Lithium-Ion Battery Pack Architecture

[mark512]

I'm looking at the design shown in this video:

https://youtu.be/bn0KtdrpoEM

I've drawn a schematic of how I believe it works:

Essentially it's a bunch of circuit boards, with each circuit board having a string of cells in series. The boards are stacked using standoffs, which also serve as bus bars to connect all the boards in parallel. There is also a colored ribbon cable (shown at 11:00 in the video) that plugs into all the boards and connects all the corresponding cell taps together and to the battery management system.

From what I understand, it's best to first connect cells in parallel, and then connect the paralleled cells in series. This design sort of does that, but all the cells are paralleled via the ribbon cable which has very small diameter conductors. It definitely doesn't look like they could handle the full current that the cells can produce, but I'm not even sure how to estimate the current that those conductors would carry. I'm trying to evaluate this design, and that's where I'm stuck at.

Thanks in advance!

 

[IRstuff]

And you don't have any EEs in your company?

While it's bad form as far as I'm concerned, it looks like the main power flow is through the standoffs; I think the ribbon cable is for monitoring the voltage balance of each board.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[itsmoked]

The wires in that ribbon cable are good for about 1A. That's it.

However, if you look at his Populating Jehu's DIY Powerwal PCB v1.3 video you will see that he's fused every battery's connection to that ribbon cable.

Some of Jehu's designs are a little... sketchy but I'm subscribed.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[moltenmetal]

The RIGHT way to build a pack is to create a number of large parallel groups of cells (which act as one large cell), then to arrange THOSE in series. A BMS channel monitors the voltage of each large cell.

Yes, you can cheat and arrange prefabricated groups of series cells in parallel, with BMS channels effectively acting as short circuits between individual cells in those series groups. And yes, you MUST fuse every one of those BMS wires if you want it to be safe, because if a cell were ever to fail, the currents flowing through those BMS wires would be substantial.

Jehu Garcia has at numerous past times, advocated the use of high energy density Li ion cells WITHOUT a BMS, which is a totally unsafe practice which risks fire, injury and possibly even death in my opinion. I'd take anything that guy says with an appropriate measure of salt, varying between a teaspoon and a front-end loader bucket full.

 

[mark512]

Thank you all for your responses! Sketchy design suspicions confirmed.

The RIGHT way to build a pack is to create a number of large parallel groups of cells (which act as one large cell), then to arrange THOSE in series.

Excellent. I was under the impression that that's the right way, but given Jehu's popular videos/kits, I was wondering if he might know something that I don't, but clearly the answer is NO.

 

[IRstuff]

Popular is not the equivalent of right.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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