Why not set the cutoff end at 2.5v? What I’m getting from these replies is that the cell will bounce back up anyway if you’re not riding extremely slowly.
I have all my hard cutoffs at 2.5v and all my packs are in good health.
@Spanajohn clear as mud or what? Bet you didn’t expect to start a firce debate on the properties of Liion cells did ya?
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number is scary
All of the cells we use are rated down to 2.5V for every cycle while still retaining their spec’d cycle life.
Not much capacity below 2.8V, or even higher, but having a 2.5V hard cutoff keeps the cell within spec and allows you to use as much capacity as possible while minimizing how much voltage sag can affect your range.
Since it allows you to run your pack for longer, and the internal resistance goes up as the cell nears being empty, your cells can run hotter. I recommend that anyone dropping their cutoffs a lot should monitor pack temps until they know how their pack behaves with the new cutoffs.
For the hottest cells in the pack (probably in the middle)…
Below 45°C is great for long cell life.
Below 60°C helps prevent accelerated cell aging.
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The problem is when one group starts to drift you can go below 2.5v per cell cutoff. With smart bms it would be easier to monitor this. I like 2.7v end cutoff if the pack is still healthy.
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That’s a good point! The lower the cutoff voltage is the more important a good BMS is.
When using the malectric spot welder is a 12v lawn mower battery sufficient?
It needs to be capable of high current discharge. I want to guess probably not, car batteries work because they can crank out a shit ton of current in order to start a vehicle
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Looks good so far, sharp corners on the nickel could be rounded off imho but probably no big deal. Any reason you cut the nickel in half for the edge cells from the p groups?
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Looks fine so far. One thing I like to do with folded over nickel is double insulate the positive terminal at the shoulder like so:
All you do is cut a piece of fish to about 13mm (1/2") and score it down the middle with a knife. It’s a easy way to add a lot of safety to a pack. Not everyone does it but I think it’s a key safety protocol.
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going to be using this glue and cheap mini gun for holding cells together. Do i need to buy a temperature-controlled gun? I know this shit gets hot af, says it gets up to 193c
As long as you use good glue and the gun gets hot enough, it doesn’t really matter.
My main concern with that glue gun is the low power and small size - it’s going to take a good while to heat up, and it’ll be really easy to outrun it by gluing faster than the glue gun can melt the glue.
Even if the glue is melted, the temperature of the molten glue really affects how well it sticks to things, so a small glue gun tends to be really variable.
I don’t think you need a temperature-controlled glue gun, but a bigger, more powerful one will help keep the temps stable.
My absolute favorite is the SureBonder DT-360F, which not only has waaaaay more power (60W) so it can melt more glue, but it has a 30-minute shut off if left unattended, does dual-temperature, has a check valve in the nozzle to keep glue ooze to a minimum while it’s idle, and has interchangeable nozzles so if you need to glue down in a tight crevice or whatever, you can.
Oh, and it’s only like $18 on Amazon.
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Just glued and fishpaper’d the cells, checked with a heat gun and the glue wasn’t hotter than 40c for more than a second. I can see how a quality gun with bigger sticks would be beneficial
is this glue ok to use to seal up a solder inside a dc connector? or is this the stuff i need?
Lost a p group today 
07
recycle pack was going good for a while. This is the second pack to die this way. The first p group went to 0 volts after charging. Im thinking it might be a bms problem. Its a daly 40a 10s and the group that died is the exact same one as the previous pack.
When the first battery died because it lost a p group I swapped to this battery and the same p group died (bms is on the deck so it stayed the same). Could it just be bad luck? Bad build design? Or did my bms kill it.
Some help troubleshooting would be welcome.
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I wouldn’t expect to see too much difference between them for that application, although for weatherproofing/water resistance I would much prefer to see either conformal coating or neutral-cure silicone instead of hot glue. Hot glue tends to get brittle in the cold and over time, plus it melts (obviously).
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If buying my batteries from a legit vendor do i 100% have to check every cell before using it? Whats the fastest way to do this? I started with a magnet to pull each battery out of the box to bring it to my multimeter.
On my last ~25 batteries(that were stuck in the center) I pulled it out the entire grid it was in, placed it on its side, and brought my multimeter to the cells that were still held in the cardboard, and rapid-fire checked them 10x quicker. Only issue with this method is having to very carefully cut the bottom edges of the cardboard box the batteries are stored in
Getting my nickel to complete my pack in a few hours.
I see 6 weld spots on each battery is common. Is it not advised to do 4 weld spots per battery?
For kweld users whats your sweetspot joules for 0.2 nickel?
For wiring the packs together with 12awg wire, when is 3 strands needed over 2?
Idk I just do it as I’m gluing them, pull it out, measure, line up to glue. It’s very fast
4 is lazy imo. General rule of thumb is to assume 5a per weld spot. So, for P42a, 6 welds approx good for 30a. (not counting nickel pressing onto the cell)
For me and my battery setup I weld P42a at 54j. Some other people have different results. It depends a lot on your cells, and each person will have different resutls. It’s advisable to test it out and see what the right setting is for you
Depends on how much current you expect to draw. Generally I build my packs based on the amount of P groups though, so for Max continuous draw.
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12s8p p42a pack. 2wd reacher v5 6385+stormcore60D+ atm. The motors are 205kv and im concered about torque so ill probably pushing them as hard as i can. would 2x 12awg wire be sufficient for series connections? What about if I moved to 4wd in the future?