Homogenizing Battery Acid?

[Clifford]

I have 3 Wal-Mart Deep Cycle Batteries connected in series.

The cell specific gravities range as follows:

Negative Terminal (+ on one bat) - 1" off scale to red (somewhat higher than water, but...  would be around 1050???

Middle cells almost all just off the scale to the green (1325) & quite uniform.

Positive Terminal (- on one bat)  - approx 1250

Looking at the "caps", over the cells with the lower readings are white (no boiling), the others are slightly blackened (apparently a little boiling during charging).

Ok...  Amps & Volts...

Batts charge at about 2 Amps (13+ volts).

Batts drop to 11 V or so upon disconnecting charger (panels), but generally keep above 10.8

Batts drop to below 10.5 on approx 100W load (I think),

I.E.  My inverter beeps when running my laptop and charging the battery, but it stops beeping when the laptop batteries are full and I'm running off of wall current.

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Can I homogenize the acid in the cells?  Will it help?

Other suggestions?

Any idea why the end cells uniformly have much lower readings than the middle cells, and seem to be charging less?

I've been meaning to try to build a pulse desulfator, but haven't gotten it done yet.  Perhaps it will help.

I can certainly see the advantage of having single cell batts, so the cells can be rearranged while "repairing" or "replacing" certain cells.

[Nando]

You should have indicated each battery and each cell like:

Amp hour ;----------- for each battery -- deep cycle does not say capacity

Bat1 - cell1 ; cell2 ; cell3 ; -------- ETC and under each the volts and the cell hygrometer readings.

This way I could tell you what to do to each battery to equalize and re-juvenate the bad cells ( 1050)

You need to equalize to 2.45 to 2.5 volts/ cell for several hours, depending on the amp-hour .

Then you need to discharge to 1.85 volts/ cell and do equalization again -- do this cycling 3 or 4 times to see how the battery improves and the cell hygro reading go up to 1250 +

Electronic de-sulphation may take some time to accomplish the job and still you need to do Power equalization or the de-sulphation will not take effect.

Electronic de-suphation may go well if the battery is equalized in between de-sulphation pulses.

Nando

[Clifford]

Not sure of the exact capacity of the batteries.  I looked for the rating in Ah, but I think there was only a CCA rating.

Two of the batteries are essentially identical.

Negative Terminal:

Cell 1 - Specific Gravity 1050 (approx)

Cell 2 - Specific Gravity 1325

Cell 3 - Specific Gravity 1325

Cell 4 - Specific Gravity 1325

Cell 5 - Specific Gravity 1325

Cell 6 - Specific Gravity 1275

Postitive Terminal.

The third battery is just the opposite.

Negative Terminal:

Cell 1 - Specific Gravity 1275

Cell 2 - Specific Gravity 1325

Cell 3 - Specific Gravity 1325

Cell 4 - Specific Gravity 1325

Cell 5 - Specific Gravity 1325

Cell 6 - Specific Gravity 1050 (approx)

Postitive Terminal.

There were some slight variations, but it seemed to be quite consistant with the middle cells all being "high-normal", and one of the end cells being slightly low, and the other "end cell" being very depressed.

At first I was thinking that the cells had shorted out.

But, if one cell was completely shorted, I would get 2.1V x 5 = 10.5V.  However, the batteries have a slightly higher "charged" voltage.... (around 11V), thus the last cells can hold a slight amount of charge.

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I guess I was thinking of mixing all of the sulfuric acid from the different cells together....  Or, attempting to drain the low cells and add more sulfuric acid.  But, the problem is that the plates are caked with sulfur, then perhaps it wouldn't help.

----- Clifford ----

[Ungrounded Lightning Rod]

No, don't mix the acid in the different cells.  The sulfate ion is still there - reacted into the plates.  Equalizing the acid concentration will unbalance the cells further.

The cells need an equalizing charge.  (One or both of the low cells may be damaged as well - sulfated and/or with flakes from the plates producing a high-resistance short gradually discharging the cell.  But let's get them equalized before worrying about that.)

To equalize them:

 - Make sure the water level is up.  Add DISTILLED water if not.

 - Charge them up to 14.4 volts, slowly over several hours.  Stop when the battery has been at 14.4 volts for an hour or so or if you've driven as many amp-hours through them as the battery rating.  (Note that this will make the full cells generate hydrogen gas and the popping bubbles may drive a fine mist of acid into the air.  So do it away from things that could be corroded by the acid.)

 - Recehck the water level, topping off any cells that lost water during the process.

After running a load for a few minutes (to remove the "surface charge") the battery should be back in the normal voltage range.

Then check the specific gravity:  If the end cells are still low they are sulfated.  You may be able to improve this by putting the battery on a trickle charger and a pulse-type desulfator for a few weeks.

Also:  After taking off the surface charge and letting the battery sit for an hour or more (to come to room temperature), read the voltage with an accurate digital volt meter and/or measure the specific gravity.  Then let it set for a few days and repeat the reading (at about the same temperature).  If there has been a significant drop - especially focussed in some cells - the battery has a high-resistance short from flakes.  (This would mean end-of life.  You CAN sometimes repair it by charging, dumping electrolyte, washing out the flakes, and adding electrolyte.  But even if successful the affected cells would be lower capacity and you don't want that kind of imbalance between units in a battery bank.  Also it leaves you with some nasty toxic waste and you have to buy sulfuric acid.  Better to buy new batteries and have done with it.)

[Ungrounded Lightning Rod]

If you need to keep the cells in service - and whatever is attached to them can handle the overvoltage of an equalizing charge - you can equalize them while still hooked up.  (Multiply the 14.4V times 3 and equalize the whole three-battery-in-series bank.)

Desulfation can also be done in service if the load can handle the pulses from the desulfator.

You don't say what your charge controller is.  You might be able to tell it to give the batteries an equalizing charge - or adjust the regulation voltage temporarily to cause that to happen.