Battery box for lipos

[j bjork]

I am building a box for my lipo packs for the bike.

I have some questions, mainly how much pressure is good to have on them?
I hope that will lower the risk of puffing to mont them with some pressure.

This is what the box looks like:

I also think it would be good to drill holes to the sides of the cells, to release pressure if a cell vents?

Where the hand points:

Or is it enough to have the top open?

I plan to use this rubber under the cells, and possibly between packs and aluminum where i can fit it:

I will use the other, flat side against the packs. But if I put pressure on it, it will still not be even distributed over the cell surface. Do you think it will be ok, or do I have to find something without the ribs?

 

[motomech]

I haven't had any bricks swell up in years. As I look back, puffed cells were probably more a result of my mis-treating the LiPoly (Dis-charging past the 80% rule), than anything else. I still wrap my bricks tightly with Gorilla tape for protection as I carry them stacked freely in a frame bag, I doubt the usefulness of pro-actively putting pressure on them, especially as this traps heat in the enclosure.
The other thing is, todays LiPoly is better than years past. I would justify this statement by the rarity of receiving bricks w/ bad cells from HK these days. It just doesn't seem to happen anymore, at least not w/ the Turnigy and MultiStar stuff I use.
The best pro-active approach to realize the best LiPoly service life, is the carry enough as to not have to go below 3.75 V or so.
Nice box, but overkill IMO.

 

[dogman dan]

All my cells have eventually puffed slightly, by two years old. Haven't had a puff failure in some time though, a truly contaminated cell.

I notice your cells run two ways in the assembly. Don't crush half of them flatwise, while crushing the others end wise. Looks like your box bolts up to do just that, apply pressure only flat wise. . shim to get the pressure you need on the packs, flatwise. Endwise, they can have all kinds of space. Looks like you have it snug, and that's fine. They will only grow flatwise as they swell in use. Limiting that is your goal. Most of this last paragraph is not aimed at you, but others reading who may not notice details.


Best lipo box ive seen. Really great work. It will heat sink nice in summer. But in winter, like simpler tight aluminum boxes I have made, it will definitely need a tea cozy or something to insulate, when the temps are below 50f. All that heat sink becomes cold sink if its freezing out.

No need to drill holes, if the cells need to vent, they will out the top. That would be most likely from having a paralleled pack disconnect, resulting in another pack discharging to 0v. So tape up all those plugs, or make hard parallel connections that cannot fail.

I have no numbers for you, but definitely squeeze them till they won't move while riding, flatwise. I would not try to make it smaller though, than the original dimensions. So what I mean is, if its 50 mm thick, don't make your box to squeeze them down to 45 mm. Just get them tight so they don't jiggle. Then it won't matter too much what is under them. Definitely do put something thick and soft under them anyway. Its amazing where a pebble can find its way into. Be harsh to find a rock in the bottom some day, wore a hole and ruined a pack.

 

[j bjork]

Thank you both

It will only be pressure on the flat side. It is 2 sets of packs, mounted in 2 directions because of space limitations.
They have one"door" each, and 3mm aluminum plate between them.

 

[dogman dan]

Yep, I saw that. Others with no experience might copy your box, but not quite right. That's the reason I talked about that. The only way I can see to improve your box would be more angles on the sides, just for heat sink, rather than compression. But that won't be needed unless you are racing and really hammering those cells.

 

[fechter]

Having the cells completely surrounded by aluminum might prevent flames from shooting out if the pack decides to go off. There should be a vent somewhere that aims in a safe direction.

 

[j bjork]

Hello, I thougt I should update a little of how it turned out.

I drilled holes to the sides, it was a lot of work to get them smooth on the inside..
I did´nt want any sharp edges possibly damaging the cells.

Pictures of an empty box. Seems like I did´nt get any pictures of what it looks like when it got finished.

A picture of it in the bike: