potting compound for batteries

[GoldenBunip]

I’ve posted this before but planning to do another and like to hear what you think. been good so far.

So far, sure. What do you plan to do to replace a bad BMS or a weak cell group?

Would you pot a tower PC? How about your home electrical breaker box? What I see is a repairable thing made unrepairable for no reason that makes sense to me.

You don’t. It’s a sealed unit.
For the pc analogy, it’s like a games console or MacBook.
On the upside there is no chance of any spot weld or wire coming off, or any water getting in.


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[Hummina Shadeeba]

I’ve posted this before but planning to do another and like to hear what you think. been good so far.

So far, sure. What do you plan to do to replace a bad BMS or a weak cell group?

Would you pot a tower PC? How about your home electrical breaker box? What I see is a repairable thing made unrepairable for no reason that makes sense to me.

I’m assuming the best and I think most batteries in our use are assumed good and rarely repaired. I think the likelihood of being damaged from not being potted vs the cells being damage to bring with and needing to be removed is a toss up but I feel safer on this end.
The next one I’m going to add wire’s for balancers externally.

Guess I’ll get the better version with capacitors https://m.youtube.com/watch?v=PZygp7DxpTM

 

[Chalo]

I’m assuming the best and I think most batteries in our use are assumed good and rarely repaired. I think the likelihood of being damaged from not being potted vs the cells being damage to bring with and needing to be removed is a toss up but I feel safer on this end.

I repair batteries frequently for pedicab drivers, and once in a while for e-bike owners. Some are beyond help, but a majority are fixable. I've never done one that failed from external cell damage. It's always bad BMS or dead cells, or both.

Most of the ones I can't feasibly repair have pouch cells that are glued together into a lump, such that the dead cell can't be extracted (and direct replacement cells aren't available to me anyway).

 

[Hummina Shadeeba]

A bad bms sounds dangerous. I feel safest with external balancing and I can monitor cell health. If a cell fails its a loss and can’t repair it but cells are so cheap these days.

I feel guilty making these potted batteries in a resin that can’t be melted down to extract the cells later and while sinking them in ABS would allow that, and the melt temp of abs likely won’t be damaging, it’s still a bigger production melting it down and pouring it. ..and I have another gallon of this same stuff still.. but I think potting in abs, if it’s not too stiff, sounds the best.

 

[Chalo]

A bad bms sounds dangerous.

Well, most of them cut off the pack when they go bad, which isn't dangerous. But a few of them drain a cell group (or groups) after that, which can become dangerous later. I try to convince these guys to deal with a busted pack right away, rather than after letting it sit in the corner for months, but they are running hardscrabble businesses.

A solid majority of dead BMSes I have replaced were the victims of an accidental short circuit on the output. Because you can't make people not do dumb things.

 

[TorontoBuilder]

Yes I'm looking for structural strength, but also elastomeric flexibility to help absorb shock.

Not concerned about heat conductivity, but dielectric insulation of course AMAP.

I think the ideal would be the stuff Crocs are made from, aka "Croslite", closed cell polymer, some say EVA (ethylene Vinyl-Acetate) ?

Also the stuff Vitamix uses for their flexible lids, aka thermoplastic rubber 

I've made a few pieces of custom test and datalogging equipment with ICs and battery packs set in pelican cases that I poured dielectric clear silicone gel. Once the material sets it provides great shock absorption and yet you can easily remove the set gel or stick probes thru the material. I plan to make batteries in a similar fashion, except I'll use a custom made case with sides that come off.

I'll lay the pack on stand offs in the case and pour the gel around the case. with 3/8" clearance it wont take a lot of material and yet it will insulate and protect the pack

 

[john61ct]

Link to a good source?

 

[Chalo]

Link to a good source?

Smooth-on is the usual source for such things.

 

[john61ct]

Link to a good source?

Smooth-on is the usual source for such things.

> translucent platinum-cure silicones such as Dragon Skin[emoji769] and Ecoflex[emoji769] products.

> Slacker[emoji769] will change the “feel” of the silicone rubber to a softer and more “flesh-like” material. It also alters the rebound properties of the silicone, making it feel more like human tissue.

Eeeww

 

[Hummina Shadeeba]

Platinum cure silicone is the most expensive and don’t think would offer any benefit over tin cure (maybe should do a test to make sure the battery doesn’t inhibit cure). Maybe both would have less thermal conductivity than a urethane resin. If u want a more rigid structure the silicones only go to 60a and will have a much higher viscosity when pouring something like 60a than urethane resin. Some of the silicones are so soft as to not add any structure and can become easy to rip when the material is thin (I wouldnt go under 80a duro myself). I think best and cheapest would be 80a or harder urethane poured in a Vaseline or coconut oil (mold release) covered plastic box. Going 90a or harder you can really reduce the amount of resin to be lighter and it’s going to be solid and strong. I think 60d is maybe as hard as you want to go for thermal expansion and bangs aren’t going to crack it.