potting compound for batteries

[goatman]

no I didn't miss that part about air, I figure with this battery hanging upside down under the bar that in order to create heat the throttle will be cracked wide open and if the throttle is cracked wide open there will be a lot of air being forced through the straws. kind of how a radiator works for cooling the motor on a vehicle.

13s ill have 24 or 36 straws perforating the battery vertically, 4p will be 3 or 6 straws perforating horizontaly. I believe that will be way more cooling than a battery in a hailong case or a battery wrapped in neoprene and heatshrink stuffed in a waterproof battery box. I have 2 other batteries that will be going in box and my plan for them is plasti dip the battery ends so its pretty much waterproof and that's it like the member above mentioned, if the plasti dip works, I didn't find liquid tape today but im heading to port moody tomorrow, there should be a marine store somewhere there, I guess people that fix boats swear by liquid tape

 

[john61ct]

OK, if no enclosure, way I'd go maybe, just pot the cylinder ends, leave the full air gaps from the inside sections.

Plastic mesh like strong pet screening for the sides to keep crud out?

 

[goatman]

OK, if no enclosure, way I'd go maybe, just pot the cylinder ends, leave the full air gaps from the inside sections.

Plastic mesh like strong pet screening for the sides to keep crud out?

no this battery will be solid plasti dip perforated core, mud could be an issue, good point.

 

[goatman]

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took 3 days and almost 2 cans of plasti dip to make it a block, im going to re wire it tomorrow and test it for heat before going any further. I would never plasti dip the core again, too time consuming and too expensive but plasti dipping the ends was quick and easy. I plasti dipped the bms.
I think punxor? mentioned cooling the battery with copper bus bars. ill see how this works but now I have a plan for my next pack. bus bars, kapton tape, aluminum heat sink and plasti dip. also I think you need to get rid of the plastic wrap on the 18650 if you want to cool the cells

 

[Vbruun]

Just use building silicone. It is really cheap and plasty enough to go in if you make the right kind of tool for it.

 

[goatman]

can anyone share what they are doing to pot a battery?
I use cell holders so I can fill the cavities easily enough
do you need to seal the positive end of the 18650 with silicone first?
I was thinking of just taping off the sides with electrical tape, putting it in a mold and pouring epoxy over the entire battery but I don't know if that's a dangerous stupid thing to do

what john said, I poured plasti dip on the battery ends it doesn't short out the cell and if you look at bike builds page, Marin wild cat trail you can see how the plasti dip peels off. im really liking the plasti dip for the nickelstrip and wires but not for the core another compound yes but I don't know what

 

[goatman]

sorry not the marin build, scorpion fx build thread, if you use plasti dip do it outside or you will get real stoned from it.

 

[goatman]

I wouldn't use plasti dip for potting the core but the straws worked perfectly, I put a flashlight in a box turned the lights out and it looked like 36 leds but my camera is crap, what you see in the pics is what the entire battery looks like.

 

[goatman]

to test the battery I used my DMM, its cool outside and I wanted to see how warm it would get so I wrapped a shirt around the battery and put it in the case and closed the lid tight.

78f as I took it off the charger

after 3km, no pedalling, the battery 13s4p /18650pd 10 amp cells running at about 1000watts/35km/h up slight grade.

after 10km no pedalling and upto 1500 watts, 102f/38c

after 10 minutes inside the house

wrapped in a shirt, stuffed in a box with no airflow it definitely gets warm using it at 30 amps. ill try it again with no shirt but still in the box. the battery temp after being inside for 2 hours was 80f.

 

[goatman]

same test but no shirt starting temp was 77f

after 3km

after climbing a medium grade for 1km at about 9km mark

got home at 10km mark after riding on a flat stretch

after 5 minutes inside

atleast the temperature was able to start dropping while it was being used, next ride ill expose it to the outside air

 

[goatman]

these were recycled cells and they were at 29 volts
time to see if its repairable

get a section started



and peel it back



nice and clean but it ripped all the bms wires off



close up of the plasti dip



6 parallel groups were at zero, panasonic 18650pd self discharged over the winter but

cut wires and snap the corners off



trim the wrapper on negative end with razor



push on positive end with insulated plier handle



bobs your uncle



pull wrapper out and there was a void in there



put in new battery





totally fixable but this pack isnt worth repairing, i have another 17s3p pack of these cells that are self discharging

 

[Hummina Shadeeba]

what about the gas release valves being sealed with resin is that a possible danger and maybe it depends on the cells?



And will heat be more so contained within the pack with the resin working as an insulator?


ive been using some relatively hard transparent polyurethane to pot cells and it seems good but I just got some less powerful cells that get warm easily and i wonder if they're not a good candidate for potting.



in this pack above you were repairing...how you know which cell is faulty as theyre in parallel?

