Good morning/evening/night everyone. I’ve built a few batteries mostly for astrophotography field rigs using Samsung 30Qs in either 3s20p, or 4s20p with very low voltage (12VDC), and amperage requirements (typical draw on these rigs is between 2A continuous with 5A peak with CMOS coolers), but esk8 is a slightly different beast with higher voltage, and amperage requirements I’m totally not used to.
Quick overview (see diagrams for more detail):
Samsung 40T3 cells (I debated Molicel P45As, but the former are $3.99 right now)
10mm x .15mm nickel
positive terminal covered with ringed fish paper for added redundancy
P groups assembled with 21700 cell holders. I love the fact that I don’t have to glue cells together, and spacing for cooling along with reduced contact is awesome IMO
P groups will be then wrapped in fish paper
I’m hoping to find a source for 50mm nickel plates to be used for series connections (see diagram)
2.5mm (10 AWG) for series connections (I think 2mm/12AWG is ok)
BesTech BMS (80A) with eSwitch
BMS bypass aka charge only
Bullet connectors on the BMS for modularity, and easy swap in/out
XT90 Loop key. I don’t see why I need to power the entire board to charge the battery so I’m using both the eSwitch on the BMS, and an XT90 loop key
Fused charge port. I normally use 1mm wire (18AWG), and disregard fuses because the wires are so small they’ll melt if anything goes wrong (feel free to tell me otherwise)
Misc:
Malectrics spot welder with a 700cca battery as the power source
This will not be sufficient to carry the current in your 6p config. I’d recommmend sourcing some 0.15mm or 0.2mm x 30mm nickel.
What kind of board are you building? If this is a street board you won’t need 10 awg for the series connections or the main output terminals. 12awg will be sufficient for the main terminals and either 1 x 12awg or 2 x 14awg for the series connections. If, however you are building a Mountainboard, 10 awg for the main terminals and 2 x 12 awg for the series should be sufficient.
If you want to wire a bms for modularity, this is the type of harness you want to make. Bullet connectors will be a possible point of failure and if one were to come loose and it were attached to one of the main terminals of your pack, the chance for catastrophic failure, thermal runaway, fire etc… would be significant. This harness, courtesy of @glyphiks is much more robust and far safer.
This is not a great way to do your series connections unless you’re building a brick pack as it will be prone to failure in a high-vibration environment. Batteries in Esk8s need a pack that will flex w the board and it appears as though you’re building a flat pack. See above for my comments re series connections and note that the best material is high-strand silicone wire or, failing that, tinned, braided copper.
Absolutely. Don’t rely on the wire to melt unless you’re positive you have the correct calculation as to the required gauge. Having a fuse blow quickly can be the difference between a popped fuse costing $3 to replace or a major fire. Unless you’re 100% certain the gauge of your wire will act as a fuse, I’d fuse the port without question. It’s a known quantity, inexpensive and easy to implement and will function as intended.
Other than that, looks like a solid plan and the wiring diagrams look good
The BMS comes with an e-switch so I have two choices I either short the wires so it’s always on, and risk a parasitic bleed which could kill my battery if it sits for too long
I’ll have a look around for some. I’ve been debating about simply dropping down to a 4P config because of weight savings, and I like these nickel strips
I hate the 6P layout because it would force me to glue/silicone them together.
I did find these 6P p-group tabs tabs which I like better than the above.
Just your run of the mill street board for my daily commute in the Bay Area
Why the hell didn’t I think of that!? It’s basically what I (or most) would do for the loop key. Done easy enough.
Makes sense. Looking at the AMP rating for a 1mm wire (18AWG) it can withstand up to 14A whereas the Molicel P42A is rated for 8.4A max continuous charge, and the Samsung 40T3 is 6A.
Looking at my chargers they have fuses in them, but that won’t protect against stuff at the charge port regardless of active charging. Shit. Disconnecting batteries now until fuses come in
Is there a general rule people like to follow for fuses on the charge port? EG: 1.5x - 2x the current output from the power supply? 2A charge output = 4A fuse?
I found these minimalist fuses that look great. Anyone here have experience with these?
Nothing wrong with that and in 6p you would be generating minimal heat as the amp draw per cell would be negligible. If ur set on using cell holders that’s one thing bur gluing ur cells is nbd as long as u reinforce the structural stability. Re the tabs, imo this is just the smart money. Saves a fuck ton of time and effort for a nominal cost. If u decide to go 6p, absolutely do it.
Yep spot on. ~ 2x the charging current is good.
Not familiar w Hawk but auto fuses are frequently used in esk8 so if the vendor is legit it’s a good choice. Just make sure the rated voltage is at least 51v (as I’m sure u know but bears mentioning).
