RoboteQ AX2550/2850 user manual Overvoltage Protection, Undervoltage Protection

Connecting Power and Motors to the Controller

Important Warning

Avoid switching Off or cutting open the main power cables (thick black and red wires) while the motors are spinning. Damage to the controller may occur.

Overvoltage Protection

The AX2500/2850 includes a battery voltage monitoring circuit that will cause the output transistors to be turned Off if the main battery voltage applied on the thick red and black wires rises above 43V.

This protection is designed to prevent the voltage created by the motors during regenera- tion to be “amplified” to unsafe levels by the switching circuit.

The controller will resume normal operation when the measured voltage drops below 43V.

Undervoltage Protection

In order to ensure that the power MOSFET transistors are switched properly, the AX2500/ 2850 monitors the internal 12V power supply that is used by the MOSFET drivers. If the internal voltage drops below 10V, the controller’s output stage is turned Off. The rest of the controller’s electronics, including the microcomputer will remain operational as long as the internal voltage is above 8V.

The internal voltage will be the output of the DC/DC converter which will be a solid 12V as long as either of the main battery or backup voltage is higher than 12.5V. If the main and backup voltage drop below 12.V, the DC/DC converter’s output will be approximately 0.5V lower than the higher of the main or backup voltage.

Using the Controller with a Power Supply

Using a transformer or a switching power supply is possible but requires special care as the current will want to flow back from the motors to the power supply during regenera- tion. As discussed in “Power Regeneration Considerations” on page 31, if the supply is not able to absorb and dissipate regenerated current, the voltage will increase until the over- voltage protection circuit cuts off the motors. While this process should not be harmful to the controller, it may be to the power supply, unless one or more of the protective steps below are taken:

•Use a power supply that will not suffer damage in case that a voltage is applied at its output that is higher than the transformer’s own output voltage. This information is seldom published in commercial power supplies, so it is not always possible to obtain positive reassurance that the supply will survive such a condition.

•Avoid deceleration that is quicker than the natural deceleration due to the friction in the motor assembly (motor, gears, load). Any deceleration that would be quicker than natural friction means that braking energy will need to be taken out from the system, and cause a reverse current flow and voltage rise. See “Programmable Acceleration” on page 40.

•Place a battery in parallel with the power supply output. This will provide a reservoir into which regeneration current can flow. It will also be very helpful for delivering

32 AX2500/2850 Motor Controller User’s Manual Version 1.7. February 1, 2005