I’m probably not in a position to use a bigger iron, I typically avoid making the solder point too close to the edge. I’m not unfamiliar with the issue though, usually, the easy way to avoid soaking the wire is to tin the end only and then melt a pool and stick it in. I use leaded kester 60/40 and using more power usually just makes it flow up the wire better, it flows maybe too well for the application of soldering braid to nickel.
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I find that using a hemostat or pair of pliers, gripping firmly at the point where I don’t want the solder going past, helps pull out the heat that would otherwise allow the solder to keep going up the braid.
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Every battery builder should own 20 pairs of them. They are so useful
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Well, you learn something new every day. I always understood shorts as any unintended path the electricity may take and as such, that the space between p-groups would potentially be a spot for that to happen. But I fully understand what you are both saying, and now that I think about it, there’s very little chance that electricity would pass through those two points of nickel as the copper series connections would be significantly less resistance unless some heat built up.
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This I don’t fully understand. Do you mean that anything putting pressure on the nickle could potentially puncture the can?
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No I meant that the nickel taps welded to the pgroups could potentially contact the other rows nickel tabs which would result in a short, I would put a physical barrier like a cheap thin cutting board in between the two rows to stop that before heatshrinking up the battery.
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It is an unintended path (between series connected p-groups) and it is a short-circuit as there could be lower resistance than the wiring. But, as you mentioned, is this short-circuit of any consequence?
As always…let’s look at the numbers.
Two inches of 12AWG wire = 26.5uOhm resistance
Each soldered connection = Estimated 1mOhm resistance (could be a lot less)
This makes the resistance between the series-connected p-groups equal to about 1.0133mOhms if two wires are used to join p-groups.
At 50A there is a total voltage drop of 1.0133mOhms * 50A = 51mV. That will be the total voltage difference between two p-groups at 50A.
So while there will be a direct short-circuit between the two series p-groups I just don’t think there will be a lot of current flow (for that 51mV difference in voltage) being shunted away from the wires. The point or points that will be touching will probably have a higher resistance than the soldered wires as the area of the touching points will be small.
Of course, if other p-groups that are not directly connected touch then you can have huge amounts of current flowing and lots of sparks, flames, etc.
If a large area of nickel touches between series-connected p-groups then you could have a lower resistance connection and that could divert more current from the wired connections, causing a visible spark. But I don’t know if this is a real concern or not.
Interestingly, if there were sparks that means a lower resistance connection was formed by the p-groups touching and that means there is less voltage sag and the performance of the pack was improved. Only by a tiny bit, but it’s there.
I guess “best practices” would guide us to insulate p-groups because the long term effects of this touching is unknown. Would a million tiny sparks cause a problem in a few months? Once they are touching would the p-groups stay that way, preventing any new sparks?
I don’t know the answer to these questions. But adding insulation would keep me from having to worry about it until it was extensively tested and an answer provided.
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Yeah I kapton-ed over the edges of the tabs, and rounded and sometimes filed the edges of the tabs. I think there’s a decent distance between them so the whole pack would have to fold on top of itself down its length for them to contact. Going to double check that physical scenario this evening though, obviously with the kapton still in place so I don’t short them
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It may be a non-issue altogether, the camera angle can exacerbate how close the tabs are.
All great info, I can see the video being over 30 minutes now though so I might split it up
This is kind of the first time I’ve heard this, what are some steps to prevent that? Reducing extra wire length?
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Lmao electrician packs
Sure I can include a safety segment at the beginning. I had one in a different battery video but this one is much higher power than either of those builds
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Yes, length has a big effect on the inductance of the wiring.
The area of the loop formed by the two wires carrying the outgoing and returning battery current also affects the inductance. If the wires are very close together then their magnetic fields can partially cancel out and that lowers their inductance. Twisting them together is fantastic for this as it ensures they are as close as possible and the twisting cancels even more of the fields.
But if the two main leads are run down opposite sides of the pack, or are otherwise separated at any point, then their magnetic fields can’t cancel each other out (or do this less as the distance increases) and the inductance ends up being higher than it could have been. This causes the voltage to spike higher.
I don’t have the data now needed to decide which might be better, shorter length or smaller loop area, when only one can be done. All we can do is try to minimize both, length and loop area.
The calculations wouldn’t be a nightmare though, comparing a couple different scenarios to see which has a greater effect on the inductance…length or loop area.
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This is what we’re discussing right now. @Battery_Mooch provided a very comprehensive opinion on which (and correct me if I’m wrong here Mooch) he concluded that we really don’t know the ling term implications on not insulating the ends between connected p-groups and as such, should err on the aide of caution until testing can be done.
Has anyone had a problem here in their battery? Other than additional time/materials, what would be the drawback(s) of insulating this part of your pack?
You should talk about vibrations and micro-flexing, and how our application has a different set of dangers to our packs than other applications, causing us to have to build our packs to a higher standard.
I cant count the number of times I have seen a “made my first ebike battery” post from a guy who builds powerwalls, and so of course he built his ebike pack to powerwall standards instead of ebike standards.
Or the guy who builds his pack with completely solder soaked connections, or nickel-only series connections, and when someone points out how those are bound to break down over time they say “dont worry, it’s a rigid pack, there will be no flexing.”
Bitch there will always be flexing, and vibrations are a fucking killer.
People need to understand that if they are building a pack that will be going into anything that moves.
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I do wonder how a solder pot would do on AWG 10/8 cables. Compared to ions
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A couple mm of extra length, which may or may not be an issue.
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Interesting, this is honestly the first time I’ve heard this at all. I’m sure it is a valid concern but I guess maybe our battery leads aren’t long enough to really see huge inductance. It’s also interesting to mention that twisting them helps, I suppose when you run them from one XT90 to another they’re close enough to cancel, like you said.
Fair enough, none of mine are insulated and I haven’t seen any issues quite yet. I suspect if you did not secure your battery well enough within your enclosure p-group to p-group vibrations could pose some issues given enough time.
Good point. It really sounds like I have two videos here, my 12s7p video and then “How to Safely Build Esk8 Packs: Important Tips & Tricks”
yeah I feel that
Lol it’s not even that hard to build a pack to flex, my 10s4p using your strips in that one video is a perfect example. Besides, using nickel strips in a flat pack for series is so antiquated.
Yeah makes sense
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A lot of people don’t know about this, including it seems some engineers creating the ESC’s we use.
We have enough inductance in our battery leads right now to require honking huge capacitors on our ESC’s, without which there is a good chance some would fry at pack voltages near the ESC rating. 
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Solder pots work well but there’s almost no reason for anybody here to have one except for the major battery vendors, even then I think it’s overkill. You absolutely have to have great ventilation for them. Like, fume hood level ventilation.
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