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Old 08-04-2020, 03:12 PM   #1
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Charge acceptance rates

I think I should quit reading stuff! I had always gone under the assumption based on Nigel Calder's book that FLAs would take a charge acceptance rate of 20-25% of the total amp. hours of the bank. I just looked at the Trojan website and it appears to say that 13% is the maximum charge acceptance rate. Am I missing something? I have a bank of 10 Trojan 105s with 1125 amp hours. I use two Zena 150 amp alts that put out about 240 amps at cruising rpms. I've had this setup for 14yrs and am on year 8 with the present bank. Any thoughts?

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Old 08-04-2020, 03:15 PM   #2
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Just because your alternators can produce a certain amperage doesn't mean your batteries will actually accept a charge at that rate.
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Old 08-04-2020, 03:16 PM   #3
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On top of that, the manufacturer's recommendation for max charge rate for ideal lifespan (and keeping battery temp down during charging) may be lower than the max they'll accept after being drawn down significantly.
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Old 08-04-2020, 03:18 PM   #4
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Quote:
Originally Posted by rslifkin View Post
On top of that, the manufacturer's recommendation for max charge rate for ideal lifespan (and keeping battery temp down during charging) may be lower than the max they'll accept after being drawn down significantly.
Yes and this is probably the most important consideration.

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Old 08-04-2020, 03:23 PM   #5
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I've never had the temp go above 65deg even when equalizing. I was just curious on the big discrepancy between Calder and Trojan.

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Old 08-04-2020, 05:28 PM   #6
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Calder info is generalized. Further , common info & practice WAS 20-25% C. For flooded wet cells
Looks like Trojan has dropped their rating.
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Old 08-04-2020, 05:37 PM   #7
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If it has worked well for 14 years, why mess with success? FLA batteries have not changed that much.
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Old 08-04-2020, 06:22 PM   #8
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I've never paid very much attention to acceptance rates, because my charging sources are relatively meager (solar mostly, with a bit of smallish alternator). Out of curiosity I just went and looked up the Lifeline acceptance rate (that's what I have). If I understand it correctly, they recommend .2C minimum (20 amps for 100ah battery) and 5C maximum (500a for 100ah battery).

In comparison, 13% would be....13amps for 100ah battery. I know AGM have a higher acceptance rate, but that does seem really low, doesn't it?

OTOH, if your batteries are 8 years old (and assuming you use them regularly), you can't say you haven't done well with them.

Okay, I got more curious and looked up Trojan's flooded cell recommendation. They say 10-13% of C20 (the 20 is small). Does that mean something different than "C" as Lifeline uses it. What is the little 20 about? In comparison, they list their (Trojan) AGM as 20% of C20. So are they expressing it differently than Lifeline and it's not really so low? Or is that just how flooded cells are?

Next, I Googled. Oh, C20 is the 20 hour rating. So I guess it is apples to apples with Lifeline and that's why the AGM acceptance rating is a big thing (for those like you who have large charging ability).

So I guess it goes back to your 8 years is none too shabby; maybe pretend you didn't read it?

I guess if I get a trawler with a big alternator I, too, might have to start concerning myself with acceptance rate vs. my slow but steady "tortoise" solar panels
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