Tell me about using copper sheets in lieu of wires

[CGameProgrammer]

I want to completely rewire my A123 10s6p packs; right now I simply hooked up six 10s groups (from DeWalt packs) in parallel using insulated wire without cutting the existing tabs. Easy, but paralleled cells are not adjacent so I have to use insulated wire which isn't really safe (it's cheap wire and vibration can rub away the insulation, causing a really bad short), and it's kind of bulky too.

So I want to rewire it as 10s of 6p, meaning i just put 6 cells in parallel then hook those up in series. For each 6p string, I'm considering using copper sheet metal instead of wire. I figure I can drill a small hole in it wherever solder should go to make the soldering easier. But I have no idea what thickness I would need for 50 amps max draw, or how wide the strips should be, assuming that matters. I'm leaning towards the sheets because I'm lazy and removing the insulation from all the wire I'd otherwise need (there are three of these 10s6p packs) would be really tedious.

Also copper sheeting would allow for this elegance:

The yellow things are supposed to be the copper strips. Obviously there'd also be three of them on the bottom in this case. (The picture is 8s6p but it's just for illustration.) This makes individual cell replacement more difficult but I can just use a Dremel to cut out the copper sheeting holding a given cell on, pop it out, and put a replacement in using normal wire.

 

[paultrafalgar]

Two thoughts:
1. Have you thought of hammering small bore copper pipe to create your strips? I used 22mm pipe hammered flat to connect my house battery bank, but you'd want 10mm or suchlike.
2. This is an interesting alternative (by that genius paultrafalgar :wink: )
http://endless-sphere.com/forums/viewtopic.php?f=14&t=8617&p=131191#p131191

 

[fechter]

Soldering a copper sheet will be very difficult. It's hard enough to solder the cells by themselves. It will take a very large iron. It would make it easier if the copper was slotted to prevent some of the heat flow away from the solder joint. Keep in mind that most of the current will be going from one cell bank to the next and very little current will be going between cells in a given bank except on the 2 ends of the pack.

Below is sort of what I'm suggesting (bad drawing). The slots could be narrower.

The copper should not be too thick or it will put a lot of mechanical stress on the ends of the cells. It should have a bit of flex. I'm not sure what thickness is best. It also helps to drill a hole over the center of each cell end to feed solder into.

 

[GGoodrum]

If you leave most of the original tabs in place, you can solder your strips to those. I like Richard's idea about cutting slots like he's shown, but if you don't have the tabs on there, I'd say you are going to have a VERY hard time soldering anything to the cells themselves. It takes special flux, special solder and a special touch. I have never mastered the latter, which is why I use copper straping tape and nickel-plated springs.

-- Gary

 

[CGameProgrammer]

I am certainly not removing the existing tabs; just cutting them in half to separate the two cells each one joins.

Fechter, when you say "bank", do you mean parallel-string, e.g. 1s6p? And is your picture meant to be a 2s4p pack? (There's no indication of +/-.) If I do just end up using wire (the mechanical stress thing is a good point), do you know if uninsulated wire (ideally stranded) can be bought anywhere?

Another thing I might do is use a narrow copper sheet for parallel strings, then join them in series with wire. This shouldn't result in any mechanical stress. For soldering, my plan had been to drill a small hole in the copper sheet wherever solder should go and let it drip down the hole. Might still result in cold solder joints though, I guess...

 

[fechter]

Fechter, when you say "bank", do you mean parallel-string, e.g. 1s6p? And is your picture meant to be a 2s4p pack? (There's no indication of +/-.) If I do just end up using wire (the mechanical stress thing is a good point), do you know if uninsulated wire (ideally stranded) can be bought anywhere?

Another thing I might do is use a narrow copper sheet for parallel strings, then join them in series with wire. This shouldn't result in any mechanical stress. For soldering, my plan had been to drill a small hole in the copper sheet wherever solder should go and let it drip down the hole. Might still result in cold solder joints though, I guess...

Yes on the first two.
Here's a place that has humongous flat braid:
http://www.allelectronics.com/make-a-store/category/825200/Wire-/-Cable/Ground-Wire/1.html

I stripped the jacket off pieces of coaxial cable to get copper braid. RG-8 is good stuff.

On my cells, I had connecting bars already, and just needed to connect the sections together with heavy wire.

 

[Doctorbass]

Fechter, when you say "bank", do you mean parallel-string, e.g. 1s6p? And is your picture meant to be a 2s4p pack? (There's no indication of +/-.) If I do just end up using wire (the mechanical stress thing is a good point), do you know if uninsulated wire (ideally stranded) can be bought anywhere?

