Weird voltages on battery system

simmtron · April 2016

any thoughts? I have an off grid solar system with 4 T105's series and then parallel for my 12 volt system. I woke up yesterday with my system showing 11.7 volts. It never goes below 12.3 by morning. So I checked the batterieswith a voltmeter and 2 were showing 6.2 volts and 2 were showing 5.7 volts. I thought 2 bad batteries? I took the lower voltage batteries out and just have 2 hooked up. After checking the 2 batteries out that showed 5.7volts, they now show 6.3 volts and S/G is showning 1.25 approx in every cell.

simmtron · April 2016

I did leave them overnight with a jumper in series and in the morning the 2 batteries still showed 12.75 volts.

BB. · May 2016

It could be that they need balancing. Did you measure the specific gravity before you recharged them (or perhaps you did not recharge them and they "recovered" to 6.3v/1.25sg after resting)?

Also, they could be getting old (or some other damage like insufficient charging, let the plates get exposed to air, whatever). And what you are seeing is two batteries that have less capacity than the others. So, they are the first to go "flat" with your light loads--But the others could be going soon too.

It is possible that you are seeing signs of "sulfation"--And the batteries will not recover from that (storing at less than ~75% state of charge, kept warm/not (you are in Florida, insufficient equalization when needed?).

How old are these batteries? If over 3 years old, they may be getting end of life. If over 5-6 years old in a warm/hot climate (flooded cell/lead acid deep cycle batteries)--Very likely near end of life anyway.

-Bill

simmtron · May 2016

they are just over 3 years old. We are full time off grid and I never let the batteries get below 12.1 volts under load and normally 12.3 is low in the morning. We are in the Mexican Caribbean so it is hot 12 months of the year so I know that will shorten life expectancy. But it was weird that all of a sudden one morning that voltage would go to 11.7 in the morning. Loads have not changed. Funny that S/G would be pretty much full after removing batteries from system. Then I was wondering if removing them I tipped them on their side and they seem to be normal again. Wondering if plate material may have built up at bottom of battery and removing them removed a short . They have not been moved for the 3 years. Have reconnected them and see how they fair in the morning.

westbranch · May 2016

have they ever had an EQ charge regime?

vtmaps · May 2016

simmtron said:

Funny that S/G would be pretty much full after removing batteries from system.

A battery with reduced capacity can have normal SG. If the reduced capacity were due to sulfation, the SG would be low because some of the sulfuric acid was sequestered from the electrolyte (in the form of sulfate crystals). But there are many other causes of reduced capacity, including old age.

It is quite possible that your problems are compounded by having parallel batteries. When parallel batteries become mismatched (inevitable) some of them work harder... after awhile when you turn off the charger (or sun sets), some batteries may actually be discharging into the other batteries. The lifespan of a parallel battery bank is shorter than the lifespan of a single string of cells. This is because the weakest cell sets the capacity and lifespan of the entire bank. The more cells you have the greater the chance of a weak cell. Usually by the time you notice something wrong, the weak cell has dragged down the entire bank quite a bit.

You may feel that your daily discharges are shallow, but if the cells are not perfectly matched, some of the cells may be working at a higher daily depth of discharge. Your batteries may be at the end of their lives after three years of daily cycling. If I recall correctly, your batteries, if discharged to 50% daily, have about a 2 year lifespan.

simmtron said:

Then I was wondering if removing them I tipped them on their side and they seem to be normal again. Wondering if plate material may have built up at bottom of battery and removing them removed a short .

A very interesting thing to wonder. Plate material shedding is a known mechanism of a shorted cell.

--vtMaps

simmtron · May 2016

westbranch said:

have they ever had an EQ charge regime?

yes I equalizie every couple of months. The batteries are at full charge everyday pretty much and nevr get below 70% state of charge.

simmtron · May 2016

Just found the receipt , and I have had the batteries 4 years (didn't seem that long) I guess with the daily use and being 95 f most of the summer (shorter lifespan) They could just be cooked. I know when I bought these at Napa here in Mexico the manufacture date was 8 month earlier and they don't keep the voltage topped up here like up north, hey could have been reduced capacity from the start. I'm just wondering now when buying new batteries weather to get Trojan T105's or Sam's club energizer golf cart batteries. The Sam's club here seem to always be within 3 months of manufacture, The Trojans here in Mexico you never know how old they are. Price is $1550 pesos Sam's and $2600 Trojans. $91 us and $152 respectively.

Johann · May 2016

BB. said:

It could be that they need balancing. Did you measure the specific gravity before you recharged them (or perhaps you did not recharge them and they "recovered" to 6.3v/1.25sg after resting)?

Also, they could be getting old (or some other damage like insufficient charging, let the plates get exposed to air, whatever). And what you are seeing is two batteries that have less capacity than the others. So, they are the first to go "flat" with your light loads--But the others could be going soon too.

It is possible that you are seeing signs of "sulfation"--And the batteries will not recover from that (storing at less than ~75% state of charge, kept warm/not (you are in Florida, insufficient equalization when needed?).

How old are these batteries? If over 3 years old, they may be getting end of life. If over 5-6 years old in a warm/hot climate (flooded cell/lead acid deep cycle batteries)--Very likely near end of life anyway.

-Bill

How do you balance a battery?
As far as I understand this, balancing a battery is not the same as equalizing a battery.
Could you touch the basics on this matter?
Thank you.

BB. · May 2016

Sorry, being a bit less than clear here... Balance the charging can also be Equalize charging (bringing all cells up to the same level of charge--typically 100% state of charge). That is what I intended to type.

There is a second which setting up the wiring so that you get "balanced" current between strings of batteries. This web page gives a good explanation.

http://smartgauge.co.uk/smartgauge.html

-Bill

Photowhit · May 2016

Trojan's, at least in the states have a date stamp;

http://www.trojanbattery.com/pdf/TRJN_0522_date_code.pdf

simmtron · May 2016

Photowhit said:

Trojan's, at least in the states have a date stamp;
http://www.trojanbattery.com/pdf/TRJN_0522_date_code.pdf

i have found most batteries have a date stamp, although sometimes not the day, just month and year.

Weird voltages on battery system

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