Latest VESC-Tool and FW. Duty cycle (Arbeitszyklus) and the four different Amp settings are important to understand.
Quick example:
Battery voltage 50V, Motor max 80A, Battery max 40A
At 50% Duty cycle you can push 80A towards the motor while only 40A flow from the battery towards the VESC.
Reason: At 50% duty cycle the motor is operated at 25V (50% of 50V) and 80A = 2000W output
The battery delivers 50V at 40A =2000W
The VESC scales down the voltage and ups the Amps. 2000W Motor side = 2000W Battery Side
Once you surpass 50% duty cycle you can’t push 80A towards the motor any longer. The Amp flow would be reduced by the VESC till your amp flow is limited to 40A at 100% duty cycle (40A x 50V 2000W).
The higher “Motor Max” value will give you more power at slow speed, but will be reduced to “Battery Max” at high speed. This can be helpful when you want to go up a hill at slow speed.
So if you want to push 80A at 100% duty cycle (95% is realistic max), you also need to set battery max to 80A (80A x 50V= 4000W).
For braking it is similar, basically just reversed:
Battery 12S, 50V fully charged, Motor Max Regen = -40A , Batter Max Regen= -20A
At high RPM your motor generates at high voltage (e.g. 50V). In this case the “Battery Max Regen” value determines the braking strength. 50V x -20A = -1000W braking power.
At slower speed the motor generates at lower voltage and the “Motor Max Regen” becomes more dominant.
25V x 40A =1000W braking power. Again, your VESC will scale up Voltage towards the battery and lower the Amps. The battery will see 50V and 20A while the motor generates at 25V and 40A.
Your “Battery Max Regen” is set to -20A and this will not be exceeded! The VESC will not allow the motor to generate more Amps at a certain Voltage (Watts) than you can push safely towards your battery at charging voltage (per your definition of “Battery Max Regen”).
possible: 25V x-40A = 50V x -20A = -1000W
not possible: 40Vx -40A = 50V x 32A = -1600W (-32A exceeds -20A Battery Max Regen)
VESC will reduce to: 40V x -25A = 50V x -20A = -1000W
Motor Amps will be reduced to -25A to meet the Battery Max Regen setting
Its pretty much the same thing as for acceleration, just reversed.
Duty Cycle impacts the Motor Voltage. 10% =5V, 20%=10V, … 100%=50V.
Amps will be scaled up or down to never exceed the defined Battery or Motor settings (current control).
What can you do wrong?
If you set “Battery Max Regen” too low, you will have weak brakes at speed (since your motor generates at high voltage), which will get better the slower you get and the more the motor voltage drops (assuming that “Motor Max Regen” is set higher as in our example).
When do you need good brakes? At Speed! So check your Battery Max Regen to meet the desired braking strength. This is why you need a big Amp swallowing battery and why small battery packs don’t work for good brakes.
Also note: Symmetric settings (Battery Max = Motor Max, Battery Regen = Motor Regen). will give you perfect linear negative and positive acceleration. No need for funky Watt control modes. The more asymmetric you go, the more you will experience a non linear response. Your battery has to be able to cope with the currents anyway if you want good brakes. You can’t store the generated energy in the UNIVERSE.
Do the maths:
Break strength at full RPM (speed) = Battery Charge Voltage (V) x Battery Max Regen (A) = X Watt
Max output power of the electrical System = Battery Voltage (V) x Battery Max (A) = X Watts.
Your Battery is usually the Bottleneck!
Frank