Another thing I might do is use a narrow copper sheet for parallel strings, then join them in series with wire. This shouldn't result in any mechanical stress. For soldering, my plan had been to drill a small hole in the copper sheet wherever solder should go and let it drip down the hole. Might still result in cold solder joints though, I guess...

Yes on the first two.
Here's a place that has humongous flat braid:
http://www.allelectronics.com/make-a-store/category/825200/Wire-/-Cable/Ground-Wire/1.html

I stripped the jacket off pieces of coaxial cable to get copper braid. RG-8 is good stuff.

On my cells, I had connecting bars already, and just needed to connect the sections together with heavy wire.

I second on the flat braid.. the link you shoen is a good source!! i'll order dozens of them!

I really think they are the BEST OF THE BEST for A123 cells link!! excellent find!!


Oh.. Fechter, where did yopu got the A123 spotwelded flat strip??? (i'm interested on that source too

Doc

 

[fechter]

Oh.. Fechter, where did yopu got the A123 spotwelded flat strip??? (i'm interested on that source too

Doc

My cells came with the strips. A bunch of the spot welds were broken, but I found out the cells actually had thin nickel discs spot welded to the ends and the bars were welded to those. The discs made soldering very easy. I believe the bars are nickel, and are quite thick. I think one reason a lot of welds broke is due to the stiffness of the bars. Obviously they didn't have the spot welder dialed in right either.

 

[Doctorbass]

Oh.. Fechter, where did yopu got the A123 spotwelded flat strip??? (i'm interested on that source too

Doc

My cells came with the strips. A bunch of the spot welds were broken, but I found out the cells actually had thin nickel discs spot welded to the ends and the bars were welded to those. The discs made soldering very easy. I believe the bars are nickel, and are quite thick. I think one reason a lot of welds broke is due to the stiffness of the bars. Obviously they didn't have the spot welder dialed in right either.

I ordered 10 of the 4 gauge 24" braids from Allelectronics... that will be for my drag racing bike setup.. I expect to get serious continuous 100A+ current during the 19-20sec race...

When you say that they came with the cell.. do you mean you got them from A123 and asked for the strips?

I just want to know where did you got them? (the strips)


Doc

 

[GGoodrum]

I believe Richard's a123 cells came from a Prius plug-in upgrade package that HyMotion offers. They came with the welded strips.

-- Gary

 

[fechter]

When you say that they came with the cell.. do you mean you got them from A123 and asked for the strips?

I just want to know where did you got them? (the strips)


Doc

I can't divulge the source of these right now. Let's say I pulled them out of a dumpster somewhere. Many of the cells had vented and spewed white crusty stuff all over. I guess their BMS wasn't so good. I still got enough good cells (I hope) for my bike pack.

 

[CGameProgrammer]

Yup, one of my cells has that white crusty stuff too. It's 0.12V and sadly it was connected in parallel to five otherwise-good cells so they too were forced down to 0.12V. Hopefully they can make a decent recovery once I get my single-cell charger I ordered.

 

[Doctorbass]

Yup, one of my cells has that white crusty stuff too. It's 0.12V and sadly it was connected in parallel to five otherwise-good cells so they too were forced down to 0.12V. Hopefully they can make a decent recovery once I get my single-cell charger I ordered.

I know about that white crusty stuff...

There was many dewalt that i got that was floaded or that was exposed to intense rain.... i did not sold them even thou they had great voltage for 80% of the cells..

in fact many cells i got had this white crusty stuff without compromizing their performance.. but that just make a doubt in my mind...

Does the white stuff you talk about appeard by itself on the cell.. or it was due to external exposure of water or other oxide?..

This white crusty stuff seems to me some alluminium oxide from reaction with water...



Doc

 

[lawsonuw]

Looks like the KillaCycle packs use copper foil as an interconnect. http://www.killacycle.com/photos/battery-assembly-110s-x-9p/DSCN2391.JPG I'd guess the sheets are only 0.005 to 0.010 inches thick at most. My guess is that soldering foil is challenging. The killaCycle pack has the foil spot welded onto the cells, the solders the foil between cells. (Isn't there a DIY spot welder thread in this forum section too?)

Lawson

 

[CGameProgrammer]

Does the white stuff you talk about appeard by itself on the cell.. or it was due to external exposure of water or other oxide?..

Nah, it was just the one mentioned here. I kept using it anyway and it worked fine til I left the pack sitting unused for one year. But now its voltage is so low than it's entered the state of no return, along with the five poor bastards it was paralleled to.

Oh well. Managed to snag two new 36V packs from ebay for $199 with free shipping. $10/cell is even less (slightly) than what I paid 1.5 years ago when demand was lower, which was $10.68/cell including shipping.

