User Manual

Measured and Calculated Currents
Advanced Digital Motor Controller User Manual 29
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FIGURE 1-4. Instant and average current waveforms
The relation between Battery Current and Motor current is given in the formula below:
Motor Current = Battery Current / PWM Ratio
Example: If the controller reports 10A of battery current while at 10% PWM, the current in
the motor is 10 / 0.1 = 100A.
Measured and Calculated Currents
Some Roboteq Brushed DC motor controllers, have current sensors for measuring the
battery current and estimate the motor current. At 20% PWM and above, the motor cur-
rent is computed using the formula above. Below 20%, and approaching 0%, this method
causes unstable and imprecise readings. At these levels the formula used is
Motor Current = Battery Current / 0.20
This approximation creates a more stable value but one that is increasingly inaccurate as
the PWM approaches 0%. This approximation produces usable value nevertheless.
Roboteq’s Brushless motor controllers use sensors on the motor outputs or/and on the
battery ground terminal. Controllers using sensors on the battery terminal outputs suffer
the same limitation at low PWM as discussed above.
Controllers with sensors on the motor terminals provide accurate motor current sensing in
all conditions, and provide a good estimate battery current value. Some controller models
have sensors on the motor and on the battery terminals, and provide the most accurate
current sensing as all are actually measured values.
Whether sensors are on the motor or/and battery terminals can be found in the product’s
datasheet
Important Warning
Do not connect a motor that is rated at a higher current than the controller.