An HBControls Power Controller is a solid-state relay pre-assembled onto either a DIN or panel-mount heat sink. Each Power Controller is ready-to-use, eliminating the need for thermal calculations or heat sink selection. The maximum allowable load current for the assembled solid-state relay in a 40°C ambient temperature is provided in the datasheet for each controller. Solid-state relays are electronic relays that, unlike electromechanical relays and contactors, have no moving parts. As a result, their lifespan is significantly longer than comparable electromechanical relays. The typical MTBF (mean time between failures) for a solid-state relay is >7 million hours. Solid-state relays can also operate significantly faster, with on/off times measured in cycles rather than seconds. An instantaneous (also called a "random turn-on) solid-state relay can switch power to a load is less than 100µS. Solid state relay power controllers are similar to electromechanical relays and mercury contactors in terms of functionality. All of these devices switch power to or from an electrical load upon the application of an input or control signal. As previously mentioned, solid-state relays contain no moving parts, making them faster, quiet and highly reliable. Some of the benefits of using a solid-state relay power controller are: * Longer life expectancy and number of operations * Resistant to shock and vibration * Silent operation - no acoustical noise * Fast response time * No mechanical or moving parts

In terms of function, all three switching technologies are very similar to each other. That is, each switches power to/from an electrical load when voltage is applied to their input. However, electromechanical relays and mercury contactors utilize mechanical contacts to perform the switching function. HBC Power Controllers utilize solid state relays, which have no moving parts and perform the switching function exceptionally fast without any acoustical noise. The lack of moving parts also means that the life expectancy of a Power Controller is significantly longer than a comparable mechanical relay.

The most common AC output Power Controllers utilize solid state relays with two back-to-back (inverse-parallel) SCRs in the output. These SCRs conduct load current when the AC sine wave is positive with respect to its anode. In other words, during a normal conduction cycle, one SCR will carry the full load current during ½ of the AC sine wave and the other will carry the load current once the polarity of the sine wave reverses. Most DC output Power Controllers utilize MOSFET solid state relays, which typically have a very low on-state impedance (Rds) and dissipate a minimal amount of power compared to AC output SSRs in applications below 100A of load current. Unlike AC output SSRs, DC controllers utilizing MOSFET SSRs can be wired in parallel to reduce power dissipation and effectively increase the maximum load-current rating. AC output controllers 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. MOSFET controllers can be wired in inverse-series with the load to switch AC load current. This is an effective method for significantly reducing conducted emissions or minimizing power dissipation. However, since two relays are required the cost of doing so is often prohibitive. Consideration must also be given to the maximum off-state voltage rating of the controller, which can be damaged if exceeded by the peak AC voltage.

AC output solid state relays are not perfect switches, having a forward voltage drop (Vf) of approximately 1Vrms when in the on state. Therefore, they dissipate power in the form of heat at a rate of about 1W per ampere of load current. An SSR switching 50 amps of load current will dissipate approximately 50W of power. For the sake of simplicity, if we assume that the thermal conductivity of air is 20°C/W, then the base plate of a solid state relay would reach roughly 1,000°C when carrying 50 amps while suspended in free-air. It would, of course, actually melt long before then, but the calculation makes the point. HBControls Power Controllers utilize highly efficient heat sinks to prevent the solid state relay from overheating during normal use. Datasheets for each controller provide maximum allowable current ratings in a given ambient temperature, eliminating the need for thermal calculations or heat sink selection.

Because solid state relays dissipate heat in direct proportion to load current, and the fact that SSR life expectancy is dependent upon how well that heat is dissipated, the maximum allowable load current rating will almost always change whenever it is installed in an application. For example, a 90 amp solid state relay can carry 90 amps of load current only if it is mounted to a heat sink that can effectively dissipate 90W of power in the given ambient. If the heat sink is too small for 90W of dissipation, then the load current must be reduced to prevent the relay from overheating. Generally, it’s advised to keep the base plate temperature of an SSR below 80°C, although in many applications they can operate safely and reliably with a base plate temperature up to 100°C. If we wanted to switch 90 amps of load current in a 40°C ambient environment and keep the base plate temperature below 80°C, then we must prevent the base plate temperature from increasing by more than 40°C (80°C - 40°C ambient) while dissipating 90W of power. That means we would need at least a 0.44°C/W heat sink (+40°C allowable rise / 90W). If the same relay were mounted to a 2°C/W heat sink, for example, then the maximum allowable load current would be 20A (20A x 2°C/W = +40°C temperature rise). Without any type of external heat sink, most AC output solid state relays cannot carry more than 5 to 7 amps of load current in a 40°C ambient. The base plate of the relay helps dissipate some of the heat, but its thermal efficiency is limited by size. HBControls Power Controllers utilize highly efficient heat sinks to prevent the solid state relay from overheating during normal use. Datasheets for each controller provide maximum allowable current ratings in a given ambient temperature, eliminating the need for thermal calculations or heat sink selection.

