Can MAC 8T take 2000W+?
- Thread starter brucejun
- Start date
E-HP said:
If you want the motor to pull high power other that in acceleration, uphill or headwind you need to have very poor motor efficiency. The bike will only need certain amount of power to maintain specific speed. That`s purely physics. When we apply field weakening we can only use more power through efficiency. Otherwise at constant speed the load stays the same and so does the power usage.
What goes to using simulator. The graph and table labeled as graph describes watts as "motor power". The values presented in "graph table" are output figures that are affected by motor and controller efficiency. Figures described in "electrical" table are the ones experienced by the motor. So these are the "motor will pull" figures. We can alter the controller resistance value to point the efficiency only to the motor. Of course battery internal resistance plays big role too so that can be changed accordingly.
When we have 40A limiting BMS in use we can have situation where on flat ground during acceleration the motor pulls 2000w or more starting from 12.2 mph up to just below (like 0.2 mph) the topspeed (36.3 mph). The max power (~2200w) area are is quite broad from ~14mph to just under 35mph.
Situation at 12mph where motor pulls just under 100 phase amps at ~20V (2000w) or with poor efficiency of 68.5%. Motor converts this 2001w to output power of 1371W.
https://ebikes.ca/tools/simulator.html?motor=GMAC8T&batt=cust_58_0.050_21&wheel=28i&frame=mountain&mass=100&hp=0&axis=mph&cont=cust_40_100_0.001_V&cont_b=cust_40_100_0.001_V&motor_b=GMAC8T&batt_b=cust_58_0.100_18&wheel_b=28i&frame_b=mountain&mass_b=100&hp_b=0
Situation at 36mph where motor pulls just under 44 phase amps against back emf voltage (2000w) the efficiency is now 86.3%. Motor converts this 2006w to output power of 1732W.
https://ebikes.ca/tools/simulator.html?motor=GMAC8T&batt=cust_58_0.050_21&wheel=28i&frame=mountain&mass=100&hp=0&axis=mph&cont=cust_40_100_0.001_V&cont_b=cust_40_100_0.001_V&motor_b=GMAC8T&batt_b=cust_58_0.100_18&wheel_b=28i&frame_b=mountain&mass_b=100&hp_b=0
OK, at least I can see what you're doing. The simplifying assumption is that the controller has no losses, so the battery watts equals the motor watts, plus the heating watts (the 2000 battery watts equals the 1300 motor watts, plus 700 heating watts, in the first example). From what I see, this still only represents the power and efficiency when the bike is accelerating, not continuous. So, what is the continuous scenario where the efficiency would be so low? If you are only talking about under acceleration, then how many hard accelerations could you have before the motor melts?TuomasK said:Ok. Maybe I'll start with screen shots as nobody else bothers.
E-HP said:OK, at least I can see what you're doing. The simplifying assumption is that the controller has no losses, so the battery watts equals the motor watts, plus the heating watts (the 2000 battery watts equals the 1300 motor watts, plus 700 heating watts, in the first example). From what I see, this still only represents the power and efficiency when the bike is accelerating, not continuous. So, what is the continuous scenario where the efficiency would be so low? If you are only talking about under acceleration, then how many hard accelerations could you have before the motor melts?TuomasK said:Ok. Maybe I'll start with screen shots as nobody else bothers.
Yes. For this example simplified the scenario little by cutting down the controller resistance so its 99%+ efficient. So "all" losses from the motor itself.
Practically only scenario where constant 2000w can occur is increased load (uphill, headwind etc.). No matter what motor used its the same unless efficiency is poorer. I would say riding wisely the motor would hold ok but also IT would be easy to burn it
