cg_ebiker said:
3. Motor is the handicap here - rated at 4-5kW at 48V but manufacturer says it can handle 60V max with peaks up to 12kW.
The motor can handle probably 200v or more. But it spins faster the more voltage it gets, so with a non-current/torque throttle controller, you get more speed with more throttle (approximately). So the thing is what speed you want out of it, vs the kV (RPM per volt) the motor has, vs the wheel size, and any gearing between the motor and the wheel, determines the voltage you would want to use.
The practical limit for motors is actually phase amps, not volts, (and not battery amps) as there is a point at which it causes more heating than torque.
6.I've had a quick look at used EV cells but they seem to be over £500 for the voltage and capacity I would need as well as being used so would have more wear and less life. They also look very heavy for what they are. All together I think i might give this one a miss unless someone can persuade me otherwise!
Cost: I don't know what used cells run these days. New EIG cells are £10 each (in groups of 50) from Jimbob01 over in the for sale section; mine are used from someone that changed to different cells, testing out different stuff, IIRC. So a 14s1p pack, 52v 20Ah, 1kwh, 100A capable *continuous* and 200A burst for 10 seconds, would cost only £140 for the cells (if bought in lots of 50--I'm sure he'd sell them in lower quantities but the cost might be higher--even so it's still cheap), and he has busbars to connect them that would be something like another £20ish. Double that cost for 2kWh and 200A continuous and 400A burst. The only catch would be shipping if you're not in the UK, it might double the cost of the battery.
Lifespan: EV cells may have a thousand or more cycles capability before significant degradation. 18650 may have a few hundred. Depends on the specific cell. The EIG cells I have on my trike were used when I got them years ago, how used I don't know, but they're still doing well--not new-well, but just fine for my purposes (about 4kw max right now). I'll find out soon if they perform as well at double the power level. The ones I used on CrazyBike2 were used twice as hard (at 1p vs 2p, same power levels), and still performing well by the time I started using them on SB Cruiser, years later (before I changed to the new set of used cells in 2p).
I haven't used the Leaf cells myself but reports seem to be similar.
Weight: IIRC my 14s2p "52v" 40Ah EIG pack weighs 35lbs; it's not in a container, just the cells and heavy brass busbars (which probably are a couple pounds or more; you could use regular wire and ring terminals instead but busbars make it easy). My 14s1p in a heavy steel ammocan is about 20lbs. IIRC the A123 20Ah pach I have, in an identical ammocan, weighs about 30lbs.
Generally EV cells will be lower internal resistance, meaning less voltage sag and less power wasted as heat inside the cells. I don't recall ever noticing a temperature difference in the cells between sitting at ambient for hours, and using them hard for a while, though I don't have a temperature sensor in there so it's all hand-tested.
Where the 18650 stuff generally has noticeable temperature changes. The one old Luna pack I have here is only 4p, and not very good cells, so it can't even run the trike, it would probably get hot enough to damage it, if not actually fail dramatically. The one time I did test it out on the trike on a much less powerful early version, it got very hot, almost 25F hotter than ambient, in a very short ride. So it's probably not the best example. I'd love to long-term test a better pack, that's big enough to handle the trike's demands, technically equal to the EIG 2p pack (200A/400A@10sec), and see the differences, but it's too much work to build one (welding it all up, etc) even if I had the cells here.
I don't use a BMS, and the cells remain balanced throughout the discharge range, full to empty, any time I have manually checked them. Can't say that about the 18650 pack even when used at low loads--it requires the BMS to keep it balanced. :/
However, the main thing is that they are compact, low-resistance (and consistent properties between cells!), easy-to-connect (bolt together, for Leaf and EIG) cells. The last part is my favorite bit because everything else I have to do to build my stuff is hard enough, but I appreciate the rest of them too.
Which type is a better fit for you depends on your needs, desires, budget, and DIY ability.
7.For the 30Q cells i worked out I would build a 14s12p pack to give around 1.4kWh and 180A discharge. For the P42A I worked out a 14s7p pack for 1.5kWh and 210A discharge.
Keep in mind that the harder you use the cells, the less capacity you will actually get out of them. While a cell may be rated for say, 10A and 3Ah, you wont' really get both of those at the same time. How much different it is depends on the cells' internal resistance, and thus how much of the power it puts out is wasted as heat. The discharge curve charts on various battery test threads and sites will help you figure that out--it's not just about the specification numbers.
Note that most of this stuff doesn't matter for most bikes--it's the ones that need the high currents that make it harder to build a good battery for that is still small and affordable.
