one direction: from the house batteries to the start battery.
Keep in mind that the typical start battery requires VERY LITTLE CHARGING to keep it topped off. But, flooded LA batteries do need to be kept at a high state of charge to slow the sulfation process.
BTW, both AGM and flooded batteries like to be charged at over 14 VDC. Lifelines like 14.4-14.8VDC, while the Trojan T-105s like 14.6-15.0VDC during the absorption phase. I assume you have a smart controller for those panels?
Last edited by btrayfors; 10-18-2013 at 05:57 PM.