Solid State Relay question.

[julianf]

Im trying to remotly diagnose a friends system.

He has the standard PID / SSR setup.

With the system wired as id expect it to be, the load output of the SSR is 240v all the time.

The LED on the PID and SSR pulses away, but the terminal on the SSR remains at 240v.

If the SSR is removed from the system (isolated completely) and checked with a multimeter, it shows no continuity across the load terminals.

If a 240v feed is connected to one of the load terminals, sure enough, the other terminal goes to 240v also!?!? (this is with no control lines connected at all - just the one 240v feed to one of the load terminals)


My conclusion was - SSR is knackered.

...so he purchased another one.  Which behaves in an identical way : /

Either he has purchased two duff relays, or im missing somthing that should be obvious?

[Bill]

Did you measure the controlling voltage pulses from the PID to the SSR? What is the switching specification for the SSR?

[julianf]

Did you measure the controlling voltage pulses from the PID to the SSR? What is the switching specification for the SSR?

Did not measure the PID output.

The SSR is, i assume, normally closed.  He just bought it, cheap from china, off ebay.

Ive just looked on google image search - im 99% certain its this one -

[julianf]

...basically, if no connections are made, there is no continuity between terminals 1 and 2

if one single connection is made to terminal 1, of 240v ac, then 240v ac also shows at terminal 2.

[high compression ii]

That SSR Pictured--Is 'contacts' Normally Open, so there should be No power flow with no signal/supply to the 'control' connections.

Has the system ever worked...?

I ask, as maybe somethow--he's sending 240V down to the control of the SSR and destroying the control-circuits inside.

Alternatively--he's using a 'Neon Screwdriver' which is illuminating due to the normal leakage of the internal Triacs of the SSR with no load connected....

[Julian]

When I've played with SSRs I found that you couldn't measure continuity through terms 1 & 2, irrespective of supply on terms 3 & 4.

If you rig up terms 1 & 2 in a 240v circuit and something like a car battery on terms 3 & 4, it should work OK.

[high compression ii]

When I've played with SSRs I found that you couldn't measure continuity through terms 1 & 2, irrespective of supply on terms 3 & 4.

If you rig up terms 1 & 2 in a 240v circuit and something like a car battery on terms 3 & 4, it should work OK.

Yup--Thats exactly how they work--Cant measure with a normal meter as there's four semiconductor junctions in a Triac, so you need around 3V at least across them to allow current flow....Meters--even on 'Semi' test usually are 1.5V or maybe up to 2V and aint enough to forward-bias the triacs

You can use something as small as a PP3 9V Battery on the Control input to turn the SSR 'ON'  Any supply of DC between 3V and 32V can be used as the control-volts to an SSR

--There are Some SSR's that use 240V ac as the control volts--but Not the type pictured, and they are less common....

[julianf]

Sorry - i had a blip in concentration, and said that i assumed the relay was NC, when i ment to say NO.

...but, without a control line, its closed.  Indeed, with a control line its closed also (however, the LED on the relay itself blinks as you would expect).

Fair point about not being able to measure continuity with a multimeter, however, thats ancillary to the real problem - the relay (both of them) seem to be closed all the time, regardless  of control line.

The system has never worked - its a new setup.

[Julian]

When I've played with SSRs I found that you couldn't measure continuity through terms 1 & 2, irrespective of supply on terms 3 & 4.

If you rig up terms 1 & 2 in a 240v circuit and something like a car battery on terms 3 & 4, it should work OK.

Yup--Thats exactly how they work--Cant measure with a normal meter as there's four semiconductor junctions in a Triac, so you need around 3V at least across them to allow current flow....Meters--even on 'Semi' test usually are 1.5V or maybe up to 2V and aint enough to forward-bias the triacs

You can use something as small as a PP3 9V Battery on the Control input to turn the SSR 'ON'  Any supply of DC between 3V and 32V can be used as the control-volts to an SSR

--There are Some SSR's that use 240V ac as the control volts--but Not the type pictured, and they are less common....

Hey, I can do electronics me!

[julianf]

Oh - one last thing - he purchased the SSR and the PID / Thermocouple as a package off ebay.

So, id assume, the SSR is 12v control.

[high compression ii]

Wish I Bloody Could!

As to the problem. Seems to me, either he has somehow damaged the SSR's or he's using a neon-screwdriver to test for continuity.

Can you ask him to replace the heater with a lamp-bulb,--say 100W 240V to confirm that its actually faulty...?

--I wonder, if he's switching the Neutral side with the SSR instead of the Live--giving the impression its not switching--the way he's measuring it.....

[julianf]

Test was a mutimeter on the terminal, not a screwdriver.

It was me who originally wired the unit, but i passed it over to him before even a plug was put on it (ie untested).

It would be embarrasing if ive made a pigs ear of it, but, hey, its possible!


He lives an hour and a half away, hence remote dianostics.

[therecklessengineer]

This might be an idiot question, but you're not measuring the voltage across it are you? With one multimeter lead on one terminal and one on the other?

[julianf]

2nd terminal to ground

[julianf]

ps.

i dont mind any suggestions - i mean there's somthing stopping it from working!