Reconfiguring a "standard" Headway pack

Lock

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Guess I'm gonna pick up one of these:
http://www.evcomponents.com/ProductDetails.asp?ProductCode=H4810
Headway_H4810-2T.jpg

...thing is, I need to reconfigure the pack into one pack w/each cell laid out side by side in one row. So one long skinny pack less than 2" thick, `bout 6" wide and about 2 feet in length...

Not sure whether the supplied plactic holders can be chopped up and pressed into service and don't much care...

What I am curious about is the wiring from each cell to the BMS... Some of the wires as supplied will need to be lengthened (replaced...) And would wires of significantly different lengths affect the balancing process? My gut sense is telling me that all the wires should be replaced with one standard length that's long enough for the longest length needed, and the slack in the rest of the "too long" wires just be left alone as that...

But... does length (different lengths mixed together) really matter?

All thoughts appreciated!
tks
lock
 
Thank you sir! ... seems an awfully good price for 48V 20Ah? Perhaps the pic doesn't match the product being offered... I count 16 38120S cells though?
Splitting the pack in 1/2 doesn't give me the form factor I need though (less than 2" thick)... still need to know about wire length but will just go with all the same length just in case
Cheers
Lock
 
i recognized the 4 hole plates they used for the 20Ah packs, what you get will look the same except the 4 hole connectors will be 2 hole connectors and only connect 2 batteries instead of 4.

and different BMS for 16S on your pack.
 
Lock,
I'm with you on this, I want this pack, but not in a square. I'm digging around and I'll keep watching this thread, if I find any info I'll add it here. :)
 
I believe the answer to your question regarding balancing wire length is, as usual, "it depends". Looking at a real world example:

27 gauge balancing wires having resistance of 0.0043 ohms/inch.
An A123 pack having a difference in balance wire length of 13 inches.
A Fetcher/Goodrum BMS has a balance current of 500mA.
So, (0.0043)( 13)(0.5)= 0.028V difference between the closest and furthest cells.

Obviously, with larger diam balancing wires and/or a reduced balancing current, the length difference will not have as great an effect.

If you use 12 gauge wires for balancing and 200mA balancing current, this voltage difference shrinks to 0.3mV.

Eric
 
use 24G for the sense wires, 12G for the jumper between the 2 halves and wait until the pack is assembled and in place before running the sense wires so you can then fit them to the space you have. length is not important. the shunt balancing current is about 180mA so the voltage drop is not significant in any case.
 
dnmun said:
you could do somethng like patrickza did with his kona kahuna build, since you have even more space inside the triangle on the surly.

Exactly what I was thinking.
 
...use 24G for the sense wires...length is not important. the shunt balancing current is about 180mA so the voltage drop is not significant in any case.

Thanks all. I expect to replace the sense wires, so might up the 24 gauge only a couple of notches (thicker) just thinking it might make things a bit more robust for all future vibrations and handling... I am only interested in erroring on the side of "over-built". :)

Cheers
Lock
 
sense wires don't really need to be large, they only carry current when the cell is bypassed so no matter. i don't know the size of sense wire on the headway BMS but 24G on pings is enuff for you too i would expect. don't let the sense wires rub and vibrate on sharp metal edges, headway uses those anti chafing sleeves for protection, but just dabs of silicone rubber to hold the wire in critical spots would be fine.
 
Thanks dnmun and Eric for the info, and thanks Lock for bringing up the question. I ordered one of these packs today, can't wait to dig into it.
 
Certainly a very attractive package for the $. If I got one I would have to reconfigure it as well, but even more extensively.

I have what I think is a silly question, but since I am new and inexperienced I thought you all might cut me some slack :? ... I need to eventually set up a 16 cell 8s2p system. Would there be a way (not overly complicated) to modify the BMS on this pack to function for a 24 V system? I imagine the difficulty would arise with the overall voltage cutoffs that the board is pre-designed and built to function at.

Secondly, I wonder if there was way to bypass some of the BMS features and simply employ the balancing features for the pack using this board. Any feedback along these lines would greatly appreciated. :)
 
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