# Making a Battery Pack - solder tabs



## PhantomPhoton (Aug 4, 2008)

Hey all,
I need to build myself a new battery pack and so far I can't find any pre-assembled packs that meet my specifications. So I'm looking at making my own. The thing is I've never used solder tabs so I'm wondering if I can get some guidance on them. I really don't know how they work. I've undone plenty of them breaking apart packs before, but I have no idea how to hook up one cell to it's destined neighbor.
I've googled today and did a cpf seach a while back on it but haven't come up with any instructions. If anyone has a link or can give me a crash course, I'd really appreciate it.

By the way I need to solder 10 D NiMh cells in series in a 1X10 arrangement. I'm eyeing the 12000mAh Titanium cells at battery junction. Suggestions on the specific cells to use are welcime too. I"ll be powering a 75Watt short arc HID. My ballast is rated from 11.?V to 14.4V.

Thanks


----------



## jchoo (Aug 4, 2008)

How do you want the pack arranged? I always like to make my packs with the + and - ends coming off of adjacent cells so when I shrink wrap it the leads are as short as possible. If you need to fit into a particular space, take that into consideration as well. If you're building a brick, with the cells all parallel to one another, it's quite easy to build the pack. If you are building a stick (out of 10 D cells?) it becomes a bit more difficult.

First, you need to measure the voltage of each cell - you don't want to assemble a pack out of cells with different states of charge. Then, figure out how you're going to lay out the cells. If I were building a 10D pack, I'd do it in two rows of five, arranged like this when viewed from the top:

```
Connector ====== (1+)(2-)(3+)(4-)(5+)
                 (0-)(9+)(8-)(7+)(6-)
```
To do this easily, use some wooden paint stirring sticks cut to length and some tape, holding the pack tightly together in your desired shape.

In this example, I'll connect the positive end of the connector to the #1 cell, and the negative to the #0 cell. That means I will lay out the bars/jumpers to connect 2- and 3+, 4- and 5+, 9+ and 8-, and finally 7+ and 6-. I like to use a high wattage iron with a very large chisel tip. Because excessive heat damages cells, you want to spend as little time as possible with the iron in contact with the cell. High wattage and a large transfer surface minimizes this time. I use rosin core silver solder to tin the ends of all 10 cells and the ends of all the bars/tabs to make the assembly go more smoothly. Once you get it all laid out you should be able to simply hold the bar/tab in place with the tip of a screwdriver while you apply the hot iron. It should only take a second or two to flow the tinned ends together, then remove the heat immediately. Work your way around one side of the pack - if you laid out your pack like I did, you'd solder 4 bars (8 cells) and two wires (for your connector leads). If you don't know how to determine if a solder joint is good (not "cold"), then I suggest practice before you start working on cells. Once you're sure everything is good on that side, flip over your pack. If you've got it taped up properly, you should not have anything move or fall out of place.

Now that you've flipped the pack, you need to apply the last 5 bars. Bear in mind that your pack now looks like this:

```
(0+)(9-)(8+)(7-)(6+)
Connector ====== (1-)(2+)(3-)(4+)(5-)
```
Since you already have connected the other ends of 2-3,4-5,9-8, and 7-6, we need to continue the circuit. On this side, we'll connect 1-2,3-4, 5-6, 7-8, and 9-0. Same drill, tin everything before you assemble. High heat, work quickly so you don't damage cells. After you've finished, measure the voltage across your connector. For charged nimh cells you should be right about 11.5-13v depending on how recent the charge was. If you don't get this, check all your solder joints; you may have a cold one. If not, you may have damaged a cell.

Good luck, and sorry for the cruddy ASCII!

PS - check out http://www.battlepacks.com/ to see what I mean about a "brick" pack. I put together two 30 cell 36v Sub-C NiMH packs for my last robot - you can surely do this.


----------



## SafetyBob (Aug 5, 2008)

Jchoo, thanks for the instructions. I need to rebuild a dewalt drill/driver I have with 16 sub c's in it. I have a good example, but I am with PhantomPhoton, I figured on buying batteries with tabs already on them and just connecting them together with some solder. 

You are recommending silver solder and not the regular kind of solder we use hooking up our lights? 

Bob E.


----------



## PhantomPhoton (Aug 5, 2008)

Thanks for the description of how to use the tabs Jchoo, I think I understand what to do now. I'll keep looking for a tutorial with pictures out there on the web, it has to exist somewhere. 

Like I said above I'm stuck making a 1x10 pack to make it fit within the holder of the previous one. So the setup of the pack will be pretty straight forward. Balance them all up individually, lay em all out side by side, flip over every other one and solder them in series down the line.


