I was thinking anything less than half a volt is a small difference but 15mV is fine (though a bigger PITA to arrive at). 
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how important is it to have a large amount of the 10awg wire covering the nickel? Asking because on my 18s battery all the joints are great and spaced well, except for my main +/- discharge leads could definitely have some more of the wire touching the nickel. I assume this is just for better heat transfer?
Ideally, you want as much contact as possible. Even âfanning outâ the wire to increase the amount of nickel it touches.
This isnât really for helping with heat transfer as there shouldnât be a lot of heat in any connection, the cells, the nickel, or the wire. If there is then something could be undersized for your setup.
Maximizing the wire-to-nickel contact is to reduce the resistance of the connection. This helps limit the packâs voltage sag. Itâs not a huge thing but it is one of the âbest practicesâ you can use when building a pack.
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Hey guys,
Rebuilding my G2 black pack with P42 cells,
Would you rather weld them like this:
or like this, which Iâm afraid I have to put to much pressure to weld them to the positive because of the fishpaper ring:
Last scenario is I make a small tool to press a small dimple on the positive side to offset it inside 0.2mm, if I can avoid that itâs better (too lazy to print a one time use tool)
Just print some circles with the correct spacing, thats how I do it. 5 min print.
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Do you mean to glue on the neg. side? Or to do the dimple?
I would 100% recommend option 1, its plenty enough, its easier and thereâs just no real need to go as big as option 2.
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Iâll do that then, it would have added a bit of cross-sectionnal area so a bit less losses but the hubs donât draw much current on the battery anyway
hello friends!
weâve gotten a lot of snow/rain lately so I havenât been riding. whatâs a good storage voltage for p42a cells? currently looking like this
already been wet for a week now, and supposed to rain for another 1-2 weeks before it dries up 
Where they are right now is fine.
The particular voltage doesnât matter much as long as youâve brought them down some from full charge without bringing them so low that they drop below 2.5V before you can check their voltages again (and possibly charge them up a bit).
Youâll often see 50% mentioned though, about 3.6V.
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Iâve heard a bit of conflicting information on this and Iâd also like some clarification, generally Iâve heard anywhere from 3.6v-3.8v/cell is good for li-ion storage. Are higher numbers to account for longer duration of storage? Is there a true âperfect storage voltageâ for a certain set of parameters?
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As I mentioned, it doesnât much matter but storing at a higher voltage does give you more time before you might need to check their voltage.
Cells age faster at higher voltages so bring them down.
Cells can discharge down below 2.5V by themselves (over a long time) or from attached electronics so donât bring them too low or check their voltages occasionally.
Thatâs it.
The lower the voltage the slower, by just a tiny bit, the aging. But the lower you go the more likely the chance they might drop below 2.5V (which could damage them) while in storage. Choose the number that best fits your situation.
You might choose 3.8V if you have a board that brings the pack down quickly while in storage (from the attached) electronics. You might choose 3.0V if you have cells in good condition, no attached electronics, and check their voltages every month.
The difference in cell aging between 3.8V (or whatever voltage) and 3.0V (or whatever voltage) isnât big though. It just doesnât matter that much. Theyâre aging every day no matter what you do.
Most people hate this kind of open-ended situation though, where it just doesnât matter that they have a wide range of voltages to choose from, and just want the single âcorrectâ number to use. Because itâs in the middle the 50% number is often recommended.
Not for any specific technical reason.
For reference though, the manufacturers leave their cells at 30% for shipping. This lowers the available energy that can create problems if the cells are crushed or otherwise short-circuited.
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Thank you very much for the thorough response, as always youâre a gem mooch 
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I have an idea that is not my best idea, but I want to know if there is a way it can be done safely.
I have two 18650 packs that I am thinking about combining.
- 12s5p LG m29 (2800mAh)
- 10s5p Molicel p26a (2600mAh)
What I would like to do is add 6 p groups from the m29 pack to the p26a pack, so that I have a 16s5p battery.
I know that this is not ideal because the different p-groups will have different internal resistance/capacity and drain at different rates.
Assuming I did the following, am I missing anything?
- top balance the cells.
- enable balance while charging >4.15v
- set my ESC voltage cutoff based on whatever total voltage yields 3.0v for the faster draining p-groups.
- smart BMS to monitor everything.
This does seem like a pain in the ass, and Iâm probably not going to do it, but is there anything Iâm not thinking about above?
Alternatively, I could weld up some new p-groups of p26a, but this will have the same issues as above, to a less extreme extent.
Has anyone added new p-groups to an old battery before?
This is a much better idea IMO. Whether it can be done (relatively) safely or not depends on your pack assembly skills and your BMS.
Yes, mixing old and new cells of the same type isnât ideal but with a good BMS it can be done.
Mixing M29 cells in with P26Aâs will cripple the performance of that pack. It will go from a 100A-125A pack down to a 25A-35A pack with the huge voltage sag of the M29 cells severely limiting your range.
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Good to know, thank you Mooch.
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Are these 18s p42a BMS setting ok? Iâve never seen this much of a voltage difference, this was after my first full charge. was at 0.80 difference @ 30% battery before this charge.
*quick ride later and now its 0.30
Once everything is 100% balanced at full charge (all cells at 4.20v or whatever your full charge voltage is set at), run the pack down to <50% and check the voltage difference down there.
Once balanced, the pack should stay pretty close during the entire discharge. If one of the cells/groups starts really getting away from the others during discharge, thatâs a sign of significant capacity mismatch (that cell/group having significantly less/more capacity than all the others), which can, for example, be caused by a loose weld.
As long as the voltage delta keeps getting better over time, I wouldnât worry too much about it. But if it starts to get worse, thatâs the time to be concerned.
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Hey kids.
Can anyone provide a link for a reliable source for 0.15 x 30mm nickel strips please?
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To add to what @MysticalDork said, step 1 for you here is to get the pack âtop balancedâ.
To do that you are going to want to switch off âBal. only when chargingâ, and save that config. I would also change the âdelta to balanceâ to 20mv.
Leave the pack alone and in like 2 days your pack should be balanced at full charge with a delta between groups under 20mv.
If you go on a ride and after 15 miles, P5 is significantly lower than the others, you have a problem with that P group.
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