User Manual

Using the Controller with a Power Supply
Advanced Digital Motor Controller User Manual 31
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 regeneration. As
discussed in “Power Regeneration Considerations” above, 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 its own output voltage. This information is seldom pub-
lished 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.
• 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. The diagram below
shows an example of such a circuit. The controller must be configured so that its
digital output is activated when an overvoltage condition is detected. The MOSFET
and brake resistor value must be sized according to the expected regeneration
current that must be absorbed.
IXTN170P10P
12V Zener
*Zener
*Zener:
- Not needed with supply up to 40V
- 20V with supply up to 60V
100K
Brake Resistor
1 to 10 Ohm, High Wattage
Depending on Braking Energy
47K
Supply
+
GNDGND
Controller
VMot
Controller
DOut
G
D
S
FIGURE 1-5. regen brake resistor
Note: The schematic above is provided for reference only. It may not work in all conditions.