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Lead Acid Batteries

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codan

New Member
Hi All,

I have two big Lead Acid Batteries, i assume they are 6v & each give 6v with a multi meter & series wired to give 12v output.

Because they are wired for 12v output, can i use a 12v Charger to charge these if i leave them wired for the 12v while charging??

Is there any obvious way to recognise a 6v lead acid battery from a 12v battery without testing them.
Are the number of plates etc different or?

If i need a 6v charger, can i just use a 12v charger with the correct value resistors in series to give say 7v for charging.

Thanks
 

dknguyen

Well-Known Member
Most Helpful Member
If they are the same capacity and have the same charge levels in them then you can series connect them and charge them from a 12V charger. They have to have some of the same charge though (you can check this by measuring the voltage on a DMM).

NOTE: This does not apply to all types of batteries. Some types are very sensitive to voltage imbalance and very bad things happen if they are overcharged or unbalanced. SPecial chargers are required for these types that individually monitor each cell voltage as they are series charging.

No, you cannot use a resistor to get a 12V charger to work with a 6V battery. Chargers work by controlling the current into the battery, and the resistor will distort what the charger is trying to do.
 
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colin55

Well-Known Member
Generally the number of filling holes gives an indication of the number of cells. Sometimes the filling holes are hidden under rubber stoppers.
You can charge the two 6v batteries in series just like a 12v battery - provided they look and feel the same weight and are as old as each other.
 

codan

New Member
Thanks for the quick replies,

The batteries have three double filler holes along the top --three down one side of the top & another three parallel to them on the other side.
 

colin55

Well-Known Member
You really have to work out if they are truck or fork-lift batteries or "donkey cells" that sit around for 20 years and supply old-style 32v lighting etc.
If the filler holes have "bleed holes," to let fumes escape, the batteries are possibly not sealed batteries. "Sealed lead acid batteries” have a slightly different composition on each plate so that the cells do not gas until a higher charging voltage is reached.
If you are charging the batteries with a simple "car battery charger" it will not have a voltage cut-off and the batteries will keep charging.
In this case you will have to work out the amp-hr capacity of the cell by discharging it to nearly zero and charge it until a "floating voltage" is obtained.
This is the point when the voltage rises to a higher level for "no apparent reason."
Many cells don't like to be deep discharged just like they don't like to be left lying around in an uncharged condition, so the whole thing is much more complicated than first meets the eye.



.
 

codan

New Member
The batteries, came off a truck but where used to power something other than the truck.

The truck is 24v & has 2x 12v batteries in series--24v.

These other batteries where mounted further back on the chassis & had various heavy leads running everywhere.

I am sure the truck came from a mine & maybe even had a drilling rig on it, maybe these two big batteries where used for lights etc for the drilling rig.
 

colin55

Well-Known Member
The only thing you can do is look at batteries like this at a battery shop (truck shop or fork-lift shop), where they will tell you the capacity of the cells.
It may have 11 plates, 13 plates or more.
It could be 100amp-hr or more. It could be anything.
Then you have to work out how many amps your charger will deliver and divide the two. It may take days to charge.
 

bryan1

Well-Known Member
G'day Codan,
Surely there must be a name plate on the batteries and some pic's of them will save a thousand guess's. As you say they were located further back on the truck it's a good chance they will be deep cycle batteries. If you can't supply a pic then how about measuring them up for physical size.

Cheers Bryan
 

codan

New Member
A bit dark to take some pictures at the moment, no name tags or stickers just Black Batteries.
They are 500mm long x 270 wide x 290 high.

Both Poles at one end as shown below--top view.

+ O O O<-------Filler Caps

- O O O<-------Filler Caps
 
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colin55

Well-Known Member
Have you tried putting a piece of wire from a length of hook-up flex across the two terminls?

This will tell you a lot.
 

tcmtech

Banned
Most Helpful Member
To me thats most often a 12 volt battery configuration. It may have 3 shorted cells and just be giving you a 6 volt reading. Or be stone dead junk too!
 

codan

New Member
The filler caps in the diagram above are actually in line with each other on the battery, tried editing it but it keeps on misaligning it for some reason?
 

colin55

Well-Known Member
That's why I asked you to test them with a piece of wire.
It will tell you if the battery has CURRENT.
 

bryan1

Well-Known Member
Hi Codan,
dont listen to that ol' git above if those baterries do have current you'll have burnt fingers at best. Try this put the batteries in series then hookup a load like a 12 volt car light to them, put a dmm across the leads and turn the light on. If the voltage drops very quickly like to 2 or 3 volts then those batteries are dead or dead flat. If so just hook ya 12 volt charger up to them and check them doing the same again after say 6 hours. If the light stays on for 10 minutes or so they might be ok.

try this first and later I'll find the info for doing a amp/hour test for you.

Cheers Bryan
 

Sceadwian

Banned
Yes, it will tell him if it has current by vaporizing the wire he's holding in his hand =\
 

codan

New Member
Thanks Guys, i setup a test light like mentioned & the batteries have Voltage but NO current, i hooked the charger up & i'll let it run overnight & let you know how they go.

Thanks again.
 

Sceadwian

Banned
Make sure it's not near anything, if the battery has shorted cells or something else weird with it the remaining cells could boil over.
 

bryan1

Well-Known Member
Have you tried putting a piece of wire from a length of hook-up flex across the two terminls?

This will tell you a lot.

Suggesting that someone short a battery out to test it could kill someone and the op did state the size of the battery was unknown.

Misleading infomation of this serious nature shouldn't be allowed in this forum and i'm sure many other members will agree that aswell
 

colin55

Well-Known Member
One strand from a length of hook-up flex will draw no more than a 21 watt 12v globe, so you obviously don't know what you are talking about.
One strand is exactly the same gauge as a 3 amp fuse.
 
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