flat tire said:
I can get VTC4 for less than the LG or Samsung cells. The thing is, is it worth taking such a big hit in capacity (2Ah vs 3Ah) if I'm planning for at least 200 cells now...that's a lot to give up when I should have enough cells in parallel at 20S to handle my power requirements.
BEWARE of VTC4 cells unless you have a VERY RELIABLE SOURCE (like Doctorbass for instance)
They are THE MOST CONTERFEITED CELLS in the world (lot's of people want them for their vaping habit.... lots of amps means lot of smoke)...
So much rewraps of fakes...
Yes, big hit in capacity with VTC4 as you say... You probably don't need 30A/cell unless you use a monster of a controller for your ebike motor...
Telsa cells are really intersting too ! They're not NMC chemistry bur rather LCA... LCA typically deliver mid-amp load range (like 8A max), but they pack monstrous energy density (3000 mAh ballpack around 240 Wh/kilo). They are rather expensiver though.
I choose VTC4 because they are hard to damage and I have them for 1.50$ CAD per cell at my door (1.12 USD/cell)....
The thing is you cannot have both... 18650 are either designed for really high drain but with mid- to low- range capacity or high capacity but that's at low amp-load. Plus if you push a high capacity cell at high amp, it will NOT deliver it's promised mAh (tested at 0.2C LOL), will heat up a lot and end up damaged...
Of course you can get an "all-around" cell, with mid-amp load potential and mid-range capacity, like the GA or PF cells.... 8 to 10A max.... and 3000 or 2600 mAh.... But dont go for the NCRB cells (4.8A max; 3400 mAh at 0.2C) unless you'll have a very low power setup (less thant 10Amp controller for 4P battery).
Personally, I prefer a heavy battery that will give me some "willy joy"- kind of power and last a loooong life, rather than a light battery that heats up a lot and deteriorates quickly (good range at 1st cycle, but notice sag, and then.... battery giving less and less range and I'm always hitting LVC under load even though there is still 1 third of the Whrs left in the battery).
The bottom line is, there is a sweet spot between HIGH CAPACITY and HIGH AMPERAGE to find, so that you can have a battery that is not too big, not too heavy, but still lives a long life and give you lot's of enjoyable time.
I would ask people that have similar setup as your what battery they use and what their experience is with that battery (how does your battery hold up so far ? Do you ride a lot in a week ? Is there a lot of steep hills ? Do you like to lean on the throttle a lot or you go for slow econo-range style driving ?).
Experience beats theory in that matter.
- But it's hard to go wrong with high en cells like 30Q, HG2, VTC4, VTC6, 25R. They are great.
- Using more all-around cells (Like the GA, Tesla cell, PF cell, etc) might give you more range (more mAh), but you have less error margin (you must watch your amp consumption a bit more in order not to overstress the cells, unless of course you make a massive battery with lots and lots of cells in parallel to conterbalance the slightly lower amp-rating)
- To me, cells like the NCRB that offer sky-high capacities (that is 3400 mAh) are like a fake promesses .... Yes they will deliver that much mAh, but in a lab and at a 0,68A(0.2C) load per cell.... So a 4P pack will give you 3400 mAh per cell, yes, but that is if your ebikle is using just 2.72 Amps load... Is that even possible ???? Not really. Pull out 20A from that pack and they will sag a lot and probably give you a lot less mAh that a PF cell at the same load... In the end, your were better with a lower capacity cell that had more power... At least they dont heat up like crazy and go tits-up on you after 50 cycles.
Of course, I must say... I'm no battery expert. I just enjoy reading on that subject a lot.... Think I should have been an engeneer in another life, as I enjoy playing with batteries a lot.... building/thinkering with electric stuff... I enjoy it almost more than my work actually.... I have a strong scientific background.