Battery Question (Another)

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pissativlypossed

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Hi,

My domestic battery bank consists of 4 x 110 ah units wired in parallel and charged either by a 90 amp alternator or the on-board charger, a three stage unit. On checking and topping up with distilled water over the weekend I was concerned that the one battery required almost three times more then the others. What I cant understand is why this should be, it being the second in the line.

The boat and the battery installation are only two years old and the total voltage seems fine.

Any ideas please?
 
Parallel Batteries

If the three batteries are truly wired in parallel, they have no position "in line", but share the loads equally. One possible explanation is that, last time they were topped up, the middle battery was somehow left out.

If this is not the case, the only remaining explanation is that a cell in that battery is on the way out. Is this a battery type where each cell is topped up individually, or is it one where the water all goes in one hole? If every cell was thirsty, that would mean every cell is in trouble - most unlikely if it's the same age as the other two. Are the batteries marked with manufacture date? Is the troublesome one significantly older / different brand?

Sorry, I'm asking more Q's than you did and probablynot much help.
 
Another one to say the battery is suspected with some fault. IIRC when batteries are wired together they are receiving charge not equally but as they need - one that is lower will receive more. So if this one looses charge faster then others - it will be charged more, evaporating more water in result.

Theoretically possible that this one is OK itself, just for some reason more current is drawn from it. Like having better connection then others. Not much likely on 4 bat bank, but I had such situation with twin batteries, one was low on water, other not - on inspecting the other had a bit corroded connections. Might have been a coincidence, I'm not electrician :confused:

Hope someone more educated in the field will clarify that for me too.
 
Before doing anything else I'd test the electrolyte density with an hydrometer, it may reveal if the battery is failing to hold a charge and which cell, if any, is defective. Also by testing the others if they are in a similar condition or not.

If the densities are low and variable then, I fear, that it may be time to replace the battery. As others have said, the one battery may be in trouble because it is effectively working harder than the others due to the wiring not being balanced.
 
Last edited:
It's got nothing to do with the wiring. The most likely explanation is that the battery is failing or has failed. Disconnect it from the bank and test it separately.
 
Magnette said:
^
Only if they are connected correctly!
http://www.smartgauge.co.uk/batt_con.html
Well worth a read as many are connected wrongly
Click to expand...

Here we go then! I just hope (as a none sparky) that I ask the question, and describe the set up properly. Reason for asking? I may have a problem on my leisure bank.

Our boat is 24 volts and 2 years ago I fitted 6 new 110AH batteries. Two batteries for starting, so connected in series, and 4 batteries connected in both series and parallel to provide 24 volts at 220AH for the domestic side of things. Set up like this where should the load on the leisure bank be extracted and should charging current go to the same terminals? Charging etc goes through a standard 1-2-both-off switch. Obviously the question refers directly to the leisure bank. I don't have a smart charger, I just use the voltage meter a lot!
 
I'd risk to say the Smartgauge article is right, as happen to remember the 'method 3' there is proper way.
Nevertheless OP's battery may be faulty, even if because it was working too hard...
Thanks for the link :)
 
oldfatgit said:
Does you mean that the advice from Smartgauge is not true?
Click to expand...

The Smartgauge article isn't saying anything new - people have known for decades that there's an optimum way to wire battery banks! However, not wiring the bank in the optimum way couldn't and wouldn't cause the symptoms the OP reported.
 
This is a bit of a stretch, but if that battery gets hotter, perhaps from being more insulated or being surrounded by the other hot batteries when charging, then more electrolyte would evaporate from that one than the others.

Just a thought, though I can't see it accounting for all that extra missing electrolyte.
 
Last edited:
Battery wiring

stuhaynes said:
Here we go then! I just hope (as a none sparky) that I ask the question, and describe the set up properly. Reason for asking? I may have a problem on my leisure bank.

Our boat is 24 volts and 2 years ago I fitted 6 new 110AH batteries. Two batteries for starting, so connected in series, and 4 batteries connected in both series and parallel to provide 24 volts at 220AH for the domestic side of things. Set up like this where should the load on the leisure bank be extracted and should charging current go to the same terminals? Charging etc goes through a standard 1-2-both-off switch. Obviously the question refers directly to the leisure bank. I don't have a smart charger, I just use the voltage meter a lot!
Click to expand...

The OP should isolate each battery and operate for a time on each battery individually. It will soon become obvious if the centre battery has a problem. If it charges and discharges similar to the other 2 then probably it is just a temp rise being in the middle.

Re Stuhaynes question. The wiring for the batteries in parallel is not so critical for 24 volt because currents are much less than 12v however. Each pair will be in series so treat as a single 24v battery.
The pos and negative supplies might go to one battery then have short leads to the other battery.
This means that the second battery will have more wiring (the 2 short leads) so more resistance so current will come from the first battery in preference. (to a small degree)
You can make the wiring equal length to both batteries by taking one lead +ve or -ve of the first battery and take it to the post of the second battery. Now the current from each battery must flow through one of the short jumper leads.
Referrence to the OP concern I would always connect parallel batteries with a way to disconnect the battery. (switch or just take the lead off) Then occasionally you can operate on just one battery then the other and compare performance (especially when they get old). If they remain in parallel a failure in one cell will drag the other battery down or the good one will hold the bad up and you may not know there is a problem. good luck olewill
 
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