Anyone in the United States good at building a flexible flat pack? DM me I’m looking for someone to build me one.
Here is a list of a few trusted builders in the US
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Those guys don’t look like they make packs anymore. F it I’ll just get a mboard battery.
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Amen
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So I’m preparing to do my first ever battery build, and I figured a good way for me to test my knowledge would be for me to write out what I think to be the correct procedure for doing it and then maybe someone here with experience could read it and tell me if there are any gaps. The pack is 12s8p p42a. I’ve omitted some of the finer points here since I’m lazy.
Alright, here goes:
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Dial in spot welder
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I have a maletrics spot welder and one 3ah 75c “turnigy graphene” lipo. I’m assuming this power source won’t be enough, so I’ll likely use a car battery.
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Proper spot welds should have some color to them but should not look super melty. Welds can be tested by tearing the welds apart. The nickel should fail before the weld leaving material on the cell, and in a messy way (bending and tearing of the nickel should occur, the break should not be clean)
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3 pairs of welds per side per cell is good.
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Avoid center of cathode of cells
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Test cells
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Measure cell voltage and capacity. All cells should be balanced to the same voltage and cells of differing capacity should be distributed so that p groups generally have very similar capacities.
- I got my cells from 18650 battery store. The cells are all within <.01v out of the box. I’m assuming I can omit the capacity testing step since it seems likely the cells are very close in capacity?
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Mechanical cell connection
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Hot glue cells together in sets of 4 in a row and apply fish paper rings
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Pair up sets of 4 into sets of 8, glue together wrap in fish paper
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Question: how are the groups of 4 combined into sets of 8? Where do you apply glue?
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Extra tape cad be added at this time for structural integrity (strapping tape)
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Nickel + series connections
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Question: I’m using .2mm nickel from mboards, is there any concern about this being a bottleneck for the pack?
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Scratch up tabs so nickel can be tinned
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Clean nickel (i plan to use 99% isopropyl alcohol)
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Add pools of solder to roughed up tabs so that series connections can be made quickly later
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Due to the large amount of contact with the wire desired, it may be best to solder the main xt90’s leads to the nickel for the first and last p group before they are soldered.
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Question : would it be reasonable to leave an extra one of these leads in the pack at the other end for a potential future upgrade to 4wd? In the meantime i’d probably use a loop key like jumper so it can be ignored.
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Weld nickel to cells
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Add little u shaped 12 awg wire pieces for series connections, 2 per connection is enough. They should not touch each other ideally.
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Thin closed cell foam can be added between the nickel sides of adjacent p groups to make the pack more flex tolerant.
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BMS
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Wire as per given diagram, don’t let any balance leads cross, if they have to make a fish paper bridge. As usual for electrical stuff be sure to implement strain relief and make sure nothing could rub/abrade or slice wire insulation.
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Finish
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Probe balance leads to make sure correct voltages are seen
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Once bms is installed, check the smart bms app
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Wrap pack in heat shrink or more tape, add foam padding before installation in the enclosure.
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Safety
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Eye protection while soldering and welding is good
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Fume extractors/methods of not breathing soldering fumes are good
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Plan for what to do in case of cell combustion (sand bucket or place to throw cell/pack) is good
Any and all suggestions are welcome and appreciated. Thanks for reading!
E: sorry abt the formatting, I’m not really sure how to fix it
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What causes this, checked the charger and wiring. Everything checks out. Fused charge port…4A charger 50V. A few weeks back I lost the charge port cover so I used some tape to cover it. I replaced the cover. Is it possible some tape residue got inside and caused the plug to heat up?
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very likely
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Sigh this is a super long post but pretty much everything you said sounds good
Check out my vid here that is basically exactly what you’re doing and let me know if it is useful
I’ll try and read it again later if I have time
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Am I a joke to you!?
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That’s a good list and you’ve covered many key points. One that you missed was checking the voltages for each p group in progression once you’ve completed all the series connections.
Additionally, I’d skip checking capacity for cells. They will be very consistent from any established cell manufacturer and checking the capacity for 50 or a 100 cells will take you weeks. This will seriously extend the amount of time needed to build your pack and will lead to fatigue and some frustration in my opinion
Use new cells from an established vendor and you don’t really have to worry about this bit. Opinions may differ but that my $0.02.
Edit:
Well fack I missed this verbiage. Sorry for the redundancy lol.
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I figured you’re too big of a deal to work on a single lowly battery pack. <3
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Anyone k ow the best place to source cells in Canada? 18650canada is a scam and last time I ordered from the states the shipping fees from DHL were almost half the cost of the package.
Where did u order from? Bulk battery doesn’t use DHL… at least to ON
I’ve yet to find a legit vendor in our country.
Updated the charge rates table.
Added about twenty new entries and the Molicel “standard” charge rates too. These are all rates from the datasheets with a “MaxLife” rate set by me that’s about 1/2 the standard rate. Try this rate if long cell life is your priority.
If a cell is not in the table, I do not know its charging ratings.
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Hi builders - question for ya…
One of my boards has a 12s3p (p42a) in it and I need it to be a 12s4p.
The 12s3p is a couple years old but still holds 10Ah (at least according to my satiator charger it takes 10Ah to charge to full) so it’s still in decent shape.
No one wants a two-year-old battery tho so it wouldn’t have much value.
So the question then: toss it and buy a 12s4p for $600 or have an extra p-group of p42as added to the existing 12s3p (is that even possible / a dumb idea)?
Going from 3p to 4p with 12 brand new cells, one in each group could potentially work. It’s probably the least unsafe way to modify an old pack, out of all the unsafe ways. But practically it’s such a huge pain in the ass that you’re basically disassembling the whole pack to do it.
If you have the skills and tools to modify every p group, you might as well build a brand new pack yourself. If you don’t, i doubt you’d be able to find someone to do it for you for much less than new pack labor cost 
But I’m no builder, so maybe someone has a better idea
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Are you doing this yourself or paying someone? If you’re doing it yourself it shouldn’t be $600 for a new pack. If you aren’t doing it yourself the added work will likely cost as much as building a new pack IMO. p42a were recently on sale for $4.5. I think that sale is over, but you can still get 50 for around $250. The rest of that $350 a builder is charging is other materials and work that will also be needed for converting a 12s3p, but there will also be a lot of added work. I haven’t and wouldn’t build packs for anyone else, but if I thought I was good enough I’d probably rather build a new 12s4p pack for $350 in time and materials than convert a 12s3p to 12s4p for $550 in time and materials or whatever it would come out to.
The only way it works out to reconfigure a pack IMO is if you’re doing it yourself, have absolutely no possible use for the old pack, and value money far far more than your time. Personally, even if I did value my money far more than my time I’d probably try to sell the 12s3p if it would be remotely usable in any common setup and put the money towards a 12s4p or something.
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I’d be paying someone. I’m no battery builder and not in the mood to burn my building down.
Thanks, will get a new battery. Sucks a bit but the 3p life just isn’t working for me.
I’ll see if I can sell the old one for $200 but seems unlikely when new cells would cost less than that.
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