RoboteQ AX2850 - Manual (Page 39)

AX2550 Motor Controller User’s Manual 39
Using the Controller with a Power Supply
backup voltage drop below 12.V, the DC/DC converter’s output will be approximately 0.5V
lower than the highest input.
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 37, 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 is taken:
•
Use a power supply that will not suffer damage in case 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 of the sys-
tem, causing a reverse current flow and voltage rise. See “Programmable Accelera-
tion” on page 47.
• 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
high current surges during motor acceleration, making it possible to use a lower
current power supply. Batteries mounted in this way should be connected for the
first time only while fully charged and should not be allowed to discharge. The
power supply will be required to output unsafe amounts of current if connected
directly to a discharged battery. Consider using a decoupling diode on the power
supply’s output to prevent battery or regeneration current to flow back into the
power supply.
• Place a resistive load in parallel with the power supply, with a circuit to enable that
load during regeneration. This solution is more complex but will provide a safe path
for the braking energy into a load designed to dissipate it. To prevent current from
flowing from the power supply into the load during normal operation, an active
switch would enable the load when the voltage rises above the nominal output of
the power supply.