They just seem like a really poor, inconsistent analog for a real cell.
Not to mention that different real cells all weld differently, and your welds need to be calibrated for the cells you’re welding.
If I were trying to teach a complete novice the fundamentals of spot welding, and I didnt care about the quality of the welds, then these might be suitable. But for actually testing a true welding technique, I think these suck.
I don’t think I’ve ever seen someone come so close to having a very, verrrry bad day without actually shorting the cell. Another mm or so and…
yep.
I’m good like that!!!
Voltages in that range are pretty typical for resting voltages after a full charge. That 95% number isn’t taking into account the voltage rise during charging and the settling back down to the resting voltage once full charging is done.
A 36mV spread isn”t a bad number either.
I’ve been told before that I need to get my SOC delta down below 5mV
Did they tell you why it needed to be so tight? Or is that just some number they guessed they wanted to have because Smaller Number = More Better?
The difference in the charged capacity of the pack between a 36mV spread and a 5mV spread is tiny. It makes no practical difference the performance of the pack to charge some cells by a few more mV.
Is it theoretically better? Sure. We could balance to a microvolt spread and get even more capacity (a thousandth of a mAh perhaps). But when the spread starts getting down to the level of the background electrical noise that the BMS is measuring it doesn’t add much to the pack’s charge.
A 5mV spread spec must also have a BMS that is accurate to a mV or so. Something I doubt most of these BMS’ can do.
A tiny delta can also significantly increase charging time.
I also notice the spread goes up to 70-80mV at different SOCs, is that bad? Sometimes while charging I see spreads that high too.
That is completely normal and expected. You are “top balancing” only. That means the cells are free to do their own thing as they discharge to different voltage levels during the discharge (due to the small differences between the cells).
You can ignore these differences until they result in one or more cells approaching 2.5V a lot sooner than other cells when the pack reaches your desired cutoff voltage. Then it’s time to replace the pack (if not sooner due to performance drops before then).
Won’t the electrodes melt the plastic? At least my kweld electrodes would, I think.
Looks really cool though, might try something similar for shits and giggles.
these are things that would be super nice to have.
dang
Is this supposed to be a welding circle guide or something?
Very pretty. But assuming this is the negative end of a p42a group, the inner welds worry me.
The inner guides are for the positive side, all in a measured circle.
What’s shakin everyone. I’m in the midst of planning an e-bike battery build and wanted some opinions on bms bypass. In the caseof esk8 and EUC there’s obv several good reasons to bypass the bms and I won’t rehash that discussion. For en e-bike tho, the breaks are mechanical and the protections offered by the bms make a lot more sense in this case. It will be a low-current battery (40amps) and the controller will only pull 30 amps anyway. There’s a lot in the “For” column far as I can tell and I can’t really think of any drawbacks aside from discharge through the bms as a possible point-of-failure. Can anyone else give me a good reason not to bypass? TIA
In that case I’d discharge through the BMS. If you aren’t relying on electronic regenerative brakes, the downsides of discharging through the BMS are much much lower.
