With the advantages of stable and fast switching time, solid-state relays are widely used in various heating equipment. Are you having trouble selecting a solid state relay? In this blog, we will provide you with a step-by-step guide on how to choose the right solid state relay for your application.
Step 1: Determine Rated Current And Voltage Of The SSR
Solid-state relays are classified and sold mainly by current difference. The larger the output current, the higher the price of the SSR. Of course, the larger the output current, the more load the SSR can drive.
When selecting a solid state relay, the first thing to consider is the output current, and the second thing to consider is the output voltage.The operating voltage of SSR can be single-phase 110VAC or 220VAC, or three-phase 380VAC or higher.
We, Lorentzzi®, as one of the best SSR manufacturers in China, can produce a current range from a minimum of 10 amps to a maximum of 120 amps for single phase solid state relays and from 10 amps to a maximum of 120 amps for three phase solid state relays.
Step 2: Determine The Load Types
As we all know, the load types can be resistive loads (such as heaters, resistors or incandescent lamps), capacitive loads (such as capacitors) and inductive loads (inductors, transformers, etc.).
Different types of loads require solid-state relays with different rated currents to work. According to our experience, resistive loads generally require 2 times the rated current, while for capacitive and inductive loads, the appropriate solid-state relay current should be 5-7 times the rated current of the load.
Step 3: Adding Overload Protection For The Solid State Relay
Overloads can cause the semiconductor switching elements inside the SSR, such as triacs (for AC SSRs with currents less than 40 amps), transistors (for AC SSRs with currents greater than 40 amps), MOSFETs (for DC SSRs) to be damaged by currents exceeding their rated currents. This damage is usually permanent and cannot be restored.
You may wonder why SSR below 40 amps use triac while SSR current above 40 amps use transistor, because triac maximum load current is not more than 40 amps, here below is the evidence:
Picture source: https://en.wikipedia.org/wiki/TRIAC
So when using the SSR, please add a fast fuse on the load terminal, generally the fast fuse current should be 1.5 times than the maximum SSR output current.
More solutions for the Solid state relay problems, please read this article: Solid State Relay Problems and Solutions: The Ultimate Guide.
Step 4: Determine The Dimensions And Installation Method
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SSR-25LA, 4-20 mA Proportional Control Solid State Voltage Regulator
Solid State Relay -
3 Phase Solid State Relay 100 Amp, DC To AC, SSR-100DA
Solid State Relay -
DIN Rail Solid State Relay With Heatsink
Single phase solid state relay -
SSR 100DD DC DC Solid State Relay Module
Single phase solid state relay
The product sizes of solid-state relays on the market are basically the same, but the SSRs produced by some manufacturers may be slightly different, so before installing the SSR, please carefully check the drawings to avoid installation difficulties.
The installation method can be screw fixing or DIN rail mounting. Please confirm which installation method is more convenient for you. Generally speaking, DIN rail SSR is more convenient to use than panel mounted SSR.
We, Lorentzzi, can produce the best quality SSRs for both mounting methods, please contact us for more details.
Step 5: Brand And Quality Certification
Using SSRs from big brands has low risk and reliable quality, so when choosing solid-state relays, try to use SSRs from big brands.
Another important thing to do is to check the SSR certification, usually, the more certifications the better. SSR certifications can be UL, RoHS, CE, CCC, CSA, etc.
Step 6: Heat Dissipation Considerations
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Heatsink With Cooling Fan For Solid State Relay
Accessories -
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Y-110 Heat Sink For Industrial SSR
Accessories -
H-150 Heatsink For Three Phase SSR
Accessories
Since SSR uses semiconductors such as thyristors or MOSFETs to conduct or load, a voltage drop of about 1.5V will occur. Therefore, the greater the current flowing into these semiconductors, the more heat will be generated(P=UI).
To let the heat dissipate efficiently, a suitable heat sink should be taken into consideration or the massive heat will damage the semiconductor.
Step 7: Special Load Conditions
As mentioned above, for some special loads, such as incandescent lamps, electric furnaces, motors etc., they will generate a large surge current when they are turned on, so it is necessary to select an SSR that can withstand this surge current.
Step 8: Control Method Of Solid State Relays
The control mode of solid-state relays can be zero-crossing type or random conduction type.
Zero-crossing triggered SSRs will wait for the AC power supply voltage to cross zero (i.e., when the voltage is close to 0V) before turning on when a valid control signal is applied to the input terminal.
Random trigger SSR is when the input end applies a valid control signal, the output end will be turned on immediately (in microseconds) without waiting for the voltage to cross zero. This type of SSR has a fast response speed.
Therefore, zero-crossing SSR is often used in places with strict requirements on electromagnetic interference, such as household appliances, industrial control and power compensation, etc. Random turn-on SSR is suitable for occasions that require fast switching and voltage regulation control, such as lighting adjustment, motor speed control, etc.
Conclusion
When you are trying to choose a solid state relay, considering the above 8 points can help you decide which SSR is better for your application.
Lorentzzi® is a China solid state relay manufacturer that can provide high quality, reliable SSRs to meet all your requirements, please contact us now to start cooperation!
