How to wire this AC SSR?

[n4te]

I want to use an AQH3213AZ SSR. The schematic is:



I'm good on the left side, but I'm not sure on the right side. Do I connect my 24VAC to pin 8, then my irrigation valve to pins 5 and 6, with pin 5 also connected to the other side of the 24VAC? My snubber RC would go between pins 5 and 6.

The SnapEDA component shows only pins 8 and 5 -- it has pins 5 and 6 connected internally. Is that right? In that case do I connect 24VAC to pin 8, then my irrigation valve to pin 6, with the other side of the valve going to ground? My snubber RC would go between pins 8 and 6.

[Zero999]

The data sheet shows pins 5 and 6 going in series with the load.
https://api.pim.na.industrial.panasonic.com/file_stream/main/fileversion/2787

Your drawing shows the zero crossing version, which isn't suitable for 24V AC, as the peak voltage is well-below that.

I wouldn't recommend a TRIAC SSR relay for such a low voltage. MOSFET would have much lower losses. Obviously it needs to have two MOSFETs connected back-to-back, as it's AC.

[n4te]

The data sheet shows pins 5 and 6 going in series with the load.

To be clear, you mean that 5 and 6 are indeed connected internally?

The example shows only pin 6 connected, which seems to back that up:

Your drawing shows the zero crossing version, which isn't suitable for 24V AC, as the peak voltage is well-below that.

By "that" I guess you mean where it says "Zero cross voltage, maximum, 50V" for zero crossing (PDF page 3)? Isn't that a maximum?

I'm open to changing to something else, but I need 16 of these relays so ideally each one is a single component.

[Zero999]

Sorry, I meant, the load should be in series with pin 6 and 8. 

The zero crossing voltage is the voltage which it has to be below, in order to fire. If the voltage is about 50V, it might not fire and the peak voltage of 24VAC is just 34V, so it's unlikely to work.

It's possible to get MOSFET SSRs which are just one part.

Here's an example. No doubt there are lower cost parts which can do the job. I just did a quick Google search for MOSFET solid state relay data sheets.
https://docs.rs-online.com/6a0b/0900766b80db8698.pdf

[BeBuLamar]

The SSR is rated at 200VAC and thus I don't think it would work for 24VAC.

[n4te]

The zero crossing voltage is the voltage which it has to be below, in order to fire. If the voltage is about 50V, it might not fire and the peak voltage of 24VAC is just 34V, so it's unlikely to work.

Ah, thanks. I didn't realize how important that characteristic is. However, it looks like the zero crossing should work at about 30V:



I guess if you guys still think it's not a good choice 24VAC irrigation valves (solenoid, 350 mA inrush, 190 mA holding, 60 Hz) then I should find something else. I tried Digikey with this search but it comes up with basically just 2 options: the AQH3213 or CPC1964B (SCR). Are my search parameters wrong? I choose AC, zero crossing, and 1A+ (in stock only).

The ASSR-1611 looks OK (though I'm clearly not the best judge), except it doesn't have zero crossing. Do I need that? Maybe that's why my search returns so few results. Is it rarely needed?

I need to read more about MOSFET vs SCR vs TRIAC SSRs.

[Zero999]

The zero crossing voltage is the voltage which it has to be below, in order to fire. If the voltage is about 50V, it might not fire and the peak voltage of 24VAC is just 34V, so it's unlikely to work.

Ah, thanks. I didn't realize how important that characteristic is. However, it looks like the zero crossing should work at about 30V:

Not properly. It'll switch on when the voltage is over 30V, which means the output will look like a lamp dimmer set to just over 50% power level.

[wraper]

The zero crossing voltage is the voltage which it has to be below, in order to fire. If the voltage is about 50V, it might not fire and the peak voltage of 24VAC is just 34V, so it's unlikely to work.

Ah, thanks. I didn't realize how important that characteristic is. However, it looks like the zero crossing should work at about 30V:

Not properly. It'll switch on when the voltage is over 30V, which means the output will look like a lamp dimmer set to just over 50% power level.

