Power Guard Guide
Introduction
In this guide, we will provide an overview of power guards and discuss how they can be used in motor applications to protect your system and improve reliability.
What Is a Power Guard?
A power guard protects your power supply and other devices in your system from power surges caused by motors.
As shown in the image above, a power guard allows power to flow freely from the power supply to the motor controller, but it prevents any power from flowing in the reverse direction.
Why Is a Power Guard Necessary?
In motor applications, regenerated energy from the motor can cause power surges. These surges may lead to system instability and, in many cases, irreparable damage to the power supply, motor controller, and other devices in the system.
Power Surge Example
The video below shows how a voltage surge can damage your system.
How Does a Power Guard Work?
A power guard can be thought of as a one-way valve for electricity. A power supply is connected to the input of the power guard, and the output is connected to a motor controller.
If the voltage on the output of the power guard increases beyond a predetermined safe limit (i.e. the Trip Voltage has been exceeded), the power guard will immediately attempt to regulate the voltage. It does this by converting the extra energy into heat.
Some power guards designed by Phidgets Inc. have advanced sensing and capabilities, however, all power guards generally function in the manner described above.
Does My Application Require a Power Guard?
Most motor applications will require a Power Guard Phidget. Review the information below for more information.
Power Supply
| Power Supply Type | Power Guard Required? | Information | |
|---|---|---|---|
| AC to DC | Yes | These types of power supplies are typically very sensitive to any type of overvoltage event. For small events (1-2V), they may reset causing your system to lose power for a few seconds. Larger events will likely cause irreparable damage. | |
| Lead-acid Battery | No | When using a properly sized lead-acid battery, power surges from your motor will be absorbed by the battery. | |
| Other Rechargeable Batteries | Varies | Use a Power Guard Phidget unless you are certain that your battery is capable of absorbing excess power. |
Regenerative Charging
If your application requires regenerative charging and you have a suitable rechargeable battery, you do not need to consider a power guard in your design.
Small Motors
If the rated current of your motor is less than 1.5A, you do not need to consider a power guard in your design.
Built-In Power Guards
The following controllers have built-in power guards, so you do not need to consider an external power guard in your design:
Selecting a Power Guard Phidget
If you have determined that a Power Guard Phidget is required for your application, review the following information.
Small Motors
If the rated current of your motor is between 1.5A and 5A, the Power Guard Phidget 30V 5A (SAF2000_0) will be sufficient. Otherwise, view the tables below.
DC Motor Controllers
BLDC Motor Controllers
| Controller Name | Recommended Power Guard |
|---|---|
| 30V 50A BLDC Motor Phidget (DCC1120_0) | Power Guard Phidget 30V 50A (SAF2020_0) |
| Brushless DC Motor Phidget (DCC1100_0) | Power Guard Phidget 30V 50A (SAF2020_0) |
Stepper Motor Controllers
| Controller | Recommended Power Guard |
|---|---|
| 8A Stepper Phidget (STC1002_0) | Power Guard Phidget 30V 5A (SAF2000_0) |
| PhidgetStepper Bipolar HC (1067_0B) | N/A. This device features a built-in power guard. |
| 4A Stepper Phidget (STC1005_0) | N/A. This device features a built-in power guard. |
Power Guard FAQ
Can I Use Multiple Power Guard Phidgets in Parallel
No, we do not recommend using Power Guard Phidgets in parallel. The trip voltage of two power guards will never be the exact same, meaning one will trip first thus negating any potential benefit of using them together.
Can I Use One Power Guard Phidget with Multiple Motor Controllers?
Yes, as long as the worst-case regenerated current is not higher than the continuous current rating of your Power Guard Phidget. Check out System Monitoring for information about how to determine your worst-case regenerated current.
Why Aren't Power Guards Built Into All Motor Controllers?
There are a few reasons:
- Motor controllers with a built-in power guard are not able to regenerate power.
- Motor controllers with a built-in power guard must be designed for worst-case regenerated current. This means larger boards and increased costs for all users, even those who will not operate at these limits.
How Should I Connect Other Devices To My System?
If your system includes a power guard, it is important to connect all other devices upstream of the power guard. This will ensure that they are protected from any power surges.
