Question: 2V from 12V lead acid battery

[SamTexas]

I searched the web but could not find an answer.
So a 12V lead acid battery consists of six 2V cells in series. I would like to access one of those cells so I can have a 2V battery.
Is there a way to do it without destroying the battery?
Thanks.

 

[Jeremy Harris]

This was something that used to be fairly easy to do, back when they brought the individual cell connections out on the top of the battery, but I think you're going to struggle to find a way to do it now, as they seem to make the cell-to-cell connections inside nowadays. It's been years since I've seen a relatively small lead acid battery with the individual cell connections on the top, but some of the big heavy duty ones might still be made like this.

I think you might be forced to use a voltage regulator to get the 2V you need, I'm afraid, unless you can find a battery with the old style interconnections.

 

[Punx0r]

Do you want a 2V battery or a 12V battery with a 2V tap?

If a 2V battery then just buy one. Like:

 

[SamTexas]

Thanks guys.
Jeremy: Yes I remember those old batteries.
PunxOr: I want a 12V battery with a 2V tap.

I'm still hoping someone has found a clever way to do this without destroying the battery.

 

[dogman dan]

I sure don't know of a safe way to open modern lead batteries to do anything.

I did notice the other day at the Lowes building supply, they had some very cute little sla's. I think they might have been for solar security lighting or something like that. I didn't notice what voltage though, they might be 6v or something like that. they looked about 1 ah size.

Nicads or such would of course be 1.5v or 3v.

Your best bet might be a dc dc converter in the end.

 

[cassschr1]

I took apart a sla 12v 12a acouple of years ago. IIRC you could drill and tap on the cell connectors if you know there location inside the battery. I would get a shot battery, cut the top off, and proceed accordinly, of course the same brand that your planning on using.

 

[amberwolf]

Even if you can do it, you then need a 2V charger, to charge that single cell, as you will no longer bea ble to just charge the whole battery as a single unit until you rebalance that cell to match the others.

Otherwise you can either overcharge the other cells, or undercharge that one, possibly eventually causing battery failure.

I recommend poking aroudn the web for the very simple to build Roman Black 2-transistor converters.

 

[SamTexas]

Even if you can do it, you then need a 2V charger, to charge that single cell, as you will no longer bea ble to just charge the whole battery as a single unit ...

Why not?

Actually that's one of the goals I have for this little experiment: To see lead acid cells self balance when properly charged in series.

 

[Jeremy Harris]

Actually that's one of the goals I have for this little experiment: To see lead acid cells self balance when properly charged in series.

This depends on the type of lead acid cell and the time you're prepared to wait.

Ordinary wet cell batteries balance OK by just allowing the fully charged cells to gas during overcharge, the only downsides being the need to water some cells more frequently and the need to ensure that the battery doesn't get too hot. SLAs are more problematic, particularly gel type cells, as the gas recombination chemistry they use is far less tolerant of overcharge. They will still balance when on a series charge for a long time, but the charge current needs to be pretty low to prevent excessive internal gassing. If they are allowed to gas internally then the cells will swell and can blow the vents, with a permanent loss of electrolyte. AFAIK, AGM cells are between SLAs and wet cells, and will tolerate higher levels of internal gassing than gel cells, but they aren't as tolerant as wet cells, I believe.

 

[SamTexas]

That's my understanding too. They all self balance. It's just a matter of applying the correct voltage for each of the different type of lead acid cells.