# Electrically conductive/conducting Epoxy



## Tubor (Aug 7, 2008)

Hi all,
Can anyone recommend a good electrically-conductive epoxy which you use to cold-weld and the like? Is JB Weld electrically conductive? I am trying to create a battery pack using li-ions and soldering isn't working. Thanks.


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## Illum (Aug 7, 2008)

I'm still trying to find such a thing

the best advice I can give from experience is to find something concave to sit batteries on, clamp it down using a large vice grip from the top then apply epoxy between the cells, it'll look ugly when its finished but it keeps batteries in line:green:


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## Tubor (Aug 7, 2008)

It's for the electrical connections between the batteries to avoid having to solder them. You see I've been trying to solder the terminals directly but haven't been doing it properly because I don't want to heat the battery up too much in case I damage them!  :sweat:And I think that's why it's not working. I think there is such a thing but it's very expensive and I was hoping for a cheaper/simpler solution.


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## PhotonFanatic (Aug 7, 2008)

Tubor said:


> Hi all,
> Can anyone recommend a good electrically-conductive epoxy which you use to cold-weld and the like? Is JB Weld electrically conductive? I am trying to create a battery pack using li-ions and soldering isn't working. Thanks.



I've used MG Chemicals electrically conductive epoxy--comes in two 14g tubes. Google search on that, or try the catalog number: 8331-14g

Not that expensive, either. Mouser has it for $24, for instance.


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## mudman cj (Aug 7, 2008)

I have found that conductive epoxies are not as strong as solder, so I would recommend that if you use conductive epoxy to establish electrical connections between the button of one cell and the flat cathode of the next, that you also reinforce the joints with a good non-conductive epoxy by filling the remainder of the space all around the buttons with the structural epoxy.


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## Torque1st (Aug 7, 2008)

Learn to solder the cells. R/C racing magazines frequently have good tutorials on how to solder the cells. 

DO NOT attempt to use conductive epoxy.


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## Oznog (Aug 8, 2008)

I got some "wire glue" from I think KaiDomain awhile back. It's not a 2-component. Just got it "because".

Even 2-part epoxy would be a terrible idea. The electrical connection will inevitably be fairly high resistance. Look at the Arctic Silver for reference- the _thermal_ resistance is "low" for grease but still MUCH higher (orders of magnitude higher) than pure silver because the particles have limited contact with each other and the substrate, because there's a layer of binder coating each particle and two spheres will only touch over an almost infintesimally small portion of its total cross-section. I expect any electrical conductor will exhibit a similar penalty over the conductive material upon which it is based. Under current this will form heat right at the epoxy layer and epoxy doesn't take really high heat. Stresses from thermal expansion will be high. And in fact epoxy is not even a really stellar performer for metal-metal bonds, especially on tabs where there's a peeling force. 

Do not solder lithium or NiMH cells. Especially lithium. It's dangerous and is VERY likely to damage these expensive cells whether you realize it or not. Given the differences in cell construction, it's hard to predict what would happen with soldering. The only thing we can be sure of is the mfgs don't allow for it.

What you need to do is build a capacitive spot welder. There are many descriptions of people doing this with a big stereo booster cap, a large SCR, and a couple of pieces of solid copper ground wire filed down to make electrodes. Such as http://www.ledhacks.com/power/battery_tab_welder.htm

Get the nickel tab from SunStone Engineering


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## Tubor (Aug 8, 2008)

Thanks guys, a few options there. :twothumbs The welding option sounds like the best one but I'm unsure if I'll be able to do that at home on the lounge table :naughty: and then keep all the stuff safe afterwards when packed away, I expect so but I might go with the epoxy option for now and see what results I get with that. It's not for a particularly high current application - old laptop - so I may be alright with it. Hail to the king baby.


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## mudman cj (Aug 8, 2008)

The two part _electrically_ conductive silver epoxy I use states a volume resistivity of <0.001 Ohm*cm. Given a tab area of 1cm^2 and a bond thickness of 0.05cm (conservative estimates IMO), this would result in a resistance of 0.00005 Ohms.

To reiterate, I think your biggest concern should be the mechanical integrity of the joints.


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## Tubor (Aug 8, 2008)

That sounds pretty low. OK I'll use additional epoxy on the joints thanks for the advise.:thumbsup:


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## darkzero (Aug 9, 2008)

I haven't tried the MG stuff yet but I use the Circuit Works Electrically Conductive Epoxy. As with any epoxy, it's critical with this stuff to mix them evenly otherwise it won't cure very strong. Takes long to cure but I heat it to speed up the process. Works pretty good.


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## VanIsleDSM (Aug 9, 2008)

Anything I've ever used from MG chemicals has been an absolutely amazing product. They're a great company.


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