 

[goatman]

those were salvaged cells that would have seen 5 amps max

if an entire p-group is at at 2 volts or less theyre garbage

people say potted batteries cant be repaired, thats why i showed that they can.

the phaserunner has 2 potting compounds
1 for the electronics and 1 for the shell
what if used an aluminum base plate for mounting and as a heatsink?

i think the vent depends on the battery
i really liked the 5000mah mnke 26650 til i saw this youtube, it blew up even though it was venting
https://www.youtube.com/watch?v=nL2TT3darhY

if lunas wolf had their compound for the battery and then something like plasti-dip sides, it would easily be repairable
too bad somebody doesnt sell something like that

 

[Hummina Shadeeba]

How u know if a cell in parallel is bad though and it can be charged and will show the same voltage as the others in parallel? It’ll be a weak group but unless disconnected I don’t see how you’d be able to know.

 

[goatman]

it drags the whole p-group voltage down
if that happens you snip the parallel connections
some cells might bounce back in voltage and the bad ones will stay at 0 volts
but once a cells been drained down i believe its days as a high amp cell are done

i bricked a 25r pack down to 0 volts by leaving a watt meter connected for about a month
brought them back up to full charge
some almost went thermal, they were toast
then i made a 13s3p range extender with the rest and lost a p-group pretty much spontaneously
no fire, smoke or heat, just 0 volts
couldnt handle amps
then i made a 5s7p pack out of them for my ryobi circular saw, i think that was 2 years ago and theyre working perfectly balanced and happy today

 

[GoldenBunip]

Bog standard water clear polyester resin works just fine. You make a box out of the type of plastic it doesn't stick to. Mix up the resin and pour it in. Peel off the plastic and you're done. Could probably do just the ends to save weight.
https://www.ebay.co.uk/itm/324717856674

I made this with a 10S5P battery and it worked a treat. fully waterproofed. I tested it by putting it in a bucket of water overnight (left the XT90 out of the water) and it was fine. This was my first attempt, so it's a bit thick.

Eventually, the BMS failed, but that was because the block fell out of the quad it was on and probably got run over. Was quite bashed up the next day when I found it. Recovery the cells, and confirmed it was the BMS, by smashing the resin off.

 

[Hummina Shadeeba]

I think it’s safer to use a soft resin. Something that allows slight expansion.

 

[GoldenBunip]

I think it’s safer to use a soft resin. Something that allows slight expansion.

What expansion are you thinking going to happen with steel wrapped batteries!!
Hint, if it’s any, that battery is f’ed.

Thermal conductivity of polyester resin is quite good at 0.15 to 0.4 W m-1 K-1, (water is ~.6) so it conducted the head away well, whist it’s specific heat is 1/4 of water it’s still 1000times that of air.


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[Hummina Shadeeba]

So I’m told by people who sell the resin for potting batteries. I forget what duro but not so brittle that u can crack it. So they tell me. I think 60D

https://www.researchgate.net/publication/283720424_A_novel_thermal_swelling_model_for_a_rechargeable_lithium-ion_battery_cell

 

[TrotterBob]

What expansion are you thinking going to happen with steel wrapped batteries!!
Hint, if it’s any, that battery is f’ed.

18650 batteries have aluminum shells, as do most cylindrical cells. And they have a safety vent in case they are overcharged or suffer an internal short. Potting cylindrical cells in a hard resin could be a potential bomb if something goes wrong with the cells and they have nowhere to expand or vent.

I couldnt find anything on li-ion or lipo cells, but I do know that LifePO4 cells naturally expand by 1 to 3% when fully charged. It isnt much and the pressure of the aluminum case provides enough pushback to prevent the cells from deforming under normal circumstances, especially with cylindrical cells.

Potting 18650s in a soft material or doing a partial potting might be a better idea vs encasing them in a hard resin.

 

[GoldenBunip]

My original plan was to just pot the ends.... but then ended up just filling the whole lot.
I did pot the BMS with the cells to prevent any overcharge bomb-making :wink:
The force of a venting cell would break the resin - Humm I'm typing that without proof... I do have a lot of resin left and some spare cells. I feel a vital experiment should be done.

Was a test battery anyways. Quite liked the clean look, with the cells and welds visible, which was the point for the bike I was building before other projects came along.

TBH it's easier to just make a box and put packaging foam in it, which is what my current batteries are. Also much much easier to fix/mod/add to.

 

[john61ct]

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 

 

[Hummina Shadeeba]

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

It’s a pretty hard resin still. Could’ve used less

 

[GoldenBunip]

That looks sweet.


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[Chalo]

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.