Battery wiring for 100a trouble..

Hello all -

I’m having trouble connecting my 24 LifePo4 cells in Series. These are 3.2v, 50ah. Now, the terminals do not have screws/holes for me to connect nickel or copper plates for connecting purposes. Therefore I must solder or spot weld these (assuming no other options). Since my controller is drawing 100a continuous, I need a piece of nickel or copper that contains enough volume to allow my batteries to discharge with the least amount of resistance. The nickel strips for 18650’s seem to be not enough. Anything larger however, whether a big piece of nickel or even copper, I feel spot welding will damage my cells potentially. I understand soldering isn’t ideal due to the duration of the heat supplied on the pad. What do you guys do in situations like this?

Thanks,

Joe

Check out this thread:
"Copper/nickel sandwich" buses for series connections

What are those circular marks on the tabs? They look like it had some sort of pressure fit contact in the past.
Anything over 0.2mm nickel gets hard to spot weld but it can be done, the trouble is even 0.3mm Ni only carries ~2a per 1mm of width. Those tabs look pretty robust so I'd guess they'd handle the current fine.
0.1mm cu with 0.1ni sandwiched is easier to weld and handles the equivalent of. 5mm Ni ~3a/mm width. At 30mm wide this is getting there. If you can weld 0.15mm cu with 0.1ni on top at 30mm wide you'd be done...theoretically.
I'd do a heat test on a strip @100a and also I would test a spot welded sample to see if the tab is going to generate heat. I'd be thinking 20 or so pairs of neat little spot welds in a few rows would suffice.

I have similar need and I will try to build something like this:

copper for series and nickel for parallel

Any idea what those terminals are made of? Spot welding may be difficult. Whatever those cells were made for must have had a way to connect them. It would be nice to see how somebody else connected them.

I believe they are lazer welded, look at the passat modules in my yamaha thread.

fechter said:

Any idea what those terminals are made of? Spot welding may be difficult. Whatever those cells were made for must have had a way to connect them. It would be nice to see how somebody else connected them.

Click to expand...

they are laser welded. The laser welders are not affordable for DIY

Hey all,

I recently made a post about connecting my 24 LifePo4 cells in series to create a 72v, 100a cont. pack. Here’s the old post for more detail: https://endless-sphere.com/forums/viewtopic.php?f=10&t=112103. I apologize if linking the post is breaking some rules or something. The terminals are nickel, I have discovered, so spot welding may be an option but I’m not sure how to approach this.

I came up with a “solution” that I’d like some input on. I ended up purchasing nickel strips, 0.15mm. I took a copper pipe (that I purchased), removed exterior oxidation and hammered them into flat bars to connect the terminals in series. They should handle 100a more than fine. However, the copper of course cannot directly connect to the nickel terminals due to it’s thickness (I also don’t know how easy Cu spot welds to Ni). My plan was to wrap some of the nickel strips around the copper and spot weld itself onto the copper, from there, I would spot weld the hanging edges of the nickel sheet to the thin, nickel terminal. I’ll provide pictures to further explain my intentions.

I have a few questions. First, is this a bad idea for whatever reason to use purchased copper pipes? I removed some exterior oxidation but the interior of the pipes still have been exposed for a while. Second, I am concerned this method will not create a good enough contact between the terminals and the nickel around the copper. Third, are there any other suggestions or thoughts that can help save me from going this route.

I appreciate your guys’ responses and patience, I hope I summarized this well enough but I’ll be here to listen and answer any questions.

Thanks again,

Joe

Have you read through this?

https://endless-sphere.com/forums/viewtopic.php?p=1662507#p1662507

john61ct said:

Have you read through this?

https://endless-sphere.com/forums/viewtopic.php?p=1662507#p1662507

Click to expand...

I have, however I feel it doesn’t apply since I’m dealing with two terminals and a small area of conduction. I need thicker copper to handle the amperage rather than 0.15mm of copper. I could be mistaken. If I do need thicker copper then I need a way to mount it and I’m still contemplating different ideas.

Also, stupid question. Do I need the copper to make contact with the terminals rather than through the nickel? If it must go through the nickel to reach the copper (which is the less resistive path) ITLL STILL GO THROUGH THE NICKEL? Assuming no copper is making any contact. Therefore, the nickel would potentially resist current leading out of the anode and into the cathode generating heat. Am I mistaken?

Nickel is much higher resistance

only used for the spot welding process

other side of the copper

which yes you want in direct contact with your terminal.

Tin-plated copper best to prevent corrosion, oxidizing layer adding resistance to the connection over time.

fechter said:

Any idea what those terminals are made of? Spot welding may be difficult. Whatever those cells were made for must have had a way to connect them. It would be nice to see how somebody else connected them.

Click to expand...

I created a new post yet I guess I didn’t need to. The terminals can have nickel spot welded to them is all I know.