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Connecting Power and Motors to the Controller
38 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007
It is therefore essential that the AX2550 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 AX2550 includes an overvolt-
age protection circuit to prevent damage to the output transistors (see “Overvoltage Pro-
tection” on page 38). 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 10 on page 32.
Please download the Application Note “Understanding Regeneration” from the
www.roboteq.com for an in-depth discussion of this complex but important topic.
Important Warning
Use the AX2550 only with a rechargeable battery as supply to the Motor Power wires
(thick black and red wires). If a transformer or power supply is used, damage to the
controller and/or power supply may occur during regeneration. See “Using the Con-
troller with a Power Supply” on page 39 for details.
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 AX2550 includes a battery voltage monitoring circuit that will cause the output transis-
tors 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 AX2550
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 control-
ler’s electronics, including the microcomputer, will remain operational as long as the inter-
nal 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