Potting Batteries, Thoughts and Experiments

[spinningmagnets]

Part of the reason I am following this is that I think it is not a horrible thing to only have to replace a 5P "sub pack" instead of keeping the ability to open and replace a single cell in a string.

There is a market for a loose-cell pack like the NTS/snath-style box. When the cells wear out, dump them and slip in new loose cells. One cell goes bad? find it and swap out. However...in the real world I think those benefits are over-hyped (no problem if that is your thing). If I had a pack made from 12 series-ed sub-packs (each 5P), and one cell in one sub-pack went bad? It would be very sweet to be able to just unplug and swap-out one 5P sub-pack...$3 cells X 5 = $15, maybe $40 retail? This would be a real boon to ebike shops and ebike rental outlets...

The same process and assembly line could be used to make 1P/6S packs for powerboards (or any other combo that works for any particular customer demographic...)

 

[MrDude_1]

I am assuming the resin is fairly rigid, and I believe this is leading to the failures of the first test. The advantage of using a plastic case (like Bosch) is that the case is somewhat disposable in favour of protecting the cell. Like in a car, it is the crumple zone for an impact test. Following the rigidity assumption, the potted battery has no give, no area to take the impact. Accordingly, in the absence of kevlar arguably it is transferred to the battery/ cells. A fairer comparison would have been to cut down a Bosch case, suspend the same number of cells within it and drop that. I suspect the case will be destroyed but the cells will survive.

You know, I just had a thought about this... You just need two molds. First make one mold to pot the batteries in a softer silicone like layer.. thats compressible. and absorbing. and you could use standoffs to make holding/assembly easy as pinholes are not a problem.. because.
you take the now silicone potted batteries, and pot them in the polyurethane resin (or whatever it is hes using)... that would make a hard, protecting outer shell. use different standoff locations from the first mold, and you'll have a sealed pack.

 

[Hummina Shadeeba]

Maybe it wasn't written about but there didn't seem to be any attempt to keep the gas release valve in the potted cells intact. I imagine these cells had their valve filed with solid resin and luckily, somehow, were able to release the pressure and not explode in this experiment! In my looking for exploding cells it's rare to happen but when it does it can be very powerful.

In the video the cells are described as gassing and it seems to happen pretty abruptly but I can't tell where the smoke is coming from. It does seem to come from the bottom of the pack which is showing to be very hot.

And the guy using his t-shirt to keep the fumes out... not as bad as having epoxy shrapnel in you I guess.


https://batterybro.com/blogs/18650-wholesale-battery-reviews/19043075-understanding-18650-explosions-with-mount-st-helens

https://batterybro.com/blogs/18650-wholesale-battery-reviews/18306003-battery-safety-101-anatomy-ptc-vs-pcb-vs-cid

maybe I'm wrong and potting them completely without any provision made for the vent is fine but at this point it seems too unsafe and I'm trying to figure a way to cover my valves with coconut oil and then melt it out through a release hole

 

[methods]

And this is why Justin owns the board
Thanks for the transparent engineering effort Justin. Great video. Keep up the good work.


Jozzer brings up a really good point... Recycling, Up Cycling, Re-purposing, rebuilding, binning, salvaging....
I hate the future where our landfills are full of chunks of epoxy full of precious goodies.

Potting is an excellent stop gap measure for low volume high reliability solutions in early development (Justin's tooling costs are noted).

What we eventually converge on?
I like the individual fuses on the Tesla cells - not sure if the benefits scale to 1P that well.
I like the idea of really advanced foam and rubber around the cells creating something more like a rubrics cube-super-bounce ball than an ice cube.
I really, really, really, really, really like the idea of being able to remove 8 fasteners, drop out any weak 18650 cells, pop in a few new ones (mix and match) and get back on the road.

We can make a seal that is good enough. Where not good enough we can pack with desiccant.

thanks,
-methods

 

[Hummina Shadeeba]

Maybe these cells are a safer chemistry and don't have a gas vent. I read the IMR chemistry doesn't use one. I read that if ur at the point ur cells are releasing gas your on your way to runaway anyway. Still seems like potting in hard material could make a bomb though.

