Summary

Apologies if this explanation is a bit random ...last thing at night ....

Large box for the spot welder as I did not like my board hanging off the battery

You need to remove the original pot and fit an external pot and also move the display to the lid.

The pot I used was a 2W Wire Wound multi turn 50kOhm. When removing the original pot..note the wiring, it is not as expected..the pot wiper IS not the centre pin on the original PCB mounted pot.

There is a low frame inside to support 3x 18650 cells. I used a 9 pin DIN socket for the balance wires for the 18650 cells, so pack balance and charging can be done without opening the box.

Switch is a 2 pole 6 way rotary. I used one pole for power and one pole for selection Auto Pulse or not.

Hex holes in the base are 8mm across the flats.

TVS diode fitted below the board...clamped and soldered to ring terminals then heat shrieked to prevent shorting to the base of the board.

Shoktty Diode tabs need drilling to accept the bolts and a copper strip needed to extend it to the other thick wire.

I put a 6.5mm mono jack plug on the lid too, to allow connection of the foot switch for manual pulse instead of auto pulse.

4 holes in the base to enable fitting of rubber feet, Keyhole slot to allow hanging of the box on 'mushroom head' nut. Had planned to make a frame to hang the box alongside the battery so the cables hang downwards.

Box screws together with 6 screws, think I used No.4 size 15mm long.

Obviously you need x4 of the cable clamps

Next job is to create a 'pistol grip' with trigger style gun to allow single handed application of the probes and manual triggering. Any one seen anything suitable ?

I printed in low quality mode on a MakerBot Replicator 2. Quality good enough, though the top layer of the lid was pretty poor.

Do not think I have missed any info..feel free to leave a comment and i'll try and get back to you ASAP

For those that have not come across this project, the links are below. The developer Marc is a very helpful guy, who has helped me in no end of ways.

https://malectrics.eu/product/diy-arduino-battery-spot-welder-prebuilt-kit-v2-2/

http://www.instructables.com/id/DIY-Arduino-Battery-Spot-Welder/