Soldering iron for 18650 packs

I’m working on a 10s4p

This is the build of my 10S4P using a soldering iron and nickel strips.

I would say pre soldering the strip helped and plenty of flux was useful. You need to be in and out quick to stop the battery heating up. I hot glued my cells together first and would recommend doing this. You will probably want to reinforce the nickel strip with single core copper across the series connection.




I did some testing on Nickel strips I got off eBay. at 12v 10 amps they got hot, and at 20 amps they discolored and began to fail. At 40-50v 20A I don’t think they will work well at all. nickel (or nickel plated steel like most eBay strips are) don’t conduct electricity well. If you are going for 18650 batteries, it’s probably because you want a premium battery. One that can output a ton of current, so it’s worth making sure all the connections can handle the current. The 12 AWG wires will handle 20A no problem. The 8 AWG will handle 60-70A no problem. Might be able to go to 6 AWG if you have more than 4 in parallel. The concern of soldering batteries I believe is over-rated. As long as you are careful not to overheat the battery, I don’t see the problem.


i just used normal 1,5mm copper wire for my 10s3p and iam happy with that , no issues so far.

But much tbh

Get some 14awg high strand awg and decent flux, some nice solder and a Denzel with sand bit and ur good to go this is what 12awg looks like

How necessary are sticky insulators? And where did you buy the copper braid?

I read somewhere, on Endless Sphere I believe?, a story of a guy’s 18650 pack using nickel strips. When he was using a lot of current from his battery, the strips got so hot they melted through the plastic insulation on the 18650 cells and shorted them out. The picture below shows the positive and negative are actually right next to each other, only separated by a thin plastic insulation. If that’s damaged or melts, the cell will short out.

The idea behind the sticky insulators is that they protect against heated connections, either through the soldering process or thin nickel strips that heat up under high current loads.

The copper braided wire was ordered form McMaster Carr - the link is in my post above. You can also find copper braid from eBay, but I found it’s sometimes a lot thinner and may not be 12AWG equiv.

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Thanks for the quick and informative reply!

Sorry I also forgot to ask of rosin core solder is particularly important, as I do not have access to that at the moment.

My understanding is that rosin core solder is just solder with a type of flux built into it. It helps the solder “stick” to whatever you are soldering. I don’t see a reason why you couldn’t just use flux and regular solder together.

you can totally use flux and regular solder. You can also use flux and rosin core for stuff that’s giving you a hard time.

also… if you buy flux in bottles like i do…

these are awesome. and dirt cheap. and they don’t really seem to clog much with dried flux for some reason.

i got some of these and a solder pot for tinning big wires and now tinning is no longer a hassle. its actually kind of fun watching the flux boil out of the wire as the 50/50 wicks up the 10awg wire like oil in a lamp wick.

The solder pot i got was $20 on amazon too. along with a big bar of 50/50 solder to go in it.


Why using bigger dimensions on the parallel connecting wires than on series connections?

Load on series connections are bigger right, so the other way around would make more sense, wouldn’t it?

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Hey @longhairedboy what bland of oil solvent and flux do you use? Do you clean all your solder jobs with oil solvent after finish soldering or you use it before applying heat?

Instead of nickel strips I just 0.2mm copper sheet..

Its much easier to solder than nickel strips and for the same area can carry more current iirc.

You can go thicker than 0.2mm but that thickness is easy to cut with regular scissors to any size you need. If I need higer current I just use double or triple layers.

Copper has like 5 times better conductivity than nickel, I use copper braid, also with braid is easier to make it a bit more flexible the :battery:. Some flux and 100+watts solder and ready to go.

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i use liquid flux in a little needle tipped squirt bottle. Cleanup i use rubbing alcohol and a clean white rag.

and i pour it into this for application during jobs:

i use rubbing alcohol to clean up the tips on the bottles as well.

In this case for a 12s4p battery:

Series connections - 4 x 12 awg wires, one on each series line (6 awg equiv) Parallel Connections - 1 x 8awg wire

so technically the series has a better connection than parallel like you said.

Load per series is 20A x 4 which 12awg x 4 will handle, and load on parallel is 80a which 8awg, while a little undersized for continuous load, should handle. VESC 4 will likely overheat before the wires do, though the VESC 6 may change things.

Some pics to clarify:

12awg on the series lines

8awg on the parallel lines


The problem with using wire and solder directly to the battery ends is that for a low guage wire (12/14 awg) you need A LOT of heat to melt a large amount of solder to engulf the whole wire and make it grip to the cell. The problem with that is, the batteries are great conductors of heat and most of the heat from the soldering iron gets conducted into the metal of the cell, thus damaging the inners of the cell.

If you want to make a flexible battery but still use solder, the best option is to weld small tabs of nickel to the ends of the cells, with enough nickel so that it can be slightly bent away from the cell, then rough up that nickel with a sharp end or sand paper and solder to that. The nickel basically absorbs most of the heat and much less dissipates to the cell.

You can make a spot welder from a car battery, a solenoid relay and some heavy guage cable for next to nothing, like mine…