Testing a Solid State Relay????

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ibew441dc

Senior Member
I am far from an electronics expert.... actually as of late I realize I am very much a novice in this arena, but have stepped into another area of our industry that is different than my norm (400hertz aircraft ground power, DC motors/drives, ect.).

How does one test a solid state relay? To be honest, in my entire career I have never had to do this, in the past if I had to change a ssr it was because it was obviously fried.
 

mcclary's electrical

Senior Member
Location
VA
I am far from an electronics expert.... actually as of late I realize I am very much a novice in this arena, but have stepped into another area of our industry that is different than my norm (400hertz aircraft ground power, DC motors/drives, ect.).

How does one test a solid state relay? To be honest, in my entire career I have never had to do this, in the past if I had to change a ssr it was because it was obviously fried.

Know the control voltage of the relay, engergize with "said" voltage to the coil and it should change states. Verify each set of contacts with continuity check to make sure each contact either opens or closes.
 

ibew441dc

Senior Member
Know the control voltage of the relay, engergize with "said" voltage to the coil and it should change states. Verify each set of contacts with continuity check to make sure each contact either opens or closes.

Im pretty sure there is no coil???? but I follow what you mean. Is there a way to test it de-energized?
 
Depends on the type. Single MOSFET SSR's are for DC loads and dual MOSFET SSR's are for AC circuits as the MOSFET's are connected (internally) back to back to provide a reverse bias in both directions. (basic diode operation)

Using a meter or continuity tester does not work on dual MOSFET due to the meters DC nature. The easiest way is to just hook them up.

SSR's use opto coupled setup inside the case so it is completely electrically isolated from the "coil" and "contact". It uses an LED inside of the unit to activate a photo diode to power the gate of the MOSFET so you will get zero conductivity between the trigger side of the relay and the contact side.
 

ohmhead

Senior Member
Location
ORLANDO FLA
Well its kinda hard to explain but if you have a ohm meter with a diode function you can test but it depends on the type of scr or gto used it takes voltage to turn off a scr turn off with a negative to the gate and that depends on the type used pnpn or npnp .

If a scr is turned on by the posistive cycle of a ac wave it will stay on until it is turned off by the negative cycle meaning there not like the old transistors basic base collector or emitter if you test you must know what you have in that drive before you test read this http://www.allaboutcircuits.com/vol_3/chpt_7/5.html

This will give a basic understanding but power must be on to truly give you a test across the scr in a high powered drive it takes a current thur or voltage applied at gate to test on /off state .

Is this a small dc motor drive or a large high current dc drive ? With power off !!!

If small use diode checker on ohmmeter.

You can turn on a scr with you finger just touching the gate thats how sensitive they are take care
 
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mcclary's electrical

Senior Member
Location
VA
No, not really as simple as putting the meter on ohms and checking for continuity. I would try to test it in place or as Larry pointed out use a test load.

I think we're picturing two different things. Yes, I would test it in place, and yes sometimes a load is needed for a test. But that doesn't mean you can't read it with a meter.

are you telling me if you put a meter between 1&2, while applying control voltage, I could not read this relay with a meter?
 
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iwire

Moderator
Staff member
Location
Massachusetts
I think we're picturing two different things. Yes, I would test it in place, and yes sometimes a load is needed for a test. But that doesn't mean you can't read it with a meter. http://w.sordselectric.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=SE&Product_Code=SSRAP40A3&Category_Code=SSRPC

are you telling me if you put a meter between 1&2, while applying control voltage, I could not read this relay with a meter?


Yes, that is what I am saying, your meter may indicate the relay is 'closed' when it is really not.
 

mcclary's electrical

Senior Member
Location
VA
I can't get that link to work so my last post makes no sense. Let me find the link. But what
I mean is there are many kinds of SSR's and many can be read with a meter. under load or not.
 

iwire

Moderator
Staff member
Location
Massachusetts
I can't get that link to work so my last post makes no sense. Let me find the link. But what
I mean is there are many kinds of SSR's and many can be read with a meter. under load or not.

I have no doubt, but as a general rule testing a solid state relay with a just an ohmmeter is just not the most reliable way to do it. You would first have to know with certainty the the device under test can be tested with a meter.


Keep in mind it is a 'semiconductor'

Any of various solid crystalline substances, such as germanium or silicon, having electrical conductivity greater than insulators but less than good conductors, and used especially as a base material for computer chips and other electronic devices.

so even when 'off' they will pass current.
 

ohmhead

Senior Member
Location
ORLANDO FLA
I relaize that but it can still be read with meter

Well yes and no you can test a scr with a ohmmeter but in the diode test function is best . You can use a ohmmeter meg ohms .

The test only will give you a short or a open test on the scr doesnt really tell you if the scr is bad as it can be open or closed /shorted at anypoint in time its doesnt work like a relay in the sense of open and closed continuity. A SCR has resistance in its conduction mode of working open or closed i know this doesnt make lots of sense but thats how they work it also has resistance when conducting meaning closed .

Look at this if the resistance was shown on a meter you would think its bad or not making contact when in fact it is a high resistance when you check a scr off or on this is usally in the meg ohm range .
Also the test must be the correct polarity not just continuity it will only test from gate to cathode or from cathode to anode in a one way direction of polarity and most high powered scr s need to be taken out of circuit to do this .

One needs to know the spec of the scr to test the op needs to give more input to what he is testing .

Mean what type of discrete device is he testing ?

Thers more to testing then what we normally do as electricans thats why i like running conduit everyday its more fun .:D
 

zog

Senior Member
Location
Charlotte, NC
This thread is funny, no one has any idea of what type of relay the OP is asking about and everyone has these ideas how to test it. Soliod state relays can be very complex and some Baslers sna SEL's can have over 100 different functions that need to be tested with special equipment and complex software. So lets hold off on the ohmeter or light bulb as a load until the OP comes back and tells us what it is he needs to test.
 
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