# How to connect cell tabs



## halestorm (Apr 28, 2009)

I'm trying to come up with a solution for connecting to pouch cell tabs on groups of batteries that are not directly adjacent (in other words I can't just mash the tabs all together).

Specifically, I'm trying to join the cells of multiple Chevy Volt battery modules in parallel. Attached is a picture of a single module, and a picture/schematic showing how I'd like to wire them.

I have a couple of ideas but I don't really like what I've come up with. There must be some nice, clean solution I don't know about, for making a good solid connection to the tabs. Any ideas?

Thanks,


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## Yabert (Feb 7, 2010)

Hi

I have the same problem because i'm interested to build a 48S 6P with my 96S 3P Volt battery pack.
The ideas...

*Clamping (mechanical):* I don't think it's reliable and a loose clamp will cause serious problem. The price for well build clamp should be fairly high.

*Welding (lead):* I fear to damaged cells because the tabs will conduct the heat very well.

*Screw:* I've think about drill two small holes per tabs and link a bus bar with two small screw with lock washer and lock nut. But, drill small hole will be difficult and capturing all the metal chip would be hard and I don't talk about putting the small screws in place. Well, I don't like it.

*Spot welding:* I think it's the better one. Each bus bar should be connect with 3 or 4 spot weld on each tab (6-8 spot weld on each bus bar).

If anyone have others ideas, please share. We are in brainstorm!


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## Tomdb (Jan 28, 2013)

how about drilling into the plastic between the plates and then a small flat but flexible "busbar" screwed down onto the serial tab. 

The current between the parallel cells will be minimal, if these cells are matched (since this is an oem pack i would geuss quality should be good).


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## kennybobby (Aug 10, 2012)

halestorm said:


> I'm trying to come up with a solution for connecting to pouch cell tabs on groups of batteries that are not directly adjacent (in other words I can't just mash the tabs all together).
> 
> Specifically, I'm trying to join the cells of multiple Chevy Volt battery modules in parallel. Attached is a picture of a single module, and a picture/schematic showing how I'd like to wire them.
> 
> ...


i think your math is off--you can't make a 6p/12s pack with only 24 cells.


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## piotrsko (Dec 9, 2007)

Don't think the OP wants to illustrate the whole VOLT pack and 96 cells

I still like # 12 x 1/2" sms through the existing holes with #2 weld cable and homemade copper pipe crimp fittings


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## dcb (Dec 5, 2009)

I don't really know what I'm looking at in the pictures, how are the modules wired internally? Has anyone done a teardown of a module? 

Need to know which tabs are + and - on the battery and which cell group they belong to. got 7 tabs on one side and 6 on the other so maybe you can map that out and post a more detailed diagram?


If a module is basically a series string of 3P pouches, you can probably get away with hooking the modules in parallel and just soldering some balancing leads (making sure the voltage potential is the same first) in place. 

It only needs to handle 1/6 your max current draw in the event of a pouch failure (assuming 2 modules in parallel). Still you should secure them with some silicone so they don't go shorting stuff out if they melt.

Edit: I found this thread http://www.diyelectriccar.com/forums/showthread.php/chevy-volt-new-battery-configuration-93404.html

similiar issue though, I think some 4 gauge soldered on and secured balance wires would be fine, but the ends of the module strings should be more deliberate with a bolt on bus to parallel them.

I have the exact opposite problem  trying to get 15 volts out of my leaf modules.


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## piotrsko (Dec 9, 2007)

I use 1/4 max current of 750 amps which is why I suggested 2 awg. I have gotten them to 750 often, they ought to go as high as 900 @ 10C, Yabert hints at possibly 15C, they could go more still. Nobody but chevy knows for sure, chevy ain't talking to the public about more than 4C.


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## dcb (Dec 5, 2009)

I'd be happy with 365v 45Ah myself  plenty of inexpensive 3 phase motors would be also. Just need an inexpensive controller (got one) and inexpensive bms (working on it) and a way to charge it. 

A buck-mode controller shouldn't be to terrible to put together if you are targeting a brushed motor, couple igbts and a microcontroller and a current sensor. The motor is already a huge inductor:










ultimately you just change the duty cycle of the igbt (or get fancy with synchronized rectification)


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## Hollie Maea (Dec 9, 2009)

Yabert said:


> *Screw:* I've think about drill two small holes per tabs and link a bus bar with two small screw with lock washer and lock nut. But, drill small hole will be difficult and capturing all the metal chip would be hard and I don't talk about putting the small screws in place. Well, I don't like it.


A punch solves that problem.


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## halestorm (Apr 28, 2009)

Hollie Maea said:


> A punch solves that problem.


I thought about that; I think that'd be a great idea but I haven't be able to find a suitable punch. First, as you can probably see from the pictures, there isn't much room between the tabs, so you have a physical constraint there on the size of the tool. The second constraint isn't apparent unless you've handled one of these batteries. You have to punch not just through the light gauge material of the cell tabs themselves but also through the steel "U" shaped part which joins neighboring cells.


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## halestorm (Apr 28, 2009)

kennybobby said:


> i think your math is off--you can't make a 6p/12s pack with only 24 cells.


Attached is an annotated picture of one of the Chevy Volt modules that might help you understand better. Each 48v module is comprised of 36 cells in 3p12s configuration. This should answer dcb's question, too.

My original intention was to connect in parallel all of the cells from two such modules to net a 6p12s "supermodule", as outlined in my original post. This would require a connection from each cell tab of two adjoining modules. This is proving to be somewhat difficult.

Unless a clean solution presents itself I'm leaning towards joining two modules in parallel -- so instead of a true 6p12s it will be two 3p12s in parallel -- a series/parallel combination. In other words, something more like the top panel in the other attached picture, rather than the bottom panel, the latter being what I was initially going for.


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## boekel (Nov 10, 2010)

Can't you just use the existing connectors for the BMS boards?


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## Yabert (Feb 7, 2010)

halestorm said:


> You have to punch not just through the light gauge material of the cell tabs themselves but also through the *steel* "U" shaped part which joins neighboring cells.


Plated copper...



boekel said:


> Can't you just use the existing connectors for the BMS boards?


It's not safe because if there is a difference between two cells, a current will flow in those tiny 22 Ga wire (or smaller Ga?).


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## halestorm (Apr 28, 2009)

Yabert said:


> It's not safe because if there is a difference between two cells, a current will flow in those tiny 22 Ga wire (or smaller Ga?).


I agree; that wire is too small of a gauge. Plus it is being used for the BMS.


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## halestorm (Apr 28, 2009)

Yabert said:


> *Clamping (mechanical):* I don't think it's reliable and a loose clamp will cause serious problem. The price for well build clamp should be fairly high.


I agree, not ideal, but unfortunately the only one I can imagine implementing.



Yabert said:


> *Screw:* I've think about drill two small holes per tabs and link a bus bar with two small screw with lock washer and lock nut. But, drill small hole will be difficult and capturing all the metal chip would be hard and I don't talk about putting the small screws in place. Well, I don't like it.


Plus you could drive the screw through something critical, like say, a battery pouch or the coolant path.



Yabert said:


> *Spot welding:* I think it's the better one. Each bus bar should be connect with 3 or 4 spot weld on each tab (6-8 spot weld on each bus bar).


Maybe!


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