can't get the SSR to work - need help

I tried now to connect 220V light bulb as load to the SSR.
The bulb is always on. and sometimes while i turned on the SSR control the the light intensity raised up. one more thing i noticed, the resistor is worming up.
Maybe i need anothe kind of snubber circuit? maybe a parallel resistor to the load? or maybe something is wrong with the snubber i've connected?
what do you think?

hazico said:

I tried now to connect 220V light bulb as load to the SSR.
The bulb is always on. and sometimes while i turned on the SSR control the the light intensity raised up. one more thing i noticed, the resistor is worming up.
Maybe i need anothe kind of snubber circuit? maybe a parallel resistor to the load? or maybe something is wrong with the snubber i've connected?
what do you think?

Click to expand...

hi,
If you are only driving a 220V tungsten lamp [ and nothing else] and you are connecting the control voltage to SSR to turn ON the lamp, connecting the control pin to 0V to turn the lamp OFF and the lamp dosnt go OFF, the SSR is most likely blown s/c.

You say the snubber resistor gets warm and the light changes intensity, this should not happen if the SSR is fully ON.

My best guess is the SSR is dead.!

In your original circuit, when using a transformer, which is an inductive load under certain conditions, you need a 100R/0.1uF snubber.
I suspect you tried to drive the transformer initially without a snubber, thats probably when the SSR died...

Yes initially i tried to drive the transformer without a snubber. (you think that can damage the SSR?)
And the last experiment with the lamp i did with the snubber. i'm going to try the lamp again without the snubber and see what happens...

I have more confusing conclusions...
I connected the lamp again, but now without the snubber, and aply the main 220V, nothing at the control input. the lamp is OFF all good by now.
Then i've apply the 9V battery to the control input and the lamp turned ON! excellent!.
I then moved the battery and apply it 3 more times, the lamp turned on and off accordingly to the control input status. but the in the fifth time it stayed off not matter what i apply to the control.
I disconnected the main power and the lamp and then tried again ant it only turned on once and then stayed off.
I know you all think the SSR is dead but something here is making me believe that maybe it's not dead and something here is unstable.

Just check the 9V battery has not fallen very low after a few switch ON tests.?????

I tried after that to control with DC transformer...
the buttom of the SSR is covered with metal plate, it should be grounded or something?

hazico said:

I tried after that to control with DC transformer...
the buttom of the SSR is covered with metal plate, it should be grounded or something?

Click to expand...

The datasheet says thats for contacting a heatsink if required,, no ground required.

hazico, the behavior you are describing is perfectly in keeping with operating your SSR without a heat sink. Heat sinking requirements are described in the spec sheet. You don't tell us the wattage of your 220V bulb, but it is probably high enough that you should have provided a heat sink. The spec sheet says a heat sink is required for currents over 3 amps. What current is your lamp drawing?

If you are going to mess around with electronics, you should realize that a product spec sheet is there for your benefit. It contains information that you NEED if you are going to apply a product correctly and avoid damage to your component.

If you are lucky your SSR has some form of overtemperature protection built in. That may be the reason it stopped turning on. If that is the case, it may return to normal performance after cooling down. Even if it does recover, there is no guarantee that it has not been overstressed and may fail early or have reduced capabilities.

There may actually be no overtemperature protective circuitry in your SSR. It may have stopped turning on because the excessive internal temperature simply caused the circuit to malfunction.

In the paying attention to detail department, notice that the original discussion of the snubber indicated that (1) the snubber was to compensate for an inductive load (so it is unnecessary for the resistive load of a lamp, and (2) the snubber values were described as being for a 115 volt application. "It might have to be adjusted for a 220 volt load."

So, if you DO have to drive a 220VAC inductive load, the values of the snubber components should be adjusted. I really don't claim to have any expertise in snubber design, but if the .01uF 100 Ohm snubber is getting warm on 220 VAC, I would try increasing the value of the resistor and reduce the value of the capacitor. For starters, I'd try 200 ohms and .005 uF, but that's a pure guess not based upon any theory.

