Power Supplies and Shunts
Reliable Current Supplies for Dynamic Motion Profiles
Because servo motors are inductive, they may run highly dynamic motion profiles. As a result, their current demand can vary widely. Surge currents from stand still to maximum load may be extremely high, yet steady state current demand over time may be relatively mild. Therefore, proper care should be taken when selecting power supplies. Moog Animatics offers linear (unregulated), switch mode (switcher) and shunt supplies, all designed to reliably and safely meet your current and motion performance requirements.
Which is Better, Linear or Switcher Supplies?
Moog Animatics offers two basic types of power supplies. The chart to the left gives a brief comparison of the two types of supplies. Each power supply option offers unique advantages, as described below:
Linear (Unregulated) supplies can handle large surge current loads., such as multiple motors starting and stopping at once. This is because linear supplies typically contain large output capacitors to handle those surges well. Linear supplies will slowly drop the output voltage while supplying more and more current. Given that they are minimum components, they provide low failure rates and long life, for many years. Linear supplies can also support more Back EMF form motors generating higher than supplied DC bus voltage.
Switch Mode supplies (switchers) are highly regulated and sustain constant voltage up to the maximum current rating, with no drop in voltage up to that rating. These capabilities are ideal for achieving higher speeds under sustained continuous loads. Switch mode supplies are Universal AC input voltage, so they can run off 110 VAC, up to 240 VAC, making it easier to design into equipment that may end up in other countries with different AC voltages.
WARNING: Improper power supply sizing may result in motor position error faults, motor resets, and machine faults.
Shunts for Overvoltage Protection
Moog Animatics offers several shunt options for use with DC input servo motors in 100, 200 and 300 Watt size ranges. Shunts are needed to protect the servo controller and drive stages from overvoltage, which can originate from the following sources:
- Back EMF due to back driving the motors
- Sudden or hard decelerations
- Hard stop crashes (immediate deceleration to zero speed)
- Vertical load drops
- When voltage exceeds the trigger level, the shunts automatically add an additional load to the DC bus by connecting large load resistors across the bus. Trigger voltage is typically 49.5 VDC.
NOTE: Shunts start loading the bus at 49.5 VDC and rising, and will be fully loaded at 53 VDC.
WARNING: If the shunt is connected to an adjustable power supply, the output voltage must be set at or below 48 VDC. If the output voltage is sustained above the trip point of the shunt, overheating and damage may result.