 

[redilast]

Maybe these cells are a safer chemistry and don't have a gas vent. I read the IMR chemistry doesn't use one. I read that if ur at the point ur cells are releasing gas your on your way to runaway anyway. Still seems like potting in hard material could make a bomb though.

It seems like this could be easily avoided by putting small blowoff caps on the vent side of each cell. Then if they do need to vent they still can release their pressure without having to blow up all the potting.

Another idea would be to put some additives in the potting material to help cool and heatsink the cells. Maybe mixing in some aluminum oxide or something similar?

 

[spinningmagnets]

There is a recipe around here somewhere for "phase change" material. It turns from firm to "play dough" consistency when it absorbs heat. A thin layer of that between the cells and a hardshell would be a sweet setup...

 

[Ianhill]

A non flammable wax may be a good choice.

 

[1JohnFoster]

Maybe these cells are a safer chemistry and don't have a gas vent. I read the IMR chemistry doesn't use one. I read that if ur at the point ur cells are releasing gas your on your way to runaway anyway. Still seems like potting in hard material could make a bomb though.

With potted (or even just cased string) Li batteries you could build in a pressure "fuse". Might be hard to design reliably. Would not want to imply to noobs like me who charge with anything that a battery is foolproof.

I somehow acquired these Panasonic VRLA SV-1's a long time ago, but could not find docs.

Always wondered if the 1/8" hose barbs were for daisychaining to a pressure switch that was supposed to shut down charging.

 

[Punx0r]

They're for a vent hose

 

[Nordle]

Is it allowed to carry multiple (<100Wh) packs on a flight?

 

[1JohnFoster]

They're for a vent hose

So just to direct the gas and spew out of the battery box?
Are vent hoses ever used to sense over-charging?

These are AGM so not supposed to vent a lot.

 

[Punx0r]

They don't look like VR/AGM, but if they are then the vent is probably for if/when it vents to safely direct gas/electrolyte.

 

[redilast]

Is it allowed to carry multiple (<100Wh) packs on a flight?

https://www.faa.gov/about/initiatives/hazmat_safety/more_info/?hazmat=7

Seems to indicate there might not be a limit for batteries <100whrs as long as they are for personal use and not for resale or not customer samples. But with airline approval you can carry 2 spares in the 101-160 Whr range it appears.

 

[Hummina Shadeeba]

Potted 18650s with compression and copper strip. 12s4p. Plan to balance and monitor simply using an altered voltmeter that I'll connect to cells through small drill holes in the side. Have to figure out how to get a cheap voltmeter to discharge more energy though. Replace the resistance in the device I guess.

Made a 90a duro rubber stray. Added connections and batteries. Squeezed it all with duct tape and poured a layer of the same rubber.

Not as nice looking as id hoped and I'm still at risk of bottoming out my dropped thru drop deck but at least they aren't lipos under there now. And I now have about a 25 mile range

Benefits are not having to spot weld or solder, Using copper strip is more conductive, the battery flexes and can dampen vibrations from my stiff deck
I'd read from one person on here (liveforphysics) that compression connections were lower resistance and I took that at face value and tried.

Stilly have t cleaned it up, filled in the gaps at the end where the board's curve is too much, and was going to add a painting of a hard layer.

This too too much work and was a three pour process. A better mold could've been made that would make a tray that would have holes in it so then could skip the final gluing of the parts to the deck.

I won't do it this way again and want to simplify it and incorporate the batteries into the board and do the potting there. Then, with the vescs and hub motors and my nice remote..ill have to take up another hobby

 

[LeonardoJanus]

Are resins current conductors while solidify?
I would prefer mechanical holders and modular system with parallel sub-pack. 8) 8)

 

[spinningmagnets]

Most randomly-selected epoxies are NON-conductive. The potting on this is specifically selected to be especially non-conductive.

 

[justin_le]

Is it allowed to carry multiple (<100Wh) packs on a flight?

My record so far is 6 pieces, but the security person went to double check with their supervisor who didn't seem 100% sure of things but let it go. Any time I've had 4 or less there has never been a hint of an issue.


I'm very curious to hear about other people's experience in this area, but myself I've been really surprised at how little of a hassle it has been.

