Author Topic: Specific gravity not corresponding to voltage  (Read 2065 times)

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Dutch John

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Specific gravity not corresponding to voltage
« on: February 11, 2012, 02:37:37 AM »
For almost a year now, I am experimenting with junk truck batteries. When disposed, often one out of a set of two of these flooded lead/acid batteries is still fairly good. Half of my battery bank consists of former truck batteries, and it looks like they do fine and sometimes even benefit from the easy life they get now.

I've had a few junk batteries that read 12.8 volt after sitting for a week. Seems good, but specific gravity can show a number as low as 1.20 on all cells. Periods of equalizing followed by periods of sitting and vise versa improves the gravity slowly to 1.26, sometimes 1.28. When equalizing, the voltage rushes from 12.8 to 15.5 volt within a minute and he batteries mildly gas. The batteries are rated 225 Ah and charged at about 12 amp during equalizing. My charger can do 25 amps, but the batteries never take the full number during equalizing.

Now my question: what's wrong with a battery that shows an excellent voltage, but a not corresponding low specific gravity?

Regards,
DJ

Isaiah

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Re: Specific gravity not corresponding to voltage
« Reply #1 on: February 11, 2012, 04:57:56 AM »
Try running a desulfator on the battery's
http://www.infinitumstore.com/12v-infinitum-desulfator . I don't sell or have any interest or monetary gains in this company.
 they are a good unit  and we haven't had one fail yet.
I would put one on the battery making the problem and we run them on the bank all the time. they are some on ebay also .
Here is a link to a thread on another forum that may be of help to you.
http://www.thebackshed.com/forum/forum_posts.asp?TID=2979&PN=1.   just be safe  for your body when working on battery's.
and be patient when trying to bring a battery back some will come back some wont
good luck
 Isaiah

PeterDe

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Re: Specific gravity not corresponding to voltage
« Reply #2 on: February 17, 2012, 01:44:28 AM »
What also could have occured somewhere along the way is that the cell (or cells) with the low SG was over filled and some of the electrolyte came out of the battery.  SG is just a measure of the relative density of the electrolyte.  so if someone put too much water in and some of the electrolyte overflowed, the SG in that cell will never return to the same as the rest.  However if that cell is just a weaker cell, then what you would have to do is to continue charging the battery for some time longer than normal.  However when you are trying to help that one cell you over charging the other cells which will accelerate their aging, and you will need to add water to them to replace the water that has off gassed due to their being over charged.

As we all realize battery system made up of individual 2 volt cells (with lead acid technology) it is easier to maintain them and to keep them all working sor tof equally because you can do single cell charging.  However they are more expensive.

Dutch John

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Re: Specific gravity not corresponding to voltage
« Reply #3 on: February 18, 2012, 12:23:07 AM »
We are not talking about one cell that is bad; all have the same SG. We are also not talking about one battery that shows not corresponding numbers. Most suffer of this. The batteries come dirty from grease and road dust. No white smears of sulfuric crystals, so no overfilling.

I assume that these batteries suffer from sulfation. Truck or car batteries seldom see a higher voltage than 14 and certainly these semi tractions, since these are charged after the starting battery is full and often at a .7 Volt lower voltage. So they miss the the last charging part.

The four batteries I am reviving now have improved from 1.20 to 1.24 SG within one week. Voltage after one day sitting remains 12.8. Having periods of sitting over night helps improving the SG, since the first charge after sitting makes the SG jump a small step. Further long time charging without pauses is of no use. Guess during sitting the electrolite is being absorbed by the spongy lead? Then reacting during the next charge, while also some electrolised water pushes off some of the hard sulphate cristals?

Regards,
DJ