How to build a battery pack?

[Bicurico]

Hi,

I own several devices, mostly TV/CATV/SAT field meter which use battery packs. Most of them are not OK anymore, after years of use.

I would like to know what is the correct method to build a battery pack. They seem to consist only of regular NiMH cells (1.2V AA type), which then are soldered together to form the pack, i.e. 6 of them form a 7.2V cell. After soldering them together with small pads, they are wrapped in plastic foil. All of this I understand.

In the past I tried to build such a cell out of AA NiHM batteries for end users, but I was not successfull in even soldering them together. Also, no idea how to put them in shrink wrapped plastic.

So, what would be the correct way of building my own NiMH battery packs? What tools do I need and wher do I get the metal plates from?

The idea is to use somethinig like this: http://www.ebay.com/itm/32x-AA-3000mAh-2A-1-2-V-Ni-MH-Rechargeable-Battery-BTY-Cell-for-MP3-RC-Toys-/350931874729

Regards,
Vitor

[anishkgt]

Well to start with I presume you know how to group the cells with voltage and capacity. With that done it just a question for joining them together as in soldering or spot welding.

Spot welding is one way and the recommended way to go. These days since li-ion cells are better compared to NiMh in all respects I'd recommend you use that. To charge you could get hold of a cheap RC charger like the imax B6. A spot like the sunkko or rewind a MOT and use it Spot weld. Heat shirnk covers are available ready on ebay or AliExpress and Banggood.

Hope this helps.


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[Bicurico]

I don't know go to spot weld. That is my main question. What would be the cheapest reasonable device to do so?

Grouping the cells is obvious to me and I need to use NiMH, becausee I want to leave the device unchanged and the charging circuit is made for s cell tho only.

Regards,
Vitor

[sokoloff]

I don't know go to spot weld. That is my main question. What would be the cheapest reasonable device to do so?

I bought one of these (or something similar; there are a lot of vendors reselling the same thing).


The learning curve is about 10 minutes long. Watch a couple of youtube videos while you wait for it to arrive and you should be all set after about 10 practice welds. The machine does the work; you just need to know how to adjust it.

[Gregg]

I have had really good results soldering wires or the thin stainless strips to individual cells. 
Clean the battery ends with very find sandpaper or better yet Scotchbrite.  Use the liquid acid flux commonly used for stainless steel; a tiny bit will work and not make too much of a mess.  Use the silver alloy lead free solder, the higher the silver content the better it will wet out on the battery ends and make the job go faster.  Use a hot soldering iron and tin the tip with the new solder several times to get rid of any lead that may be on the tip.  The trick is to get the battery terminal tinned as quickly as possible as to not heat the cell any more than necessary; tin one terminal at a time and allow each cell to cool while doing the others.  A small dot of solder on the battery only big enough to bond the wire is the goal.  Pre-tin the jumpers with the same solder and you should be able to quickly bond them to the batteries without heating them up enough to cause damage whatever flux residue from tinning the batteries will be sufficient to help bond the jumpers.  Clean off the flux residue with water and a little detergent using an old tooth brush.  You have to get all the flux washed away or it will turn nasty in a short while. 
Also, the acid flux vapor can cause all sorts of things in the vicinity to corrode; you may want to use it outside or away from your usual electronic workbench.  If you are like me, it is easier to move this operation than to clean everything off your bench