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Old 12-02-2018, 08:59   #1
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20 Hour Rate in Parallel

All,

If a 20 hour discharge rate of a battery is 5.8 Amps is it honest to think about the 20 hour discharge rate of three batteries in parallel as being 17.4 A? That is relevant to us because our actual discharge rate at night is below 17.4 A (maybe 10-12), so we should be getting more than the rated 20 hour Amp rating out of the battery.. right? How would that impact how you program your capacity into the battery monitor?

For the next one I know I am "splitting hairs" and its just academic in nature but I am curious:

What about using a battery monitor... if single battery is listed as being full at 0.5 Amps acceptance does that translate to 1.5 A for three batteries in parallel? What about if you have four 6V batteries in series-parallel?

- z
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Old 12-02-2018, 09:45   #2
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Re: 20 Hour Rate in Parallel

17.4a is the correct parallel rate for 3 batteries.

1.5a for those 3 in parallel is 0.005C.

What’s the capacity (a-hr) and 20hr rate for a single 6v battery?
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Old 12-02-2018, 10:18   #3
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Re: 20 Hour Rate in Parallel

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Originally Posted by Adelie View Post
What’s the capacity (a-hr) and 20hr rate for a single 6v battery?
We recently replaced 4 x 6V Trojan T-145 bank which each had a 20 hour rate of 260 Ah. But they list a 100 hour rate as well...287 Ah or about 10% more. Don't know if that is typical or not.

It was in a 12 volt config... series-parallel.

Although the question is just academic in nature the reason I bring it up is that my daily use calculations (and I really do have a good knowledge of how many Ah we use in a given day) should have shown us drawing our new firefly batteries below 60%, probably closer to 40%, but they recharge so fast from the solar compared to the older flooded batteries that we have not yet drawn them below 63%.

Part of that is (I assume) that we are actually drawing less than the 20Ah rate from the batteries overnight so we are starting our day out with less of a deficit in Ah.
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Old 12-02-2018, 10:32   #4
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Re: 20 Hour Rate in Parallel

For State of Health testing purposes, batts should be loaded separately if practical, to spot and maybe remove any early failures.

But when paralleling them together, Peukerts means the whole will have greater capacity than the sum of the parts. But underestimating residual capacity for BM SoC calculations is fine, better than over.

endAmps should just be a flat multiplier though
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Old 12-02-2018, 13:24   #5
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Re: 20 Hour Rate in Parallel

Quote:
Originally Posted by zboss View Post
We recently replaced 4 x 6V Trojan T-145 bank which each had a 20 hour rate of 260 Ah. But they list a 100 hour rate as well...287 Ah or about 10% more. Don't know if that is typical or not.

It was in a 12 volt config... series-parallel.

Although the question is just academic in nature the reason I bring it up is that my daily use calculations (and I really do have a good knowledge of how many Ah we use in a given day) should have shown us drawing our new firefly batteries below 60%, probably closer to 40%, but they recharge so fast from the solar compared to the older flooded batteries that we have not yet drawn them below 63%.

Part of that is (I assume) that we are actually drawing less than the 20Ah rate from the batteries overnight so we are starting our day out with less of a deficit in Ah.
OK so the 20hr capacity of the T-145's is 260 a-hr which gives a rate of 13amps.
100hr capacity is 287 a-hr which gives a 2.87 amp rate.

So 4 of these batteries in series-parallel will give you
20h: 520 a-hr, at 26amps
100hr: 574 amp-hr at 5.74amps.
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Old 12-02-2018, 19:43   #6
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Re: 20 Hour Rate in Parallel

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Originally Posted by zboss View Post
All,
How would that impact how you program your capacity into the battery monitor?


- z
you program the 20h rate. it will know if you are drawing over or under and comp for it in the batt %.

IE if you have 300ah battery. and draw 100a load. say after an hour. the meter will say -100ah but it will say like ~40%.instead of 66%. because of the high load.

if you are drawing under the c20 rate. the battery will last longer (draw more ah) before it hits 50%. not by much though.

this is the peukert setting.
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Old 12-02-2018, 19:51   #7
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Re: 20 Hour Rate in Parallel

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Part of that is (I assume) that we are actually drawing less than the 20Ah rate from the batteries overnight so we are starting our day out with less of a deficit in Ah.
an ah is an ah. if you take one out, it's one gone. doesn't matter how fast or slow. you have used the same amount up.

battery % however will differ on speed of used.
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Old 12-02-2018, 19:54   #8
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Re: 20 Hour Rate in Parallel

Inferior BMs don't ask for Peukert coefficient, nor charge efficiency.

And you need to update the AH capacity as tgat walks down over time.

And all AH-counters should regularly be reset at 100% Full, best done manually.

SmartGauge is more accurate for SoC, needs none of the above complications.

But nice to see AH in and out as well, so best is both. But most consider that pricey overkill.
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Old 12-02-2018, 20:19   #9
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Re: 20 Hour Rate in Parallel

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an ah is an ah.
Yes but just to clarify further, a battery stores more AH when they're drawn more slowly.

AH capacity is lower at high C rates
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