Resistance Soldering Bus Strips to 18650 Cells

[parabellum]

any heat that is there decreases rapidly as the copper wicks it away, the can itself never really shows any detectable heat change to touch.

what do the welds feel like to touch after resistance soldering?
that may be the critical issue here i think.

Resistance soldering involves more heat then spot-welding for sure. You can touch the weld after a second or 2 after removing electrodes but they feel hot, in 5 more seconds in is just warm (and l cold leave my finger on). Unfortunately both of my IR thermometer need batteries, will try to get some before next weekend.

As you see, I use smashed piece’s of 60/40 solder wire with flux core, it is less the ideal. Solder paste could be quicker and easier option.

 

[cheapcookie]

Dual-Heat Soldering Gun anyone ????

I passed on one of these guns a few months ago for free 0$... shame

I am sure one would apply as much heat with one of these than with resistance soldering.

I don't understand why we are trying to weld huge copper tabs.

Are you guys pulling 50 amps from the poor cells ?

 

[parabellum]

I don't understand why we are trying to weld huge copper tabs.

Because we can.

Are you guys pulling 50 amps from the poor cells ?

What if you stumble over Sony VTC4 cells? Then, overall, good contact and low resistance are good things and cells are improving quickly.

Dual-Heat Soldering Gun anyone ????

I passed on one of these guns a few months ago for free 0$... shame

I am sure one would apply as much heat with one of these than with resistance soldering.

That is interesting idea. But I am afraid, it is not about how much heat, but how quick you can pump it in a precise spot.
I got 100W gun some years ago and it was lame, ended modifying it for my son wood art drawing.
Unfortunately, no solder gun here now but it would be interesting if someone shares time figures to compare.
Anyone?

 

[spinningmagnets]

Are you guys pulling 50 amps from the poor cells?

The next generation of cells can put out temporary peaks of 30A each. If you are happy with 10A-15A per cell, you are right that it is probably best to stick with a proven spot-welder and 0.15mm thick nickel ribbon...

But...I am having fun experimenting with this, so...why not?

 

[sn0wchyld]

ill post some photo's soon, but a quick update:
ive wired a circuit to put my heat gun in series with the transformer, and rewound it (the transformer) with some oversized 0g wire on the secondary. Results are very promising...

No heat gun: input 240v, 6A output 1.5v, 700A - 1000W out into a 12g but splice terminal, ~75% efficiency. Not too shabby. Unsurprisingly gets to solder melting temperature in <1s .
Heat gun high power (didn't mesure input) - 350A out, 525W, much more usable. Still a bit too quick though, ~250A would be better for this size of connector i think.
Heat gun low power (no input) - 95A - 140W. A bit too slow surprisingly. Probably loosing too much in the SS bolts im using as contactors in the clamp, so actual power into the part might be half this, will get better voltage measurements later.
All in all im pretty happy with this relatively simple circuit to control the power. The wasted heat by the heat gun isn't significant as I only need ~4-10s bursts. I had been worried that the transformer would saturate with the new 0G wire shorted, but looks like its fine at 6A max draw from the wall.

So for anyone looking at a rudimentary power control for a transformer, a series-ed heat gun (or hair dryer/toaster etc) will work quite well, and should add a good safety margin incase the transformer would otherwise saturate (and thus form effectively a dead short for whatever voltage remains). There's a number of 100-500W heaters available on ebay etc (search '220v heater') for ~$5-10 each, so it'd be easy to build a much higher resolution power control using about $30-40 worth of parts. Just make sure you wire it so the mains cant be touched, and everything is grounded (other than the mains ). basically, 'Dont try this at home' i guess heheh.

will post some pics later.

 

[spinningmagnets]

Adjustable heat gun in series? Great idea!

 

[atarijedi]

I have been thinking about this since I saw that demo video with the soldering gun (thinking about buying a 300W soldering gun and modding it). Has anyone tried an automotive battery charger? In "engine start" mode, they can get pretty high amperage. Or is the 12-14V they output too high?

