Hello everyone! this forum has been a great help in looking at other people’s battery builds and wanted to post mine up for feedback and inspiration. I am wrapping up my first battery build and looking for some community feedback for anything that I might have missed.
Specifications:
12s4p layout of Molicel P42A’s
All cells were checked prior to assembly and within 0.05V of eachother
0.2mm pre-punched slotted nickel strips from Duck Battery Systems
12s BMS from Duck Battery Systems
Series connections with 2x 12 AWG silicone wire
Bypass discharge with 8AWG output wires
Output fused through 150A fast blow fuse
Charger to be fused with 10A fast blow fuse
All P packs welded with Maletric spot welder and 640 CCA battery 3x per cell
All P packs insulated with fish paper and Kapton tape wrapped
Finishing will be completed with fish paper insulation of all terminals followed by Kapton tape wrap and final shrink wrap.
Battery will be going through a Lacroix Stormcore 60D+, so maximum of 120A draw, likely throttled to 90A for the Amass XT90s connector. Continuous rating for 4xP42As is 180A.
Charging will be done with a 50.4V 4A charger which is 1/4C.
Happy to have any feedback from the community, thanks!
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Good job learning from others’ mistakes. This is a very good pack for a first build.
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Hey, thanks for the feedback! I have some prior experience in electrical and electronics fabrication, but this is my first foray into batteries. Will be happy if anything wrong is found so I can fix it before buttoning it up!
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I should also add that all positive terminals were insulated with 4p 21700 fish paper rings before welding which may have been overkill since the P42A’s already had another insulator ring under the wrap on the positive terminals.
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Overkill on batteries is always the right thing to do. Great looking pack!
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@ZachTetra gives good advice. He’s helped me a lot. Great guy!
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Thanks for the feedback Bill! My thoughts as well. There is not such thing as overkill with things that are capable of spontaneous combustion…
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Thanks for dropping in the tag Aviator, Zach seems quite knowledgeable from other topics I have seen.
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Welcome to esk8.news!
That’s not overkill at all. It’s necessary IMO.
The top insulating ring on all round Li-Ion cells is plastic and can melt if the cell is overheating. Using a thick fishpaper ring on top of the cell helps prevent any additional problems (beyond what’s causing the overheating) and keeps sharp nickel strip corners from being an issue too.
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Any video showing this? Never heard of that before.
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No, no video. But any thermoplastic melts. 
I’ve had it happen on cells during testing at high rates. I can’t tell you that every ring will melt at some temp that is lower than what’s needed for thermal runaway (where the ring is no longer an issue) but it’s happened to me more than once. IIRC the cell was around 120°C-something.
I’m not talking about any reasonable temp. It needs to get HOT. But that’s exactly when you don’t need (additional) short-circuits or other issues popping up. Whatever is causing the extra heat is problem enough.
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I’m personally not a big fan of the positive terminal. It doesn’t look like it has been flown fully. You made a blop on the battery, tinned the cable but both did not fully melt when putting them together.
Could be still totally fine with the current connection, I’m not just a fan of it but I’m also no expert 
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Those big joints are a pain. I bet it would help if you had a second iron clamped to the nickel somehow then another one on the wire.
I use some hot air that works a treat but watch out, can heat a cell if not paying attention.
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I’ll second what @xsynatic has said re the main pos terminal. You may want to try and reflow that joint. Otherwise that is an uber impressive first effort. Kudos 
Edit I would possibly also consider swapping your fast blow fuse on the main pos for a slow blow. Considering that losing power suddenly would also kill your brakes that’s prob a much better design choice. Most people would rather ride a ball of flame to a full stop than save their electronics at the expense of their life (or great personal injury), myself included. My $0.02
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Thanks Mooch, I had not considered the possibility of the top ring melting, just followed some of the better reviewed battery builds and took inspiration.
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Thank you xsynatic, for the initial solder I am certain that it flowed all the way through due to flattening of the puddle that was first laid on the strip. You could feel it compress once the heat soaked through the tinned cable. I then added additional solder around that joint to increase the surface area of the cable contact. That solder may not be fully integrated with the first pool. In this case would you still recommend a re-solder of the joint to make it homogenous?
Hey Foster, totally agree the big joints can get a little tricky. I basically turn up the iron all the way and let it heat soak before attempting those joints. Something that I found helped was having a cold pair of pliers so that after the heat soaked through the wire to the initial pool laid on the nickel I could then compress part of the wire and pool and solidify at the same time, otherwise I had issues with the wire wanting to lift while the solder was still liquid due to the amount of heat that the large joint could hold.
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Technically I would BUT the fact that the solder joint is right above the cells i would refrain from making a recommendation as i am not educated enough on the matter of batteries, wether the insulation and stuff in between is enough to keep it safe from the heat or not.
So my recommendation is to ask people that know more about it.
@Skyart
@Battery_Mooch
@BenjaminF
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Thanks for the feedback Common. Please read other replies re: soldering.
For the fuse, swapping to a slow blow may also be a good idea. I just don’t know if there will be a real difference since while riding you will not be able to tell if your slow blow is, well, blowing until you lose power. I am also OK with destroying electronics to save life and limb. My main goal with the 150A main fuse was to be so far over what I am planning to pull from the pack that during normal course of operation there should be no way to approach that current limit. I wanted the 150A to protect the battery (mainly for storage/charging) so that if there is a short downstream that starts pulling very high current from the pack then it will blow that fuse to prevent the pack catching on fire in my house.
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Unfortunately, there’s no way to know. All we can really do is guess. @evilrman will have to decide on his own.
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