The battery builders club

If we bypass the BMS (and I totally get the safety reasons why to do so), how do we control that the battery stays balanced while discharging? Do our vescs take care of it?

How shitty is it if I get frustrated with the slow pace of battery builds in my garage and I step in and finish it?

@jansen, (if he reads this, free tank of gas,:sunglasses:) lol, he won’t.

Slow loris.
I know, don’t touch another man’s stuff.
What if it takes 4 full days to attach balance leads?

God dammit, hurry the fuck up. Yes you.

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As long as the cells are legit, new and purchased around the same time, their capacity should be sufficiently close enough that this happens on its own. Having your bms wired for discharge has nothing to do with discharge uniformity. It provides other protections- e.g. over-discharge protection, overcurrent protection, short-circuit protection. If you notice a p group that is not uniformly discharging, you’ll also likely observe it charging faster than other groups. This is most often indicative of broken welds or occasionally a dead cell.

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I plugged in the balance lead with reversed polarity….twice. :triumph::roll_eyes:

Repaired burned trace, swapped out new jst connector and burned pin.

Bms was wrapped in fish paper and kapton. I assumed the polarity of balance leads was like 90% of the other bms’s I have encountered. I was mistaken.

Lesson learned:

Verify bms input labels on the actual pcb markings.


So frustrating. :face_with_symbols_over_mouth::face_with_symbols_over_mouth::face_with_symbols_over_mouth:
Glad you got it worked out though!


I forgot how much of a pain it is so weld Molicel cans. :expressionless:

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I hear people talking about this all the time, but I’ve never had an issue with it. What’s the rub?


1/10 cells just doesn’t stick, I can get good connections at 50J on 0.2mm for most of the cells but every now and then there’s a few that just don’t stick, I can dent the can and vaporize the nickel but still nothing

What welder do you use?

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Is it super obvious that it doesn’t stick?

Well it just falls off when I do the first tack

  • Malectrics
  • 800CCA car battery, floating at 13.75V supplied by my 18A lab PSU
  • My welds usually benchmark around 666A and 4.5V
  • I pretty much never sharpen my tips
  • 1m long 6AWG welding leads
  • kweld probes

Perhaps you’re pressing too hard? I think I remember @A13XR3 saying something about how spot welding exploits the gap between conductors to spike the resistance and make the weld. If you press too hard there’s no gap, and therefore very little resistance. But :man_shrugging:


Very likely, spotwelding physics needs resistance to perform the weld. You push down too hard and eliminate the air gap, your resistance decreases, weaker weld. Light but firm touch is the key.


Hmm it seems I missed the sweet spot then

54J for me, haven’t had this issue in the past on my kweld

How pointy are your tips?

Not too crazy

I usually file off the blackened part before welding


Damn son, you need to sharpen dem tips

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Really? Mine look like that too, and they weld fine.