Battery innards

[Graham_Wright]

How are cells inside a lead acid battery connected together - anybody?

 

[Dave_Seager]

In each cell the plates are interleaved. Each set of plates, positive and negative, is connected to a terminal that protrudes through the lid of the cell. Usually, the cells are placed side by side in alternate directions so that each terminal is next to the opposite polarity terminal of its neighbouring cell or cells. Adjacent cells are connected by bus bars, bridging pairs of terminals, positive to negative forming a zig-zag path. The two ends of the chain of cells are brought out as the terminals for connection to the external circuit. On older batteries the bus bars were visible. Most modern batteries now have an additional lid which covers the bus bars to prevent accidental short circuits so only the main terminals are visible.


+...- +...- +...-
|| || || || || ||
- +...- +...- +

 

[Salty John]

Typically like this:

From Miner Brotherton's book - The 12volt bible for boats.

 

[Plevier]

Typically, on an automated line:
The pack of plates and separators for each cell is assembled. Each plate has a tab extending up at one top corner. The pack is assembled with + tabs at one side and - tabs at the other.
The pack is inverted so the tabs are downwards, the tabs are dipped in cleaning and fluxing baths and then into moulds and molten lead is poured round each set of tabs. This forms 2 bus bars, + and -, connecting the plates. Each bus bar is cast with a tab at one end, + and - at opposite ends of the cell pack and projecting away from the plates.
The cell packs then go the right way up and are put into the battery box so the bus bar tabs are pointing upwards and are against the internal divider walls in the box. At any one divider wall a + and - tab will be adjacent separated by the divider wall. The wall has a hole in it between the tabs and the tabs are clamped together with copper electrodes and electrically spot welded through the hole. This also gives a leakproof seal.
The cell packs destined to be at each end of the battery will have been cast with one longer round tab (post) each. The battery lid has the external terminals incorporated in the moulding. When the lid is put on the post will come up through a hole in the terminal and they will be fused together with a gas torch. The post may be copper cored.
This should make sense when you match it to the drawing in Salty John's post!

 

[Graham_Wright]

Typically, on an automated line:
The pack of plates and separators for each cell is assembled. Each plate has a tab extending up at one top corner. The pack is assembled with + tabs at one side and - tabs at the other.
The pack is inverted so the tabs are downwards, the tabs are dipped in cleaning and fluxing baths and then into moulds and molten lead is poured round each set of tabs. This forms 2 bus bars, + and -, connecting the plates. Each bus bar is cast with a tab at one end, + and - at opposite ends of the cell pack and projecting away from the plates.
The cell packs then go the right way up and are put into the battery box so the bus bar tabs are pointing upwards and are against the internal divider walls in the box. At any one divider wall a + and - tab will be adjacent separated by the divider wall. The wall has a hole in it between the tabs and the tabs are clamped together with copper electrodes and electrically spot welded through the hole. This also gives a leakproof seal.
The cell packs destined to be at each end of the battery will have been cast with one longer round tab (post) each. The battery lid has the external terminals incorporated in the moulding. When the lid is put on the post will come up through a hole in the terminal and they will be fused together with a gas torch. The post may be copper cored.
This should make sense when you match it to the drawing in Salty John's post!

Thata was the answer I needed!

Now to explain.

In the local scrap yard, I found a pallet of new Sonnenschein AGM batteries, big ones, very big.

They were all unfilled. The first I filled with battery acid and it worked fine. So did the second. The third did not. Through the fill holes, I established that the cells were not connected one to the other. I cut the top off and found this to be the case. These are far too big for the boat but I do have other uses which are static. The protruding tabs are undrilled and are difficult of access. It seems from your reply that each group may well be capable of being lifted out. I would then be able to drill them (although it is not impossible in situ). I am curious to see how continuity is established through the wall to enable spot welding. Is there a lead filler In the wall?

Thanks for very helpful and complete replies.

To complete the story. I believe these batteries (8 for £50!) came from a local company who produce battery manufacturing plant. (They used to be a customer of my company). I assume they were a prototype run to validate the equipment.

 

[Plevier]

Interesting.
How big is very big? Got a model number? Dimensions, photo? Scrap value suggests maybe 20kg each - not that big.
If they are really big the procedure is likely to be a bit different - you didn't say why you were asking.
Bear in mind AGM (how do you know they are by the way? You mention filling holes; are they small with non-return valves in? Is the separator material fluffy?) need special filling and first charging procedures. They will work if you overfill them but they won't be non-gassing.
No there isn't a lead insert in the wall, just a hole. The lead tabs extrude through it under the pressure of the electrodes and weld together.
If you bolt them together I don't think they will last long!

 

[Graham_Wright]

Interesting.
How big is very big? Got a model number? Dimensions, photo? Scrap value suggests maybe 20kg each - not that big.
If they are really big the procedure is likely to be a bit different - you didn't say why you were asking.
Bear in mind AGM (how do you know they are by the way? You mention filling holes; are they small with non-return valves in? Is the separator material fluffy?) need special filling and first charging procedures. They will work if you overfill them but they won't be non-gassing.
No there isn't a lead insert in the wall, just a hole. The lead tabs extrude through it under the pressure of the electrodes and weld together.
If you bolt them together I don't think they will last long!

Size 530L X 320H X 130W.. weight 35Kg.
I think I found a found a name and reference number on one of them but I've lost it. I'm sure it declared AGM. The filling holes are unfilled! No plugs.

Yes the filling is fluffy.

I bought them with the boat in mind but they are too tall. They will now serve to start our domestic standby generator and provide emergency lighting. (When our trip switch trips, it causes a certain amount of domestic "excitement"!)

When the first two were filled, they appeared fully charged immediately. If you can add to your advice on initial charging, it would be appreciated.

My company has a 1800 amp stud welder. With a bit of leverage on some contrived clamps, the gap may we narrow enough to spark across and melt the plastic. Probably an idea to do it before filling!

Thanks again for the help.

 

[Plevier]

Those are tall. Not intended for high rate. Probably 150Ah or so at that weight (if they are 12V). Fluffy separators = AGM.
You'll have to overfill them and just treat them as wet cells for charging. precise conditions are guesswork. 14.5-15V for about 12hrs would give them a good boost to start them off - switch off if they get hot. Why do you say they seem fully charged? (You can't really tell other than by a discharge test).
The plastic divider wall should have a hole in it and the clamp pressure squeezes the tabs into contact before you pass current to weld. No sparking! I've no idea what current, I did applications not production, just had an overview of manufacturing.