Author Topic: Center Batteries: Sucking Down Water  (Read 1233 times)

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shaniac

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Center Batteries: Sucking Down Water
« on: April 03, 2008, 06:45:54 AM »
Greetings, as always thanks for all your great advice, this board is a blessing in so many ways.


I have a 24V battery bank of Interstate L-16s. 3 sets of 4 for our off grid home. They are old and need to be replaced, but as I save up the cash to do so I am experiencing this very odd problem.


The batteries are stored in the following format.

http://flanaganandsun.com/FlanaganandSunRenewableEnergy/nfblog/wp-content/uploads/battery_bank.JPG

Please note this sample bank is wired differently, but the image shows how the 12 batteries are stacked next to each other.


My four in the middle drink water like a fish, but the four on each ends sip slowly. Are the four in the middle just blowing through more water because they get warmer being centrally located, or is the water consumption a sign of something else?


The bank does not hold much of a charge any more. One hour after sunset, with no loads on them they rest at 25.1 instead of 25.3 as they should.


I know I need to pull each one off the system and test them individually to see if I have a bad cell anywhere but I have not found a free afternoon yet where I can kill all power to the house.


What do you think the water consumption is telling me?

What other questions can I answer to help you guys out.

And last but not least, where should teh batter temp sensor go? On the end where it is currently located or in the middle where it is hottest?


Thanks again in advance.

Shane

« Last Edit: April 03, 2008, 06:45:54 AM by (unknown) »

Flux

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Re: Center Batteries: Sucking Down Water
« Reply #1 on: April 03, 2008, 01:45:30 AM »
Assuming that you have reasonably matched resistance leads connecting the strings, I suspect that the middle string has lost a cell.


The middle string will be holding volts at gassing level rather than just above float. The rapid drop after charge and low capacity agree with this.


Drop the middle string off, you can work with the other 2 strings and load the middle string with some car lamps or something and measure the individual voltages. I also suspect you will find one cell in that string with different water consumption and sg that is way off the others.


Flux

« Last Edit: April 03, 2008, 01:45:30 AM by Flux »

Simple serf

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Re: Center Batteries: Sucking Down Water
« Reply #2 on: April 14, 2008, 10:23:01 PM »
Our Floor scrubbers do this same thing when they have a cell that went bad. Test each battery, and replace the faulty one with a good used battery, as a stopgap measure until you replace the whole thing. This is what we have done in the past at work and it has worked ok. We generally go through a set of batteries every 1-1.5 years, taking them down to about 80% discharged every night.
« Last Edit: April 14, 2008, 10:23:01 PM by Simple serf »

random

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Re: Center Batteries: Sucking Down Water
« Reply #3 on: February 24, 2009, 04:54:18 AM »
Check the voltage levels of the individual batteries.  They should be within a volt, ideally within a couple tenths.


Within a string that has some age on it, you may eventually develop some weak sisters.  They will only accept a lower charge, for whatever reasons.  In the same string, the stronger batteries have to make up for the weak ones.


Offhand I don't remember whether it's the strong or the weak batteries that are thirstier but it doesn't really matter -- the thirst develops near the end of the battery's useful lifetime.  You are going to need to replace the batteries that won't accept and hold a full charge, and as I remember those are going to be the heavy drinkers.


Not holding a charge is symptomatic of an aging bank or a few bad batteries.  You don't have to pull them out of the bank to test individual voltages.  A few weak batteries will over time destroy the stronger batteries in the string because they are being overworked.


The battery temp sensor(s) should go somewhere in the middle of the bank, their location isn't critical.  I have mine taped onto a piece of plastic so I can pull batteries if needed without the sensors interfering.  The sensors are being used to give a ballpark value, not a very precise one -- at 110F the batteries need fewer volts to charge them than at 20F, but the difference between 70F and 73F is negligable and the temp anywhere in the bank (unless it is truly huge) are going to be within a few degrees.


Lordy, I just noticed the date on your post, I have been gone from here for a long time.

« Last Edit: February 24, 2009, 04:54:18 AM by random »