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Soldering

Cantclimbtom

Active member
I am a practical engineer kind of person, but never much electronics (beyond fixing the occasional dry joint on a board etc) but very embarrassingly I am struggling to solder a wire onto a battery, totally failing.

I've got some 18500 button top batteries. I want to solder 3 in parallel and shrink wrap them.

Starting with the button on the first battery, I clean it with some sandpaper, wipe a little flux over it, put the copper wire in place and try to solder it. The solder flows and sticks to the copper wire but seems totally repelled by the battery. I can't even solder just a small blob of solder onto it.

Is this just some weird batteries I have, or is this a normal problem for batteries in general. And do I need a different approach from just solder wire on top?

How should I be doing this?
 

aricooperdavis

Moderator
Those batteries dissipate the heat from your soldering iron really quickly. Ideally you'd spot weld a tab onto them, but it is possible to solder directly to them if you get a good soldering iron with a really fat wedge tip that won't instantly cool down the moment you touch the terminal. Obviously, be wary of letting them overheat so you don't damage the battery, and don't forget that solder provides an electrical joint rather than a physical one as it's quite brittle.
 

MarkS

Moderator
[Cross posted with aricooperdavis, but probably still relevant]

They are a bit tricky in my experience. I suspect due in no small part due to very good thermal conductivity and reasonable thermal mass. The way I've done it before is to sand and also score the battery surface slightly. The heat does damage batteries though, and I remember the heating time being longer than I'd have liked (although ultimately it didn't noticeably affect the battery capacity). I think they tend to be connected by spot welding nickel tabs to them in commercial applications.

I'm sure someone more knowledgeable and experienced than me will be able to add more.

 

Cantclimbtom

Active member
Thanks, so no Obvious gotchas then?
I have a big flat tip on it, I was only at 300C but I'll try again on 400C and see if I can get some solder to stick to the terminal. Fingers crossed...
 

aricooperdavis

Moderator
Might be worth having a look at DIY eBike/eScooter forums as they make up big battery packs like this. I'm sure I have seen some YouTube videos about that demonstrate it. No obvious gotchas I don't think!
 

Cantclimbtom

Active member
aricooperdavis said:
Might be worth having a look at DIY eBike/eScooter forums as they make up big battery packs like this. I'm sure I have seen some YouTube videos about that demonstrate it. No obvious gotchas I don't think!
If I  hadn't already bought the batteries....  :(
I heat the battery as much as I dare, I'm cooking it, re-apply flux and the solder is still repelled into a ball and rolls off the button, maybe non button top would have been less bad choice

"BOTHER"!!  :mad: that's a waste of a purchase of 4 * 18500 batteries :(  not sure of any other use for them.

Edit, I did YouTube it before I posted but saw nothing about this issue there
 

AlexR

Member
If you?re ever up here again I can spot weld them for you, though repeated soldering has likely damaged them to some degree.
They are an absolute arse to solder by conventional means, effectively the oxide layer present on stainless steel (in this case) but also aluminium makes it very hard for the solder to mate. There are solder pastes specifically designed for this application, but they are expensive.
Otherwise the method you and others have described is the way it?s done, sand surface, liberally cover in flux, scrape a bit more, put a fresh piece of solder on, bang on your beefiest soldering iron to wet the 18650 surface with solder as quickly as possible. Then wipe clean and mate with wire previously wetted with solder.

If it?s any consolation, I?ve written off at least 4 18650?s because I just couldn?t get the wire on.
 

Cantclimbtom

Active member
Odd... the underside (flat) seems to solder normally, bit of a pig of a job using the method you describe of pre-soldering wire and metal and then joining the two (all with a load of flux) but the solder sticks.

It's whatever metal the button on top (+) is made from.

Note to self, never ever buy button tops if you are going to solder them
 

Cantclimbtom

Active member
AlexR said:
If you?re ever up here again I can spot weld them for you....
Thanks, if I'm up the peaks again,  soldering the bottoms was difficult but do-able. I did a pretty shoddy looking but functional job. But I just can't solder the tops, the metal looks different and the solder and the top won't go near each other
 

aricooperdavis

Moderator
You can drill a tiny hole (if you're extremely careful) in the top of the button top and effectively tie your copper wire through the hole and the other vent holes, then cover it liberally in solder. It won't stand up to any wear and tear so you'll need to do loads of wrapping, and it's probably quite high resistance, but it's better than wasting those batteries!
 

wormster

Member
The anode and cathode are nickel which makes soldering difficult. Resistance welding is the correct method of stringing cells together (warning!! - we weld our cells at 100% S.O.C. and use specialist welder and settings, if you want your cells to go FOOM and splatter nasty stuff over you and the bench carry on, otherwise Biff down at Little Monkey may be able to help)
 

royfellows

Active member
Naw , naw, naw

I have been soldering direct to batteries for about 15 year, and know of at least one major company that does the same.

