# Chevy Volt new battery configuration



## Yabert (Feb 7, 2010)

I actually have a 16 Kwh Chevrelet Volt battery (288 cells, 96S 3P for 365v 45Ah). I’ve disassemble this one and my ultimate goal would be to build a square battery pack (48S 6P for 182v 60Ah) as in the picture (represent as 4x 91v 45Ah). But for that, I need to parallel two groups of 3P cells in 6P. Since I'm not interested to cut the cells tabs, the only way to do this is to connect groups of 3P with a short bus bars or wires (say 10 AWG wire, partial example on picture).
Now, I know it's not the best idea since the current will flow in this wire if there is a difference of capacity and internal resistance between two 3P modules.

-So, first: Do you think about another manner to connect two 3P modules?

-Second: If no other solution is possible, do you think this can be acceptable considering this below?

Internal resistance worst case: Let say the first 3P module = 1 mhom and the second 3P module 0.5 mhom.
During continuous discharge (say 120A or less in my case). The first module will supply 40A and the second module 80A. So, 20A in the wire to equalize all things. Right?
During peak discharge (say 900A for 2 sec). The first module will supply 300A and the second module 600A. So, 150A in the wire to equalize all things. Right?
But this should never happen since the chevy volt cells probably have close internal resistance...

Difference of capacity worst case: Let say the first 3P module is at 0% DOD and the second 3P module is at 5% DOD. In this situation, 60A will flow in the wire...
But this should never happen since the weakness module will always be helped by the better one during the discharge.
And of course this situation should never happen since I can easily take care to gently drive when I go under 20% DOD (maybe only 3-4 times a years).
I think use a BMS to turn off charger at high voltage and turn off controller in low voltage event.

So, please correct me if I'm wrong and share your advices.
Thanks


_Please don't pollute this thread with inappropriate questions about Volt battery._


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## Yabert (Feb 7, 2010)

McRat said:


> Why wouldn't you just connect each battery block at the end?


FIRE, FIRE, FIRE... haha! I exaggerate, but an imbalance between each 96v block can cause serious problem. I'm not interested to use 96 bms boards.

Take care with pop rivet connections. Bad tension/compression after some heat/cold dilatation and galvanic corrosion come in mind...
And it's why I'm not interest to separate each cell because, as mecanical designer, I know than this battery is very well designed and that is a lost of time and money to try to reinvent the wheel... exept if you are intent to use 15Ah cells alone.
So, please share your experiment of using single cell on the thread 2012 chevy Volt battery
Thanks


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## Yabert (Feb 7, 2010)

grandfather said:


> Sure, you can do that, but keep in mind that the wire size must be large enough for any current flow that you may have


In my case, that imply serious size of wire/bus bar and I'm not specially interested with...



> Have you thought about cutting the tab connector along the 3 holes in between the pack tabs with a small cutoff blade?


Yeah... but if I can find better way to go...
Thanks for your input.


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## Karter2 (Nov 17, 2011)

Yabert said:


> ... I need to parallel two groups of 3P cells in 6P. Since I'm not interested to cut the cells tabs, the only way to do this is to connect groups of 3P with a short bus bars or wires (say 10 AWG wire, partial example on picture).
> Now, I know it's not the best idea since the current will flow in this wire if there is a difference of capacity and internal resistance between two 3P modules.
> 
> -So, first: Do you think about another manner to connect two 3P modules?
> ...


 I understand your logic for planning these parallel interconnects, and see your concerns also.
But, assuming you will be checking every 3p group for capacity, IR etc, and eliminating all defects, many of your "fail" scenarios will be all but eliminated. ( 3p groups are unlikely to vary much in IR if they are "healthy")
However, the sensible answer to cater for the worst , would be to fuse each of the interconnects to prevent any wiring overloads.


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## Yabert (Feb 7, 2010)

Karter, your mind sound good, but to me an healthy battery today isn't a guarantee of healthy battery in two year. Check today isn't a bullet-proof solution for long term.

And about the fuse, this can be catastrophic because the weak cell will continue to be discharge without the help of the best cell...


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## Karter2 (Nov 17, 2011)

Yabert said:


> And about the fuse, this can be catastrophic because the weak cell will continue to be discharge without the help of the best cell...


 True...but less of a catastrophe than 150 amps through a 10g balance wire !
Unless you use either a BMS to monitor each module (96 channel ?), or some other form of monitoring (fuse detection ?..48 channel ), then you will have a level of risk for cell failure.



> to me an healthy battery today isn't a guarantee of healthy battery in two year. Check today isn't a bullet-proof solution for long term.


Also, i believe our "DIY" battery packs ought to be subject to regular (annual ?) maintenance inspection which should include cell level capacity and IR checks, as well as other routine checks. That would reduce the probability of a major cell/module failure


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## aeroscott (Jan 5, 2008)

Why, not run 3p by 48s , 3p by 48s,3p by48,3p by 48s with separate amps and volts gauges and contactors .


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## Yabert (Feb 7, 2010)

I actually started to draw my battery pack (4x 4Kwh). Considering I need to entering this inside a Smart Fortwo, it's really tight and as you can see on the cut view, there is less than 1/2'' (13mm) around the plastic battery casing and the aluminum battery box.

So my question is, do you know good insulating material with small thickness? Soft or semi-rigid instead of a rigid.
I use my car 1/4 of year at temperature between -5°C and -30°C...



aeroscott said:


> Why, not run 3p by 48s , 3p by 48s,3p by48,3p by 48s with separate amps and volts gauges and contactors .


For me, 3p by 48s + 3p by 48s is like having 96 bms board...


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## Duncan (Dec 8, 2008)

Hi Yabert

I have had some issues with the Headway cells failing (some of which was my fault) and in a parallel first then series config taking several other cells down with them

I decide on a different config,
I now have four strings of 40 cells each string has a Lee Hart Batt-Bridge
so I have four green LED's on my dash with eight red high intensity LED's to warn of failure
If I get a red I can disconnect that string and limp home on the others

You could use two strings with Batt-Bridges to warn of any issues


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## z_power (Dec 17, 2011)

"Mylar" is one of the names of insulating material, sold in sheets or rolls. It'ss a foil, quite rigid like document "shirts". I bought a few square maters at local shop supplying motor rewinders.


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## Yabert (Feb 7, 2010)

Thanks Duncan... this idea of few Batt-Bridges to verified each 12s or 24s module doesn't sound unrealistic.

Thanks for the Mylar, Z.


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## racunniff (Jan 14, 2009)

z_power said:


> "Mylar" is one of the names of insulating material, sold in sheets or rolls. It'ss a foil, quite rigid like document "shirts". I bought a few square maters at local shop supplying motor rewinders.


Make sure you don't get aluminized (or otherwise metallized) Mylar. It conducts. Was the stuff you got at the motor rewinder supply intended as an insulator between windings? If so, you're probably good.

http://en.wikipedia.org/wiki/BoPET


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## z_power (Dec 17, 2011)

When I was googling to find local supplier it was easier to buy metalized stuff - each shop with equipment for diy marijuana farmers had it (light reflector probably)


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## kennybobby (Aug 10, 2012)

*Kapton*

i think Kapton may be a better choice than mylar.


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