Spot Welding Battery Packs

[parabellum]

when the mosfets turn off their is a huge inductive spike

On JP spot werder "riba2233" sales tread you will find solution to that as well.

 

[Alan B]

The timescale here is very important. Normal battery testing doesn't look at what happens in the first 10 or 20 milliseconds. It doesn't register till hundreds of milliseconds and more have passed. If these battery welders weren't getting 1000 amps or more they would not be getting these welding results that they are getting.

 

[okashira]

Thanks it all makes sense.

I will look at a basic plan over the next few days.

But I mention the lack of caps because when the mosfets turn off their is a huge inductive spike.
Now because its low inductance it happens much faster but has less energy so I be the lead battery is sagging more then you suggest.

My training is as a motorcycle mechanic and I test shitty lead batteries all the time.

I have seen what 700 amps from a diesel truck will do to a pair of starting batteries and it can sag all the way to 0v if the batteries are week. But a single starting lead battery with 700 amps will typically sag to the 6-8v range. I suspect some of these diy kits work so well because the battery sags so far to stop the current from climbing to high and If I use good caps or even lithium I will need to make sure I am more careful getting it just right.

I have a few phases here I can look at using but I think the best thing to do will be design something from scratch.

Time for bed thanks again.

I get 3000 amps from 9v battery
Inductive spike solved by flyback diode and tvs diodes

 

[Arlo1]

I get 3000 amps from 9v battery Cool how did you measure it?
Inductive spike solved by flyback diode and tvs diodes

I get that but I am surprised the lead battery takes the power fast enough this is what the caps do in most cases.

 

[okashira]

With an oscilloscope