So say my battery can only put out 100a… and i have 2 motors set at 60a each, and vesc is limited to 100 battery amps. Does this mean i wont reach the top speed of my motors?
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that depends on the load, terrain, gearing, kv and tire size.
if your battery can do 100a and you have 2 motors, you want the battery current limit on each vesc to be 50a, but you can safely set the motor current limit higher.
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Lets assume perfect conditions. The motors want to reach 120a to acheive 100% duty cycle but vesc is limiting to 100a, surely i wont reach full speed right?
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with no load the motor will reach full speed with likely less than an amp, so it depends on the load and gearing.
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Cheers dudes, very helpful. I’m gonna have to go back over this a few times with less beer in me for it to sink in. But it is making more sense to me now.
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motor_current = (pwm_effective_voltage - bemf_voltage) / winding_resistance_ohms
motor_current = A
pwm_effective_voltage = B
bemf_voltage = C
winding_resistance_ohms = D
A = (B - C) / D
can be rearranged:
B = (A * D) + C
therefore:
pwm_effective_voltage = (motor_current * winding_resistance_ohms) + bemf_voltage
&
battery_voltage * duty_cycle_%_bldc = pwm_effective_voltage
therefore:
duty_cycle_%_bldc = pwm_effective_voltage / battery_voltage
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Currently got no working builds 
trying to understand this stuff so i dont fuck anything up.
My flipsky dual6.6 just shit itself and im wondering if its because i set the braking too high. Max motor amps were 35 and i set braking to -60. 10s5p 30q
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So would it be likely that I cooked the esc by having it too high?
Motor amps
Cheers dude. I am comfortable that none of that happened so I can conclude that the flipsky dual 6.6 is a piece of shit. And ive successfully derailed my own thread
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this chart shows 48v, 30a bat limit setting per motor, 120a motor current limit setting per motor, 190kv, 100mm, 2.5:1 gearing, 2 motors:
^you can see from the bottom left chart this board will do about 40mph on flat ground and about 35mph on a 10% slope, and about 20mph a 31.5% slope.
blue and black lines top left chart show the motor current (blue) and battery current (black)
the downward slope of the motor current (blue line top left chart) during acceleration is caused by hitting the 30a battery current limit at low rpms.
the drop in battery current at the right side of the chart is caused by hitting 95% duty cycle and then continuing to accelerate (the bemf voltage prevents drawing significant amperage)
edit: i updated the chart because i originally had the wrong vehicle mass inputted.
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I’m glad you asked this, I have rough understandings of a lot of these values but motor current always confused me. Does that just come from the manufacturers spec?
For example, I’m running these motors and see they listed 65 and 60A ratings. If been running them up to 80A motor current and have seen no issue.
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In the case above, the rider wouldn’t be able to draw above 60a motor while above 20mph, even if they set it higher, because of the 30a battery limit setting.
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Is there an app or website or spreadsheet I can use to generate these graphs for my ride?
Thank you so much @glyphiks for asking this question. That said I might have to go back over this thread a few times with some beer in me for it to sink in better.
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I haven’t made it available to download but I’ll think about it after making some adjustments for usability.
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biggest wrong thinking is to believe that these are equal.
motors are 3 phase AC and large amounts of current can be moved from one phase to another meaning that there can be lots of current moving inside the motor without taking power from the battery. the amount of battery current needed to sustain a motor current depends on lots of factors like speed and load.
This is the best way to think about it:
At low speeds you cant pull much power out of the battery as your not doing much work. your motor current will be the important factor here.
motor current = low end torque
at high speeds you can use much more battery power as your doing lots of work. you battery current will be the limitng factor here.
battery current = High speed torque
As for duty cycle. your motors have a set kv rating. This is basically rpm/volt. so rpm/volt multiplied by voltage gives you your max speed in rpm. Duty cycle is the % of this that your currently at. eg 50% duty cycle is 50% max speed.
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this isn’t right, the duty cycle % is the % on-time of the battery current, and it determines the effective voltage seen by the motor.
In BLDC 10% duty cycle means 10% of the time, current is being supplied by the battery. Through a quirk of physics, it also means the motor “sees” 10% of the battery voltage. It also means the battery current will be 10% of the motor current.
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Where did you pull this value from? I mentioned no battery limit setting in my case.
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Merely to illustrate how a battery current limit affects the motor current limit.
If there was no battery current limit, the motor current will be a straight line across and the battery current will be a flat ramp that almost meets up with the motor current line at 95% duty cycle.
Another interesting part of the graph is where the red line crosses above the yellow line in the top left chart. Thats no load speed where the back emf voltage produced by the motor starts to exceed the max effective voltage at 95% duty cycle. The motor can’t go any faster than this rpm under its own power.
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Ok thank you for clarifying. At a 10s5p 30q pack, I have my my max battery current set to 95A but have always worried about motor max constraints
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