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Soldering to sheet metal problems
#1
Hey all,

I am on my 3rd battery back design and I think I have nailed down a very effective and economical solution for my 'bus bars' using sheet metal.

My issue is that I can't get my fuse-wire solder joints to stick to the aluminum sheet metal because its essentially a massive heat sink.
At the very best I get a very week/dry joint that will break with very little force.
Here is what I have tried so far:
  • Using a good solder station and max heat ~800C
  • Using lead free solder, 21 gauge
  • Using a thick flat solder tip for surface contact - works really well on the 18650 cells
  • Using a good rosin flux in large, small and none amounts
  • Cleaning the surface area with different cleaners - alcohol, degreaser etc.
  • Sanding and grinding down the sheet to roughen the surface
  • Heating the surface up as much as possible with the solder tip before applying the joint
  • Using all combinations of above methods
  • Spot welder doesn't work because the fuse wire blows and 5A
Really hoping someone can let me know if there is a good technique for this. Thank you for any helpful comments  Smile

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#2
Aluminum is very difficult to solder to. I would recommend not using aluminum.

eptac.com Wrote:You need an aggressive flux, a high activity flux with activators, such as an ORH1 flux. This flux is very active and cleaning is a must to removed the residual fluxes left behind after the solder joint is created, and in your case, after the shield is soldered. I would recommend an ultrasonic cleaner to do this to verify the flux is removed from beneath the shield. You can use existing tin/lead solders and lead-free solders to do this soldering. If the product is new, or was built after 2008, then the lead-free solder is a must to do this work.
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#3
An added point, and this is for any type of sheet metal, is to heat the whole sheet up to work on. If you can, have a stove or something that would allow you to heat the whole plate up. You might not be able to get to 300C with it, depending on the heat source, but you should be able to use your iron on it to bring those spots to temperature. Then solder all your wires to the plate leaving enough wire to connect to the cells.
After the plates have cooled down, attach them to the packs and solder the wires directly to the cells.

So basically you solder all your connections to the sheet metal first, then solder the wires to the cells after everything has cooled down.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#4
(06-12-2018, 11:44 PM)mike Wrote: Aluminum is very difficult to solder to. I would recommend not using aluminum.

eptac.com Wrote:You need an aggressive flux, a high activity flux with activators, such as an ORH1 flux. This flux is very active and cleaning is a must to removed the residual fluxes left behind after the solder joint is created, and in your case, after the shield is soldered. I would recommend an ultrasonic cleaner to do this to verify the flux is removed from beneath the shield. You can use existing tin/lead solders and lead-free solders to do this soldering. If the product is new, or was built after 2008, then the lead-free solder is a must to do this work.

The only other metal that can be used is copper. I tried using copper but it has very poor machinablity properties; without expensive machine punching tools it's almost impossible to work with as you can see below. 

Copper is also 3 times as expensive as aluminum so its not nearly as cost effective. Aluminum is a dream material to machine.

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#5
To punch holes in the copper, you could sandwich it between two pieces of wood. Possibly even two plates of steel. Have a hole where you need to drill and just move the plate to each spot to drill. If using steel plates, you could even use a punch. Take a steel tube of about 1/2" and fasten it to a drill press. Don't turn the press on, just use it for a punch. Then the steel plates would have 9/16" holes in them and you press through the hole in the plates into the copper with the steel tube. It'll cut a hole right through the copper.
You can do different measurements, you just want to make sure the steel plate is about 1/16" large than the tubing. In metric that would be about 1.5mm difference.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#6
my idea:
solder the fusewire to a piece of nickel stripe and than spotweld that one to the aluminium block
Korishan likes this post
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#7
Press the fuse wire instead. Ie make a small gap or wedge in the alu hole and then press that together with the fuse wire inside.
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#8
I'm going a similar way and a metal engineer told me to nickel plate the aluminum sheets...

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#9
One option is to use a Resistance Soldering Unit (RSU). they can be purchased, but they are pricey for even a small one. Instead they are very easy to make from a trash-day microwave oven. Search Youtube to see the safe ways to harvest a transformer, and re-wire the secondary coil with 3-6 coils of fat wire. That converts the output from high volts and low amps into low volts (3V-6V) and very high AC amps. Check out youtubes for examples of a very high amp spot-welder, which is essentially the same thing.

They can be activated by a simple $20 table-saw foot-switch. The amount of amps you get will be the result of how much copper mass is passing through the transformer window, divided by the number of turns/volts of your system. If the converted transformer has way too many amps, simply re-wind it with more turns (12V is the highest I recommend, but any voltage up to 48V is fairly safe), because...the watts will stay the same, and more volts you have it converts to fewer amps (amps are where the heat is) or...pass less copper mass through the window. If you use a smaller coil through the transformer window, fill the remaining space with something non conductive to prevent the coil-wires from vibrating.

pic of converted transformer
https://endless-sphere.com/forums/downlo...205954&t=1

discussion of all the details, DIY RSU
https://endless-sphere.com/forums/viewto...14&t=88965

discussion about DIY spot welder
https://endless-sphere.com/forums/viewto...14&t=85023

Concerning the machining of copper. Pure soft copper has an IACS conductivity of 100/100. Tellurium copper (C14500) has a conductivity of 93/100, still very good, and MUCH better than nickel at 22/100, and even aluminum at 61/100. The addition of a tiny amount of tellurium make the copper just brittle enough that is can be machined much like brass. I broke many drill bits on pure soft copper, but with a little care, I haven't broken any using C14500.

https://www.bluesea.com/resources/108/El..._Materials

https://endless-sphere.com/forums/viewto...8#p1382093
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#10
There are some core concepts to soldering that need to be understood. It's just not melting metal and sticking things together. To form a joint the interface between the solder and the base metal needs to alloy together. Two things will prevent or hinder alloying and that's oxidation, and not being clean. Solder will flow to the hottest point so you must have an iron with a high enough thermal output to get the surface to temperature. When soldering to a large metal mass or a sheet of metal that's a big heatsink and you need an iron that can put out enough heat to get it hot enough for solder to flow onto it. That's influenced by thermal mass and contact area. A tiny tip isn't going to be making enough contact to transfer a lot of heat. Also note that oxidation on the tip will act as an insulator. The hotter your iron tip is the quicker it will oxidize. Roughly ever 50C increase or decrease will affect the life by 2x either cutting it in half or doubling it.

I personally use leaded solder. I have quite a number of different types. I work within a RHOS exception area though. There are some high reliability lead-free alloys. AIM's REL22 is an example but it's $88USD/lb. Don't make your life more difficult using solder with a crap flux core. The flux in solder is normally targeted at small joints. If you're doing a larger surface or to bare metals a flux pen will make things easier. There are fluxes made for that but if you don't clean them off properly they'll corrode the metal.

If you have to turn your iron all the way up to solder something then it's the wrong iron for the job. Crap solder joints are also less reliable.
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