Well, I just realized something that I can't believe I didn't realize earlier. I think it's because I was originally thinking about making a 14s pack, instead of a 20s. My plan being to use Sanyo 20700A 30A 3100mAh cells to create a SMALL battery pack that can put out ~3000 watts. While I figure I'll have to see how it holds up, but I technically should be able to run a 20s2p pack with these cells and be able to make the power. I'm getting these cells from Bosch 18v 6.3ah packs.... which have copper plates connecting them, and are encased in plastic that's supposed to be some special kind that promotes cooling. I think it's because I origin ally was expecting to be running a 52v pack, with 3-4 cells in parallel, and would at the very least need to rearrange thing... but with a 72v 20s pack, I'm technically all set as is. The 20s2p pack is essentially just 4 of these Bosch packs in series. I'm still going to get one of these welders.... but looks like I could potentially not need one, without doing much damage soldering anything to these batteries directly.
Now I need to figure out how exactly I want to arrange/connect these. I suppose one major decision is whether or not to use a BMS. Originally I was 99% sure I was gonna need to get a 20s BMS that could handle 50 or more amps. While I still need to do more research, I've been seeing quite a few videos/posts about people recommending NOT to. I've seen people splitting their pack into 2 cells they run in series, and then making use out of those LIPO balance chargers/dischargers. Given many of them were running lower volts than 72, but there are a few 10s LIPO chargers available that could work for charging/balancing... some of them recommending to lower the max charge volts down from 4.2 to 4, to extend battery life. I'll be doing more research on what makes sense here... my original plan was to get a pretty serious high amp 20s smart BMS, where I could adjust output current, etc. via bluetooth and a phone app (or a Cycle Analyst, which was another addon I am definitely planning on looking into). On top of the cycle analyst, I was also very much considering getting a Cycle Satiator charger... while $300 isn't exactly cheap for a charger, it seems like a worth it purchase, considering it has the potential to work on such a huge range of batteries, with lots of nice options to help keep your batteries healthy/strong. But if going without a BMS is actually a good option, I already need to buy a LIPO charger for the batteries that I'm getting for this welder, I could kill two birds with one stone (but that's just a bonus, def not making a decision based on that... I am making it on what is actually a better choice when it comes to keeping the batteries healthy).
Another option could be to actually just run the 4 packs as separate batteries in series. One benefit here is, there is a chance I could simply just utilize the BMS that is already on the batteries from Bosch (tho def don't know if this is a good idea or not... would definitely be the easiest). I'm also not sure how well running 4 in series would work out with the power I'll be needing. I suppose XT90 connectors and some thick 10 gauge or so wire should be able handle it... but not sure about the current battery connections handling 4 times their current load. Given it is some nice copper, and I could possibly add some more connections to help with the additional load.... not to mention, seems like it may be a good idea to do as little damage as possible to what's already there.
Sadly I do have one small issue already, tho I'm hoping this welder will solve it. I have removed the plastic covers from 2 Bosch battery packs so far, and sadly, one of them unearthed the fact that one of the batteries welds did not hold, and the copper is definitely not making a good connection with that battery. So looks like I'll be welding copper in at least 1 spot with this thing, hopefully.
Anyway... time for some more research... and any/all advice is more than welcome... whether or not it's fact or opinion, both can help.