----------



## AlexGT (Aug 5, 2008)

Hope this helps

Part 1
http://www.youtube.com/watch?v=xb9IacvCwUY&feature=related

Part 2

http://www.youtube.com/watch?v=d3U0-V1CNeo&feature=related

Part 3

http://www.youtube.com/watch?v=mu30MMTG3PY

HTH
AlexGT


----------



## AlexGT (Aug 5, 2008)

Found another one here

http://www.youtube.com/watch?v=IelXfcrIXCc

AlexGT


----------



## jchoo (Aug 5, 2008)

Yep, that's pretty much it - just don't make that mistake of soldering two cells together, then flipping them over and dropping a bar across those two cells (causing a direct short with a bar/wire that can handle 30+amps isn't pretty!).

I like silver solder because joints made with it have more tenstile strength, and battery packs are subject to an awful lot of stresses because of the mass involved. If you're working with sub-c cells, your life will be made a lot easier if you get one of these:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXD183&P=6

They're great, and almost necessary sometimes!

I'll dig out one of my 30 cell packs tonight after work and take some pics. Sometimes, you just have to get a little creative with your cell layout in order to get stuff to fit.


----------



## wptski (Aug 5, 2008)

Checking the battery pack with volt meter doesn't really test the "quality" of the connections and won't tell if you will get a voltage drop accross the conection with a load applied. Only testing with a battery impedance tester/meter, using a CBA-II or checking/comparing voltage drops with a load applied would tell you if you really have good electrical connections on your pack .


----------



## jchoo (Aug 5, 2008)

wptski said:


> Checking the battery pack with volt meter doesn't really test the "quality" of the connections and won't tell if you will get a voltage drop accross the conection with a load applied. Only testing with a battery impedance tester/meter, using a CBA-II or checking/comparing voltage drops with a load applied would tell you if you really have good electrical connections on your pack .



True, but if he's got a cold solder joint he probably won't have continuity, let alone the full expected voltage of the pack. I was just trying to give him an easy way to check that he got the polarity of each cell correct and the thing put together properly.


----------



## wptski (Aug 5, 2008)

jchoo said:


> True, but if he's got a cold solder joint he probably won't have continuity, let alone the full expected voltage of the pack. I was just trying to give him an easy way to check that he got the polarity of each cell correct and the thing put together properly.


Yes, it's only good for finding a open and that's it.


----------



## jchoo (Aug 5, 2008)

wptski said:


> Yes, it's only good for finding a open and that's it.



Or if he wasn't observant enough to notice a cell with reversed polarity. Not the end of the world, until you try to charge it...


----------



## Mr Happy (Aug 5, 2008)

jchoo said:


> I like silver solder because joints made with it have more tenstile strength, and battery packs are subject to an awful lot of stresses because of the mass involved.


I am puzzled by this advice for a couple of reasons.

Firstly, silver solder requires higher soldering temperatures. This forum is full of advice not to solder NiMH cells but to use welded tabs instead. NiMH cells contain plastic membranes and the heat of soldering can damage them. Since tin/lead solder makes good joints at lower temperatures, this would minimize the risk of temperature damage to the cells.

Secondly, electrical solder joints should not normally be used to handle mechanical loads. The cells in a pack should be physically supported by other means such as glue and/or shrink wrap, and the electrical connections should be allowed to have a little flex to absorb mechanical shocks.

On following the links pointed to above, I see lots of soldering to bare cells going on. How is it that the RC fraternity is so routinely going against the advice not to solder cells?


----------



## PhantomPhoton (Aug 5, 2008)

I'm planning on using welded tabs for this project. I just can't seem to find specific instructions (especially with pictures ) on how to "use" welded tabs to connect the cells.

Those videos were pretty helpful in general though, thanks Jchoo.


----------



## wptski (Aug 5, 2008)

PhantomPhoton said:


> I'm planning on using welded tabs for this project. I just can't seem to find specific instructions (especially with pictures ) on how to "use" welded tabs to connect the cells.
> 
> Those videos were pretty helpful in general though, thanks Jchoo.


You can order "some" cell w/wo tabs, so you can figure your layout and get x amount with and x amount without tabs. You just solder the free tabs to another cell which cuts the soldering down about a half.

Not sure if LuxLuthor is still around here but he has a tab welding machine.


----------



## wptski (Aug 5, 2008)

jchoo said:


> Or if he wasn't observant enough to notice a cell with reversed polarity. Not the end of the world, until you try to charge it...


I myself would charge/discharge the pack before applying shrink wrap. I've never built a pack from scratch but ordered the basic pack and wired the harness myself. I always cycled each cell, one at a time, a few times.


----------



## jchoo (Aug 5, 2008)

Mr Happy said:


> I am puzzled by this advice for a couple of reasons.
> 
> Firstly, silver solder requires higher soldering temperatures. This forum is full of advice not to solder NiMH cells but to use welded tabs instead. NiMH cells contain plastic membranes and the heat of soldering can damage them. Since tin/lead solder makes good joints at lower temperatures, this would minimize the risk of temperature damage to the cells.
> 
> ...



