Your numbers look correct.
I’d rather call that 'optimum battery restistance, as you also don’t want to greatly undercut that number to prevent overcurrent problems.
I wouldn’t recommend 8S, as you’ll blow the kWeld input protection when fully charging these to 8*4.2 = 33.6V. And using a high voltage only makes sense when you already have such a pack lying around. I wouldn’t purposely build such a dedicated kWeld pack, because the power loss and generated heat in that pack will be huge. Remember, P = I^2 * R. At 1500A and 14.5mOhms you get 33kW of power dissipation in the battery during the pulses (!)
Selecting the right battery type and configuration isn’t an easy task, and these theoretical calculations can only be a starting point. Hence my recommendations of tested combinations on the kWeld product page.
I haven’t made own tests, but from customer feedback I’d say any fresh/good brand 65AH starter battery will do. For high amps go for 100AH, but depending on brand/model/age you migh get close to overcurrent.
I’ve got reports that the green (90C burst) model has weak cell interconnects that can melt from high energy welding with kWeld. The 150C models might be better though, but I don’t have info on that.
These are numbers at which the cell still maintains a certain voltage. kWeld is short circuiting them and pulls more amperage from the same cell. But The burst current rating is a good indication (unless the manufacturer is hugely overrating them for marketing). 475A burst should be well within the “window”.
I have started working on this after our family/business move and the lag created by that. The plan is to make an limited number of addon modules for existing kCap users who like to have the additional protection as a matter of courtesy, and then add the functionality to a redesigned kCap.
The website says the pack resistance of the 4S 1600mAh pack is 14mOhms, you’d at least need two in parallel and maybe even three to get a decent amount of current (please do the math excercise above to check).
This is the 4AH model at 10 milliOhms, two of them in parallel sounds good. A 5AH/3S battery usually lasts for 200 to 1000 welds depending on joule setting (discharging only by 2/3, I’d recommend to not go below 3V per cell).
