RoboteQ AX2850 user manual Battery Current vs. Motor Current, Temperature Max Amps

Battery Current vs. Motor Current

When the measured temperature reaches 80oC, the controller’s maximum current limit begins to drop to reach 0A at 100oC. Above 100oC, the controller’s power stage turns itself off completely.

TABLE 5. Effect of Case temperature on Max Amps Limit

Temperature	Max Amps
Below 80 oC	120A
80 oC	120A
85 oC	80A
90 oC	40A
95 oC	20A
100 oC	0
Above 100 oC	Both Power Stages OFF

The numbers in the table are the max Amps allowed by the controller at a given tempera- ture point. If the Amps limit is manually set to a lower value, then the controller will limit the current to the lowest of the manual and temperature-adjusted max values.

This capability ensures that the controller will be able to work safely with practically all motor types and will adjust itself automatically for the various load and environmental con- ditions. The time it takes for the heat sink’s temperature to rise depends on the current output, ambient temperature, and available air flow (natural or forced).

Note that the measured temperature is measured on the heat sink near the Power Transis- tors and will rise and fall faster than the outside surface.

Battery Current vs. Motor Current

The controller measures and limits the current that flows from the battery. Current that flows through the motor is typically higher. This counter-intuitive phenomenon is due to the “flyback” current in the motor’s inductance. In some cases, the motor current can be extremely high, causing heat and potentially damage while battery current appears low or reasonable.

The motor’s power is controlled by varying the On/Off duty cycle of the battery voltage 16,000 times per second to the motor from 0% (motor off) to 100 (motor on). Because of the flyback effect, during the Off time current continues to flow at nearly the same peak - and not the average - level as during the On time. At low PWM ratios, the peak current - and therefore motor current - can be very high as shown in Figure 20, “Instant and average current waveforms,” on page 46.

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.

AX2550 Motor Controller User’s Manual 45