So I made my own e-bike kit, it was not too hard since I already pretty much did it before with a previous 48V motor. But this one, even though it's rated 500W basically the same as the other one, is 36V and has a higher Kv which is making the spin up to the 3250 rated rpm more difficult. Everything seems to be fine except: in top gear at 50% throttle (est. 500W out of 100W peak) on a slight 1-3% incline the motor itself is fine but the controller overheats. I cannot feel it getting hot from the outside, but the display shuts off after 1-2 miles of continuous throttle so it must be deep inside, probably the mosfets. I'll tell you what I 'think' is the problem and the two solutions, and could you let me know which one (or a 3rd / 4th solution) may be more correct.
I'm overvolting the 36V motor with a 48V battery. I don't think it's causing the problem in top gear. If anything it should be helping the issue because it's making the motor spin faster and that's exactly what it needs when you remember that human pedaling is normally only 60-80 rpm.
The BLDC motor without gearing is rated at 1.6 Nm torque at 500W (3.2+ Nm 1000W peak). Ungeared rated rpm as above is 3250. Internal gear reduction is 9.85:1. So it's basically making 15 Nm of torque at 500W at the 11mm keyed output shaft (MY1018z brushless). I have a 16T freewheel (lowest teeth possible for the 11mm adapter) mated with a singlespeed chain to a 40T chainring. So that's 2.5x 2nd stage reduction. There is a 2nd chain (3rd stage) but most of it's overdrive. 38t chainring on the same crank spindle mated to an 11-52T cassette. This means that 52, 46, and 40t for cogs 1-3 are additional reduction, BUT...everything else from 4th to 11th gear is overdrive and lowers torque/reduction. That's the problem. 11th gear is 11T and now we are going in reverse for reduction: 15 Nm output shaft x 2.5x 2nd stage = 37.5 Nm, but then 11/38 = 0.29, so 37.5 Nm x 0.29 = only 10.9x reduction in top gear. The AI is telling me that the rpm is 1970 (80 crank rpm x 2.5 x 9.85 = 1970 rpm, is that correct, regardless of gearing and throttle input?) It's saying that motor rpm doesn't dictate controller heat, only electrical duty cycle and current duration overheats controllers. And that 1970 rpm is not enough for EMF to drop current, so the controller is going crazy trying to raise current since the torque is not enough to overcome wind resistance past 15 mph. So I can increase the 2nd stage chainring size from 40T to 52T which gives a 30% increase in torque and 2560 rpm rated. I don't want to lower the 3rd stage cassette chainring down below 38T; I already have 38T on two other analog bikes and it's starting to get ridiculous if the top end is lower on an e-bike than on a normal bike.
The controller is 22A max. I can get a 30A controller but I would need to trim off the power wires to get a better XT60 battery terminal fit. I've ordered the XT60 pigtails and shrink tubing. The phase wires are also an issue but in the past I've simply electrical taped the crimped ones to the controller o-rings and it worked fine. Hall wires are white housing male to white housing female so that's not an issue. The goal would NOT be to run more than 1000W peak through a 1440W peak controller. Instead, the 12 mosfets would simply be for the controller to soak up more heat from the 11T overdrive gear. Keep in mind that the motor itself is running cool, it normally doesn't get over 43C with a digital sensor, so it's the controller. I can run more a bit more amps through a 30A controller and limit it to for example 22.5A, 24A, 25.5A or 27A max with a KT display and C5 parameter.
What do you guys think; is there any other solution besides 2 and/or 3 that will help the top end for a mid-drive? BTW the motor itself is a $61 absolute steal; the controllers are actualy more expensive lol.