Spot welding suggestions

Batteries, Chargers, and Battery Management Systems.
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mhoward   1 µW

1 µW
Posts: 4
Joined: Feb 16 2021 10:58pm

Spot welding suggestions

Post by mhoward » Feb 16 2021 11:18pm

I've been cramming information the last few weeks and am in process of building my own battery pack. I have salvaged some nice Panasonic NCR18650BDs that have essentially 97-102% rated capacity with my Vapcell S4 Plus chargers.

I bought one of the PCB spot welders from eBay (I know this is very frowned upon, it's hard justifying spending $200 on a spot welder) and wanted to get some feedback on what I may be doing wrong. I have the welder connected to a 600CCA deep cycle battery with about 10 inches of 14 gauge wire well soldered to about 5 inches of 12 gauge wire to an XT60 connector to the board. I added the 14 gauge wire to try to reduce the current flow. The lead wire is 10 guage and the tips are in the picture. I installed the capacitor on the top of the board but cut it off after it fried (hence the solder on the top of the board in the pictures).

I learned over the life of this spot welder that
1 - I needed to round the copper tips to get a more consistent spot weld
2 - Apparently this is a form of "resistance welding" (quotes for me :D ) and catching the edge of a positive terminal on a battery can make a nice hole in the nickel. As will not pressing down hard enough to make sure the current goes through the battery surface.
3 - I had better results touching the negative tip first, then positive and waiting the timer.
4 - I am terrible at soldering.

The only real issue I had is with
1 - Every so often, the welder would let out an explosive weld that would punch holes through the nickel. I am assuming this is mainly from poor technique, with me not having good pressure and contact with the material. However you can see on my battery pack on the photo, my last weld I believe was pretty well pressuring the nickel against the battery. That weld fried the unit and I am assuming I fried a mosfet and just let through too much current? After it fried, if I touched the tips to any metal, it would just shoot out sparks and apparently I was just shorting the battery. On my next board I am going to give the unit more breaks to cool down as I feel like I may have overworked it too quickly.
My question then is - am I correct on why it was shooting the explosive welds? Is there anything else I can be doing different?

2 - Every so often I would just touch the leads onto the material and it would let off a weld without waiting for the timer. I am worried I may just get "well thats what buying a cheap pcb welder gets you" responses (and probably an earned response), but is there anything about the assembly or this unit that you can see might be causing this? I didn't pay attention to the bottom of the board to see if it was arcing between the soldered posts and was wondering if that may contribute? Is it something I am doing wrong?

I'm also thinking maybe I shouldn't use the capacitor on my next one if the 600CCA is already a strong enough current.

This forum has been INVALUABLE for me getting to this point and I love all the information I have read, so thank you in advance for the amazing wealth of knowledge shared already.
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