Definition   A solid state relay (SSR) is an electrically operated switch with no moving components.   Basic Function   Solid state relays are electrically operated switches used to isolate circuits or batteries, detect faults on transmission and distribution lines, and control large amounts of power using a smaller control signal.   Unlike electromechanical relays, solid state relays are constructed of solid components such as transistors, resistors,...
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Q & A on Solid State Relays

We asked our users for their input on Solid State Relays. Here are the results of 79 users familiar with Solid State Relays.

Who Took Our Poll? | Design Trends | Applications and Use | Features | Buying Advice

Who Took Our Poll?Top

Design TrendsTop

Q:
What new technologies are influencing solid state relay design?
12 answers
Answers:
Isolation from one circuit to another. Speed of response of the semiconductor. Small voltage at device transformed to bigger voltage at output.
~Christopher F, Engineer, Mysore, India
Development of semiconductor devices, e.g. organic semiconductors.
~Vijay S, Professor in Electrical engineering department, Hyderabad, India
Cooling with heatsinks, overvoltage and current protection.
~LeRoy B, Research & Development, Aumsville, OR
PLC controlled green energy.
~Matti Niemi, Technical Specialist, VAASA, FINLAND
Fpga designs direct control
~Bob L, Engineer, Cape coral, FL
Digital control systems.
~James H, Design Engineer, Hodgen, OK
Triac opto isolators
~Gunnar H, Resource and development, Siglufjordur, Iceland
Mos, fet, opto, rf
~Terry B, Design Engineer, Wellington, Newe Zealand
Power consumption
~Brent G, Research & Development, Melbourne, Australia
Smd technologies
~Technical Support/Services, Potosi, Bolivia
SSPC
~Engineering, Consulting, Bengbu, China
Dk
~Justin E, Technical Support, Melbourne, Australia

Q:
From your perspective, which companies are creating the most innovative solid state relays?
11 answers
Answers:
Omron, National Semiconductors, Semikron, Vishay.
~Christopher F, Engineer, Mysore, India
Crydom, SGS-Thomson Microelectronics, Philips
~Jim Rose, Design Engineer, Tucson, AZ
Crydom, Power IO
~LeRoy B, Research & Development, Aumsville, OR
Allen Bradley
~Technical Support/Services, Potosi, Bolivia
Unsure
~Terry B, Design Engineer, Wellington, Newe Zealand
Opto22
~Brent G, Research & Development, Melbourne, Australia
Celduc
~Matti Niemi, Technical Specialist, VAASA, FINLAND
Myself
~Gunnar H, Resource and development, Siglufjordur, Iceland
SSAC
~James H, Design Engineer, Hodgen, OK
DDC
~Engineering, Consulting, Bengbu, China
Dk
~Justin E, Technical Support, Melbourne, Australia

Applications and UseTop

Q:
What are some of the applications you have used solid state relays for?
16 answers
Answers:
Control of signal paths, LV dc and switching mains ac v, with delay for HV dc application in thermionic equipment.
~Terry B, Design Engineer, Wellington, Newe Zealand
I have seen them used in trigger circuits, isolation, UPS switching and monitoring.
~Christopher F, Engineer, Mysore, India
Switching highly inductive light and heavy loads with RC snubbers across them.
~Jim Rose, Design Engineer, Tucson, AZ
Traffic light system Messages sign control Parking lot control
~Candiac, Canada
Heater controls, RF power controls, isolation, motor control.
~LeRoy B, Research & Development, Aumsville, OR
Sequential turn on for computers and audio equipment.
~Gunnar H, Resource and development, Siglufjordur, Iceland
Windmill in building, solar panels, stirling engine
~Matti Niemi, Technical Specialist, VAASA, FINLAND
Espresso machines and water boilers
~Justin E, Technical Support, Melbourne, Australia
So far none other than teaching.
~Vijay S, Professor in Electrical engineering department, Hyderabad, India
For non inductive applications
~Technical Support/Services, Potosi, Bolivia
Low voltage motor starters.
~James H, Design Engineer, Hodgen, OK
Driving electric heat
~Marketing/Sales, St. Paul, MN
Hazardous areas
~Engineering, Design, Austin, TX
Home automation
~Bob L, Engineer, Cape coral, FL
System control
~Brent G, Research & Development, Melbourne, Australia
Industrial use
~Engineering, Consulting, Bengbu, China

Q:
Please share with us any “non-standard” applications that solid state relays have been used for.
7 answers
Answers:
I use it in windmill between rectifier and battery. Generator frequency and voltage can change very much. Solid state relay has multipurpose function in system. Generator current controller, generator protection, voltage controller for battery and so on.
~Matti Niemi, Technical Specialist, VAASA, FINLAND
Control of lighting - on and off, dimmer circuit. Some in a cooker oven on and off. Can be controlled by IC for temperature and other devices.
~Christopher F, Engineer, Mysore, India
We use delay relays to drive a higher power switching relay with external snubbing when working/designing thermionic equipment.
~Terry B, Design Engineer, Wellington, Newe Zealand
Driving electric heating elements with a PWM (1 second period).
~Marketing/Sales, St. Paul, MN
Running a temp stable fridge and hot water urn.
~Justin E, Technical Support, Melbourne, Australia
Emergency fire systems in computer rooms.
~James H, Design Engineer, Hodgen, OK
Turn on and off power to a magnetron.
~LeRoy B, Research & Development, Aumsville, OR