 

[LeonardoJanus]

Most randomly-selected epoxies are NON-conductive. The potting on this is specifically selected to be especially non-conductive.

When solid or even when liquid?

 

[Hummina Shadeeba]

The 48 cells I potted above I can ride and not lose connection and all seems good except on the Meanwell charger with an inline watt meter it will jump voltages from say 47 to 49 or back. im guessing some of the parallel connections are coming in and out of circuit. ?
Regardless I don't like it anymore and am cutting them all out and do something else. i had to see if I could make pressure connections with rubber poured in tension. I'm now looking for a highly conductive pressure connection that can withstand The extreme vibrations of a skate deck

 

[spinningmagnets]

My record so far is 6 pieces, but the security person went to double check with their supervisor who didn't seem 100% sure of things but let it go. Any time I've had 4 or less there has never been a hint of an issue

If travel is the big issue for the customer demographic for these packs, I recall that Japanese tourists were pioneers in developing a travel-agent administered system where tourist baggage was shipped ahead of time from their home to the hotel destination. Customers would have a verification that their luggage had arrived before they left on vacation, and hotels were happy to provide this service. Airport check-in and arrivals were fast and convenient with no waits at the baggage pick-up.

There is a small difference between shipping a lithium battery pack on a cargo plane, and carrying one on a flight full of people, due to safety concerns. It would certainly be an inconvenience to take the time and effort to ship batteries ahead of time on a cargo plane, but I am curious as to how much of a difference there is...

 

[Peregrine]

Is it allowed to carry multiple (<100Wh) packs on a flight?

My record so far is 6 pieces, but the security person went to double check with their supervisor who didn't seem 100% sure of things but let it go. Any time I've had 4 or less there has never been a hint of an issue.

I'm very curious to hear about other people's experience in this area, but myself I've been really surprised at how little of a hassle it has been.

Yes, according to FAA rules there is no limit as long as each pack is <100Wh. They do have to be in your carry on luggage, not allowed in checked luggage at all.

The most I've personally carried was 15x RC airplane batteries, 60 Wh each (3s lipo, 5600 mAh). TSA asked why, but no further questioning. I got to take all of them with me; did it a few times.

The only battery I've ever had confiscated was in China, I had a cell phone recharging battery (~30 Wh) that didn't have a label on it. So be sure to have a label, or print one up before hand and make it look professional.

There is a small difference between shipping a lithium battery pack on a cargo plane, and carrying one on a flight full of people, due to safety concerns. It would certainly be an inconvenience to take the time and effort to ship batteries ahead of time on a cargo plane, but I am curious as to how much of a difference there is...

Shipping lithium batteries legally is quite a pain. It requires a hazmat shipping license and then can only be carried on non-passenger flights. This makes things pretty tricky actually as a lot of cargo, especially international air cargo, is carried by airlines in the baggage space that isn't filled with luggage. I don't know what percentage of air cargo it is, but I do know that airlines sell unused space to cargo companies.

 

[Hummina Shadeeba]

Luckily( excuse me god if you're listening) cells are getting safer. What's the safest Li-ion higher amp cell? I think the lg hg2@
As long as your not charging on the plane so u can run ur hover board on the plane shouldn't u be safe?

 

[Alex W]

Justin: is there any news on productizing these? A friend is working on a bike that these would be ideal for. I noticed that the non potted small packs are out of stock with no return date on your site.

thanks,
Alex

 

[justin_le]

Justin: is there any news on productizing these? A friend is working on a bike that these would be ideal for. I noticed that the non potted small packs are out of stock with no return date on your site.

Hey Alex, yeah we decided to do a fully home-brew BMS route rather than trusting a 3rd party BMS supplier for this project and have just dialed in the final touches on that. Here's a bunch of the panelized boards right after firmware programming this afternoon. You'll notice five RBG addressable LEDs and an push button, plus if you look really closely you'll spot a bluetooth antennae



We're hopeful to get all the rest of the manufacturing ironed out to release before the end of the year. We've been sitting on 500 10s x 1p packs made up of LG-MG1 cells for a while that are just waiting to get built up into these stackable modules, and I'm keen as anyone to get them in people's hands and ebike projects!