Covering 18650 cells with epoxy resin

Coming to build my pack and I'm just thinking up different ideas.

What would happen if you kapton taped connections to the cells then submerged the wrapped cells in epoxy and let it cure.

The kapton tape would act as your electrical insulation.
The epoxy would harden and prevent the connections on the cells from moving around.

Like in attached pic.

Sent from my CLT-L09 using Tapatalk

No need, epoxy is already insulating, in motors they use it in addition to motor varnish.

Guy in UK already does them to order.


Also makes the pack vibration and water proof. (Luna wolfpack is epoxy filled on the inside too.)

Oh wow, OK.

Does he spot weld them before though?

Sent from my CLT-L09 using Tapatalk

Hickbeard said:

Oh wow, OK.

Does he spot weld them before though?

Sent from my CLT-L09 using Tapatalk

Click to expand...

Yes it is spot weld like any other. BMS goes in and gets filled in too.

Argh. I was looking at alternative to spot welding. To use the epoxy to hold contacts in place.

I've found a few more older threads about it but none cover the connections. They're all SW.

Sent from my CLT-L09 using Tapatalk

Hickbeard said:

Argh. I was looking at alternative to spot welding. To use the epoxy to hold contacts in place.

I've found a few more older threads about it but none cover the connections. They're all SW.

Sent from my CLT-L09 using Tapatalk

Click to expand...

Only worthwhile alternative I know of is the vurzend 2, but you pay a cell density penalty.

I've got 14 of agnisium cell holders. Which are 5p. But I was thinking of going up to 10p.

I don't really want to spot weld myself. And am being tight in not wanting to buy the vruzend.

So looking at possible compression style ideas. If none are available I may see if I can get 14 more 5p 3d printed and double up that way.

I can get free materials through work so was looking to utilise that perk if possible.

Sent from my CLT-L09 using Tapatalk

Zero motorcycles fully pot their batteries in epoxy.

If you are considering potting for the water-resistance, maybe try a small 12V pack with silicone first. If your electrical connection method isn't working out, you can cut away the silicone and try something else with the cells. Epoxy is hard enough that dis-assembly later would certainly damage the cells and buses. If you end up being happy with the pack connectors and performance, you can build the final pack with epoxy.

A couple of builders tried magnets, and they worked fine, but interest died out. Pure nickel (and even nickel-plated steel) is perfect for the parallel connections. The current less than 1/2 amp under all conditions, and the high resistance of the bus material slows equalization.

For the series buses, nickel is OK for low amps, but I like copper. If a certain application is concerned about corrosion (near the ocean, with salty air), there are some suppliers now with nickel-plated copper, perfect for series buses, but...more expensive than simple copper sheet. Copper is 4 times more conductive than pure nickel, so a common 0.20mm nickel strip that is widely used for 10A peaks means that copper of the same size should be good for 40A peaks per cell.

The two thicknesses listed below will cut easily with scissors, and are still flexible.

0.20mm___8-mil__32 ga
0.25mm__10-mil__30 ga
https://www.riogrande.com/product/Copper-6-x-12-Sheet-32-Ga-Dead-Soft/132132

If you want to experiment, I would suggest soldering a fuse-wire to the positive end, which is quite robust and has several layers of isolation from the cells active material. The negative end is the part that is sensitive to heat, and that is where I would use a magnet to hold a copper ribbon onto it. There are cheap button magnets that have a hole in the center, and it is chamfered on one side so you can use a flush-head screw.

It's not technically difficult to make a compression box, so that when the outer side-plates are fully bolted down, the interior dimensions are locked into a precise distance apart. Once you have calculated the length of the 18650 cells and added the thickness of the conducting buses, there was a long discussion about what would make the best
"springs" to push the bus-strips onto the cell-ends.

My personal opinion is that the springs that push against the cell should not be used as an electrical conductor. The springs can be metal, and of course steel coil-springs/leaf-springs are cheap in every size, I just mean that the spring should push the bus-strip against the cell-end. We've all seen the small hobby AA-cell holders where the coil-spring is also the conductor, but those are made for devices and experiments that use less than 1A.

One of the most promising springs is a thin disc of closed-cell "Poron" foam. Think of it as a sponge that never loses its sponginess. Agniusm uses Poron foam.

No-solder/no-weld battery boxes
https://endless-sphere.com/forums/viewtopic.php?f=14&t=57810

Interesting. I have some of agnisiums strips with the poron. I might order a sheet and have a play. I have plenty of copper bus bars so was thinking of machining them down to 2-3mm.

Also got loads of nylon sheet. I like the spring idea so again might have a play with some ideas using a mix of magnet and spring.

All of this will be going in a peli case for time being so water proofing isn't a concern. It was just alternative method of connection.

I remember you saying about neodium magnets in your ebike battery article. I'll be honest I just kind of discounted that as sub par. I guess everything is sub par to SW.



Sent from my CLT-L09 using Tapatalk

Getting back to your original question about an epoxy shell holding the buses against the cell-ends. Heat/cold will cause expansion/contraction, and I don't think the epoxy would maintain a constant pressure. The cells and the epoxy might not expand/contract at the same rate...

Concerning the use of a magnet on top of a bus-ribbon. There is nothing wrong with other methods, but I am surprised at the lack of interest in them. If a button magnet is roughly the diameter of the negative end of an 18650 (I just googled 18mm X 4mm, with hole), I think most builders would be shocked at how strong their holding power is.