Q:
Do you know of any disastrous mistakes that occurred due to the incorrect usage of solid state relays?
7 answers
Answers:
5 A SSRs aren't suitable for highly inductive light loads (60 mA). These output SCRs do not latch, or hold, on these light current loads, which means that the usually poor dV/dt commutation capability of the internal opto-triac will not shut off the load, once activated. That is "inconvenient" for an elevator brake's contactor!
~Jim Rose, Design Engineer, Tucson, AZ
The relay mis-operates and the device falters. A printer may tear a page. The triac in a UPS (uninterruptible power supply) might lose voltage. Data can be lost if the UPS malfunctions.
~Christopher F, Engineer, Mysore, India
Unstable trips of fire systems due to transient voltage spikes and triac outputs causing Halon release and computer system shutdown.
~James H, Design Engineer, Hodgen, OK
With poor heatsink and cooling an SSR literally blew up and the particles caused a fab shutdown at HP.
~LeRoy B, Research & Development, Aumsville, OR
Possibilities do exist for such mistakes. I have not come across yet.
~Vijay S, Professor in Electrical engineering department, Hyderabad, India
Inappropriate specification of the output device.
~Terry B, Design Engineer, Wellington, Newe Zealand
Fire.
~Justin E, Technical Support, Melbourne, Australia

FeaturesTop

Q:
What would your design or feature "wish list" be for this product?
13 answers
Answers:
High DC current (100...300 A). Can accept high voltage peaks. 100...300 V. Can be controlled by PLC output 3...32 VDC. One wish could be AC component, where AC range is 0...200 Hz for wind generators. Built-in rectifier could be good in wind applications (AC in -> DC out).
~Matti Niemi, Technical Specialist, VAASA, FINLAND
Use of high dV/dt commutation type opto-isolated triacs (such as the Sharp IL420) for triggering back to back SCRs. Current regulated LED inputs. A 1k shunt resistor across the LED to shunt the high temperature leakage current from Darlington transistor drivers.
~Jim Rose, Design Engineer, Tucson, AZ
They are mostly used for power line control, and UPS trigger and voltage adjust. I have seen them used in stepping motor switching. Also, in multi-parallel connection.
~Christopher F, Engineer, Mysore, India
Reliability, tamper proof, Low cost, compact and indication of fault within the relay and on the line to be protected.
~Vijay S, Professor in Electrical engineering department, Hyderabad, India
Low output resistance for line voltages to reduce heat generated with small size but yet support up to 277V.
~Marketing/Sales, St. Paul, MN
A delay turn-on relay that is capable of switching 600 VDC at a current of 0.3A.
~Terry B, Design Engineer, Wellington, Newe Zealand
Overtemp controls that directly shut off the power to the output.
~LeRoy B, Research & Development, Aumsville, OR
Multiple-channel and programmable
~Engineering, Consulting, Bengbu, China
Small. Variable current output.
~Justin E, Technical Support, Melbourne, Australia
Smaller design, less expensive
~Engineering, Design, Austin, TX
AC control at a low cost.
~Bob L, Engineer, Cape coral, FL
Dry contact closure DPDT
~James H, Design Engineer, Hodgen, OK
Fail safe
~Brent G, Research & Development, Melbourne, Australia

Q:
Is there any advice you want to share with users to help them avoid common errors in selection or usage of solid state relays?
6 answers
Answers:
Make sure the device is in a proper environment. Keep the contacts and connections clean. Try to use the right type of relay, for the application. Make sure it is kept properly during use.
~Christopher F, Engineer, Mysore, India
Make sure that the load is for what's intended, random turn on or zero crossing.
~LeRoy B, Research & Development, Aumsville, OR
Contact current handling, snubbing or suppression and life expectancy.
~Terry B, Design Engineer, Wellington, Newe Zealand
Inductive loads can be tricky, noise filtering is important.
~Gunnar H, Resource and development, Siglufjordur, Iceland
Don't overload. Have failure protection.
~Justin E, Technical Support, Melbourne, Australia
Use dry contact interface.
~James H, Design Engineer, Hodgen, OK

Buying AdviceTop

Q:
Do you have any advice for people relative to buying or using solid state relays?
7 answers
Answers:
Like always, technical details are important, but the price is even more important, when talking about green power systems for homes and buildings. Payback time of the power station is one of the biggest challenges.
~Matti Niemi, Technical Specialist, VAASA, FINLAND
Check that the voltage rating is right. Make sure the operation-connection instructions are given. Ensure input and output circuits are of proper rating.
~Christopher F, Engineer, Mysore, India
Always use over rated units for voltage and current for the job. Use the 80% rule.
~LeRoy B, Research & Development, Aumsville, OR
Learn all you can about commutation problems with inductive loads.
~Jim Rose, Design Engineer, Tucson, AZ
Make sure you know what you are doing.
~Gunnar H, Resource and development, Siglufjordur, Iceland
Hold on current can be a problem.
~Terry B, Design Engineer, Wellington, Newe Zealand
Don't use triac output relays.
~James H, Design Engineer, Hodgen, OK


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