With a higher voltage battery there’s greater inefficiency in the whole system (assuming you battery wire are reasonable) as there’s more esc switching, which is widely known, but there’s also more current ripple in the motor: current that’s not producing useful torque but produces heat.
News to me.
if you increase the gear ratio when increasing voltage for the same top speed, then you can get the same performance with less motor current, and greater efficiency.
Minimizing supply voltage whenever possible will reduce current ripple proportionally
Increasing gear ratio requires a higher kv motor, less inductance, and more ripple.
You can compensate by increasing the pwm frequency which will increasing esc losses but decrease ripple in motor.
the increased voltage increases the no load rpm of the same kv motor…
the increased gear ratio increases the torque multiplication between the motor and drive wheel… so then it takes less motor torque and motor current for the same wheel torque, and you also have the same top speed.
Not what I’m talking about. I’m talking about in a motor. Regardless of gearing or not higher v results in greater current ripple.
with a hub motor/direct drive you can also increase the efficiency with higher voltage by reducing the tire diameter for the same top speed.
Only one will be most efficient though
Wait I forgot about infinity nvm
What’s the calculation? Electric cars are running 300V+ because pushing 1000 amps is just ridiculous. I wonder for eskate purposes then, what is the ideal range… 50-100v? over 100? hmmm.
the higher voltage is only an advantage in the wiring from the battery to the esc. going from esc to motor its bucked to be maybe 1000’s of amps and will be the same amount whatever the battery voltage. only amps give torque in the motor. if you forget the losses from the battery to esc it makes sense to use as low a voltage as is needed to push the current you want based on ohm’s law.
more voltage is more cells and a pain in the ass with the complexity.
so only use high voltages if you plan on using high currents.
If you go from 10s to 12s (x 1.2) & you change your gear ratio from 2.4 to 2.88 (x 1.2) then you can find out how much less motor current it takes for the same constant speed with 12s (compared to 10s) by multiplying the original motor current by (1/1.2) or (0.8333…) and the heat production will be reduced by a factor of (1/1.2^2) or (0.6944), which means for the same top speed, constant speed and acceleration, the 12s generates about 31% less heat in the motor than 10s for the same performance.
Where’s the limit/crossover? Theoretically, what if I ran 100s battery with a 24-1 gear ratio? In that case the motor would be stone cold the entire time but that can’t be the case?
of course you can. mechanical power is torque nm x angular speed rad/sec. you can make the motor turn much faster with less torque to get the same power with higher voltage, and the heat is proportional to the square of the current and torque, not the angular speed.
You’re saying there’s no loss elsewhere? Seems like everything would be running 100k RPM motors with multiple gear reductions for 99% efficiency…
you start to get more iron loss when the motor turns very fast from eddy currents in the stator iron and hysteresis. at some point these iron losses will be more significant than copper losses.
Ah yeah that’s right. I remember now. So still the question is, what’s the ideal voltage range for our purpose? Is 10-12s good enough or would 20s+ be a lot more beneficial?
iron losses are very difficult to predict, i think it has to be determined experimentally.
at 20S we can get more efficient charging so wh/mi efficiency whatevs
Errrr very high voltage (120+) solid state devices are still relatively rare and expensive. EVs are changing that but before there just wasn’t much need. Can’t weigh in on the mechanics but from a semiconductor perspective, yeah, of we could, we should definitely go higher Volts. We just can’t. Yet.
I was playing exactly with that on ebikes.ca trip simulator, now it shows each losses individually
Really cool to see both on ebike and eSkate motors the design approach they took and how the loses are split
Do you have any data for core losses on our motors? I see now 18S being thrown around, but don’t know if it really pay off since there will be significantly more iron losses, and Vedder always said the for the motors he tested the balance was around 8000 to 9000 rpm