Silver epoxy instead of soldering?

[Sunder]

Okay guys. At my wit's end. I've built one pack from scratch before, and repaired two packs... And I've never come across this problem.

Tried to assemble my 9S packs into 12S packs. Remove all the unnecessary bits no problem. Come to join the packs together, and I flux, I sandpaper, I file, I use a razor blade to cut a cross hatch on it, I degrease, I try to pre-melt solder onto the tabs before joining... Nothing works for one of the tabs. Solder simply balls on this tab while it sticks to pretty much every other tab.

I'm the first to admit that I'm not a pro-solderer. However, I've never come across this. I'm using a nice strong 65w iron, and it's always worked for me for every other pack.

What do people think about using silver (conductive epoxy) for intra-pack joins. Will it conduct well enough?

Thanks in advance. At this point, while I'm open to any advice, I doubt anything you could convince me about soldering will make me try it again with this tab in particular.

 

[parabellum]

It may be Aluminum. You need special solder and/or flux for it. Crimping may be better then epoxying.

 

[MitchJi]

Hi,

Can you use small screws or bolts, too fasten crimp-on connectors to the tabs?

 

[Sunder]

Damn, you could be right. The tabs that did work, I reused the solder already on the pack. The pack that didn't work, I supplied my own solder...

Will need to drop by Jaycar to see if they have aluminium solder.

Can you show me any examples of crimp on connectors suited to joining LiPo cells?

 

[arkmundi]

I'm currently experimenting with conductive epoxies. I tried a silver epoxy but found it would never harden. Probably because an epoxy needs to be very mixed before use and the physical texture of that epoxy made it difficult to do that. I'm now experimenting with Nickel Epoxy Adhesive from Atom Adhesives via Amazon. cure time 15 minutes At 100°C, 45 minutes At 50°C. I'm using the 2.5 gram kits at $5.99 apiece. The kits put Resin/Hardener in a plastic pouch with a breakable seal, making the mixing easy to do and make a thorough mix possible. With a short cure time, just enough in the pouch and then start another if needed. Its working out well so far in my experiment, but I have yet to finish my build and do the real test - on the road - so have not posted here at ES yet.

 

[parabellum]

Damn, you could be right. The tabs that did work, I reused the solder already on the pack. The pack that didn't work, I supplied my own solder...

Will need to drop by Jaycar to see if they have aluminium solder.

Can you show me any examples of crimp on connectors suited to joining LiPo cells?

Take a look at this tread. https://www.endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=50 cool stuff on page 2 and 4 as well.

 

[John in CR]

What do people think about using silver (conductive epoxy) for intra-pack joins. Will it conduct well enough?

It might work for a 250W ebike, but resistance is simply too high for passing your primary current through a single such connection. I would only consider it in a case where you are using it to supplement a mechanical connection with a large surface area.

 

[arkmundi]

I'd agree that some consideration is required in the use of conductive epoxy, and encourage experimentation. So far in the more successful experiments I've conducted {hahaa}, I use the join in a way the maximizes direct wire to battery surface contact, with the epoxy insuring the join. Think of it as epoxy on 3 sides of a wire strand and a thin layer of epoxy between the two conductive surfaces. All to avoid having to solder.

 

[Sunder]

What do people think about using silver (conductive epoxy) for intra-pack joins. Will it conduct well enough?

It might work for a 250W ebike, but resistance is simply too high for passing your primary current through a single such connection. I would only consider it in a case where you are using it to supplement a mechanical connection with a large surface area.

I've got the large surface area...

From what I've read, it seems like the carbon based conductive epoxies aren't for high current use, but no negative comments yet about the silver, except that one study showed it was 50x more conductive than the carbon based conductive epoxy...

Not sure what I'll do at this point. Even reading up on Aluminum solder, it sounds like it's a bit of a process, and uses some pretty harsh chemicals to get through the alu oxide.

 

[MitchJi]

Hi,

Something similar to these?:
http://www.newark.com/crimp-terminals-fork-spade-tongue

http://www.newark.com/te-connectivi...e-fork-6-crimp-yellow/dp/66H7091?CMP=KNC-GPLA

 

[Sunder]

Hi,

Something similar to these?:
http://www.newark.com/crimp-terminals-fork-spade-tongue

http://www.newark.com/te-connectivi...e-fork-6-crimp-yellow/dp/66H7091?CMP=KNC-GPLA

I'm talking about the tabs in between cells of the same pack. I can't see how those would help?

 

[TheBeastie]

I have wondered about that stuff from time to time.
The Atom Adhesives looks like a quality brand but in AU/rest of the world? you can't buy from that Amazon store.
Also looks like you have to be keen to buy from the ebay store "US $95.80 (approx. AU $103.37) " for postage.
http://www.ebay.com.au/itm/Nickel-Conductive-Epoxy-Heat-Cure-Electro-conductive-Nickel-Filled-2-5mg-1part-/161121872591?pt=LH_DefaultDomain_0&hash=item25839caacf&_uhb=1

Looks like if you want possibly dodgey Chinese options you put "Conductive glue" in ebay, I guess chinese sellers find the word epoxy too complex. Also gotta filter out thermal paste out of the search...
http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1311.R1.TR12.TRC2.A0.H1.Xcondud&_nkw=conductive+glue&_sacat=0&_from=R40

Also come across this conductive copper tape.. why not just sticky tape your problems away!
http://www.ebay.com.au/itm/1-Roll-5MM-X-30M-Conductive-Copper-Foil-Adhesive-Tape-hobby-supply-RC-/271435154235?pt=AU_B_I_Electrical_Test_Equipment&hash=item3f32cbc33b&_uhb=1

Anyway I demand you try out some of these products and report back here for my own personal convenience and gain.

