Need advice on soldering liPo battery tabs

[Rover1312]

Hey fellow DIY enthusiasts,





I could use some advice on soldering LiPo battery tabs. I have a 4S CHNL 1500mAh 100C LiPo that I used for my FPV drones. Unfortunately, my charger died mid-process, and it ended up killing 2 of the cells. To salvage it, I converted the battery to a 2S setup.





Now, I’m facing an issue with soldering the last wire to the battery tabs. I purchased some aluminum flux solder from Amazon, thinking it would do the trick, but the solder just won’t stick to the tabs.





Has anyone dealt with this before? Any tips on getting a solid connection? Should I be using a different type of flux or solder, or is there a specific technique I’m missing?





Thanks in advance for any help!

 

[adi508]

It is welded by spot welding using zinc strips

U can use a knife to scratch and then solder it. It removes the oxidation from zinc

 

[Rover1312]

It is welded by spot welding using zinc strips

U can use a knife to scratch and then solder it. It removes the oxidation from zinc

the other tab of the battery is soldered to a wire , the factory didnt use a spot welder. Ive tried scratching and everything i just cant get a good enough heat transfer. Im running my iron at 450C. This is a high discharge lipo so the tabs dont heat up that easily.

 

[Heisen]

the factory didnt use a spot welder

They did, I am 99% sure, it is not recommended to use soldering to battery aluminum tabs, so companies use spot welding.

i just cant get a good enough heat transfer.

Use chisel type tip for most heat transfer, basically the more contact you have the better the heat transfer.

With aluminum flux it is sometimes also recommended to get special solder, which is 91% Tin and 9 % Zinc.

Iron at high temperature is good, the critical part is the time to solder, in my opinion it should be under 1-2 seconds, if you can't get the joint done with quick tap, either you don't have high enough temperature or the right aluminum flux or the right solder or the right tip. That all there is to it.

If you are unable get the joint done under 2 seconds, you probably shouldn't be trying to do it again with the same setup, cause it might damage the battery.

If nothing works, then the only option is spot welding.

Also use some kind of fume extractor as these chemicals are toxic, just make sure you don't inhale them. I usually go into open ventilated area with big pedestal fan to push the fumes away from me.

 

[Rover1312]

They did, I am 99% sure, it is not recommended to use soldering to battery aluminum tabs, so companies use spot welding.


Use chisel type tip for most heat transfer, basically the more contact you have the better the heat transfer.

With aluminum flux it is sometimes also recommended to get special solder, which is 91% Tin and 9 % Zinc.

Iron at high temperature is good, the critical part is the time to solder, in my opinion it should be under 1-2 seconds, if you can't get the joint done with quick tap, either you don't have high enough temperature or the right aluminum flux or the right solder or the right tip. That all there is to it.

If you are unable get the joint done under 2 seconds, you probably shouldn't be trying to do it again with the same setup, cause it might damage the battery.

If the tabs are too much heat resistant, then the only option is spot welding.

Also use some kind of fume extractor as these chemicals are toxic, just make sure you don't inhale them. I usually go into open ventilated area with big pedestal fan to push the fumes away from me.

Hi , so all the tabs are soldered to each other , not a single spot welder was used , im assuming thats because these are high discharge batteries that can do 100A discharges and using spot welds would cause more heat while discharging.

 

[Heisen]

im assuming thats because these are high discharge batteries that can do 100A discharges and using spot welds would cause more heat while discharging.

Not true, spot welds doesn't affect discharge heat, it in fact minimizes the heat, provides low-resistance connections, which is very important for high current use.

Soldering in comparison heats the cell much more during assembly and is generally avoided it's also time consuming and expensive during manufacturing. So I am 99% certain the tabs are spot welded, if the battery is from a reputable manufacturer.

 

[Rover1312]

Not true, spot welds doesn't affect discharge heat, it in fact minimizes the heat, provides low-resistance connections, which is very important for high current use.

Soldering in comparison heats the cell much more during assembly and is generally avoided it's also time consuming and expensive during manufacturing. So I am 99% certain the tabs are spot welded, if the battery is from a reputable manufacturer.

Heres the pic , i stand corrected they used spot welds between the batteries but the main power leads are still soldered. And also balance plug wires are soldered ontop of the welds? Idk wouldnt it be better to just solder in the first place if they were gonna solder ontop of the welds

 

[adi508]

Heres the pic , i stand corrected they used spot welds between the batteries but the main power leads are still soldered. And also balance plug wires are soldered ontop of the welds? Idk wouldnt it be better to just solder in the first place if they were gonna solder ontop of the welds

This type of soldering is melted very easily. I think your soldering tip has oxidation deposited, u should reapply tin on it. Heat it first then dip in water, if your soldering iron is cheap.
Try using copper wire, before soldering with battery tin the wire properly

 

[Rover1312]

This type of soldering is melted very easily. I think your soldering tip has oxidation deposited, u should reapply tin on it. Heat it first then dip in water, if your soldering iron is cheap.
Try using copper wire, before soldering with battery tin the wire properly

My tip is fine , i clean it and its a decent iron ive been using it for a few years now sequire 65w si012 iron , the issue is heat wont goto the pads fast enough ill try a different tip

 

[Heisen]

Idk wouldnt it be better to just solder in the first place if they were gonna solder ontop of the welds

Battery terminals are usually steel or aluminum, the welded tab is usually nickel plated steel or pure nickel, after spot welding both, we either connect nickel directly to the board via soldering or we solder wire on to it.

After spot welding, we solder only to the tab not the battery terminal to avoid heat damage to the cell.

Soldering to Nickel is easier than directly soldering to aluminum, the nickel welded tabs also acts as a heat sink, so you are not directly heating the cell casing or terminals.

It's the industry standard. Soldering as far as possible from the weld.