Thermal impedance, or thermal resistance, is the measure of how resistant an object is to heat flow. The lower the impedance, the more efficiently the object will transfer heat. Thermal impedance is a critical aspect of Power Controllers as it determines how much power it can dissipate within a specified ambient temperature, which in turn determines how much load current it can effectively switch in an application. In most cases, the thermal impedance of a Power Controller is an irrelevant specification as full load-current ratings at different ambient temperatures are provided in the controller’s datasheet. However, understanding the importance of thermal impedance does help in understanding why heat sinks are required and vary in size for different ratings at different ambient temperatures.

HBControls Power Controllers utilize semiconductor-based relays to switch power to and from AC or DC loads. These relays typically utilize SCRs or MOSFETs for AC or DC loads, respectively. However, in some cases, diode or IGBT modules may be utilized when required within the application.

Electromechanical relays and contactors utilize mechanical contacts that are subjected to arcing every time they make (when closing) or break (when opening) power to / from the load. Over time, the arcing that occurs with each operation damages the contacts and eventually results in relay failure. The ‘heavier’ the load, the more significant the arc and the lower the life expectancy of the relay. Therefore, the life expectancy of an EMR typically ranges from 100,000 to 500,000 operations, which can be exceeded in just a few months in many industrial applications. Power Controllers utilizing solid state relays are not subjected to the same phenomena since they contain no moving parts. Power Controller life expectancy is usually given in hours and specified as mean-time-before-failure (MTBF) rather than operations. The typical MTBF of a Power Controller can vary between one million and ten million hours, or approximately 100 – 1,000 years.

Advantages; Life expectancy – Power Controllers can operate reliably for decades in most applications. Theoretically they can operate reliably for centuries but, since the first SSR was invented in 1972, that theory has yet to be proven. However, there are SSRs that have been in the field since the 70’s that are still operating normally and reliably. Silent operation – Power Controllers do not generate acoustical noise when switching power to/from the load since they contain no moving parts. Therefore, they are the preferred solution in many commercial or residential applications where acoustical noise can quickly become an annoyance. Shock & vibration resistance – Since Power Controllers have no moving parts they are not prone to false triggering under load in harsh environments subject to shock & vibration. Fast operation – Instantaneous turn-on Power Controllers can switch power to a load in less than 100 microseconds of receiving an input signal. This makes them ideal for phase-angle control applications where tight control over power to the load is required. PLC compatibility – As opposed to large contactors or other mechanical relays, Power Controllers can switch heavy loads with only a few milliamps of input current. Environmentally friendly – Power Controllers contain no mercury. Also, the abbreviated life expectancy of electromechanical relays means that hundred, if not thousands of EMRs will fail and have to be disposed before a single end-of-life Power Controller failure. Disadvantages; Cost – The initial purchase price of a Power Controller may be seen as prohibitive in some applications. However, due to the limited life of EMRs, the total cost of ownership of a Power Controller (the impact on cost over the life of the product in which it is used) is often significantly less than an equivalent rated EMR. Size – Power Controllers dissipate power in the form of heat during normal operation and therefore require an external heat sink in order to operate reliably. Galvanic isolation – Some applications require the load to be physically disconnected from the AC mains when in the off state. In these cases, the addition of a series electromechanical relay to provide off-state galvanic isolation might be the only viable solution. Energizing the EMR first in the sequence places the burden of switching full-load current on the SSR and significantly reduces or eliminates altogether the arcing of the EMR contacts, as does removing the input to the SSR just prior to de-energizing the EMR when switching to the off state.

