Not sure where else to throw this question out, so I will try it here...
Found a bad battery in my bank, about a month ago. Took it out tonight, and replaced it with one that was the same age, bought at the same time. (God provides for those who ask) when I place it in, I ran the charger for a little bit just to top them off since its dark and there will be no solar input till morning. Anyway, while they were under charge, I run the volt meter around them, and found another 1/2-1 volt above all the rest... They are 8v dry traction batteries. all were charging at 9.4-9.7 except one of them at 10.22. Being a starved electrolyte this concerns me. that is above the factory max according to the chart a 2.465v per cell X4 = 9.86v its a EVCG8A-A you can download the data sheet straight from discover-energy.com maybe I am not reading the chart right, but why would on in the middle of a string of 3, in the middle of the bank, charge higher than the others? They are set up, 3 in series for 24v and and 3 sets in parallel, for a total of 9 batteries. and its the one in the middle. Any Ideas as to whats going on???? :-\ Should I be concerned?
CAn you give a bit more history? Age, Charge regimen (PV),Amphrs, loads,etc.
Reason I ask is , you are right, there is something amiss.
Is the new one the one with the hi Voltage?
Quote from: shadow44 on October 23, 2013, 08:12:54 PM
They are set up, 3 in series for 24v and and 3 sets in parallel, for a total of 9 batteries. and its the one in the middle. Any Ideas as to whats going on???? :-\ Should I be concerned?
You have discovered one of the perils of parallel batteries. Parallel batteries are inherently unstable... when charging them it is hard to get the current to divide evenly among the parallel strings. No two batteries are ever exactly the same, and as they age their characteristics diverge. The more they diverge, the more uneven the current becomes through the parallel strings. The more the current is uneven, the more the batteries diverge...
As part of your regular battery maintenance you should have a DC current clamp meter to check the current in your three parallel strings of batteries. You may find that after charging you have one string discharging into another string.
As to as why it is your middle battery that seems to be affected... it could be random, or it could be because that battery is a bit warmer than the others. When a battery is warm it needs less charging voltage. If you lower the voltage to accommodate the warm battery, the cooler batteries will be undercharged. If the voltage is high enough for the cooler batteries, the warm battery will be overcharged.
Ultimately, you should plan for your next bank to have a single string of larger cells. They should all be at the same temperature. If you need to, put air spaces between each battery and put a fan in your battery box to keep the batteries at the same temperature. (this can also help with parallel batteries).
--vtMaps
Quote from: Westbranch on October 23, 2013, 09:31:10 PM
CAn you give a bit more history? Age, Charge regimen (PV),Amphrs, loads,etc.
Reason I ask is , you are right, there is something amiss.
Is the new one the one with the hi Voltage?
Well the history is not known, past the last 4 months. I bought them used. Came out of an electric car.
As far as the charge, they get 99% of the charge from my awesome midnite classic 200 from 5 250w PV panels. I have charged them once with the trace xantrex 4024 from the grid when they rested at 24.9 they are 170 ah and I load tested them when I got them, they appeared equal roughly and in decent shape. I have figured out the bad one had been dropped by the seller, and he neglected to tell me. The one with high charge voltage is not the one I replaced, but it is in the same string as the bad one was, and next to it. Being next to the one with a bad cell is what makes me wonder if it damaged that one too.
I'm not sure what to do.
I concur with VTmaps on the imbalance that can occur in >2 string batteries.
Until you figure out what is wrong, I would drop the problem string...
Next I would contact the maker for their recommendation/advice as to what may be wrong with that 1 cell..