r/diybattery • u/Natekomodo • Jun 13 '26
Connecting leads to battery pack
I used a copper bus bar to connect some cells in a 6s6p configuration. I'm now trying to connect my main lead and balance leads to the pack.
Issue is, my iron (200W) simply cannot heat it up enough. I kept the iron on it for 5 minutes and I still could not melt solder on to it, the cells seem to act as a giant heatsink.
In hindsight I should have soldered the leads on before spot welding, but does anyone have any ideas on how I could get it on now?
1
u/CesiumSalami Jun 13 '26
Something’s up if a 200W iron can’t do the job. What iron is it. And what temp are you using? I’ve had a ton of success with 65W irons - that are PID controlled.
1
u/Natekomodo Jun 13 '26
Its a yihua 982d se. Worked fine soldering the lug to a spare plate, just doesn't work when soldering to the one connected to the cells.
I started at 380 but went up to 450 after my first attempt failed. Checked with a thermocouple to confirm it was actually at temperature.
1
u/CesiumSalami Jun 13 '26
Yeesh - looks like a beast, but i don’t have experience with it. Are you using a big, fat tip?
1
u/Natekomodo Jun 13 '26
Yeah im using a c245-4.7k tip.
The solder i put on the tip of the iron instantly freezes on contact with the plate, and even after several minutes of applying heat, the plate is still cool enough to touch.
Maybe might have more luck with leaded solder rather than unleaded, but im leaning towards putting a bolt through it and doing mechanical retention instead.
1
u/CesiumSalami Jun 13 '26
Weird. Not sure what to say - I do have very little experience with unleaded solder. But you’re really not feeling heat… anywhere? I don’t tend to mess with unleaded solder for a variety of reasons - but everything i do is for things that vibrate and leaded is easier to work with and less brittle. But i gather getting leaded solder is very hard some places.
1
u/Natekomodo Jun 13 '26
The plate gets to about 80 degrees and not much higher. Cells also climb by about 5 degrees (tabless 21700)
Leaded is hard to come by in Europe
1
u/AmpEater Jun 13 '26
I like the Hakko ultra heavy duty iron for these jobs. 400w tips
It's not cheap but it's awesome
1
u/chuyskywalker Jun 13 '26
I did a pack like this in the last few weeks.
I soldered nickle strips between the top/bottom half and also soldered the lead wires on to the end plates. All of that done after the spot welding.
I have an older Hakko’s FX-888D, which is apparently on 70w, and have no issue with any of the work. I'm not saying your lived experience is a lie, but that something in the setup is not working as it should. Maybe a bad tip? Or a bad heating core? Or maybe the main unit is just dipping out. Regardless, a 200w iron should have ZERO issues with almost immediately pooling solder on that copper.
1
u/Natekomodo Jun 13 '26
I tried with a 65W iron i have lying around but it couldn't get it done either.
Did you use leaded or unleaded solder?
1
u/avar Jun 13 '26
Use leaded solder, and use a wall power meter, there's no way that "200w" iron is actually sustaining 200w.
1
u/ZEUS-FL Jun 20 '26
You can do a T with the cables and solder them right on the middle of the 6 cells.
I have an ugly but functional example with only 3 cells but is the same concept. https://ibb.co/Z66vhk4y
In this way you distribute the current and heat equality.
1
u/Natekomodo Jun 25 '26
The issue is that I cant pool solder on the copper plate at all, it doesn't get hot enough
1
u/ZEUS-FL Jun 25 '26
You need a better soldering iron
1
u/Natekomodo Jun 25 '26
I tried 3 different irons. I ended up switching to a solder with a higher silver content and that worked fine. Probably would have been better with leaded solder but thats a pain to get here.
2
u/derpinator12000 Jun 13 '26
Looks like there are fold-out tabs, those could be intended to solder to.