 

[Doctorbass]

Fechter, when you say "bank", do you mean parallel-string, e.g. 1s6p? And is your picture meant to be a 2s4p pack? (There's no indication of +/-.) If I do just end up using wire (the mechanical stress thing is a good point), do you know if uninsulated wire (ideally stranded) can be bought anywhere?

Another thing I might do is use a narrow copper sheet for parallel strings, then join them in series with wire. This shouldn't result in any mechanical stress. For soldering, my plan had been to drill a small hole in the copper sheet wherever solder should go and let it drip down the hole. Might still result in cold solder joints though, I guess...

Yes on the first two.
Here's a place that has humongous flat braid:
http://www.allelectronics.com/make-a-store/category/825200/Wire-/-Cable/Ground-Wire/1.html

I stripped the jacket off pieces of coaxial cable to get copper braid. RG-8 is good stuff.

On my cells, I had connecting bars already, and just needed to connect the sections together with heavy wire.
View attachment 8

Fechter, I received my 10 ground braid from AllElectronics...

Pretty big for a 4 gauge equivalent!!!

The braid have 7/8 to 1.0" width...!!! the same width than the diamerter of a A123!

But if i build a Xs x 10p pack, this following method will be bery interesting!

The Hole idea is to be able to solder each cell to the braid and that the heat required to solder it is very low and the dissipation is excellent.. Better than a cooper sheet...

maybe.. also.. the fact that this material is very soft almost when pried in sandwich to form a double thick.. the cooper have a little memory effect so it act like a spring itself.. so the Idea of Gary with the spring and cooper sheet could be replicated with only the double sandwich braid that make contact to every cells tab with suffisent pressure on them.

I tried many setup on these following pics: (the first one is from the Gary setup)

 

[CGameProgrammer]

I got them a while ago and meant to post about them... yeah, they are much wider than the outer diameter of an A123 cell at their widest point, though most of the braid is narrow enough. But it's 1/16" thick which would make it tricky to use, and cutting off the too-wide sections leave lots of loose strands that can come off and short stuff, though soldering the braid might help it, but I think it'd be really tedious using this stuff, so I bought regular braid instead and will try that.

 

[rkosiorek]

ground straps like that should be good for a few hundred amps. 3/8 studs can take a whack of power as well.



the thought that came to mind was to solder the braid to the cells. i think i would make a special tip for a 60W or 80W iron to do that from a chunk of 3/4" dia. copper bar. flat on the end. it would be large and heavy enough so that it would not loose much heat while making the connection.

looks like one of those plastic end caps could be sacrificed and modified to make a solder jig. the holes would have to be enlarged a bit to make room for the custom soldering tip.

first tin the cells with a generous blob of solder. assemble the cells and the strap into the final shape with the soldering jig/endcap in place. add a little liquid flux to the braid. tin the tip heavily. and then press that big heavy hot tip through the hole just long enough for the solder blob on the cell will melt and flow into the fluxed braid.

rick

 

[GGoodrum]

Hey Rick --

If you left the tabs on, soldering to these would be easier, but otherwise, it is really hard to solder a123 cells. Besides, if I was going to do that, I might as well forgo the plastic cases altogether, and just hotglue the cells together.

I assume there are narrow versions of these braided straps? I still want to do 5p configurations, not 10p, so the extra wide version seems too much. What I'd like to find is some sort of non-conductive flat material with "bumps" about every inch. These could be used under the braid to push up the material at the cells. Can you think of anything that might work like this? I really like this construction method as it makes for a very strong and solid pack, but attaching 160 springs to copper straps takes way too long.

-- Gary

 

[rkosiorek]

why not make some of your own from some plastic sheet. i like to use PVC. it becomes maleable at a fairly low temperature and is easy to shape.

first you need to make a male and female mold for what you want. wood works well. get two blocks of wood the same size and shape as the finished part. drill a hole pattern through both representing the bumps. these are small dia. pilot holes, maybe 1/8" diameter.

a the hardware store buy some pan head screws. choose ones where the head will be slightly smaller than the bump you need. screw these down to one block of wood. this is your male pattern.

in the other block countersink the holes stightly larger than the bump. this is now the female mold.

cut a piece of 1/8" PVC sheet to the right size. preheat your oven to 80C/175F. place the sheet on top a cloth covered baking sheet using the middle rack of the oven. heat for 5 min or so. place sheet between the 2 mold blocks and clamp together using a couple of clamps. let it cool down for 10 or 15 minutes to set.

make sure the kitchen is well ventilated. the fumes may be toxic.

rick

 

[lawsonuw]

I prefer Polycarbonate/lexan or Polyester/PETG for DIY thermoforming. HDPE from milk jugs allegedly works well too. Haven't had any fume issues with Polycarbonate or Polyester yet just heating them over an electric stove element till the plastic is limp.

Lawson