At this point I'd recommend bolting the SSR to a heat sink, removing the snubber, and testing the SSR for mormal operation. The spec sheet recommends a heat sink with a specific maximum thermal resistance but I think you can probably get away with an aluminum plate about 1/4" thick or thicker and about 6" square. Keep feeling the temperature of the heat sink under the position of the SSR. If it gets uncomfortably warm to the touch, use a thicker/larger plate as a heat sink. Or just buy a heat sink with a specified thermal resistance.

Good Luck.

awright

what do you say about using this relay instead of the SSR?
**broken link removed**

Hey you got an interesting thread topic here.

I have to work with SSR's on a regular basis and I can say with good confidence that they are one of the few solid state components that can go intermitent.
Usualy that optical isolator takes a hard spike and the little LED in it goes funky (Technical term).
Its just like over powering an LED, It still works but not well. Add that to a SSR and you have an official sort of functional device.

I see this on welders a lot. many use SSR phase control on the primary side to do the actual current and voltage control.

Century and there generic versions did this all the time. They had poor spike and noise filtering on the control side.
I vote for most likely dead. Toss it!

hazico said:

what do you say about using this relay instead of the SSR?
**broken link removed**

Click to expand...

I want to order it do you think it is good for what i need?

Not sure that I know enough about relay applications to tell you if that relay is adequate. However, I note that it is rated for 3A for inductive loads with power factor of 0.75 or higher. Your unloaded transformer may have a power factor much lower than 0.75. Permissible load is multiplied by the power factor so a much lower power factor indicates a much lower permissible load.

If you go to the Potter & Brumfield website and search for the Application Note, "Beware of Zero-Crossover Switching of Transformers," you see the risks inherent in switching transformers. They say that switching on a transformer at voltage zero crossover can result in surge currents up to 40 times steady-state current. Now, I know that the SSR you were using was not a zero-crossover switcher, but even random time switching is bound to occur close to the zero-crossover instant well, randomly, so those 40X surge currents could occur randomly.

Not trying to scare you and not telling you not to use your relay. Just providing a little insight into the complexities of seemingly simple application. If it was my project I would probably just go ahead and use that relay (or more likely one picked out of my junk box) and put up with the low but real possibilty of sudden death of the relay.

If this is a commercial application with significant cost implications of failure you might be well advised to retain an engineer to look at your application.

Did you ever evaluate the SSR using a resistive load and a heat sink? As I said in an earlier post, the symptoms you describe look like those to be expected from absence of a heat sink.

awright

awright said:

They say that switching on a transformer at voltage zero crossover can result in surge currents up to 40 times steady-state current.

Click to expand...

Wait - what?

I'd love to know how you get 40 times your steady state current when there's no voltage =) That's the entire point of a zero cross circuit, you have it backwards. Maybe 40 times steady state current if you switch when it's at it's peak. Depends on the winding resistance.

I questioned that myself. I often use zero cross SSR's just to prevent that. I dont recall ever seeing a transformer pop and flicker the lights using a zero crossing SSR.
But I can get transformers to pop and spike with random turn on easily.
My Grid tie inverters all use zero turn on SSR's for the line connetions. Just because it reduces the inrush currents and also gives me a self syncronizing effect too.

Just my toughts.

Did any of you access the P&B App Note? Don't tell me I'm nuts - tell the engineers at Potter & Brumfield that they are nuts. I have all the same assumptions and preconceptions as you guys. I'm not making any claims from my "expertise." I'm simply conveying a link (https://www.electro-tech-online.com/custompdfs/2009/03/13c3206.pdf) to an application note I stumbled across while searching for specs on a particular P&B relay.

Whether I agree with it or not is beside the point. (The fact is, I have difficulty understanding/believing in their argument, also.) These guys spend their time figuring out how to help customers apply their relays in a reliable manner and diagnosing failures of their relays. Apparently they have performed experiments or analyses leading them to the stated conclusion regarding zero-crossing relays and inductive loads. They are trying to help their customers avoid problems by alerting them to the issue. We are trying to help hazico solve his relay application problem in which his SSR apparently failed while switching power to an inductive load and I am offering a bit of information that he might benefit from being aware of.

