I’d like a flattish connection on the top so been practising with braid today. I’m happy with the actual process but a little bit unsure about the amount of heat that’ll go through those groups, it’s a little bit of extended time in contact with the iron, am I being overly cautious?
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What i do to limit the heat input on braid:
leaded solder because it wets at a lower temp. Tin rhe nickel and add a good blob of solder - just a little more than what you think it needs. As soon as the solder solidifies i have a paper towel soaked in 90%+ iso i wipe all the excess flux off with and evaporative cooling brings the temp down. I dont think this is a good idea on finished joints because it can weaken them to cool them so quickly but on the preparation steps idc. It will also help get rid of the burnt flux around your joints in your picture. That crap is such a pain to get off cold when the braid is connected and wiping it off a smooth blob when still warm is so much easier.
I have some danger heat sinks that i put on the the joint to pull the heat out - literally chunks of 1/4” thick copper bussing cut to half coupon size
Anything with good conductivity and a little thermal mass will work - these are way overkill but that’s how i roll.
Best practice is going to be working one joint at a time and insulate everything else on the pack so you don’t nuc it with a big heavy copper dead short here 
an old flat blade screwdriver works too just not quite as well. Press the screwdriver blade firmly into the hot area so it makes good contact to pull the heat out.
Now pre tin the braid in the same fashion, set it on something that can wick the heat so it doesn’t suck up all the solder, add flux to the cut end, i like to hang the end of the braid off the edge of whatever heat sink im using as far into free air as i want to tin it. Then tin it just so it wets out as much as you want but don’t build up a lot os solder.
I give it a good wipe to clean the burnt flux and pick the top and bottom. Bottom to the nickel, top gets some cold solder in a big blob - i add it to the braid but don’t heat it enough to wet it out - it’s just getting put there to help flood the joint when i do make the connection.
Clean everything again with iso, trust me here as you will spend so much more time and effort if you wait to clean it afterwards.
Now ive got a pre tined braid with a blob of solder ready and a nickel strip that is pre tined with another big ol puddle of solder ready. I position it how i want and just touch a small corner or something to make them stick and stop sliding around but not more. Switch to the other side of the braid and while holding the braid and pressing it down with a pick or flat blade screwdriver i make the joint - heat the extra solder on the braid a sec just to warm it then hit the nickel until the joint fully wets and the braid joins the fun.
Holding the braid down with the flat blade i watch the solder puddle - you can watch it solidify. As soon as it does i count 2 then wipe it with a cloth or paper towel to clean more flux off and put my biggest heat sink i can fit on the joint. The count 2 is important, these joints are thick so if you don’t pause a second you may ruin it. After about 30 seconds it is cool enough to touch and i do the other side the same way.
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Not at all…heat kills cells and it takes very little to decompose the electrolyte (liquid) inside.
Solder the braid on first then weld your nickel to the cells.
missed that boat with not enough forethought I’m afraid, if I can find a mm somewhere maybe I’ll be able to get away with not using it but if I do have to then Ill mitigate as best I can.
ooh ooh… nice. I dont have any on hand so will get some before I go further.
yeah gotcha, I’ll rig something up if I have to go down that path.
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I will also say, if you have a big honkin’ iron that gets really hot, it definitely helps a lot in my experience. I used to think that if I wanted to put less heat into something while soldering it, I wanted to use a lower temp, but if you’re capable of working fast, I’ve found higher temp puts way less heat into things. I posted it somewhere else before, but I have this monster of an iron:
With that, if things are pre-tinned, I can solder 10-gauge wire or copper braid with basically just a tap, and the nickel right next to the joint will not even get too hot to touch. You do have to be quick, though, because you’re adding heat super fast. The benefit is you’re not having heat sucked off into the rest of the stuff if you’re quick enough, but the downside is a little bit too long and you’ve added way too much.
I inherited that iron and wasn’t using it for a while because I thought it was absurd overkill, but now I quite like it for doing any larger joints. Similar irons are expensive as hell new, but you might be able to find a used one reasonably somewhere.
Also, I’m not sure if everyone here would agree with me that a giant really hot iron is what you want, but it has worked for me.
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Guy I sold a board to crashed it bad and smashed it up. Wanted me to repair it and check if the battery was still ok. No, no it’s not 
Probably repairable but man I can’t be fucked. BMS also seems dead.
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Good call man, don’t know what kinda forces tore that off. Big un knowables
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There is significant risk involved in even handling that pack in it’s current condition.
It looks like the negative shoulder of the can is exposed there, right near the main positive terminal of the pack.
There is no way of knowing how extensive the damage is without fully tearing down that pack and the costs involved with that should outweigh the cost of a new pack.
Those cell holders make for a robust pack, but make it near impossible to tear down/repair the battery.
Old mate needs to chalk that one up as a loss. You’d be mad to take that on.
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Thanks for the feedback. I’ll give him the bad news.
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I thought that was just some funky strand tinning only for me to realize it’s a nickel strip bundled up and then torn apart.
Yeah he did a good job of it! Smashed the pelicase lid clean off. Those things are tough too so must have hit something with force!
He told me his remote went full throttle and he had to bail at top speed and his board hit a construction fence. He broke his shoulder apart and had surgery to put a metal plate in. Needs his knee done too as tore his ACL.
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Which remote out of curiosity?
