Actually, now that I’m looking at it closer I think I am still blowing small holes, but they do seem to be sticking very well. I think I’ll turn it down just a bit, but I don’t know if I should use that one.
Put some iso on it and check for bubbles. There’s a possibility you could have burned through the can.
Electrolyte smells sweet.
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Hi! I am building my first battery pack and I would like to share my progress here. I would appreciate any feedback, especially any major flaws I might have made.
Basic pack info:
- 12s5p
- Samsung 40T cells (was aiming for P42As, but were out of stock at purchase time)
- P packs are in 3D printed (PETG) cases (credit: @janpom)
- parallel connection: 0.15mm nickel
- series connections: 3x 12 AWG
- main discharge leads are 8 AWG
- charging leads are 16 AWG (except the positive lead which is smaller - I was able to get inline fuse case with this wire only)
- LLT Power smart BMS (charge only)
- Charge and discharge lines will both be fused (thinking about 10A and 150A). I am aware of the downsides of the fuse on discharge line, but I am really paranoid about the pack going kabooom while at rest so I decided to accept this.
- Balancing lines are fused with 500mA
After series connections:
After balancing leads:
I am planning to put temperature sensors on the bottom side.
Thanks!
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Looks good. Familiar as well. 
3x12 AWG is an overkill. 2x12 AWG would have been more than enough. It of course doesn’t hurt to overbuild though.
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Quick question, how many times is it safe to Dremel off shitty spot welds and do them again? I’ve done it 3x to a cell without any indication of failure but I’d like to know a safe threshold to where grinding it down will make it too thin.
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I got lipo questions ya’ll. See this post for reference:
@mynamesmatt this project is awesome.
I have a similar lipo problem. I have 4, 3s packs I want to put in series. Possibly parallel another 4 x 3s pack.
What do you think about the extra lead length incurred by leaving the stock xt90s on the relatively long leads on the 2s packs?
Do these lead lengths add to the ripple voltages that can pop Esc’s? I think the answer is yes, and the solution is more Caps on the mains just before the esc’s. But maybe it’s not a big concern if you have current headroom to play with on your Esc set up?
My other concern is added resistance from long series connections, bc in my case, I don’t trust a BMS. I want to balance charge at 1C (15A) and intermittently keep an eye on IR’s.
Will these longer series connections cause my Balance charger to misread cell voltages on either side of these extra long series connections? My charger can do 12s or 6s x2.
I know these series connections will give me wacky cell IR’s near the long series connection but that’s ok, I’m taking initial reads of new packs and comparing relative changes in the future.
Don’t mean to make this about me, but my use case is real similar. I suspect my average Amp draw is a bit higher (however Metr calculates avg Current) I used to routinely log avg currents of 120-180A over 5-10 mins, in the last year it’s been closer to 80-100A.
I presume higher currents magnify my two concerns above (?)
@moestooge @Battery_Mooch are these concerns for my use case even valid?
Yellow arrows are “long series connections” I refer to above. My tattu 12s (6s X2) packs only have one and it’s 8awg wire with as150s connecting.
My proposed zeee 12s (3s x4) has 3 long connections (10awg 
). I want to cut them really short.
On old packs, I have noticed irregular and inconsistent IR’s on cells directly adjacent to the long series connection. (Cells 6 and 7 if you count up to 12). Maybe dirty or worn out balanced leads 
.
Ripple voltage is a real problem I’m dealing with on the quad unity Esc setup. If I’m riding aggressively, It spits out drv over Volts at the frequency you see tesla cars drive by in socal.
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Interesting thought. Honestly, that’s a question for the experts haha
In my scenario, the packs are 2x4s in parallel, x3 in series to get me 12s2p 12ah.
I think if the battery leads were more than say 700-800mm, there would be an issue with ripple voltage as you mentioned. but with batteries in parallel, i dont think they’d have an effect. The series connections…? maybe? No idea
LiPo is fucking awesome and unfortunately the grounds have not been very well tested for esk8 and its a bit disappointing.
But yeah i think overall that’s a @Battery_Mooch and @MoeStooge question
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As mentioned, 3x12AWG is overkill, 3x14AWG or 2x12AWG is enough. Also, depending on the ESC you plan to use, said ESC might pop way before the 150A fuse pops. 10A for a fused charge port is kinda common, If you only slow charge a 5A fuse might also be enough.
8AWG discharge is a pain to get into any connector, and most ESC utilise a XT90 tops, which isn’t rated higher that 10AWG anyways, so there’s another overkill. You probaly won’t draw more than an average of 50A with even the biggest MTBs (excluding some absolute monsters), so 8AWG is very much overkill.
