# Large Cylindrical Battery Pack Connections



## steven4601 (Nov 11, 2010)

Hopefully I do not post too many questions on this forum, but I think this question is worth asking: 
I have a question regarding connectors but first i try to form an image what my traction pack is intended to be like:

Working out a plan where it is possible to remove sections of the battery pack without using an engine hoist. Various formats are needed to use the available space to its maximum efficiency.

format1. 18S 3P (just under 50lbs)
format2. 8S 3P 
format3. 7s 3P

Of each format i need four units. resulting a 132S 3P configuration. Or 422Volts 36Ah total. (using HW38140S cells)
That would mean Id need 28+ of these connectors to complete the circuit with all units.... 

The question
To connect these units together, what kind of connector is recommended? 

//Steven


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## coryrc (Aug 5, 2008)

steven4601 said:


> To connect these units together, what kind of connector is recommended?


If the ends aren't near each other, I recommend this style of welding connector (I used the Tweco version myself):

http://store.weldingdepot.com/cgi/weldingdepot/WD-1MBPx.html

If the positive and negative are by each other, how about a SB175 or SB350?


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## steven4601 (Nov 11, 2010)

Hi ,

thank you for the link to the welding connector. 
However it is rated for low voltages? Id like to be able to make and brake the connections without (additional) risks involved. 

The Anderson SB120/175 are very well suited connectors. Just 28 of them is what made me wonder if I was heading in the right direction. 


Added a sketch of how the group are to be organized. They are installed into large battery boxes with non conduction sections separating the units. My initial plan was to use a copper strap that would fold over and make the connection. That would work well, but it will only be safe in a well lit environment with all the access space. In a cramped corner of the car this sounds less than a good idea. Think the copper foil (0.5mm) will have a tendency to 'flop' around making shorts. Also it would violate the isolation requirement.


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## coryrc (Aug 5, 2008)

steven4601 said:


> However it is rated for low voltages? Id like to be able to make and brake the connections without (additional) risks involved.


Uh, I don't think there is a minimum voltage.



steven4601 said:


> The Anderson SB120/175 are very well suited connectors. Just 28 of them is what made me wonder if I was heading in the right direction.


I guess I didn't understand your question right. I thought you were asking for a connector to attach each group of batteries to each other. For other people who have done something similar, see:

http://tangocars.blogspot.com/2010/03/tango-with-32-kwhr-pack-of-headway.html


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## Yabert (Feb 7, 2010)

Hi

After a quick looking on your design, I wonder why you do not choose Calb 40Ah cells rather than 3x HW 38140??

Is it only for their better volumetric density? 
Because for the performance and the price, Calb win the game.

3x HW 38140 @ 500A = 0.006 x 500 / 3 = 1v sag
Calb 40Ah @ 500A = 0.001 x 500 = 0.5v sag

HW $ = 24$ x 396 = 9500$
Calb $ = 54$ x 132 = 7100$

So?


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## steven4601 (Nov 11, 2010)

coryrc said:


> Uh, I don't think there is a minimum voltage.
> 
> 
> 
> ...


Hi Corryrc, the picture as shown which has been done for the Tango electric car is exactly to what I was trying to explain how I planned to do my battery pack. 


Hi Yabert. Thank you your input, but allow me to explain my reasoning. 

In your calculations you have used the 1mili-ohm figure to compare the CALB SH40AHA prismatic battery to the 6mOhm 12Ah cylindrical cell. 

The real world voltage sag however produces an effective ~ 5mOhm. Which is still very impressive. This is likely limited chemically than electrically. The 38140Headways have 6 mOhm (typical) effective.

Here's a comparison sheet i made to help making the selection. Maybe the 5mOhm figure is wrongly assumed, as I never measured it personally but found it on the internet.


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## coryrc (Aug 5, 2008)

steven4601 said:


> Hi Corryrc, the picture as shown which has been done for the Tango electric car is exactly to what I was trying to explain how I planned to do my battery pack.


Ah. Yes, he uses 0.062" copper which is plenty stiff and doesn't bend. You could probably use a few sheets of thinner stuff and cut it yourself with tin snips. I wouldn't worry about it flopping around.


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## steven4601 (Nov 11, 2010)

My current levels are so low (300A) that only 20 x 0.5mm copper is required as cell links. (0.787 x 0.02")

Perhaps a slightly thicker piece might be good idea for longer runs. 

Thank you for the link/picture


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## EVfun (Mar 14, 2010)

I'm thinking that 500 amps out of a 40 amp hour CALB cell is quite likely to result in a dead cell. CALB specs them for up to 10 C peak for a matter of seconds at at time.

I was accused of brutality when I started discharging my TS cells at 5C peak. I still haven't gone past that point (yet.)


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## DavidDymaxion (Dec 1, 2008)

It seems one can pull much more current from the small cylindrical cells than the big boxy prismatic cells -- maybe the smaller cells shed heat better?

I've read the big prismatics will only do a big burst of current for a very small number of seconds, but the small cylindrical cells can do 10C for minutes.

If you don't need the big currents the bigger cells certainly have fewer connections to worry about!


Yabert said:


> Hi
> 
> After a quick looking on your design, I wonder why you do not choose Calb 40Ah cells rather than 3x HW 38140??
> 
> ...


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## bruceme (Dec 10, 2008)

coryrc said:


> Ah. Yes, he uses 0.062" copper which is plenty stiff.


fyi, very solid. 0.032 is typical light aircraft skin... 0.062 is almost plate thickness.

-Bruce


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## Yabert (Feb 7, 2010)

steven4601 said:


> Here's a comparison sheet i made to help making the selection. Maybe the 5mOhm figure is wrongly assumed, as I never measured it personally but found it on the internet.


Hum!????. Less than 1 mohm.... http://en.calb.cn/Product/?id-115.html


I personally recorded 3-4 mohm on my HW 38120S and I'm happy with....
But each time I work on my 400 cells battery pack, I think at a 48 larger cells battery pack.... Much more easy to build!
Especially since I discovered the "new" Calb 70Ah with his impressive specification: 90 Wh/Kg, 162 Wh/L, 700A peak.

I'm impress by the Calb cells (valerun claim he have 850-900w/Kg 100Ah cells) and if I had to start a new project, I probably go with Calb instead of Headway.

It's why I asked you....


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## steven4601 (Nov 11, 2010)

Hi Yabert,

IF its truly 1mOhm with a DC current load ill be gutted though . 

But im quite sure it isn't 1mOhm  The datasheets also adds the note [email protected] 1kHz , They are measuring the parasitic capacitor and its ESR, which proofs their electrical conductivity is perfect. 


Maybe you order first a sample order of 4 cells and see how they perform under load? Measure voltage under various DC loads? 

//Steven


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## Yabert (Feb 7, 2010)

Too late, I currently have the 400 HW cells.
I choose it for her good Wh/L and W/Kg spec... My battery pack is really tight and I need high power for short time.

But you? Why do you will pay more? 
Do you need continous high power? You don't have lot of space for your pack?
Why do you choose Headway?


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## steven4601 (Nov 11, 2010)

I also want/need 100kw for a short period of time (60 seconds)
smaller, lighter, more surface area for cooling and not much dearer at all.

Have you seen the screendump from my calc-sheet? That sheet helped making choices as it shows how much power can be drawn from the pack as a result of voltage sag.


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