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Old 28-02-2021, 07:20   #1
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FireFly Battery Finish Amps

I have had a few days recently where I motored in the morning and got lots of solar in the afternoon. So have gotten to absorption voltage with the batteries being acceptance limiting and accepting less than 1 amps/ea and my BM resetting. But have never gotten to this 0.5amps/G31 FF that the manual gives as the recovery charge end point.

Has any other FF user gotten to the 0.5amp/G31 end point? How long did it take at absorption?

BTW this is just a curiosity and crowd source question. I feel that in normal use getting to less than .5%C is fully charged.
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Old 28-02-2021, 19:08   #2
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Re: FireFly Battery Finish Amps

I doubt any charger will reach that point because it will move to float before that happens. pretty much all chargers move to float too early.

you'd need bench top equipment that can manually set and hold the absorb voltage forever, and you'd have to watch it and shut it off yourself.

or I guess you could manually configure the float voltage of your solar to the abosorb voltage temporary charge it it full while watching. and then change it back.
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Old 01-03-2021, 04:49   #3
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Re: FireFly Battery Finish Amps

Well I can adjust my solar to do anything as long as the sun is out. But the battery acceptance gets to around 1A/G31 and pretty much stays there for hours till the solar can not maintain absorption. My understanding is the the manual used to say 1.5A/G31 instead of the 0.5A.

So the question is, for users have you ever gotten to 0.5A/G31? If so how did you do it and how long did it take?
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Old 01-03-2021, 12:07   #4
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Re: FireFly Battery Finish Amps

To answer your specific question, I get to 0.5 Amps/G31 every time I run a full charge on shore power. And you should too.

First a system description: There are eight Firefly G-31 batteries in a series/parallel arrangement to produce a 24V bank, rated with a C20 of 464 Amp-Hrs. The charger used here is a Victron 24/3000/70/16, and a Victron MMPT solar charger as well. Measurements are collected by a Cerbo GX, and data analyzed by Grafana.

I know it will confuse things a bit, but all my graphs are in Watts, not Amps. The difference in energy content between an Amp-hr at 24 Volts and at 29 Volts is, IMO, too large to just ignore.

The the answer to the question about how long in absorption does it take to get to any specific end point VARIES, and varies a lot, depending on the charge rate. The charging rate make a large difference at what SOC you enter absorption, and therefore how long you need to wait for a specific end point.

But here goes the data...

A routine charge this morning, SOC at the start was 80.5%, charging at about 1.65kW Depending on the sunshine!) or 57 Amps, or 12% of C20. Absorbtion was triggered at 29.1V at 09:55.

At 12:10, (2 hours, 15 minutes) later, the charge acceptance rate had dropped to 116 W @ 29.1 Volts, or 4 Amps, or 1 Amp/G31, or ~1% of C20.

You can see that further holding at the absorption voltage just continues the exponential curve downward of the charge acceptance, so after another hour it has dropped to 68 Watts, or 2.3 Amps, or 0.52 Amps per G-31 or ~0.5% of C20. I call this "FULL"

This profile is fully repeatable, every charge cycle.

If you never drop down this low I can only think of two reasons: measurement error or you have an internal short in one of your batteries. It is very worth trying to sort this out and not ignore it. As I am sure you know, an internal short in one will gradually destroy ALL your batteries.

Possible mesaurement issues:
  • Have you ever "zeroed" your shunt? i.e., checked the reading with the system disconnected and known zero current flow?
  • Are you SURE there are NO loads coming directly off the battery that might be reading on the shunt as power going IN?
  • There might be others I can't think of... other than the general accuracy of the meter...

EDIT: Ooops! I labeled the wrong spot in the graph as full, but my text above is right! Also just FYI, the green line in the graph is the real time DC load on the system, and the blue line is the 1 minute averaged power into the battery.
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Old 01-03-2021, 12:48   #5
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Re: FireFly Battery Finish Amps

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To answer your specific question, I get to 0.5 Amps/G31 every time I run a full charge on shore power. And you should too.
shore power
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Old 01-03-2021, 14:30   #6
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Re: FireFly Battery Finish Amps

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shore power
Power is power... Last I checked. It's all moving electrons...

But now you know what a normal charge curve looks like... and how long it takes, just as you asked.

A "Thank you for that." would have been nice...
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Old 01-03-2021, 16:25   #7
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Re: FireFly Battery Finish Amps

You are under the mistaken belief I needed or wanted your "education" that I didn't read past the part I quoted.
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Old 01-03-2021, 20:00   #8
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Re: FireFly Battery Finish Amps

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You are under the mistaken belief I needed or wanted your "education" that I didn't read past the part I quoted.
What a great way to elicit more thoughtful and informative responses to your questions. Not.

A "thank you" would have been a normal response to Bill, now an apology is in order IMO.

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Old 02-03-2021, 04:40   #9
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Re: FireFly Battery Finish Amps

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What a great way to elicit more thoughtful and informative responses to your questions. Not.

A "thank you" would have been a normal response to Bill, now an apology is in order IMO.

Jim

IMO I don't
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Old 02-03-2021, 08:05   #10
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Re: FireFly Battery Finish Amps

We've been getting there a lot lately. We have 800 watts of wind and it's been very sunny. We wake up to batteries that are 95%+ charged at 0700 and 1000 watts solar kicks in (adaptive absorption setting) and we hit trailing amps .5/g31 at absorption volts by noon.
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Old 02-03-2021, 09:59   #11
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Re: FireFly Battery Finish Amps

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Has any other FF user gotten to the 0.5amp/G31 end point? How long did it take at absorption?

BTW this is just a curiosity and crowd source question. I feel that in normal use getting to less than .5%C is fully charged.
I getting to the 0.5 amp now. It apparently just took a few good sunny days in a row.
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