Please copy me on any arguments you have with the P&B engineers about this.

awright

OK, you drove me back to look again at the P&B App Note. Here is my shot at understanding what these guys are talking about:

You all know that current lags AC voltage by 90 degrees in a pure inductance under steady-state conditions. Therefore, under steady-state conditions, flux in the inductor core is at maximum negative value at the time the voltage is passing through zero. Since the basic characteristic of an inductor is that current (and, therefore, core flux) cannot change instantaneously, but changes gradually in response to voltage changes (how gradually depends upon the value of inductance), the sudden application of peak voltage does not, as implied by Sceadwian, result in current limited only by winding resistance. The current at the instant of abruptly applying peak voltage, in fact, starts to ramp up exponentially from its starting point of zero current and flux and reaches its normal peak value just as it would under steady-state conditions.

However, when you abruptly apply AC voltage at the zero-voltage crossing point the core flux is at zero, not at maximum negative value as it would be under steady-state conditions. Therefore, during the first quarter cycle, when flux would normally be changing from max negative to zero under steady state conditions, it is now changing from zero to some (mathematically predictable) positive value. In lay terms, the flux is getting a "head start" toward max positive flux compared to the steady-state condition.

Now, as the flux and current continue to increase (because the applied voltage is still positive up to end of the positive half-cycle), the flux will reach a higher value than under steady-state conditions because it had the "head start." If the core saturates due to this greater than normal flux, THEN you lose the current limiting effect of the inductance and the current may be limited only by the winding resistance. This is the cause of the up to 40X multiplication of steady-state current that the P&B App Note discusses.

So it sounds like what we really need is a peak voltage-switching relay rather than a zero-crossing switching relay for inductive loads. Of course, such a relay would shock loads that are resistive or capacitive.

awright

I have been reading up on several SSR manufactures relay specs and I am comming up with conflicting information too. They list there relays with zero cross turn on in the highly inductive load catigories but then say random turn on is for motors and transformers.

What gives. For as long as I can remember I have always went with the suppliers specs on what SSR to use. The seller data given does not match the manufatures specs given. Check out digikeys crydom line. the HD,HA, and TD zero cross turn on series are listed for highly inductive loads. But the data sheet says to use random turn on.

I did several tests with a 2 kva 120:240/240/480 isolation transformer a few minutes ago.
I used my signal generator as a SSR driver using the square wave output function.

The random turn on relays (crydom) all cause random power spikes and transformer inductance pops.
But the zero cross turn on SSR's dont.

Now I am really confused. Data says one thing my test says another! sellers specs say one thing manufactures specs say different.

Do I give up on years of what I thought was right and then adopt the manufactures recomendations even though my experiance and tests say different?

Am I just missing something?

Sorry for the erroneous post awright, just shows what I know about inductance in the real world =) Sounds like the choice of the core material determines weather or not this is really a problem in the real world.

Here I go again after a cocktail and a glass of wine at dinner and some Grand Marnier in the ol' easy chair. So be lenient.

tcmtech says, "My Grid tie inverters all use zero turn on SSR's for the line connections." That's probably fine and optimal since the grid is not a reactive load.

Don't forget that until a few months ago the conventional wisdom was also that deregulation of the financial markets would lead to prosperity for everyone and we know how that turned out, don't we?

Sceadwian says, "Sounds like the choice of the core material determines weather or not this is really a problem in the real world." Well, for ordinary off-the-shelf transformers we don't have much to say about core characteristics. Most of them will use plain silicon magnetic steel with a soft saturation characteristic and will be designed to operate just below the "knee" of the material as shown in the P&B App Note.

What I would take from the app note is to be alert for the possibility of an inductive load like hazico's lightly loaded transformer and avoid use of a zero-crossing SSR in that situation. Maybe even figure out a peak voltage switching circuit if I know that my load is always going to be an inductive reactance.

We still don't know for sure that hazico's SSR has failed or was simply mis-applied.

awright