Soldering contacts on 18650 batteries? - Page 1
Forum section: electronics / general

author: e100
author_rank: Frequent Contributor
timestamp: July 07, 2023, 04:58:13 am
content: How tolerant are 18650 and similar sized lithium batteries to hand soldering the end caps to make wire contacts?Commercially spot welding is used to minimize the heat soak, however all I have is a soldering iron.Does soldering with 60/40 solder cause any long term damage?

author: Gyro
author_rank: Super Contributor
timestamp: July 07, 2023, 11:12:10 am
content: Not tolerant enough, I'm sorry to say.You can get battery holders that will accept 18650 cells. This is a far safer way to go.

author: Infraviolet
author_rank: Super Contributor
timestamp: July 07, 2023, 09:07:01 pm
content: Even soldering to battery holders won't be a pleasant task. They won't bust in to flames the way an Li cell might, but you'll often find that as soon as the tab on the holder is hot enough for solder to flow on to it, it is already melting away the black plastic it is mounted in. And that was with relatively low melting point leaded solder, solders needing higher temperatures would be even worse. I honestly can't see how battery holder manufacturers expect their products can ever be used, the metling point of the plastics is always well below that needed to make a solder joint, unless one is supposed to ALWAYS spot weld or something instead?

author: coppice
author_rank: Super Contributor
timestamp: July 07, 2023, 09:12:36 pm
content: Battery holders aren't a great solution, as they take considerable space. That's not good at any time, but its a killer when trying to refurbish an existing battery pack. It is possible to get cells with tags welded on, and they are easy to solder to. The snag is your choices are very limited, and generally not the cheapest.

author: thm_w
author_rank: Super Contributor
timestamp: July 07, 2023, 09:26:29 pm
content: I've done it before without issue, but that was with a metcal station and large tip. I would not recommend doing it of course.You'll need lots of flux and might need to sand the surface.Quote from: Infraviolet on July 07, 2023, 09:07:01 pmYou can get the ones with wire leads, although they are kinda crap as well if you need to be removing and reinstalling cells, if its just once they are fine.Probably normal wave soldering doesn't put any force on the metal so maybe less risk of melting, that or we are just getting cheap plastics.Maybe SMD ones are better:https://www.aliexpress.us/item/2255800966023398.html

author: aeberbach
author_rank: Regular Contributor
timestamp: July 08, 2023, 02:24:45 am
content: If you have to have a solder connection you solder wire to nickel battery strap and then spot-weld the strap to the battery. To make packs of multiple batteries just strap from battery to battery. The gear do do this is cheap and can be had at Amazon/AliExpress. I don’t know what the professionals use…

author: e100
author_rank: Frequent Contributor
timestamp: July 08, 2023, 02:33:57 pm
content: I found a dummies guide to spot welding on the cheap. A really well done video that explains how to do good welds and what causes bad welds.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 08, 2023, 10:45:59 pm
content: Two remarks:Some of these Chinese spot welders have a design problem, where the mosfet gate drive voltage is taken directly from the input. If this is so, then sometimes the battery voltage sags enough under the high current that the fet's get starved of Ugs and enter the lineair region. This can cause an instant failure of the Fets.The solution is to add a diode between the battery and the buffer capacitor. Then the capacitor holds enough charge to buffer the gate voltage, even when the battery voltage bogs down under load.The other issue: Never pull the nickel strips with your bare hands. If your finger slips, this can cause deep cuts.I do agree with testing spot weld quality. In a good spotweld, you pull a "button" out of the base material, instead of separating the weld itself.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 11, 2023, 02:45:11 pm
content: Just don't do it.That being said, I have done it nevertheless: fine grit sandpaper, clean with alcohol, apply flux, use powerful iron with MASSIVE tip tinned well, quickly apply heat and solder with high-quality SnPb 63/37 solder, if it takes more than a few seconds you are doomed. There is no room for any hesitation.But just don't do it.