AC Output Single-Phase Power Controllers
& Solid State Relays
Frequently asked questions
What are single-phase solid-state power controllers?
A single-phase AC power controller utilizes one AC output solid-state relay to switch power to/from an AC load. They are most commonly used in 120Vac or 240Vac applications where only one load is controlled, such as a resistive heating element. However, they are also commonly used in applications using three-phase power, with one single-phase power controller connected to two or all three legs of the three-phase AC mains. In these types of applications, the input terminals of the power controllers are typically wired in parallel so that the load is fully energized via one control signal.
Can I use AC output power controllers to switch a DC load?
AC output controllers and solid-state relays cannot be used to switch DC loads since the holding current of the SCRs will prevent them from turning off when the input signal is removed. The only exception is in applications where the load current is interrupted by other means.
The best solution for switching DC power to/from a load is with an HBC DC output power controller. There are two basic types of DC power controller; bipolar transistor (XSTR) output and MOSFET output. Bipolar transistor solid-state relays and power controllers are more economical but usually limited to DC loads of less than 7 amps. For higher current loads, MOSFET output solid-state relays are used because their low on-state impedance allows for current ratings up-to 100Adc.
Can I use multiple single-phase power controllers in my panel to control more than one load?
Yes. Many applications have multiple loads that need to be turned on at different times. Very large applications, such as thermoforming machines, may use dozens of single-phase power controllers in a panel to control a vast network of heating elements. The primary consideration for using multiple power controllers in a panel is heat dissipation. The solid-state relays mounted to the power controller dissipate heat at a rate of about 1 Watt per ampere of load current. Therefore, adequate spacing must be provided between solid-state relay power controllers to allow for heat dissipation during normal operation.
How much spacing is required between AC output single-phase power controllers?
The required spacing between power controllers can vary significantly from application-to-application. It’s primarily dependent upon the load-current being switched in the application, but duty-cycle, internal ambient temperature and available airflow / ventilation are factors that must also be considered. As a general rule-of-thumb, we recommend a gap of approximately 1” / 25mm between power controllers for most applications. However, the spacing requirement may increase as load-current increases, or if there is limited airflow or excessive ambient temperatures within the panel. Please contact our technical team at 800.879.7918 / support@hbcontrols.com if you’d like to discuss your specific application’s requirements in more detail.
Can I connect more than one load to single-phase controllers?
Yes, multiple loads can be controlled with one single-phase power controller. However, there are a few important points that must be taken into consideration;
- The sum of the load-currents of the individual loads cannot exceed that maximum load-current rating of the power controller. For example, a 50 amp power controller can reliably switch power to a couple of 20 or 25 amp loads since the combined load-current is equal to or less-than the 50 amp rating of the controller. If you wanted to switch two 30 amp loads, then a power controller with a rating of at least 60 amps would be required.
- Connecting multiple loads to a single terminal can sometimes be problematic. The power cables must be adequately terminated to the output terminals of the solid-state relay. Loose connections, improper wire gauge or terminal size can lead to arcing or overheating at the output terminal, which could result in a catastrophic failure of the relay.
- Since single-phase controllers utilize one single-phase solid-state relay, the loads cannot be controlled independently. Both loads will turn-on simultaneously when the input control signal is applied.
What is meant by “100% duty-cycle”?
Duty-cycle refers to the ratio between the on-time and off-time of a solid-state relay or power controller. It is often expressed in either seconds or as a percentage. A 0% duty-cycle would mean that the relay is never turned on, while a 100% duty-cycle would mean that the solid-state relay is turned on and then continuously conducts load current. The former isn’t very practical, since you probably wouldn’t need a solid-state relay or power controller in a 0% duty-cycle application (there are a few unique exceptions). The latter, however, is important with regards to the heat sink used to dissipate the heat generated by the solid-state relay. HBControls power controllers, for example, have load-current ratings based upon a 100% duty-cycle in a 40°C ambient temperature. If a single-phase AC power controller is rated to 50 amps, then the controller’s solid-state relay can reliably and continuously conduct 50 amps of load current in an ambient temperature of 40°C, without ever exceeding its maximum temperature specification.
Is there a DIN or panel-mount option for each power controller?
In most cases, yes. The S, A, L and K series power controllers are DIN mount, by default. However, there are standard options for panel-mounting each of those product families. The “-TP” is a through-panel option, such as an HBC-50HDS-TP, which means that the top surface of the heat sink includes drilled & tapped holes for panel mounting. The “-PM” option, such as an HBC-50HDS-PM, comes with a bracket mounted to the bottom of the heat sink to allow for panel mounting.
The N series, by default, is a panel-mount power controller. The “-DIN” suffix, such as an HBC-90HDN-DIN, would include a DIN mount clip. The G and F / F7 product families are also panel mount power controllers but do not have a standard DIN mount option. This is because they are larger power controllers and the weight of the assembly is not suitable for most DIN brackets.