That being said, I also like Poron discs, but I would use two, with one on each end. Perhaps even a button magnet on the broad and flat negative end (solidly mounted, no spring or foam), and Poron over the positive bus ribbon?

This no-weld aspect is of **great** interest to me.

I agree that electrically insulating adhesive / potting compound cannot be the "hold contact" mechanism.

Compression force methods are fine, but IMO add too much cost and are usually in opposition to density, take up too much space.

Also the contact may be threatened over time by the normally violent shock/vibrations.

There are electrically conductive adhesives though!

Assume a #16 AWG tinned-copper stranded insulated (UL boat spec) wire with a flat 8mm "coin" gas-tight crimped onto the end.

Sure a Poron disk with a clamping force might be fine to hold in contact. Maybe do that as well, help reduce movement against shock/vibrations.

But what about a tiny drop of electrically conductive adhesive between the coins and cell ends, well clamped in place until fully cured?

You then have cells with a whatever-length of pure copper insulated wires coming off each end.

The physical case components now only need to do the less demanding "box in and hold in place" job, protect against excessive shock/vibrations, waterproofing etc

not be relied upon to keep those electrical contacts perfectly in place forever via compression.

And, by having a positive / negative pair coming off each cell, that opens up a world of possibilities.

Ability to make the buss xPyS connections outside the pack, perhaps swapping out for different voltages while leaving the physical case untouched.

Easily removed / replaced / upgraded BMS if any.

Use of dedicated balancers and/or balancing chargers, per-cell monitoring of SoH, resistance

easy replacement of bad cells over time.

And both low cost and space efficient.

The magnet idea seems promising but completely new to me.

Strong force, log-lasting can be sourced cheaply in the right size? Not conductive themselves or just used to clamp to a strip?

Links to past discussions and other learning resources would be greatly appreciated.

Mr Spinning Magnet Man,
Like that magnet idea but keep in mind that you relying on the copper being flexible. Paper or cloth might work better if it could conduct electricity. Copper is a wonderful easy to work with soft metal. I know this because I used to be a sheet metal roofer in one of my past lives. It was a fun life till I fell off some scaffolding.


Here is another idea from Doctorbass.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=51271&sid=2d46d98f0d67eac7824318b201fae3d9#p758973

Doctorbass said:

2009-2010-2011 ZERO MOTORCYCLES BATTERY ASSEMBLY METHOD:

One great and ingenious method that already was in use by zero motorcycle is to use copper braided strap with rubber ring to hold them on the top of neg and po of the cells! Then you can add a heatshrink to add pressure and avoid rubber to move.

Easy, cheap and easy to repair your pack.

for the rubber they used some bicycle tire rubber tube sliced to form some ring ! the advantage is that these rubber do not dry very fast and they are not too affected by moisture or temperature so they sustain pressure between the copper braided strap and cell tab very well!

Here is couples of pictures i took when i had to do some maintnance on a ZERO battery for a friend of mine. This battery was made to take 300A burst and i s a12P config meaning about 25A per cell tab and only holded by a rubber tensil pressure!
Please note that these are 26700 cells and each cylinder is in fact 2s1p ( 7.4V):

Doc

Click to expand...

Something gone wrong with copying the pictures? Will try a different method.










Looking for low cost braided copper? Try coaxial cable shielding? I got miles of it. Scrap place won't take it.


At the end of the day I think the best way to do something is the way that it is done, and that be spot welding nickel strip. I bought this from forum member riba2233
JP spot welder

Photograph by "Marty's Bad Lighting Photography Studio"

Never used it so I have no experience. Seems like a good low cost way to build a electric bicycle battery. 2 electrodes that you hold with 2 hands and a foot switch. Powered by a 12V car battery. Like the idea of a heavy 12V car battery because it will stay where ya put it on a table. Also because they are everywhere.

A discussion about using magnets to hold bus ribbon onto cell-ends has been moved here.

https://endless-sphere.com/forums/viewtopic.php?f=14&t=104405

The website ru.nkon.nl sells 18650 cells and they can tab weld metal strips onto each, then its easy to solder. It does cost extra.

Optional solder tags
U-solder tags. Note, production on demand, this takes on average 3 business days extra but might take up to 2 weeks! +€0.55
Z-solder tags. Note, production on demand, this takes on average 3 business days extra but might take up to 2 weeks! +€0.55

Shipping from them is usually 30-45 Euros, to Canada/USA.

I bought the exact spot welder as above but was unsuccessful in spot welding Nickel plated copper. It handles Nickel wonderfully though. I wonder how many amps, joules it takes to do copper and if the higher amps become a detriment to the negative side of the 18650?

This looks absolutely awesome.

Maybe this would also work with the premade tabs agnisium has?

I'll order some bits and have a play.

What would be the safety implications if one of the bands broke? Would it short out that particular parallel group?

Sent from my CLT-L09 using Tapatalk

john61ct said:

This no-weld aspect is of **great** interest to me.

There are electrically conductive adhesives though!

Click to expand...

https://uk.rs-online.com/mobile/p/conductive-adhesives/9185015/

Something like this john?

Sent from my CLT-L09 using Tapatalk

I got this guys tab welder, it welded good.
https://www.avdweb.nl/popular/spotwelder/diy-spot-welder

He has a new design
https://www.avdweb.nl/popular/spotwelder/spot-welder-controller-with-tft-display

Hickbeard said:

Something like this john?

Click to expand...

No, that's just a thermal paste