The pack looks very clean, also no welds visible, so no comment on that. I recommend you put a sheet of PVC shrink wrap on it, for additional abrasion resistance. It might not look like much, but this stuff has actually saved a board of mine from going up in flames, so better safe than sorry.
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likewise. shrink wrap might seem brittle and flimsy but it’s got the abrasion resistance where it counts. foam packing around the pack after installation also is a great safety measure.
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I’d say keep it to a minimum, but the actual limit comes down to how much of the battery can itself you’re actually taking off each time.
Ideally you would grind away only the weld nugget, and never remove any of the can material, which would mean you could try over and over without fear of getting too thin.
Obviously this is pretty much impossible in the real world though.
The other thing to keep in mind is heat input. While spot welding is much less heat-intensive than soldering, for example, there is still some heat transferred into the cell, which can be bad for the electrolyte and other magic stuff in there, so multiple rounds of welding (not to mention grinding, which can generate its own heat) are best avoided.
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Yes, longer leads = more inductance = higher voltage spikes.
But we don’t know how much of a concern that is for any particular setup without complicated testing.
We just have our “best practices”to help reduce the chances of the ESC blowing….shorter lead lengths, run the POS/NEG leads very close together everywhere, use the highest voltage rated ESC you can, add quality caps to the ESC’s input (with good low resistance connections) if concerned.
Of course, the size/shape of the packs and the enclosure determines a lot regarding the wire runs. The lowest inductance/resistance setup can often be impossible or just a PITA to do for a particular setup. All we can do is have the best balance between convenience, performance (low resistance and fast balancing), and robustness (surviving spikes).
If the series connections have a high resistance then they could mess a bit with your balancing voltage accuracy but I don’t think that will be an issue.
Just place your balancing connections in the center of the series connections to divide their resistance equally between each p-group. That way the effect is divided equally amongst the p-groups and the charging/balancing won’t be affected as much.
For voltage spikes, absolutely. The size of the spikes is directly related to the inductance (due to length) of the wires and the current through the wire.
For balancing, yes, it can affect things. But that’s minimized…well, divided up equally…if you tap the balancing leads at the series connections mid-points. If you make the balancing connections at the p-groups themselves then the voltage will be off and that can affect balancing time (but shouldn’t affect the final balancing accuracy).
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I was unaware of this best practice. Researching now. The battery harness has been chopped to its shortest ever at the cost of separated positive and negative wires… I think the positive lead might even be shorter than the ground.
Significant contributor to the events surrounding the night I cut up a 44 redember and carbon GT.
Solid solution. Thank you king Solomon. Will cut that baby in half.
I’m still going to slum it at 12s escs for this project.
Thanks for the advice, perspective, and sanity check.
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I ran a build with original XT90s on the batteries with complete disregard to inductance/resistance in the lines and it ran smooth at 12s on glorified 4.12s and then neoboxes logs show about 1.5V of drop on 45V @ ~85 battery amps and I imagine a majority from that is from the cheap LiPos. Ran for 2500km before being run over by a car and “decommissioned”
(old pictures, forgive me)
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Yes, I shamelessly copied your design. Same enclosure, same configuration, same cases. What else can one do? 
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Thank you for your feedback!
I am aware that the wiring that I used is an overkill, but this was kind of intentional. Since it is my first build I decided to add some margin for any errors that I might do. I already learned that AWG 8 is a pain when it comes to soldering XT90 on it, but I somehow managed to do it.
The reasoning behind 150A fuse it that is should never ever pop under normal circumstances. It is just there to save the battery if the ESC shorts or something like that. At which point I won’t care about ESC or any other part. The only thing I care in such scenario is battery not going up in flames.
The plan is to use shrink wrap for sure. I will do a few test runs and when I am confident that the pack behaves as it should I will wrap it.
Unfortunately I forgot to make photos of the packs after welding so I can’t really show that. I was able to get a few photos from the side of the pack, but these are just the negative sides:
On positive sides I did use insulation rings and was careful not to weld over them.
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Might be true but doesn’t matter. Should the ESC burn itself into a short you’ll still be glad you had the fuse.
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Try “inductance loop area” for a search term. Basically, the large the size of the loop for the outgoing and return current the higher the inductance of the loop. The smallest loop you can have is with the two wires next to each other.
Actually, the smallest loop is if you twist the wires together along their length but that can be hard with thicker wires.
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I see, hence the intense twist per distance automotive standards in paired sensor wiring systems, like canbus.
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This is making me worry about my 4wd where I routed +ve and -ve down opposite sides of the enclosure to the other esc…
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It’s only a worry if that adds enough inductance to cause the voltage spikes to the ESC to go over the voltage rating of the ESC. Hopefully the ESC has been designed well enough to handle it and that you are not using it at its max voltage.
Unfortunately there’s no way to know though without getting a scope and measuring the spikes.
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