Battery problem - advice sort.

[geoffd]

Hi All

I have a large bank of Lead Acid Batteries (Hoppeke) each cell is 2volt 1350AH and I have 12 wired in series i.e. 24 volt. The bank is about 5 years old.

The problem is this:

When I first had them they would charge to adsorption voltage (29 ish volts) then when the charge was stopped they would settle down to 25.8 volt.

Now they still take the adsorption charge, but very quickly settle down to 24.6 / 2..8 volts.

I equalize them regularly.

Does the panel have any advice on what might be the problem, and what I should check?

Cheers
Geoff

[Bruce S]

I would say it looks like you have a cell going south on you. Best think to really do is to break that entire bank apart as they are now and measure each cell. You could take a meter and check the cells while still connected to the bank and possibly tell which one is the culprit.
BUT better to get them apart and take measurements.
If you have a meter for testing the SG you would be able to tell much better.
Once apart the cell bringing to bank down will show itself. If there is more than one showing a low reading, it might be a very good idea to charge each one of them while completely separated from each other.
They may only be out of balance with each other and doing this could bring the pack back completely.
Best  of luck
Bruce S

[dnix71]

Whoa, those are premium and expensive. You have a friend in the telecom business? They should be good for 15 years cycling. Are they 5 years old to you or you had them for 5 years?

[wpowokal]

Geoff, I'm basically with Bruce on this, but I would just go along measuring the voltage on each battery (I'm a lazy bugger), should reveal any failing battery.

That said, Dinx has a relevant point, but you tell us the bank is around 5 years old, so taken as read,  tell us about your charging, is a regulator controlling this, for how long do the receive 29 volts?
You equalize regularly, how often is regular and at what voltage? Do the batteries have clear cases such that you can see inside? You are feeding them but are you watering them or are they sealed/gell?

My original bank is now 20 years old, was 13 years old when I received (stole) them, they were arranged in 8 banks @ 12 /bank but were only 650 A/h each, now half have fallen by the way side, the voltages you mention are typical of my batteries.

Allan

[dnix71]

You can get a "memory effect" like condition if you overcharge a battery repeatedly. The fix is a slow controlled discharge of the affected cells, followed by a proper recharge.

From wikipedia:

A common process often ascribed to memory effect is voltage depression. In this case the peak voltage of the battery drops more quickly than normal as it is used, even though the total energy remains almost the same. In modern electronic equipment that monitors the voltage to indicate battery charge, the battery appears to be draining very quickly. To the user it appears the battery is not holding its full charge, which seems similar to memory effect. This is a common problem with high-load devices such as digital cameras.

Voltage depression is caused by repeated over-charging of a battery, which causes the formation of small crystals of electrolyte on the plates. These can clog the plates, increasing resistance and lowering the voltage of some individual cells in the battery. This causes the battery as a whole to seem to discharge rapidly as those individual cells discharge quickly and the voltage of the battery as a whole suddenly falls. This effect is very common, as consumer trickle chargers typically overcharge.

The effect can be overcome by subjecting each cell of the battery to one or more deep charge/discharge cycles. This must be done to the individual cells, not a multi-cell battery; in a battery some cells may discharge before others, they are then subjected to a reverse charging current by the remaining cells, causing irreversible damage.

You need to separate the pack and bring each cell down then back up.