On the electrode front, has anyone tried using aluminum? It is a decent conductor and solder doesn't stick to it very easily (it's used for soldering heatsinks). Not as good as copper though, and I think one of the key points to resistance soldering would be to have the electrodes be more electrically conductive than the materials you are soldering, so the heat is generated in solder or in whatever you are soldering, not in the electrodes. Silver is more heat and electrically conductive than copper, that could get pricey though, and solder sticks to silver pretty good, especially ROHS silver solder!

Also, to Parabellum, in your videos I saw you connecting both electrodes to the copper strip. What if you used a slightly narrower strip, touched one electrode to the top of the battery, and the other to the copper, so the current has to pass through the solder? That might melt the solder quicker, don't know for sure though.

All this leads me back to something my brother bought for me about 6-7 years ago. Cold Heat. Remember that thing? The portable soldering iron? It's a resistance soldering device too. Pretty sure it used some sort of graphite tip. Gotta find mine, but I wonder if it would work for this. I think Weller bought them out.

 

[sn0wchyld]

I have been thinking about this since I saw that demo video with the soldering gun (thinking about buying a 300W soldering gun and modding it). Has anyone tried an automotive battery charger? In "engine start" mode, they can get pretty high amperage. Or is the 12-14V they output too high?

On the electrode front, has anyone tried using aluminum? It is a decent conductor and solder doesn't stick to it very easily (it's used for soldering heatsinks). Not as good as copper though, and I think one of the key points to resistance soldering would be to have the electrodes be more electrically conductive than the materials you are soldering, so the heat is generated in solder or in whatever you are soldering, not in the electrodes. Silver is more heat and electrically conductive than copper, that could get pricey though, and solder sticks to silver pretty good, especially ROHS silver solder!

Also, to Parabellum, in your videos I saw you connecting both electrodes to the copper strip. What if you used a slightly narrower strip, touched one electrode to the top of the battery, and the other to the copper, so the current has to pass through the solder? That might melt the solder quicker, don't know for sure though.

All this leads me back to something my brother bought for me about 6-7 years ago. Cold Heat. Remember that thing? The portable soldering iron? It's a resistance soldering device too. Pretty sure it used some sort of graphite tip. Gotta find mine, but I wonder if it would work for this. I think Weller bought them out.

i suspect (though i dont know) that the reason for using graphite or steel (specifically, stainless) is the higher melting points. Ally melts at about 600deg - not that much hotter than lead (~300), where steel is ~1500C, and graphite something like 3500+C (it doesn't actually melt, but transitions strait to a vapor). Bare in mind, the point of contact between the electrodes and the part being soldered can be quite small, and as such the current density can be very high and thus generate significant heat at that point. It will usually cool off quickly as the surrounding material has low current density and therefore sinks the heat away quickly, so that point getting hot isn't a huge concern... so long as it doesn't start to melt .

 

[spinningmagnets]

The older Weller pistol-grip soldering irons have been mentioned as an option (Thanks, Fechter). Their claim to fame was for electronics and appliance repairmen is that it heats up and is ready to work in just a few seconds, rather than waiting for a fat tip conventional soldering iron taking a few minutes to get up to working temps.

I have a 100W soldering iron of that type, and...although it does take a while to get hot, it retains its heat due to tip-mass when using it. Skinny soldring iron tips are good for tiny electronics, but as soon as you touch the skinny tip to something with a lot of thermal-conductivity and mass (like ebike connectors), the tip cools down too much. If you make the tip fat, it works on physically large connections, but...the fatter you make it, the longer it takes to warm up. The main benefit to me was it was only $20, and works great...after you let it sit for five minutes to get as hot as possible.

Wellers innovation was to make a small hand-held soldering iron that got hot very fast, and still put out a lot of BTUs for big jobs (which was packaged in a handy size). A quick google showed the insides had a simple transformer. By my reckoning, it uses only one "fat-as-possible" pass through the core, so the output is 1/2 turn. Then 60 turns on the 120V primary means the 1/2 turn output makes one-volt. The key feature for us is that the one-volt output is already routed through two output sockets, to which we could attach probes to, making an easy RSU from a $40 ebay Weller (make sure "antique vintage weller pistol soldering iron", is in the ebay search).

