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Old 05-23-2016, 06:52 AM   #23
twistedtree
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City: Vermont
Join Date: Jan 2013
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The carbon foam batteries look interesting, but I wonder about a few things.

AGMs and other lead acid batteries can be deeply discharged too. The life of the battery is determined by the number of amp-hours you run through it. The more deeply you cycle it, the fewer cycles you get, and it's nearly linear as long as you stay away from the extremes of the DOD range. There really is nothing magic about the 50% DOD limit that we tend to follow. You can run AGMs to 80% DOD on a regular basis and you will just get fewer cycles than at 50% DOD. Or you can run to only 20% DOD and get more cycles. But the total amount of power the battery is able to store and return over it's life is nearly constant. You get to decide whether to use it in lots of small chunks or fewer big chunks.

So my question, when looking at Carbon Foam batteries, is whether they really are any different, or if this phenomenon that has characterized lead acid batteries for the past 120 years is just being exploited for the first time.

On a boat, DOD matters, but I think the whole acceptance charge cycle of AGMs is the far bigger "problem". Our quest for giant battery banks is all about reducing generator time at anchor. If you run your generator long enough to charge the batteries the last 20%, you will incur a LOT of generator run time. And if you don't do the last 20% of charge, you lose another 20% of you banks capacity. So in practice you run your batteries between 50% and 80% DOD, so only utilize 30% of their capacity.

If our batteries could accept full charge rate right up until they are full then we would care a lot less about generator time, mostly because it could be utilized well. This is the huge attraction to LiFePo batteries.

So I think the other big question with Carbon Foam is what their charge acceptance characteristics are.

And then of course there is their long term life expectancy, cost per AH over their life, etc.
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