Conductive Glue for Battery Pack Construction

[theyerb]

I had a humbling experience today trying to put together my first battery pack made from 20 matched Konion cells in a planned 2p10s configuration. My soldering skills are... two weeks old. After a while, the super glue on my bench was looking appealing, so put a batter bar between two cells and then applied super glue to the sides. The capillary action between the cells and bar allowed the glue to seep nicely into the space between. The idea was that as long as the bar and battery were in contact, the glue would merely keep them from being pulled apart, and not for any conductive purposes- of course,super glue has none. It seemed like a great idea: bypass heat-inducing methods, it is really quick, no damage to the batteries, probably cheaper.

It didn't work. The capillary action worked its way between the bar and cell and lifted them apart ever so slightly, even when using a clamp with pressure.

My next idea is to use conductive glue. These types of glue are typically an epoxy with a metal powder mixed in such as graphite. Some of the glues have resistances of about 30 ohms per inch. Is that a lot? Do you think this is an idea worth looking into?

 

[Jeremy Harris]

Solder has a resistivity of about 0.00000016 ohms per inch, so if conductive glue is around 30 ohms per inch then it's about 187,500,000 times poorer as a conductor than solder.

Does that answer your question OK?

Jeremy

 

[liveforphysics]

Jeremy put it very well. Glue isn't going to cut it, not by a long shot.

The trick is to get the right solder, the right flux, and a well tinned iron that is a power monster. I recently got an iron that has a button on the side to short the resistor inside, which dumps 150w into the tip, and just 15w while at idle (just enough to stay up to temp). It was only $30 at Frys electronics, and I'm all ready liking it better than my $350 temperature controlled fancy pants soldering iron setup.

You need a lot of power to be able to locally flash heat the surface to get a good solder connection as quickly as possible. This keeps the rest of the cell cool and undamaged, while still getting a solid solder joint. Get everything clean and prepped, use 60/40 lead/tin solder with resin core, put a dab of flux on the cell and the tab, get everything into position, then strike it like killing a snake. Lots of tip pressure on a well tinned tip, the flux will boil, then feed the solder to tin the cell. You don't want to spend more than about 2 seconds for the whole process, or you are going to be getting the cell too warm.

If you are working with a little 25w iron, lead free solder, or no flux, don't even bother trying until you get setup correctly to do it right.

 

[pwbset]

My soldering skills are... two weeks old.

I feel your pain. I have very limited soldering skills. I've noticed that every soldered pack I've built will have solder points "pop" off under heavy load. I've tried getting better, but haven't. :lol: Now with 100+ cells going into a new build for summer I'm going to use contact springs and compression. Another (very important) reason I'm doing this is that I haven't done IR and capacity matching on these cells so there will be duds that I want to replace easily. Nothing worse than having a big soldered pack only to have to replace a cell in the middle.

 

[theyerb]

Thanks for the input guys. Time to get some better equipment and work on my solder skills. Cheers-

 

[Nimbuzz]

SOLDERING -- Yes 1) a good iron makes all the difference but even a $25 40 W Weller with the orange handle from the hardware store can often be adequate but quality can be inconsistent and I've found they just don't last over 10 - 15 hours. Best go to an electronics store and get a $60+ iron. If you are at the level of building packs you and the cells deserve a good iron which will last for some years. Plug the iron directly into the wall as an extension chord can drain some juice. 2) Good 60/40 rosin core solder (NOT lead free!) 3) Soldering is a 'knack' kinda thing = after a while you get it and don't know exactly what you are doing differently but it seems to go very easy now. 4) Soldering batteries is one of the trickier solder jobs as the size of the metal parts (cells) sucks away some/a lot of the heat. Start with medium wire, strip it and twist it together and solder it till you get nice smooth shiny solder coverage, then go to bigger wire to do the same, then get some old messed up cells to practice on THEN do your fancy pack. 5) Once you have the knack you've got it for life. if you seem to loose the knack it may be a bad iron or low powered house circuit or the evil lead free solder might have snuck into your kit.

6) I'd google a link about soldering technique as you need to do a lot of little things like 'tin' the iron and always keep it tinned and have a damp sponge at hand to constantly wipe the tip on. Your tip will corrode fast if it is left exposed to air -- it must be constantly covered with solder. Perhaps you can find a link on an RC site that actually tells you how to solder packs/cells. Soldering The tip will still slowly degrade and need replacement. It is easy to forget constant tinning when you are concentrating on the job. The correct size tip is important = bigger for things like cells. 7) The trick is how much to heat up the parts before applying solder. If you apply too much heat copper wire cools and leaves the wire brittle so it can eventually break from flexion at the solder joint. Excess heat can also damage cells! There are now laws that in Aeronautics solder cannot be used because even a good solder job degrades/aneals the copper. Anderson and other high tech crimpers make a superior joint because they do not heat the materials. If you find a knowledgeable guy in the electronics store he may be a good coach to help buy an iron and tip. I have basic/good solder skills but I have friends who are like magic with an iron. Watching someone like that is helpful. A little fan on your table can blow away the toxic fumes so they don't go right up your nose.

It's fun once you get the 'knack.' Good Luck! Please come back and post your progress here.

Se the new thread "Soldering 101" on this forum where others will hopefully make additional contributions.

 

[Nimbuzz]

pwbset -- Can you please explain your "contact springs and compression" technique?

Thanks,

 

[pwbset]

pwbset -- Can you please explain your "contact springs and compression" technique?

As soon as I have something to show I'll post some photos... it's like what Gary is doing with the A123s... same springs. Just got a bunch of 12ga copper also that will connect it all together. "Soon".

 

[Nimbuzz]

What's the link to what Gary is doing?

 

[theyerb]

Here's one of the popular posts on making a battery holder to bypass most soldering during battery pack construction:

http://endless-sphere.com/forums/viewtopic.php?f=14&t=8660&p=138684&hilit=leamcorp#p138684

 

[Mark_A_W]

pwbset -- Can you please explain your "contact springs and compression" technique?

Thanks,

Have you ever opened a torch (flashlight) with a couple of C or D cells in it and a spring in the cap?

 

[theyerb]

I'll answer for him: no, never... lol