In my experience, NiMH cells can handle the few seconds worth of direct contact with a soldering iron that it takes to make a joint with silver solder without any adverse effects. Because the tip is so large and the iron so hot, it rapidly transfers enough heat to tin/solder the ends of cells. Because of its high molecular density, heat does not transfer much beyond the surface of the cell, thus preventing damage. Spot welding actually creates a higher level of heat than soldering with silver solder, but it doesn't do any damage - same reason. Only the surface heats up, while the innards of the cell aren't exposed for long enough to become damaged. I have seen packs fail and burst into flames from overheating - but from current drain and abuse, not soldering.

When I quote the higher tenstile strength of silver solder, I look at it from the point of view of combat robotics. At any moment when in combat, a robot could be subject to sudden impact from weapons, collisions, falling onto the steel floor (from being tossed by another robot). This amounts to thousands of joules of energy, and shock loads of hundreds of G's. No pack, no matter how well braced and constructed, can absorb all of that energy applied to it without putting some stress on the electrical connections. I prefer to eliminate potential problems before they arise, so I took that into consideration when building my packs. This has also served me well in R/C racing. I've been involved in crashes where entire suspensions and motor pods are torn off, but the battery pack held up - where someone else involved in the crash had cells break loose and literally peel away from the pack, bending the copper buss bars. To each his own - but I'll keep on soldering if I am going to rely on a pack having the necessary strength to survive extremely rough handling.


----------



## AlexGT (Aug 5, 2008)

This shows how to install tabs and balancing wires

http://www.youtube.com/watch?v=vkDgoXikI_8


----------



## PhantomPhoton (Aug 6, 2008)

So, I'm still unsure how I would go about using the pre-installed tabs on these Titanium D 12000 mAh cells. I cannot tell how I would connect one cell to another. It may just need heat to secure wires from one to the next. Or maybe there's some solder method that I'm not seeing thinking of.
Being les dexterous than I'd like to be in my soldering skills I'd prefer to keep the iron off the cells, especially when I'm talking about $10 a cell.


----------



## jchoo (Aug 6, 2008)

Looking at those... slide the insulation off the tab, slide it over the wire. Strip the end of the wire, then tin the end of the wire and the newly exposed end of the tab. Hold them together in the orientation that will allow the shrink wrap to slide back over your joint, heat both at the same time with the iron until they join, and hold while you remove the iron and allow to solidify. Slide the shrink wrap back over the joint and you're done.


----------



## Mr Happy (Aug 6, 2008)

Yes, the key is to use short lengths of insulated wire to connect one cell to the next. You can't easily join the tabs directly to each other because the orientation won't allow more than two cells to line up that way. As jchoo noted you will want to cover the completed joints with shrink wrap to prevent accidental shorts.

You could connect a chain of tabbed cells in series like this:


```
|+|\  |+|\  |+|\  |+|\
 | | \ | | \ | | \ | |
\|-|  \|-|  \|-|  \|-|
```
Put them all in a row the same way up with the tabs facing the front (towards the viewer), and connect wire from the upper tab of one cell to the lower tab of the next.


----------



## kitelights (Aug 7, 2008)

> I am puzzled by this advice for a couple of reasons.
> 
> Firstly, silver solder requires higher soldering temperatures. This forum is full of advice not to solder NiMH cells but to use welded tabs instead. NiMH cells contain plastic membranes and the heat of soldering can damage them. Since tin/lead solder makes good joints at lower temperatures, this would minimize the risk of temperature damage to the cells.
> 
> ...


I'm puzzled too, and I cringe every time I read posts about soldering NiMH cells.



jchoo said:


> > In my experience, NiMH cells can handle the few seconds worth of direct contact with a soldering iron that it takes to make a joint with silver solder without any adverse effects.
> 
> 
> How do you know? Have you disassembled several cells after soldering to check out the membrane?
> ...


----------



## jchoo (Aug 10, 2008)

I'm not debating that the robotic spot weld used on commercial packs is superior to soldering - I don't contest that. I have been building, using, and abusing NiCd and NiMH packs for over a decade in R/C and robotics applications. I've cooked several cells myself with poor soldering techniques and equipment, and it is by drawing on this experience and through the experience of others that I offer my advice. Of course, my advice is worth what the OP paid for it. If he follows my instructions, then so be it. If he ignores them and ruins his cells, then so be it. What this all comes down to is applying enough heat quickly enough to both create the physical and electrical connection yet for short enough of a duration that the heat does not flow through the cell and damage the internals. Proper soldering is the only way for a home hobbyist to do this, and although it is an easy skill to pick up, it is not easy to perfect.


----------

