SOC suddenly jumps to 100%

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Re: SOC suddenly jumps to 100%

Postby jcheil on Mon Feb 29, 2016 7:02 am

tallgirl wrote:What is your "Parameters Met" voltage and current? Five amps into an 1,100 amp-hour bank is fully-charged. Ten amps into that size bank is fully charged ...


I would agree that 5 amps into a bank that size would be charged, but it is still not at 1.280 at that point. Seems like it needs to hang out in that range for an extra couple of hours to get there. And I absorb at 59.8v. Anything lower and it would never get even close to full. I have a feeling if I kicked it up another couple of .x volts it may reach full charge when it gets down to that 5 or 6 amps but I worry about that high of a voltage for absorb. As it is right now, temp compensation is usually raising it to 60.x in absorb now anyways. Guess that is the negative of those tall batteries. And the bank is only about 16 months old and always been that way. Others with the L16-REB's seem to have the same results.

And the parameters met voltage and current, not sure what I have it set at. I kinda gave up on it and set it to something pretty high so it would never "fake" hit parameters. But if I recall, it was something like 59.6, 5 minutes, 5 amps
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Re: SOC suddenly jumps to 100%

Postby Coyote Flats on Mon Feb 29, 2016 9:26 am

I am having the same issue and my specific gravity is 1.250 when it jumps to 100 % her are my settings

Battery monitor
840 a/h
Charged voltage 28.7 10 minutes
Return amps 0 for now
Charge factor 85


Controller

Absorb 29.8 for 4.3 hours
Float 27.8
Absorb amps 0 for now

I'm getting about 4kw/hrs charging


I am going to monitor and just work with charge factor setting for now and monitor one cell but im open to suggestions
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Re: SOC suddenly jumps to 100%

Postby Kent Osterberg on Mon Feb 29, 2016 9:32 am

I would agree that 5 amps into a bank that size would be charged, but it is still not at 1.280 at that point.

It is true that the hydrometer indication is the gold standard for determining the state of charge of the batteries. But it is not a value that can be trusted on an instantaneous basis. Take a look at this graph, it clearly shows that the the amphours returned and the specific gravity do not track each other over time. When either charging or discharging there is a time delay in specific gravity numbers because the most concentrated (or most diluted) acid will be next to the plates. Have you temperature compensated your hydrometer readings; at 59.8 volts and 11 kW of PV modules the batteries are probably running a bit warm? I'd lower the absorption voltage to 59.2 volts, which is what Trojan recommends. When the return current for your 1100-amphour battery bank reaches 5 amps, they really are full. Trojan says that they should finish at 1% to 3% of the battery capacity, you've got them charging down to 0.5% of capacity. Charging that long won't hurt the batteries, but with that high of voltage you will be using a lot of water.

With the charge efficiency factor that you are using, I would expect the FNDC to make a big positive jump every time it reaches the point that the charged parameters are met simply because the batteries will be full before the FNDC indication reaches 100%. Unfortunately, the FNDC has bugs in it that cause it to reset to 100% at other times as well. With a very low charge efficiency factor, those jumps may be large.

The charge efficiency factor is an approximation of the overall charging cycle efficiency which should normally include 5% to 10% more amphours being returned to the batteries than what is removed. The charge efficiency is not a value that will make the FNDC state of charge indication track specific gravity indications through out the charge cycle. That simply isn't possible because the charge efficiency is a dynamic value. When the batteries are below 56 volts, the charge efficiency is probably close to 100%. As the batteries begin to bubble the charge efficiency drops. When you are finishing at 5 amps, a large portion of that current is simply hydrolyzing water.
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Re: SOC suddenly jumps to 100%

Postby jcheil on Mon Feb 29, 2016 12:00 pm

My charge factor is set to 78% and the jump is usually around 92-93% to 100% but it always jumps due to the other bug (described from OB) from what I have seen. I almost never "meet [parameters" although on rare occasions I have seen it "meet" at something like 92 or 93%.

I use a hydrovolt hydrometer so it is temp compensated. If I set the CF to (for example), 85. Then the SOC indicator will get up to 97-98% and then jump, but the SG is nowhere near 97-98 at that point. Where I have it now seems to keep it somewhat in line with real SG (and I did read your link).

I did start out at 59.2v when the bank was commissioned but even after several weeks it would barely get to 1.265 by the end of the day and would have quite a bit of variances in cell readings. After discussions with many other people with these tall type of batteries, everyone's solution is 59.x volt absorbs. When I switched to that, suddenly the SG was much higher at the end of the day and there were very few cell variances.

I know trojan says 5amps is charged, but again, I can go out there right now, when the fndc is showing return amps going into the bank being 5 and the SG will still be in the high 1.26's to low 1.27's - although they may be right about something because it will never get any less than 5 return amps. I could leave it in absorb for 24 hours a day for 5 days and it will never drop below 5-ish return amps.

I don't think it is too hot because at 59.2v there is not very much gassing and at 59.8 it is only slightly more, but enough to get a better mix of the solution. Water consumption is not excessive by any means and seems to be in line with others. At 59.2v water consumption was almost non existent and after a month the cell variances were so far out an EQ was always necessary (I do one every 30 days now anyways). Again, 59.8 seemed to fix almost everything for myself and a lot of others.

But I do appreciate the opinions and ideas. I'll try anything. But I just wish that bug can be fixed and then this would never be an issue anymore.
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Re: SOC suddenly jumps to 100%

Postby Kent Osterberg on Mon Feb 29, 2016 1:04 pm

The reason the graph shows a time delay between the amphours being returned, which is what the FNDC is accounting for, and the specific gravity is that the acid is more concentrated at the plates and at the bottom of the battery until the bubbling stirs the acid up at the end of the charge. If the 78% charge efficiency is making the FNDC state of charge indication track the specific gravity during the early and middle portion of the charging cycle, then it won't reach a 100% indication until much later if it at all.
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Re: SOC suddenly jumps to 100%

Postby tallgirl on Mon Feb 29, 2016 2:02 pm

jcheil -

Unfortunatley no one has been able to convince OutBack to modify the FNDC firmware. I'd offered to do it as a subcontractor, back when I had my own business and didn't have to worry about non-compete clauses, and was turned down. Now that I'm completely out of the solar biz - and the electrically engineering anything at all biz - I don't have the time or financial incentive to design and whatnot a battery monitor. I keep trying to make the time to open source some hardware and firmware, but ... life has a way of getting in the way.
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Re: SOC suddenly jumps to 100%

Postby Coyote Flats on Mon Mar 07, 2016 2:21 pm

I solved my jump to 100 . I unplugged FNDC charged up to my SG 100% than equalized and did one cycle of discharge / charge monitored it all. Hooked up my FNDC back up did some more test comparing SG to SOC indicators and all is good. Just got to keep testing SG thanks to everyone who posted all that good info
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