RoboteQ AX1500, AX2550 Electrical Noise Reduction Techniques, Power Regeneration Considerations

Electrical Noise Reduction Techniques

be amplified beyond the controller’s capability to correct them. This is particularly the case for the main battery power wires.

Important Warning

Avoid using long cable lengths (beyond 2 feet) from the main power battery to the controller as the added inductance may cause damage to the controller when oper- ating at high currents. Try extending the motor wires instead since the added induc- tance is less harmful on this side of the controller.

If the controller must be located at a longer distance, the effects of the wire inductance may be reduced by using one or more of the following techniques:

•Twisting the power and ground wires over the full length of the wires

•Use the vehicle’s metallic chassis for ground and run the positive wire along the sur- face

•Add a capacitor (5,000uF or higher) near the controller

Electrical Noise Reduction Techniques

As discussed in the above section, the AX1500 uses fast switching technology to control the amount of power applied to the motors. While the controller incorporates several cir- cuits to keep electrical noise to a minimum, additional techniques can be used to keep the noise low when installing the AX1500 in an application. Below is a list of techniques you can try to keep noise emission low:

•Keep wires as short as possible

•Loop wires through ferrite cores

•Add snubber R/C circuit at motor terminals

•Keep controller, wires and battery enclosed in metallic body

Power Regeneration Considerations

When a motor is spinning faster than it would normally at the applied voltage, such as when moving downhill or decelerating, the motor acts like a generator. In such cases, the current will flow in the opposite direction, back to the power source.

It is therefore essential that the AX1500 be connected to rechargeable batteries. If a power supply is used instead, the current will attempt to flow back in the power supply during regeneration, potentially damaging it and/or the controller.

Regeneration can also cause potential problems if the battery is disconnected while the motors are still spinning. In such a case, and depending on the command level applied at that time, the regenerated current will attempt to flow back to the battery. Since none is present, the voltage will rise to potentially unsafe levels. The AX1500 includes an overvolt- age protection circuit to prevent damage to the output transistors (see “Overvoltage Pro- tection” on page 36). However, if there is a possiblity that the motor could be made to spin and generate a voltage higher than 40V, a path to the battery must be provided, even after a fuse is blown. This can be accomplished by inserting a diode across the fuse as shown in Figure 9 on page 30.

AX1500 Motor Controller User’s Manual 35