The loop of copper that made up the heating probe has two distinct features to help it work. Every part of the loop is twice as fat as the tip. that way the tip gets hot before any other part of the loop. The hotter the tip gets? the more resistance it has, and it spirals into a feedback loop of more heat and more resistance. The rest of the loop gets hot, just nowhere as hot as the tip.

There is a dual-power model-8200N 100W/140W unit (1-1/2 turns with a center tap?) that seems to be fairly common. The 250W model-D550 and D650 seem to be the high-amp hot-rods...

History of Weller soldering irons
http://www.stevenjohnson.com/soldering/soldering-weller-1963.htm

Weller pistol soldering iron models
http://www.stevenjohnson.com/soldering/weller.htm

The Weller patent from 1946
https://patentimages.storage.googleapis.com/pages/US2405866-1.png

1891 patent for "Electrical soldering"
http://www.google.com.gi/patents/US449258


Pic below is the inside of the 250W model D550...the two hollow nickel-plated copper shafts that hold the ends of the copper heating loop are threaded on their ID with 5/16-24 inch (fine), this is relevant because if you want to connect two thick wires (10-ga?) into the two ends to use the Weller as an RSU, you could thread-in two bolts (or all-thread rod sections). 5/16-24 is not common when you need brass bolts (I couldn't find 5/16-24 in a copper bolt), but...it can be ordered online.

I have zip-tied the trigger down, and operated the unit with a foot-switch, and it worked fine...

 

[fechter]

And when you don't want to use them for soldering anymore, they make nifty laser pistols:
https://endless-sphere.com/forums/viewtopic.php?f=1&t=65733&hilit=laser

I have one of the larger Weller guns still working as a soldering tool. It has an aluminum secondary 1/2 turn. If you removed the tip and replaced it with a pair of electrodes, it might work as a resistance soldering unit.

To limit the current on a MOT, placing a heater in series with the primary will certainly work, but is not really elegant. Another possible approach would be to place an AC motor starting capacitor in series with the primary. This will limit the current. It's possible to do the math to see how big of a capacitor will be needed for a given current (I suspect it will be rather large). An advantage of an AC cap is it won't need to dissipate much heat. If you use several in parallel, you can switch how many are connected for different levels. Just an idea....

 

[spinningmagnets]

I used to think that the tiny added light bulb on the Weller (no doubt a simple filament incandescent type) was a handy addition. I recently stumbled across a reference that when using a simple dimmer switch on an inductive load (like a transformer), it helps to put a bulb in parallel with the circuit. I then remembered that all of the youtubes of professional industrial RSU's showed a bulb lighting up when the device was on. Coincidence?

 

[sn0wchyld]

Some vids and pics of the MOT solderer:



This is the guts of the unit. used a old broken china DC power supply's case to house it. Uses 2 240v inputs, both wired to the DPDT switchin the front (right side, where the red wrie connects to) Switching it on normally starts up the fan and ON light, while the 2nd 240v input comes in via a footswitch to control the power. Basically, the fan runs whenever the unit is on, but the transformer runs only when the unit is on and the foot switch is pressed (i have a foot switch wired as part of an extension cable, so its interchangeable what it can switch)


2 turns of 0g wire, 1.5v 700A. Heats stuff up nicely

View attachment 1
Used a larger set of jumper cable clamps, and used some 12mm stainless bolts as contactors, given solder shouldn't take to it and weld them shut. Has some spare thread on the back if i want to attach something else to it (like some smaller contactors on some new/longer wire)


All packaged up. Has a small thermometer to monitor winding temps, though appears this was unnecessary. extended use only saw the windings hit about 5C above ambient.

