question

akram avatar image
akram asked

ESS with Trojan flooded batteries

Hello,

System consists of 3 mppt's 150/70, 100/50. 75/15, 3kva multiplus, Venus gx and four 6v 377ah Trojan flooded batteries on ESS. Average daily discharge upto 70% SOC

I have set the manufacturer absorption voltage of 29.4 and maximum absorption time 4 hours in all the mppt's and the multiplus charger settings, but the absorption only reaches 28.6v and less than 4 hours. When I check the gravity of the cells at 100% SOC they are measuring 1.250 instead of 1.277 which means the batteries are under charged.

What can I do to rectify this problem?

Thanks

battery chargingESS
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2 Answers
neoneddy avatar image
neoneddy answered ·

Might not be a big difference, but because these are flooded batteries, I used 14.8 as my absorb voltage. Try a balance / equalization charge as well.


Did you check multiple batteries and multiple cells? Unless you're running a 24v system you could have an unbalanced bank.


Lastly, try a full capacity test to verify the SOC. IMHO it's not the end of the world to do a full discharge test and then recharge right away. It's extended periods of low charge that kill the batteries.


If you get full capacity at your current specific gravity, I don't see the problem.



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akram avatar image akram commented ·

Hello Neoneddy

When I equalize they come up to SG 1.275 but after a week or so it's down to SG 1.250 at 100% SOC.

my system is 24v

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JohnC avatar image
JohnC answered ·

Hi Akram. What you may be seeing with the V difference is temperature compensation. If it's hot there then that would explain it.

Absorption time may also be being 'touched up' by the Victron algorithms. If you don't think it's enough, just increase it some more to compensate.

Your SG shortfall amounts to ~2%, which is actually pretty good for daily-cycling batts. (I believe SG has a linear relationship with SOC). Pbs never reach 100% within 24hrs, and indeed some batt makers will even rate them at 100 hours. All regardless of what SOC your system is set up to show.

You could push them harder with a higher V, for a longer Absorb time, but all you'll likely do is bubble off water and increase their internal temp (bad for them).

Your '70% SOC' is a little unclear. Do you go down to that, or do you drop it 70% (ie. 30% remaining)? Big difference in life expectancy - really big.

I can't see you have a 'rectification' issue at all. Indeed a little gentleness applied may well pay you back with longer batt life. Take care..


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akram avatar image akram commented ·

Hello John

I just use 30% of the capacity, and the batteries are three months old i am going soft on them so that I get longer life from them.

Average temperature during the day is around 30 C

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