# How current flows through battery nickel plate -- Diagram shown

1. Jan 4, 2016

### iDred

I'm going to weld nickel plates/tabs to 18650 cells. Each two batteries will be welded together with a nickel plate. In the center of the nickel plate will be a copper wire to take the 20 amp current flowing from the two cells at 10 amps per cell.

Since I have .2 mm thick nickel plates, to get the correct size I would need to make it 10 mm wide to handle the 10 amps. This would make the cross sectional area of the nickel plate large enough to handle 10 amps.

My question is that because I can only weld the plates to the battery positive side which has a small positive ciruclar area. Does making the plates wider than this positive area help the current flow?

Assume the diameter of this positive area is 7mm, Will making the plate 10mm wide make some of the plate useless?

Will I need to make the plate thicker and keep the plate width equal to the positive battery side area?

What I don't know is how electric will flow? Will it be a straight line from the red dots to the wire, will it spread out through the whole nickel plate?

Below is a picture to help show what I am talking about. You can see the red dot welds are centered in the wide nickel plate. The white circle is the copper top of the batter and the only place I can weld to.

2. Jan 4, 2016

### rootone

It will help if you can explain better what this projects is about.
Welding 18650 of anything is a pretty big task.
I don't think it will matter a lot about whether some parts of the nickel superstructure are not useful as current conductors,
Your description sounds like you will need a very good heat sinks, and extra nickel will certainly be useful for that purpose.

3. Jan 4, 2016

### rbelli1

18650 is a cell size. I assume that is what the OP is referring to not a quantity.

The extra width of the tab will reduce the resistance however whether this is necessary depends on your application.

Be sure both cells are charged to the same voltage before welding or you will get a nasty surprise.

BoB

4. Jan 5, 2016

### iDred

If this makes it easier to understand. In the picture below you have the wire on the left delivering 10 amps. The wire on the right taking the 10 amps.

The nickel plate between the two wires has the exact mass (cross sectional area) to handle 10 amps without heating up if the 10 amps were evenly spread through it.

My question is because of the way the wires are positioned, will this heat the nickel plate because the wire is soldered on the left is in the center and not run along the length of the nickel plate.

Will this cause the nickel plate to heat up? Am I wasting nickel plate because of the way I soldered the wires? Or is it possible the electric will spread out and utilize the whole nickel plate?

What I don't understand is how the electric will flow from the two wires.

Thank you for any help anyone can give me.

5. Jan 5, 2016

### Staff: Mentor

The current will spread out, so extra width is not wasted. I think it would be better to, for example, use foil of double thickness (0.4mm) than of double width (20mm), were you to make a comparison, because the current density at the weld points will be better with less heating.

Whether there are issues associated with spot welding to the case of 18650 cells I don't know. Do manufacturers data sheets say anything about this? You've ruled out using the "soft pack" lipolys with their tabs ready for soldering?
whatever the right term is.

Some lipolys sold for RC applications come with phenomenal discharge capabilities, if it's important to your need.

6. Jan 5, 2016

### jim hardy

i think it is difficult to solder to nickel
i had to take some Radio Shack NiCads in to work and silver plate their tabs before solder would stick

http://www.plateworld.com/editorial26.htm

He goes onto say sulfamic acid might make a useable flux.
Of course i had only plain rosin flux and it was hopeless until i plated the metal tabs.
Could you use brass shim stock instead? It'll solder really well.

good luck !

old jim

7. Jan 5, 2016

### iDred

Jim, actually soldering to nickel is very extremely easy using regular radio shack 60/40 solder. I have already done that to put together a battery pack without having a welder. I had to solder all the nickel tabs to the battery.
This is what I bought specifically for welding, but it solders to it like tinned wire.
• 50 pieces pure Ni200/Ni201 nickel (99.6% plus)

8. Jan 5, 2016

### jim hardy

Sounds like handy stuff to have around.

9. Jan 6, 2016

### Staff: Mentor

The cells were provisioned with solder tabs that solder wouldn't stick to? What use is that!

Perhaps they were manufactured to be weld tabs, to weld into an assembly.

10. Jan 6, 2016

### jim hardy

Last edited by a moderator: May 7, 2017