 

[Sunder]

Anyway I demand you try out some of these products and report back here for my own personal convenience and gain.

Going to try this out:

http://www.jaycar.com.au/productView.asp?ID=NS3033

Followed by this:

http://www.jaycar.com.au/productView.asp?ID=NM2831

Buying it at lunch time, but probably won't have time to test until the weekend.

 

[fechter]

I'll be interested in how that works out. I've never tried it, but I suspect the conductive glue won't take high current very well.

I've seen some battery tabs that were stainless steel and those you can solder with the right flux.

 

[Sunder]

No problem. I've got both the silver epoxy and the wire glue now.

I also have a multimeter, an ammeter using a shunt, and a few other odds and ends. I don't have anything that could generate a significant load.

How would you like me to test these products?

 

[TheBeastie]

Aside from just using it and seeing how you go I use these excavator light bulbs to suck power out of my lipos for testing.
http://www.ebay.com.au/itm/Universal-Excavator-DC-24V-100W-Replacement-Light-Bulb-/200861302802?pt=AU_Business_Industrial_Industrial_Supply_MRO&hash=item2ec4444012&_uhb=1
Couple of these in parallel draw power out of lipo good. Could even use the wire glue to make a connection from the battery to the bulb as they get hot... decent test.

 

[parabellum]

No problem. I've got both the silver epoxy and the wire glue now.

I also have a multimeter, an ammeter using a shunt, and a few other odds and ends. I don't have anything that could generate a significant load.

How would you like me to test these products?

Try to have a controlled environment and take as much data as possible.

 

[fechter]

Measuring the voltage drop across the connection at a known current would be a good test.

Attempting to run the full rated current of your controller through it would be another good test.

 

[kfong]

I would not trust conductive epoxies for high current applications. The epoxy itself is not conductive, only the silver suspended in it can conduct. Having a good bond requires a high epoxy content, which makes for poor conduction.

 

[TheBeastie]

Measuring the voltage drop across the connection at a known current would be a good test.

Attempting to run the full rated current of your controller through it would be another good test.

Yeah great thought, in other words if a voltage can be detected via two sides of the glued connection then there is some serious resistance, if you know the current in amps going between the glue then the ohms can be messured, or could the ohms just be messured with a ohm meter without the connection being active?

Actually one thing I just couldn't help but think about is copper tapeing combined with wire glue, because of the large surface area you gain with copper tape you would offset the lack of connection you would receive if it was just a wire glued..
Just a thought anyway, was the plan to always use the wire glue directly tab to tab? This sounds a bit awkward to achieve.

 

[Gregb]

How big are the tabs?? Can you drill a hole thru and use a bolt and nut (Brass) to press them together?

 

[Matt Gruber]

so how did this work out?
i'm using JB WELD not to conduct, but to insulate. it is like shrink wrapping the cell! (slight pressure needed until it cures).
i get a 12 mv drop at 7 amps, i find this acceptable. jumps to 25mv at 12 amps. still acceptable to me, this is with 16 AWG, would need larger wire for more amps or less drop.

 

[TheBeastie]

Yeah! Sunder said you were going to test these products.
I demand an entertaining video like this one.
[youtube]9gKYfgIGMlE[/youtube]
You got 6 hours before I go to bed, I want to watch this via the convenience of my iPad in bed tonight please.

Edit..
I started digging around on youtube (I only learn from this in video form (maybe I am the MTV generation ) )
This video shows this guy using wireglue and sticking bits together, he seems to just talk without thinking too much IMO so just with the video and judge for your self, but it did look a bit ordinary on the 25mm line on paper test with about 50ohms resistance, but the wires glued together looked decent. He only gets to showing ohms etc 26mins into the video.
https://www.youtube.com/watch?v=KvHnMncDBbk#t=1564

For sticking lipo tabs together I was thinking maybe copper tape with wireglue and strong magnets on either side of the glue job to force close contact and optionally leaving the magnets there to act as a heatsink.

 

[Matt Gruber]

what a funny video! can easily show how anything won't work.
my tests with plain JB work 100% of the time. that stuff is fantastic once you learn how to use it. (tip: apply slight pressure while it sets, so there is a good connection) if you use some saran wrap against the clamp, then it won't stick to the clamp. everything is easy once you know how.

 

[TheBeastie]

I went into jar car today to buy some wire glue and try it my self, but they were out of stock.
They were $5 cheaper then buying it on eBay etc, but now I stopped at Starbucks on the way home and had a $5 mocha so now I still without wire glue and down 5$ anyway.