Battery spot welder amperage

I need to spot weld up a lithium battery pack and wondered about this Arduino Battery spor welder instructable. . It looks very good. I will not use this much, maybe just this one time, and I am wondering if I'd really need 6 MOSFETS? Could I skimp and get by with just 2 and then I'd only need 1 of those MOSFET drivers. One MOSFET is showing it's rated for 170 amps. And it's only one for like 20 millis.

So you’re trying to save $3.00 USD?

The mosfet may be rated for 170 amps, but in actuality it’s rating is much lower; the builder of that instructable (I can’t vouch for anything in its design, btw) likely wanted to have a reasonable margin for the current - hence the 6 mosfets in the design.

You could try to use fewer - but you might end up blowing the mosfets and money in the process.

Those mosfets cost me $2.64 each and then $1.70 for the midget drivers, so it adds up to $20

With those mosfets (irf3704) they have an RdsOn of 0.009 Ohms. There are more efficient options for mosfets that may allow you to use less.

The current will still be the same regardless of the gauge so the mosfets and circuit will still need to be able to handle the same peak current.

The smaller gauge will need less time to spot weld and so the welder can be set to a much shorter pulse so in theory as long as you stuck to short pulse durations you may be able to get away with a couple fewer mosfets.

Most mosfet ratings are grossly exaggerated (unless you have an infinite heatsink!). The mosfet might be able to handle 170 amps but the package itself cannot.. Or they can only handle that current for a few micro seconds.