Thanks I really appreciate you’re input and advice. I am more nuts and bolts than mathematics.
I am converting a 1961 Lambretta using a 5 KW BLDC Motor and 300a controller with Regen braking. It will be around 200lbs with the old engine, tanks etc taken out. I am mounting the motor and suspension by fabricating a subframe so that I don’t have to cut or weld onto a classic bike and can turn it back to stock if required.
Thing is I need a bit of range as I am approx 10 miles out of town, doesn’t have to be super quick but 55 mph would be good.
If I go for 20 number 18650 in parallel x 20(3.7v) do you think that is achievable?
Cheers
That would be 20s20p (20 cells in parallel to make a group, and a string of 20 groups in series). That will give you 20 x 20 x 3.6 x 3.5 = 5 kWh. If done right, 20s20p will weigh 5/0.25 = 20kg = 44lbs. The volume (batteries only) will be 5 x 2.2 = 11 liters. Cost (new cells LG) would be approx. 20x20x3.05 = $1,220 + 20% shipping charge + 10% enclosure + 15% power supply, charger, balancer-protection, monitor.
Range will be, assuming 25 km/kWh, 5x25/1.6 = 78 miles - probably 50 miles as it is a heavy classic.
300A is overkill I think, as it does not have to be super quick. That is 300x84/5000 = 5x the rating of the BLDC and could harm the BLDC. So go for 200A or 150A even 100A output from the pack. You will probably have difficulty finding a protection board rated at 84V 150A for the pack. So divide the pack into two 20s10p modules in parallel, and that is 75A per module, and you should be able to find an off-the-shelf 20s 75A balance-protection board (you will need two). About $25 each. If one module goes bad, you will still have 25 miles range. While if the 20s20p pack goes bad, you have 0 range.
For monitoring, each module should have a bunch of double-pole selectors and a digital voltmeter so you can read the voltage of each of the 20 groups in a module. Also each module should have a digital ammeter and a fuse.
I didn't realize this was a scooter. In which case your range should be greater, maybe 35 km/kWh ideally, or up to 75 miles with a 20s20p pack. Each module can give you 35 miles range in flat paved conditions.
Build one 20s10p or 20s12p 75A module first, get it all to work, and see if you really need a second module. Also install the power supply and charger in the vehicle.