Terminating the 15Ah and 20Ah Cell-Man cells

[jonescg]

Hi guys,

After checking out the removable battery pack Dainel (Ripperton)had, I was inspired for my next electric race bike. I still want to go with A123 cells, especially since I will be able to source them through TTX-GP. I figure I could use the poly acetal plastic that Daniel has used, and opposite-stack* the cells to give me a bit more room to tension down the tabs using 2 mm aluminium and some stainless steel screws. Does acetal take a thread easily? Does it cross thread easy? I guess you could always seat some nuts into the plastic.



Since this is clearly a rip-off of Daniel's idea, I have no problem with sharing it for suggestions / improvements

What do you think?

EDIT: Should point out that I have drawn the cells in the left hand image just to show where they sit relative to the tabs. In reality all you will see is two folded up tabs with a bit of aluminium holding them down. The tabs would slip through 1 or 2 mm slits in the 12 mm thick plastic.

*this is what I mean:

[Malcolm]

I was looking at Ripperton's pack yesterday, trying to work out how those tabs were joined http://www.diyelectriccar.com/forums/sh ... 73p35.html

It looks as if those screws go through the tabs straight into the acetal block. I'm sure it would take a thread easily, but not so sure I would want to rely on it for consistent clamping, especially if you want to reconfigure cells any time in the future. Maybe use rivnuts/nutserts?

[jonescg]

I was thinking you could simply countersink / mount some nuts in the holes on the back of the acetal, otherwise, yeah, those screw-in-screw things might work OK.

I will eventually get a plywood mockup made of my idea. I reckon I'll need lots of cells in series to get close to an EMRAX's operating voltage However, that means a stack of 110 cells, or a cartridge about 840 mm deep Might need a small crane to lift them in

[Malcolm]

The countersunk nuts would work just as well and be cheaper/easier to install, but if I was building the pack I'm sure one of them would fall right into the middle of the pack just as I was finishing it. You could minimise that risk by making the nuts a push-fit into the recesses though.

Just looking at this photo again. Is that (nickel?) strip that joins the cells in parallel deliberately narrowed between the cells to act as a fuse? It's hard to make it out.

[CamLight]

It looks as if those screws go through the tabs straight into the acetal block. I'm sure it would take a thread easily, but not so sure I would want to rely on it for consistent clamping, especially if you want to reconfigure cells any time in the future. Maybe use rivnuts/nutserts?

I agree, metal inserts pulled in from behind would be a good idea here. If they can't be used, I recommend that the plastic be threaded for the largest bolt possible using UNC (coarse) threads, not UNF (fine), and should be as thick as possible (1/2" would be great).

Even then, you can't tighten the bolt too much. And, the plastic and bolt have very different expansion/contraction rates when heated/cooled and this will encourage loosening of the bolt over time. I recommend using a threadlocker compound. But, some aren't rated for use with such a slippery plastic so check the specs.

[jonescg]

Is that (nickel?) strip that joins the cells in parallel deliberately narrowed between the cells to act as a fuse? It's hard to make it out.

Nope, its all aluminium. It's only thickened in the middle to allow for a fastener to hold it down. There wouldn't be much need to have a 15 mm wide strip to hold each parallel section down if the currents aren't too high. Personally I'd make them a bit thicker, but maybe not a problem for my next bike since I will only ever be pulling a maximum of 300 A through the pack. But at 360 V that's a fair bit of power

[adriano-brazil]

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