Author Topic: When is a battery toast?  (Read 2246 times)

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acapulco

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When is a battery toast?
« on: August 07, 2008, 03:44:59 AM »
I have a 24volt sytem consisting of 2 strings of 6volt/225amphour.


1 string is Trojan T-105's, Other string is a no name job but the

batteries/casing are identical to the Trojans except they are white with red lids

instead of the maroon like the trojans.


The trojan string I bought new 3.5 years ago. The red/white no name string was given to me recently as throw aways.


First inspection of the red/whites showed they had not been maintained at all, the electrolyte levels where way low(each battery took almost a litre to top up!) and the tops where dirty and wet. Also they  show some bulging on sides. I charged them

and then left them alone for a week or so and they held at 25.3volt so I gave them a go and they appear to be going ok.


I am running both strings paralell and they seem to be ok after a few weeks or so.


Yesterday I decided to check each 6volt battery with multimeter.


First checks were made with power coming in from panels as well as power coming out from inverter. All batteries showed more or less equal voltage(+- 0.02volt).


Last night I switched to another battery bank(2 x 12v/180amphour sealed, valve regulated FullRiver) and left the other bank to settle overnight.


This morning I performed the same check of each battery(batteries remain connected to each other). The noname red&whites all showed 5.95volts. 3 of the Trojans showed 6.05volt but 1 showed 5.69volt. The positive terminal on this battery has turned black as well.


Is this battery toast?


What if anything can I
should I do?


Is it ok to have 2 different strings like these connected in paralell?


Also is it ok to run the string of Trojan's and the String of Fullriver sealed type together in paralell?


tia


Ian.

« Last Edit: August 07, 2008, 03:44:59 AM by (unknown) »

SparWeb

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Re: When is a battery toast?
« Reply #1 on: August 06, 2008, 10:51:39 PM »
It sounds like you already know the answer to the question you asked.  The real question is "can I do anything about this?"  


I can't tell from the description if there was a signigicant load on the batteries when you tested them and got those numbers.  If there was no load, then they are nearly flat, and really need a full charge and float for a while before you know where you are.  If you have the time to wait, a few days/weeks of no charge or discharge after all that and you would be able to watch if the two banks are slowly killing each other by mutual charging and discharging.  You don't say you have anything to isolate them, so I assume that as any one weak cell self-discharges, the other cells might feed it.


Obviously the low Trojan cell isn't happy, but whether an equalization cycle is all you need to fix it, well the answer is often "try it anyway and see".


These batteries aren't very old, but the environment in which they live strongly affects the life.

« Last Edit: August 06, 2008, 10:51:39 PM by SparWeb »
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
System spec: 135w BP multicrystalline panels, Xantrex C40, DIY 10ft (3m) diameter wind turbine, Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024
www.sparweb.ca

Flux

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Re: When is a battery toast?
« Reply #2 on: August 06, 2008, 11:31:59 PM »
I agree with Steven. All voltages are low as you say you were working from another bank so these were not supplying load.


First thing is to give the whole lot a good equalising charge and see how they respond.


If you can do it then it may be a good idea to give the low Trojan a good gassing on its own.


I have no idea of your charging arrangements or what state you normally keep these cells in but at present they are flat and if they have never been equalised properly then you may need something other than solar to do it.


If you have to use the solar try them direct without a controller unless your controller will let you raise the voltage to equalise them to near 30v.


I wouldn't run the Trojan types in parallel with the sealed ones, their charging requirements are very different and if you are using the charge settings for the sealed ones on the Trojans that could explain your problem. Sealed batteries can't stand much in the way of equalising but wet cells need it.


Flux

« Last Edit: August 06, 2008, 11:31:59 PM by Flux »

acapulco

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Re: When is a battery toast?
« Reply #3 on: August 09, 2008, 10:04:58 PM »
ok,


Yes i know batteries were down to 50% or so when those first readings were taken.


I charged both strings together all day from genset/charger and boiled 'em good.

but the next morning(no load taken from batteries) the open circuit voltage indicated they were only 80-85% charged. The charging did seem to bring the weak trojan back a bit but it still shows a few points under the others(0.03-0.05v lower).


I also changed the order of the string after that which seems to have evened it out better.


Because it seems the weaker string is sucking juice from the stronger trojan string I have seperated the 2 strings. this means extra walks downstairs to change banks but I can live with that for now.


I should also mention that the 3.5 year old Trojan string was running a different system for 3years, a sytem with no panels only genset/charger and the bank was pretty much run flat each and every cycle(until the inverter beeps and shuts down for undervoltage(21volt+/-0.8volt)(under load of usually say 5amp@24volt) This is probably a lot deeper cycling than ideal and considering that this bank may be on way out(?)


I seem to remember the battery shop guy saying I should expect a useful life of 3 to 5 years for the trojan's


Also am I right to think i don't really need a solar regulater considering the battery bank rarely gets to 100% and certainly doesn't stay full for any length of time ?  


Ian.

« Last Edit: August 09, 2008, 10:04:58 PM by acapulco »

SparWeb

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Re: When is a battery toast?
« Reply #4 on: August 10, 2008, 11:52:14 PM »
I have to assume that after the equalization charge, you re-filled the cells with distilled water and then charged them again for a few hours more or until the voltage went above 28V or so.  If you didn't do this yet, then you may be able to get more than the 80% you have now.


The variation in the 6V cells isn't very significant (considering their age).


Still, it's nothing to be ashamed of.  Your T's are doing rather well, considering the use they've been taking for 3 years.


Your last question: I wondered the same thing when I compared my 300W wind turbine with the 1600 Ah battery bank I have....  No way could that thing overcharge the bank, I thought.  Well, after an extremely windy spring, when it seemed like days of running the dump load, I know I was better off with the charge controller in there from day 1.

« Last Edit: August 10, 2008, 11:52:14 PM by SparWeb »
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
System spec: 135w BP multicrystalline panels, Xantrex C40, DIY 10ft (3m) diameter wind turbine, Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024
www.sparweb.ca