In use (appologies for the crap quality, only had a mopibus available) Kinda hard to see but the wires were well tinned and the 4mm 'cup' was full, so looks like a good quality solder joint with bugger all time:

[youtube]8jX0pX1LU-U[/youtube]

[youtube]tFWl1iLHXMY[/youtube]

Note the cables jumping around in the background when the power comes on POWA!!!
[youtube]lEAiWyP7sGs[/youtube]

 

[spinningmagnets]

You beat me to it! Thanks for posting these.

I can't help but notice that...not only was the 12-ga wire and joint heated up immediately, The precise nature of the heat focus was such, that...a few seconds later, you picked it up and could touch the wire and connector. That is the vital part for my goal of resistance soldering copper tabs onto 18650's. The ability to also easily solder large wire and large connectors is definitely a bonus.

 

[sn0wchyld]

You beat me to it! Thanks for posting these.

I can't help but notice that...not only was the 10-ga wire and joint heated up immediately, The precise nature of the heat focus was such that a few seconds later, you picked it up and could touch the wire and connector. That is the vital part for my goal of resistance soldering copper tabs onto 18650's. The ability to also easily solder large wire and large connectors is definitely a bonus.

yep, the heat is extremely localised, the cheapo PVC like insulation on this wire wasn't degraded at all, contrary to the result when using a soldering iron. Also much easier to keep the wire strait, and not get the outer 'clip' ring gummed up with solder.

I do however highly recommend a fume extractor (unlike what you see me doing in the 1st vid...) (mine pulls the air through a carbon filter then exhausts outside) as this has the potential to boil the lead, even if only in small amounts/extreme cases. Basically the connector would be mushy goo by that point, but all it takes is holding this thing on for long enough, as opposed to a iron which can never reach that point other than by some freak fault situation. In the above cases i'd estimate the contact points of the copper casing are hitting about 800C peak (faintly glowing red/orange) still well away from the 1700C to boil lead but far closer than the 3-400C of your typical iron. I might just have to see what 30-60 seconds of 1kw into such a part will do. you know... for science

https://www.hearth.com/talk/wiki/know-temperature-when-metal-glows-red/

 

[spinningmagnets]

I recieved a Weller 8200N 100W/140W soldering iron, since it was the most common model, and the one most likely for a reader to also find ($10-$20 on Ebay, plus shipping). I cut the tip, so it would have two copper probes, instead of a copper loop. I used 0.20mm thick copper ribbon and tried to solder them onto steel razor-knife blades.

At the max 140W setting, it took about 4 seconds to make a solid joint. The steel, copper, and the probes had cooled-off surprisingly fast immediately after, but 4 seconds seems like it's too long. I'll keep experimenting with this, but I'd avoid the 100W/140W model for the time being. The probe sockets are threaded, so it would be easy to make two independent probes. I locked the trigger "on" with a zip-tie and then used a foot-switch, which worked fine.

The 250W models are less common, but...I suspect they would work much better as an RSU.



Also bought a used set of jumper cables at the thrift store in order to harvest the 10-foot long copper wire, and will rewind the secondary on my MOT on my next day off...below is a link to a 1946 patent from an aerospace tools company, and the innovation was adding a wire-feed to put the solder in-between the two resistance-soldering probes:

http://www.google.com.gi/patents/US2604571

View attachment 1

 

[ridethelightning]

nice pics there.

I will be building some 555 processor boards specifically for MOT style spotwelders(10), that can be used with a solid state relay to control the pulse length.
ill be selling a few on a sales thread, probably~20 usd/piece.

I have recently been looking at a phase controller SSR that may be able to control the pulse length accurately within say 0.1-10ms, aswell as accurate controll of the input power. they are not cheap but hopefully will make an awesome spotwelder switch. i have bought one for testing.

im i the process of converting an old style ark welder transformer to become a spotwelder(basically a 20kg version of a MOT welder) for welding copper tabs and resistance soldering with fast pulse.
ill post pics of progress soon

 

[spinningmagnets]

That sounds great, I'll be looking forward to seeing your timers...