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Solid State Relays, Optoisolators VS Optocouplers

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At work we use different kinds of Solid state relays
What happens a lot of the solid state relays get their output is either shorted or open

What causes a solid state relays output to get shorted or open?

Some solid state relays are Opto-isolator Triac or some use Opto-isolators with Mosfets

I'm not sure what is shorting or opening the Triac or the Mosfets inside the solid state relays which is the output of the solid sate relays

Plus I'm not really use what the difference is between an Optocoupler VS an Optoisolator?

But what's inside a Solid state relay is an Opto Triac
 
First, you should read https://en.wikipedia.org/wiki/Opto-isolator

Optocoupler and optoisolater are synonyms. The most common transistor output devices have a photodiode on the output which allows a current to pass when it receives light from the LED on the input; the photodiode current is usually buffered with a transistor (which together forms what is called a phototransistor). For optotriacs, the photodiode will allow current to pass into the gate (trigger) pin to turn it on.

The FET output devices have a small solar cell (which is also a photodiode) connected to the gate of the output FETs to allow them to conduct when the light from the LED reaches them. See https://en.wikipedia.org/wiki/Photodiode for information on a photodiode and its different regions of operation.

AC SSRs will contain an optotriac as well as a standard power triac; the optotriac has a small switching capacity, and it triggers the power triac to allow a larger load to be switched. Because TRIACs latch, they must be used with AC (or at least non-continuous) load voltages/currents, or else they will stay on forever.

DC SSRs have MOSFET(s) on the output, and don't latch. If the FET is not internal to the optocoupler, then an external FET can be used in conjunction with a voltage output optocoupler.
 
TRIACs latch, they must be used with AC (or at least non-continuous) load voltages/currents, or else they will stay on forever.

So hooking up a Continuous LOAD will Short out or OPEN the Triac?

DC SSRs have MOSFET(s) on the output, and don't latch

Why does the DC SSR's use Mosfets and not Triacs? and why doesn't AC SSR doesn't use Mosfets?

Optocoupler and optoisolater are synonyms
.

Are you saying they are the SAME thing?
 
What is causing the SSR's output to cause an internal OPEN and an internal SHORT on the output of the SSR?

It's something to do with the LOAD because it's Continuous? or what?
 
There will be a photodiode being illuminated by the LED. the photodiode will allow current to pass into the gate (trigger) pin to turn it on when there is voltage across the TRIAC.
 
What is causing the SSR's output to cause an internal OPEN and an internal SHORT on the output of the SSR?

NO, I mean a BLOWN short or BLOWN open internally inside the SSR, which is a BAD SSR

I'm not talking about the photodiode
 
Semiconductor devices fail when subject to operating conditions outside of their Safe Operating Area. (SOA)

What is the output rating of the relays, and what conditions are they failing under?
 
What is the output rating of the relays, and what conditions are they failing under?

120 VAC output, failing under is a SHORTED or OPEN SSR output

Either the 120 VAC is ON all the time and you can't turn the output OFF

Or the SSR output is OPEN which there is NO output on the SSR output
 
120 VAC output, failing under is a SHORTED or OPEN SSR output

Either the 120 VAC is ON all the time and you can't turn the output OFF

Or the SSR output is OPEN which there is NO output on the SSR output

Let me repeat my question.

What is the rating of the output side of the relay? Voltage and current?

What are the operating conditions that the relay is working in when they fail? Voltage, current and temperature. What is the load? Resistive, inductive or ???
 
What is the rating of the output side of the relay? Voltage and current?

120 VAC

What are the operating conditions that the relay is working in when they fail? Voltage, current and temperature. What is the load? Resistive, inductive or ???

The Loads are either Resistive, inductive , capacitive, depends on what the customer plugs into the product or unit on the output


It must be from OVERLOADING the SSR's output
 
Let me repeat my question. Agiain.

What is the rating of the output side of the relay? Voltage and current?

And what is the output rating of your product, and does your device always work when operated within that rating? Do you have any additional protection (fuse) to prevent failure if the customer uses the product beyond the rating?

And is the rating reasonable for how your customers are expecting to use the product?
 
And what is the output rating of your product, and does your device always work when operated within that rating? Do you have any additional protection (fuse) to prevent failure if the customer uses the product beyond the rating?

No Protection Fuse, The customers most likely are overloading the unit or using multiple different loads which can be resistive, inductive or capacitive

The maximum output rating is the LOADS ohms

If the unit is output 100 watts , it will display how much load in OHMS it can handle
 
Billy

after 3 attempts, you are still not answering ChrisP's question

WHAT is the VOLTAGE and CURRENT ratings of the SSR ?

NOT what you are putting into it ( we will come to that) what is written on the SSR for its ratings??

Dave
 
Hi,


I got the impression that they have various ratings.

What you will have to do is see if there is a correlation between how the units fail and what the customers use as load.

If the units fail open then it sounds more like an overcurrent situation, but if they fail short then it sounds more like a over voltage situation, but unfortunately sometimes if they fail short then they will open anyway so it might still be hard to tell what is going on.

But in any case if the units are made of quality parts then they should not fail too soon under normal operating conditions. If the customers use a load that is too high in current or in voltage then that's going to blow the unit out. So it is one or the other.

If there is inductance involved then it could be that something else can also switch the load on and off and that could cause high spike voltages which could blow the unit. It is also necessary to use a SCR or Triac type switch if inductance is involved, not a transistor type. If there is capacitance involved then there is a turn on surge current that could be blowing the units.

So what might be nice is if you made a list of all the units that had blown in the past, and what the customers had been using for their load at the time. This would be a place to start anyway. For example, the list might look like this:
1. Unit 1 Westinghouse A342B rated 10 amps 120vac, customer load is 1/2 HP sump pump.
2. Unit 2 GE 755G rated 5 amps 120vac, customer load is 120vac 100 watt incandescent lamp fixture.
3. Unit 3 GE 755G rated 5 amps 120vac, customer load is 120vac 100 watt fluorescent lamp fixture.
4. Unit 4 GE 755G rated 5 amps 120vac, customer load is 120vac 100 watt LED lamp fixture.

Note that the customer load is detailed, and so is the make and model of the switch unit although the model numbers here are fictitious just for the purpose of illustration on the level of detail that should be incorporated. If you can get the model number of the loads used too that would be a good idea. You should also include the customer geographical location.

So the units are blowing and what we do here is see if we can find a systematic reason for this, then look into why that happens.
 
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