I’m somewhat invested in building some 18650 packs for new planes. I bought 50 molicel P28B cells, a battery spot welder, heat shrink and a variety of nickel strip for battery inter-connections. I made some poor assumptions and now not sure how to proceed. My first assumption was that .2 x 8mm strip would be fine to weld and handle the current. Second was that the spot welder would be fine for .2mm thick strips. It welds but it’s marginal at best. I started looking into how much current these strip are good for. I found that the .2 x 8mm strips are only rated for 12 amps. Not near enough for my planes. I was told at the Nats that a guy was making packs for others but he was soldering them rather than welding. I’ve never liked soldering on batteries but I found a few instructional videos to watch. Maybe that will help.
Anyone else building their own 18650 packs? Anything you can educate me further on the subject? I’ve bought the cells so they are going to be made into packs one way or another!

Thanks, Matt

First I used an online calculator to find the requiring metal cross-section for my needs, e.g.: https://energoprom.net.ua/en/calc-cabel/calc-secheniya/
Then I made 8 x 0.5 mm tabs out of copper sheet.
Finally I used regular 150W iron to solder the terminals.

Vitalis

https://batteriesamerica.com/products/battery-bars-sub-c-size-10-pcs?_pos=2&_sid=8e7499201&_ss=r

These bars are designed for Sub-C sized cells (22mm OD) and might work on the 18650.  They are gold plated and have a claimed 100amp carrying capacity.

Good to know that Brent! I’ve always thought those charts have serious safety factor built in. I know my RC helicopters pull 50-60 amps regularly with peaks over 150 amps on 10ga wire that are only spec’d to 30 amps or so. They never have any problems. I’ll see if I can’t find some of the tinned steel.

Matt

This should work best. It should be easy to solder too. 3/16 or the 1/4 should be just fine.

https://www.amazon.com/Tinned-Shielding-Protection-Screening-Sleeving/dp/B0BBZL7L3J/ref=sr_1_3?crid=V9VETXD76HCJ&keywords=Braided%2BTinned%2BCopper%2BSleeve%2B3%2F16&qid=1693840118&s=industrial&sprefix=braided%2Btinned%2Bcopper%2Bsleeve%2B3%2F16%2Cindustrial%2C88&sr=1-3&th=1

On another set of idea here is the question of how much A average do we really demand in the air. Say you use 6S and 2200mAh for a 5min 30s flight that comes up with 20A average in flight. At his point I want to mention the thin tabs that connect the batteries and start to wonder if the simple tin covered Nickel tabs are enough to get the job done and we might be too worried.

I got sidetracked on my pack building project. I know Will and others are soldering the tabs. What is everyone doing to prep the ends of the cells to accept solder? I saw one video where the guy used acid flux and it worked fantastic to get the solder to instantly tin but I don’t want acid flux on my batteries. Others have mentioned grinding on the ends of the cells. I’m not real thrilled with that idea either. I’m getting close to tackling this again, hopefully in the next week or so.

Thanks, Matt

I would not say I grind the cells. I use a small stone wheel on the end of my Dremel to "scuff" it up just a bit. I really don't grind on it or even get it hot. It works well and I have no problem with solder flow. This method is easy and fast. This is the Dremel part I use. Dremel 1/8 In. Silicon Carbide Grinding Stone
Item No.SKU# 83322. This can be found in many places on the web including Amazon which is probably where i bought mine a few years ago. I'm sure anything similar will work just as well.

Thanks Will!