1/ Score the surface of the battery, as you have been doing
2/ Add plenty of flux
3/ Melt solder onto the battery surface, observe its behaviour, keep the heat on until it flows to a puddle.
4/ Flux and solder the end of the wire with a nice little blob.
5/ Put wire to battery and flow the two together

Incidentally, the tops aren't even directly part of the battery casing, its the bottom. I have as i said been doing this for years and tested to fine limits before and after with no noticable loss in performance. If you want loss in perfance you cant beat bubious brand name Chinese batteries.  :LOL:
 

Cantclimbtom

Active member
Thanks Roy!

It's step 3 where I am struggling. The behaviour of the solder on the battery *top* is to remain on the iron tip or if in contact with the button top, to form a ball and roll away. It's odd because with worrying amounts of heat I can puddle/spread the solder on the metal of the battery bottom and I don't have that problem

If you've not seen this problem in 15 years, I must be creatively forging a new direction of idiocy

https://www.ebay.co.uk/itm/181707974804  and if you then ask why I picked those... inexperience and poor judgement may be the reply
 

royfellows

Active member
I have just took a look. The seller is a really good bloke, I used to get genuine Sanyo off him when I ran short. The battery brand, I dont know about., looks Chinese, not like Norbert to offer junk. Capacity is unimpressive.
There are supply issues at the moment, I buy in my cells from FastTech HK, for years been great, but the ones I have been getting stopped. Last batch was new part no and upon testing I had to reject one out of a batch of ten. Dont blame the Chinese, its universal. had issues with stuff off RS Online. I am using Sanyo NCR 18650GA 3500 mAh. these are what is currently available. They come overland so takes up to 3 months, so you can see why I bought some of Norb. There was a local lady close to me importing form Europe as well, but this has stopped.
These are what I am getting now

https://www.fasttech.com/p/9662582

The dud did not check out at 'factory voltage' and was odd, so put it on one side. Good as gold it slowly lost power. Dont doubt its genuine, its quality control across the board that had dived, plus of course supply.

RS are showing lead times up to well into next year on some stuff, just hope is OK when it does come.

The behaviour you describe I have seen. Abort, dont apply more heat. Add more flux and try again. You need a good iron, I use Antex 30 watt adjustable, had it for years. Use broad tip as well. Of course, it could be the cells. Most Li Ion cells, that is good ones, are Sanyo with protection circuit added (if soldering to these, be aware of electronics inside) and enclosed in the retailers wrapper. Sanyo are an Original Equipment Manufacturer (OEM) and to my knowledge dont do retail package. Samsung also OEM producer, known for their high discharge chemistry.

I am unsure about your problem, it does sound like an inadequate soldering iron, unless those cells are 'odd' in some way that affects soldering.
 

royfellows

Active member
Hi Nick, yes a good question. Its a tin of paste which I have been using since about 1965, no kidding. Its called "Fluxite Soldering Paste" and its tends to, well, last.

I am am just working in my lab.
Its not why you called, but with the drivers now unobtainable for my popular X12 I am working on an idea for my own driver module.
I am using a DC-DC converter that does not use a flyback diode and have actually got 98% efficiency from 12VDC input and 200 mA output. Normally buck converters are crap on the lower outputs. My idea is a system of analogue output control, actually Stenlight is similar but uses reed switches. My system is a bit, well, original.

I will start a new thread on it if it works out, with the high capacity batteries I use and 98% efficiency living underground for days becomes a possibility
:LOL:
 

Cantclimbtom

Active member
nickwilliams said:
What flux are you using?
A generic general purpose electronics and plumbing paste flux (I had hoped to use for either), but oddly it had the appearance of yellow hard beef dripping than a yellowish toothpaste and not liquid at room temp. I am not saying that the flux is the best, but on the bottom - of the battery the solder would flow nicely

The iron I have is cheapo adjustable and lacks horsepower, I solder about once a year, this probably doesn't help but again the base of the battery would take more heating and the button top *presumably* would be easier?

Definitely I'm somehow making this a whole lot harder that it should be

No idea :(  I'll have another go another day, maybe try drilling a tiny hole in the button to assist, if it's hollow maybe I can get solder inside it?
 
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