Lead Acid battery question

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Hi there,

I would like to make a simple question about lead acid batteries charging. This question could also conserns all rechargable batteries, but I would like to stand on Pb batteries.

While charging a 12V (6 cells) battery there is current flow trough the cells from from the 1st to the last (6th in series). When the battery voltage is near 13.8 - 14.0 (please don't stand on this), then we say that the battery is been full charged, and then we can stop charging.

I would like to know if each cell after charging has the same charge. What will be happened if one of the 6 cells is short circuit? If this is happened (and there is no posibility to see it) then each cell voltage will be at 14V/5cells.

I am asking this because someone told me that it is dangerous to charge batteries in series (let's say 10 batteries), because there might be some batteries overcharged and some not full charged. If this is true then battery manufacturers would sell only single cells (of any type of battery).

What is your opinion???

Michael.

Michael.

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1. Yes, the most common form of battery failure is with one cell under-performing.

2. Yes, it is unwise to place different cells / batteries in series for charging. ( unless they all have an identical history, in which case this is the same as the interconnected cells in a battery )

3. A traditional charger stops at the "charged voltage", but a more sophisticated one will monitor temperature, internal pressure, charge / discharge etc.

So you should get some indication that your battery is approaching end-of-service. Your charger should hopefully avoid catastrophic failure or explosion.

You should be able to get data sheets on any battery that you are intending to use. Obey the data sheet ratings.

David.

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Quote:

I am asking this because someone told me that it is dangerous to charge batteries in series (let's say 10 batteries), because there might be some batteries overcharged and some not full charged.

Quote:

2. Yes, it is unwise to place different cells / batteries in series for charging. ( unless they all have an identical history, in which case this is the same as the interconnected cells in a battery )

Both true. In the case of the multi cell battery you treat all the cells exactly the same and hope for the best.

You can tweak the cells a little by adding battery acid to the flat ones a drop at a time and checking the gravity with a tester. This might get you a few more days work out of them (assuming they are not the maintenance-free type which are sealed).

Typically, lead acid batteries last about 3 years, after which you need to replace them. The good thing is that the battery dealer will buy back the used battery for recycling. In India the buyback rate is approx. 20% of the cost of a new battery.

If you think education is expensive, try ignorance.

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In flooded lead-acid batteries you can overcharge agressively since you can replace the water lost from overcharged cells. For sealed lead-acid batteries a "smart charger" can add a fourth cell equalization phase to the usual bulk, absorption, and float phases. This is a controlled overcharge at a low enough current to hopefully give hydrogen time to recombine in any cells that are overcharging. For most other battery chemistries overcharging is dangerous and a battery management system or BMS is used to shunt current around cells as they become charged.