DIY 72v 20AH Battery Build

[@Full_Throttle_no_Brakes]

Thank you very much for this video and explanation. Can you please share the dimensions of this battery pack in millimetres?

[@fgbhrl4907]

Length of sense leads doesn't matter. You should really cover up all the areas you're not directly dealing with when welding the nickel strips. I accidently had a strip shift between rows.. insta fireworks. Also, protects against accidently setting it down on a scrap piece of wire / nickel strip / screw etc.

[@tminustoday]

Thanks for the advice! I'll completely cover any areas not being worked on with my next project, there is no reason not to.

[@alipsa823]

balance wires need to be short, the extra wire get you resistance and charging balance problems

[@tminustoday]

16" balance wires seem pretty short to me.

[@imho7250]

Did you manually top balance the pack before wrapping it to give that poor little BMS a fighting chance at maintaining that balance? Since you assembled it with harvested cells, unless you manually charged each cell to 4.20v before assembling, it is good to watch it the first charge and use an hobby charger to drain or top off each brick until you see everything in balance, the charger light green, and the BMS bleeding down any slightly high brick. Its good you added a AWG 12 collector on the nickel. Most people overlook that and just attach to one end, effectively making a snake bus with 80a/200a going through one sliver of nickel strip. The only thing I did differently was distribute the 2 B- wires along the collector, which on your battery would be between 2p/3p and 6p7p so that each segment of the AWG12 collector only carries 20a and each B- wire carries 40a/100a. Those look like Molicel 18650’s. Not sure which cell but I don’t think Molicel makes anything weak, so im sure the pack does pretty good. ANT BMS are dirt cheap now and being able to see what’s going on, especially with harvested cells, is really nice. My 80a/200a Bluetooth ANT was only $40 delivered. Its just so nice to open the app, check how the cells are doing, check for sag in each group, check for self discharge, etc. Im currently rebuilding my P42a pack because my BMS told me I had some bleeders. Not surprised because I knew I burned some holes in a few of them when spot welding but figured I would monitor them. After a few weeks when enough electrolyte leaked out the damaged cells began self discharging, progressively more and more. So Im in the process of letting them set so I can see which are bleeders and which I can reuse. Lol

[@tminustoday]

Thanks for the comment! I used the XTAR VC4+ and balanced each individual cell to 3.72v before connecting them together. Once assembled I then charged it to 100% to rebalance the cells together. So far, it's working great. I charge to 85% and every 6th charge I rebalance the pack and charge to 100%.

[@imho7250]

@@tminustoday I use ANT BMS on my battery and i set it so it will never balance automatically. I periodically charge it to about 4.100v/cell and balance it to 0.000v differential by manually starting autobalance. This begins a monitoring period where i will discharge and charge several times, charging to 50%-80% after a ride and only charging to 100% if i plan a longer ride. I view cell differential as the #1 battery health indicator, during rest as well as at max discharge current. A perfect battery would keep 0.000v difference regardless, but nobody has such a battery. Checking differential at rest after discharging it tells you how well the cell group capacities are matched and will also tell you if a cell had died (CID disconnected). Checking differential at max discharge current should be done on the new pack, establishing the baseline. If that starts growing over time, at the same battery temperature, that may indicate a decrease in health, And finally the resting differential after charging and discharging it several times tells you if there is any self discharge or severe IR imbalance in the pack (which should show up in the max discharge test). At this point I would never use anything but a Bluetooth BMS on any battery that cost more than $500. Its worth the few extra bucks to be able to see everything inside the pack without opening it.

[@TheMiniRonster]

Hey do you know could you build a 76v 20ah battery that fits in your razor dirt bikes the sx500? Also how much would that cost to make?

[@tminustoday]

You can do a 21S configuration on the SX500. I would look at upgrading the drivetrain and suspension as well if you are going to push that much voltage through that small chassis! 48v was plenty to lift the front wheel with power wheelies. Be careful and have fun if you decide to go that route!

[@brucegreen4756]

Can you build me one I have a gt08 scooter it have a 60v 27ah battery but I want a 60v 40ah battery For a longer ride

[@tminustoday]

I'm not confident enough to build a battery for someone else yet! I'd need to add fuses instead of ripping them out :P

[@massterrbarber]

Yeah, I don’t know too much about batteries what I think I know is that using pure nickel is the only way actually using nickel with steel mixed is a bad combination and can cause a shortage that’s what happened to a factory. I read about in China they were cutting corners by using Mixed nickel instead of pure nickel and just one sure it caused a whole factory to catch on a fire so I’m pretty sure the companies are not cutting corners anymore for safety reasons and lawsuit reasons. Of course a safe battery is the best battery and from what I see you’re making a big powerful battery my understanding of it I cannot comprehend what you can, but it is very interesting to watch and learn great content

[@massterrbarber]

That’s another thing I heard copper on top of the pure nickel makes it just as secure and strong your honor something buddy and you’re doing a really good job and you don’t need me to tell you that of course

[@tminustoday]

Thank you!

[@chrisregister8021]

About $200 to do with yourself or about $700 to buy one this may actually be worth the effort... 👍