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Why you should do a battery equalization charge once and a while (Read 16209 times)
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Why you should do a battery equalization charge once and a while
Aug 25th, 2011 at 2:36am
 
One of the things that happens in a lead acid battery is that one cell can be weaker than the rest. Or in a 24V configuration, one battery can get lower than the other.

If you have two 12V batteries configured as 24V, you can easily check this with a digital volt meter. When the batteries are under load, check each battery's voltage and see how far apart each one is. 0.2V to 0.5V is typical and is pretty close, but a few volts apart is a problem that will just get worse as time goes on. You should equalize the batteries as soon as possible.

Check your battery's manufacturer specs on how often to equalize and how high a voltage to take them, typically about 16.2V and for one hour every 2 months, but this depends on how heavy the battery is used. Again, check the manufacturer specs.

This is generally not done on AGM, Gel or VRLA batteries! We are only talking about flooded lead acid type batteries here.

Yea, it's going to take a little of that solar power to keep your batteries in top shape. It's just the cost of using batteries with solar. Some of the more expensive charge controllers already do this for you automatically and also monitor battery temperature.

The reason it gets worse over time is that the higher voltage battery (or single cell) comes to it's charge level sooner, then easily keeps going to a higher voltage and your charge controller kicks out before the other battery reaches full charge. This battery will outgas more, and will lose more electrolyte.

The lower battery (or single cell) stays in a lower state of charge day after day and sulfates more. It keeps going down hill from there.

We know that batteries can excessively sulfate, and that can cause a number of problems. The longer a battery goes discharged, the stronger the sulfate bonds to the plates.

"Shorted cells can be caused by sulfation. It seems that the crystal formation expands and warps the plate material."

"This is how things work when the battery is new and clean. There are several effects that come in as the battery is used. One is the process called sulfation, which is of central concern to this effort. Here is Richard Perez, from Home Power magazine #29, page 44:

The biggest problem in lead-acid cells is sulfation due to chronic undercharging. Here the sulfate ions have entered into deep bonds with the lead on the cell's plates. The sulfate ions can bond with the lead at three successively deeper energy levels. Level One is the bond we use when we normally charge and discharge the cell. After a month or so at Level One, some of the bonds form Level Two bonds which require more electric power to break. After several months of being at Level Two bond, the sulfate ions really cozy up to the lead and form Level Three bonds. Level Three bonds are not accessible electrically. No amount of recharging will break Level Three bonds. The longer the lead sulfate bond stays at a level the more likely it is to form a closer acquaintance and enter the next deeper level. This is why it is so important to fully, regularly, and completely, recharge lead-acid cells.

Equalization Charges

If the loss in capacity is due to Level Two bonding, then a repeated series of equalizing charges will break the Level Two bonds. Under equalization the Level Two bonds will first be transformed into Level One bonds, and then the sulfate ion can be kicked loose of the lead entirely and reenter the electrolyte solution. If your lead-acid cells have lost capacity, then a regime of equalizing charges is the first procedure to try. An equalization charge is a controlled overcharge of an already fully recharged cell. First recharge the cell and then continue to charge the cell at a C/20 rate for five to seven hours. During equalization charges, the cell voltage will become very high, about 2.7 VDC per cell. This overcharge contains the necessary power to break the Level Two bonds and force them to Level One. Once they reach Level One, the bond is easily broken and the sulfate ions reenter into solution in the electrolyte. "
http://home.comcast.net/~ddenhardt201263/desulfator/technotes.htm

For AGM, Gel or VRLA batteries, they use a "Balance Charge".
"Balance Charging is similar to an equalize charge cycle but is performed at a lower voltage."
http://www.discover-energy.com/faqs/equalizing_batteries
http://www.discover-energy.com/faqs/stratification_prevention
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