The many advantages of solid state relay switching devices make them applicable for a broad range of industries. But what are these advantages? Also, what are the downsides of using SSR relays? This article will explore the pros and cons of solid-state relay technology.
Solid State Relay Explained
A solid state relay, as the name suggests, is an electronic switching device that does not contain or use any moving parts. It essentially consists of a switch that is activated by an electronic signal, rather than a mechanical switch.
Most SSRs today employ opto-isolators to electrically isolate the control signal from the switching circuit. The solid state relay optocoupler is usually a combination of an LED and a phototransistor.
When the control voltage is applied to the LED, it emits light that activates the transistor. That, in turn, completes the circuit and allows current to flow through to the load circuit at the output side.
Advantages of Solid State Relay
Solid state relay advantages range from compactness to shock resistance and long life. Here are the most important of these SSR benefits to give you an idea of why this technology could be the best for your application:
1. Fast Switching Speed
One of the main advantages of solid state relay devices is their switching speed. With no mechanical parts to move, SSRs can switch in microseconds. This is a significant improvement over electromechanical relays, which can take milliseconds to operate.
The higher solid state switching speed finds great use in many applications, especially where timing is critical or where high frequencies are involved.
For example, a fast switching solid state relay is an important requirement -and commonly used – in the automation systems of homes, manufacturing industries, robotics, and communication equipment. In these applications, the fast response time allows for greater accuracy and other benefits.
2. Complete Electrical Isolation
Most SSR relays today use optical isolation to electrically isolate the control signal from the switching circuit, as mentioned earlier. This provides several benefits, most notably improved control circuit safety and arc avoidance.
The solid state relay isolation insulation between the control and load sides of an SSR input and output can be as high as 4000 Vrms. That means there is very little chance of electrical shocks or sparks, even in the event that the load produces a high reverse current.
3. Zero Voltage Switching
One of the most significant advantages of solid state relay technology is that you can turn them on and off at zero or almost voltage. This means that there is no arcing across the contacts, as there would be with an electromechanical relay.
Electrical arcing can cause pitting and erosion of the contact points, eventually leading to failure. That means an SSR will last longer, since it doesn’t experience arcing problems. That’s in addition to allowing operation n environments that contain flammable materials.
The lack of arcing also results in much quieter operation and reduced electromagnetic interference (EMI), which one of the many solid state relay benefits.
4. Compact Size
The semiconductor devices used in solid state relays are much smaller than the electromechanical components used in standard relays. This makes SSRs much more compact: a major advantage in many applications.
The smaller solid state relay dimensions also leads to lower weight and less mounting space required. This is important in applications where every ounce or square inch counts, such as in aircraft and satellite electrical systems.
5. Long Lifespan
As you already know, solid state relays have no moving parts. That means there is nothing that will wear out or break over time, which gives them a much longer lifespan than electromechanical relays.
In fact, the average solid state relay lifespan is hundreds of thousands cycles and up to several million hours of use in normal conditions. That’s over 20 years of operation! For comparison, an electromechanical relay might only last for a few ten thousand cycles before it needs to be replaced.
Solid State Relay Disadvantages
So far, we’ve only talked about the advantages of solid state relays. But like everything else, they do have some drawbacks that you should be aware of before making a purchase. Solid state relay advantages include the following:
1. Limited Voltage and Current Ratings
One of the disadvantages of solid state relays is their limited voltage and current ratings. The vast majority of SSRs can only switch low-voltage and low-current loads.
Higher voltage and current versions do exist, but they tend to be much more expensive than the standard types.
This means that when using a solid state relay, cost can be a limiting factor if heavy-duty systems are involved. As such, some industrial settings may require the use of traditional electro-mechanical relay types.
2. Output Leakage Current
When an SSR is turned off, there is a small leakage current that flows through the output. This is normal and not cause for concern unless the load is very sensitive to even small changes in current.
The solid state relay leakage current is usually in the range of 5mA to 10mA, which is not enough to damage most loads. In comparison, most load circuits can draw 150mA upwards.
Another downside of solid state relays is their cost. They are usually more expensive than comparable electromechanical relays. The high cost is due to the use of semiconductor materials and manufacturing processes required to make them.
For some applications, though, the added expense is worth it for the benefits that SSRs offer. These include applications where the shorter solid state relay response time and other properties are indispensable. But in others, the lower cost of an electromechanical relays may make them a better choice.
Solid state relays state advantages include faster switching speed, non-arcing operation, and longer lifespan. They are also more compact and weigh less than standard relays. Before considering SSRs for your application, it’s crucial that you acquaint yourself with their advantages and disadvantages. That way, you can be sure that you’re making the right choice.