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Here’s the 3rd battery that I have built. I have been running it for a little while now, but figured i’d post it here. Just looking for any constructive criticism or advice for future builds. I designed this pack in fusion360
The pack
- 14s8P
- Molicel p45b
- LTT Smart BMS 15A charge (charge only)
- 0.2 mm nickel
- QS8 battery connector
- 8ga battery leads
- (2) 10ga serries connections
- 3d printed cell holders PA6-CF
- Weipu SA20 water proof connector for charging (25A)
Considerations / random thoughts (no particular order)
- 3d printing material, pa6-cf was selected for its high layer adhesion, strong impact resistance and high heat deflection temperature. I spent a lot of time tuning in the filament profile and tweaking print settings to get the cell holders as strong as possible given the enclosure size constraints. The cells fit very tightly and need to be firmly pressed in place.
- 8 spot welds per cell (avoid center of negative terminal)
- kweld was used, approx 1550A on the welds, I forget the J, between 40-60 I think
- series connections protection - I do not like the though of series connections being pressed hard up against the other side of the deck. For this reason, I had them recessed below the top of the cell holders. to further increase protection, I added the balance wire guides to the top of the cell holders. these are both glued and mechanically fixed to the cell holders with m1.7 screws. These were an afterthought and could be printed in one piece next time.
I have 1/8" closed cell foam on the bottom of the enclosure and the underside of the deck. this is used as vibration mitigation and to take up any point loads that may occur. when the enclosure and deck are assembled, the cell spacers are clamped firmly by the foam, top and bottom. there is no load on any wires. - everything is mechanically held in place. heat sink is bolted to enclosure, vesc is bolted to heat sink, bms is connected to the vesc. I wanted everything inside fixed so that fatigue on connections over time is reduced.
- balance wires run through, the balance wire guide to minimize risk of crossover or rubbing. The wires leaving the bms are laminated in clear gorilla tape. Not my favorite detail, but I wasn’t sure what else to do. balance wire organizing can be tricky.
- typical cross section of the nickel is 55 mm x 0.2 mm. The one connection at the back of the pack is (2) 32 mm x 0.2 mm. Looking back on this, I wish that I increased the nickel thickness given how robust the rest of the conductors are.
I have the temp sensor from the bms resting against one of the nickel connections so I can monitor the temp (kinda). I have thermal epoxy that I am going to use to couple the temp sensor to the nickel ( eventually, next time that I am in there) - I think the cell holders being “open air” is a good thing for heat dissipation. The afterthought is that I don’t think that I can realistically heat a 8p p45b pack up significantly. Although the cell holders are extremely tight, maybe glue/silicone could be used to further stiffen the packs and mitigate more vibration. The “open air” design might be more beneficial with lower P count or lower quality cells more prone to heating up. The again, everything is stuffed in an enclosure anyways though, not sure how much heat can even dissipate. Maybe the cells still reach the same ultimate temp, but more uniform, and less hot spots? idk? either way, with this battery config I don’t think it really matters. I think my riding skills and the nickel are the bottleneck for heat in this case.
- don’t think that I mentioned it anywhere else, but (6) M3 standoffs are used per p-group. M3 bolts are used to clamp the ends of the p-groups together to keep things tight and separated.
I am always looking to improve, if you see something that could be done better please let me know.
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Again that thing is unreasonably nice it’s an amazing job. Can we get the files if you haven’t shared them already?
Just a small preference thing but would there be a decent improvement in current capacity from separating the series connections? It’s a fairly small cross section of 0.15-0.3mm thick nickel on the edge of where the wires solder on.
Future proofing wise those batteries are rated to a total of 360A and controllers could get to that in 4wd, or as it is now I’m a little afraid of long hard use of battery amps with all the load and heat in one little area melting the solder.
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they technically are separate, but i understand what you mean. I should have stripped back more insulation and splayed the wires out a bit to get a more intimate contact of wire to nickel. something like this sketch below. pardon my terrible ms paint skills
I think this explains what I mean a little more
I can already see someone editing one of those to look like something else
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ah yes, that too. ideally both concepts are applied. thank you for the input, I may update these connections if i get bored haha
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I love this and i think youve done really well. My two suggestions/ponderings would be as follows
In red: little tabs that bolt/screw on after soldering to provide strain relief to the joint while still allowing the pack to flex
In blue: for rigid packs, something to bolt the sections together
Are the cells secured to the holders or each other at al? I repair quite a few manufactured and diy pack where the cells can slide around in the holders (By tiny tiny amounts) and eventually break the nickel or welds. If still trying for an air gap just use a dab of silicone maybe against the holders.
This is usually after a thousand miles or so but the vibration adds up to work harden the nickel and crack it if the cells are only secured by tension and nickel but i haven’t ever seen it on glued cells
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That’s good knowledge to have. And something I have worries about. I feel fairly confident since the cell holders are tight and the end caps are bolted on.
The original design was so tight that I was shredding the wraps trying to get the cells in. When I updated the printing tolerances and parameters, it was basically as tight as it gets without shredding the wraps.
Also, the m3 standoffs are shorter than the cells. So when the end caps are screwed on tight, they are putting the nickel cell assemble in compression.
I think about the nickel welds as a moment weld though. Aka 0 tolerance. So if cells want to move at all, even if .001 mm, then the nickel spot weld is experiencing a small loading condition.
I would imagine that my cells are held in place as well as a pack that was siliconed together. Obviously I have no scientific way to measuee such a tiny movement or force.
Not sure if that makes sense or I’m just rambling, but I don’t think the cells are moving.
Each p pack is not physically tied together. But the friction fit in the enclosure is significant, the whole pack or p packs are not moving around at all.
Also, the deck enclosure setup is stiff. Maybe not as stiff as a carbon tub board like a meepo hurricane, but it is not significantly flexing. Just a little bit