Zero-crossing Power Controllers are the most common in the market. As the name implies, these controllers switch from a non-conducting to a conducting state shortly after the AC mains passes through the zero-crossing point of the sine-wave. Instantaneous turn-on Power Controllers will switch from a non-conducting to a conducting state within 100 microseconds of receiving an input signal. Both zero-crossing and instantaneous Power Controllers will continue to conduct load current after the input signal is removed until the AC sine-wave reaches the zero-crossing point. Therefore, the turn-off time is dependent upon exactly when the input signal is removed but will rarely be longer than 8.33 milliseconds on a 60Hz mains, or 10 milliseconds on a 50Hz mains.

Zero-crossing Power Controllers are the most common in the market and will only turn on shortly after the AC mains passes the zero-crossing point of the AC sine wave. Therefore, there is only a minimal amount of voltage across the load when load current begins to flow, which means that there will also be a minimal amount of inrush current. Turning on close to the zero-crossing point of the sine wave also reduces the conducted emissions of the Power Controller and makes them more compatible with applications requiring some level of compliance with EMC standards. The general rule-of-thumb for zero-crossing SSRs is that they are suitable for use with loads having a power factor between 0.7 and 1.0, although some will function normally switching loads with power factors down to 0.5. Typical loads for zero-crossing SSRs include heating elements, some lighting systems and light inductive loads. They are not suitable for use in phase-angle control applications since they won’t turn on after the sine wave has passed their zero-crossing window, which is normally less than 30Vpk. Instantaneous (or “random”) Power Controllers will turn on within 100 microseconds of the input signal being applied. They are commonly used for heavier inductive loads, such as larger motors, transformers and low power-factor solenoid or contactor coils. They are easily phase-angle controlled and can therefore be used in lighting dimming systems or with heating elements in applications where tight control over power to the load is required.

Phase-angle controllers apply a portion of the AC power to the load by turning on at various point of each sine wave. The amount of power applied is dependent upon the input signal applied. For example, applying 5V to a 0-10V input controller would result in 50% power to the load. They are ideal for dimming applications or in heating systems where tight temperature control is required. They can also generate a significant amount of conducted emissions since they often turn on closer to the peak of the AC sine wave. Therefore, additional filtering is required when installed in applications requiring some level of compliance with EMC standards. Burst-fire controllers also apply proportional power but do so by providing a series of full AC cycles to the load. The number of full cycles applied is dependent upon the percentage required, which is determined by the control signal and the time-base period of the Power Controller itself. If the controller has a time-base period of 10 AC cycles and the control signal is set to 50%, then the Power Controller will turn on for 5 AC cycles and then off for the next 5 AC cycles. Burst-fire controllers are typically used in heating applications where tight control over temperature is required. They are also used in applications where proportional control is necessary, but there is a concern over the amount of conducted emissions placed on the AC mains. They are not commonly used for lighting applications since the on/off period can create a significant amount of flicker. Typical control options for both phase-angle and burst-fire controllers include 0-10V, 0-5V, 4-20mA and potentiometer input.

Instantaneous, or “random” turn-on Power Controllers can switch power to a load in less than 100 microseconds of the control signal being applied. Zero-crossing Power Controllers will not turn on until shortly after the AC cycle passes through the zero-crossing point of the sine wave. Therefore, they will begin to conduct load current within 8.33ms on a 60Hz line, or 10ms on a 50Hz line.

Power Controllers utilize optocouplers (also called optical isolators or photocouplers) to provide electrical isolation between the input circuit and the output power circuit that’s connected to the AC mains. There are several different types of optocouplers but the most common used in Power Controllers are triac drivers, or photo triacs. In addition to providing input-to-output isolation, the type of triac driver used in the circuit also determines whether the Power Controller is instantaneous or zero-crossing. DC Power Controllers typically use photovoltaic couplers. These devices generate enough voltage to quickly drive the output MOSFETs into full saturation, preventing linear operation of the MOSFETs to reduce power dissipation. Typical Power Controller optocouplers provide 4kVpk isolation between the input and output circuit, with 12mm creepage (along the surface of the PCB) and 6.4mm clearance (spacing directly between the pins).

When connected to the AC mains, a small amount of current will flow through semiconductor power circuits, even without the presence of an input signal. The amount of leakage current is typically very low - normally less than 1mA for AC output Power Controllers and only a few hundred microamps for DC output controllers – and not hazardous to personnel. Howe