What? Zero-cross means that SSR will turn ON only when output is at below certain voltage (as said in your previous post). The problem with zero-coss at low voltages is that feature becomes nearly useless and SSR becomes nearly instant ON type. 50V max (no min) spec is quite high and it means that at 24 VAC zero-cross feature probably won't ever kick in at all and SSR will be able to turn ON at any time. How it becomes a dimmer when it will just instantly turn ON regardless of at what part of output voltage cycle input signal arrives?

[n4te]

In that case it seems like the AQH3213 should work, just the zero cross feature will do nothing useful. I have some AQH3213 parts, so using them would be convenient.

I setup this circuit:



R16 should draw 44mA. It gets warm when connected directly to 24VAC, so I expect the same from this circuit, but it doesn't get warm. Any ideas why?

I tried probing with a DMM and scope, but it didn't seem useful. I know probing an SSR is not the same as probing a mechanical switch/relay. Where should I probe to debug further?

[Zero999]

The zero crossing voltage is the voltage which it has to be below, in order to fire. If the voltage is about 50V, it might not fire and the peak voltage of 24VAC is just 34V, so it's unlikely to work.

Ah, thanks. I didn't realize how important that characteristic is. However, it looks like the zero crossing should work at about 30V:

Not properly. It'll switch on when the voltage is over 30V, which means the output will look like a lamp dimmer set to just over 50% power level.

What? Zero-cross means that SSR will turn ON only when output is at below certain voltage (as said in your previous post). The problem with zero-coss at low voltages is that feature becomes nearly useless and SSR becomes nearly instant ON type. 50V max (no min) spec is quite high and it means that at 24 VAC zero-cross feature probably won't ever kick in at all and SSR will be able to turn ON at any time. How it becomes a dimmer when it will just instantly turn ON regardless of at what part of output voltage cycle input signal arrives?

Yes. I was talking bollocks. It will work of course, but the zero crossing won't work properly. Not that it matters, as the original poster wants to control an inductive load, which is better without zero crossing.

In that case it seems like the AQH3213 should work, just the zero cross feature will do nothing useful. I have some AQH3213 parts, so using them would be convenient.

I setup this circuit:



R16 should draw 44mA. It gets warm when connected directly to 24VAC, so I expect the same from this circuit, but it doesn't get warm. Any ideas why?

I tried probing with a DMM and scope, but it didn't seem useful. I know probing an SSR is not the same as probing a mechanical switch/relay. Where should I probe to debug further?

The load should be connected to pin 5, not pin 6.

The resistor doesn't get hot, because it's in series with a capacitor. It's a snubber network, which damps the high voltage pulses generated by the coil.

[n4te]

The load should be connected to pin 5, not pin 6.

I think you mean pin 6 (shown in the datasheet) not 5 (shown in my schematic). The schematic symbol (from SnapEDA) only shows pin 5 and the pattern has pins 5 and 6 connected internally. I actually wired it to pin 6.

The resistor doesn't get hot, because it's in series with a capacitor. It's a snubber network, which damps the high voltage pulses generated by the coil.

No coil yet, just the 546 ohm resistor? What does the snubber do to the resistor? How many mA should I expect to see? If it's expected to be unable to draw the 44mA, maybe it's actually working correctly. What would be a better test? I don't have an irrigation valve on hand.

[Zero999]

https://www.st.com/resource/en/application_note/an437-rc-snubber-circuit-design-for-triacs-stmicroelectronics.pdf

[n4te]

Thanks. I read that and absorbed some of it, though my understanding of TRIACs is still pretty weak.

Right now I'm just trying to test my relay without an irrigation valve. If I understand correctly, the snubber's impedance at 60Hz is ~27.5K. That's quite a bit higher than the 546 ohm resistor and so should have little affect on the current draw -- I should still see ~44mA and the resistor should get hot. It doesn't though, why?

[Zero999]

The resistor has a 100nF capacitor in series with it, which dominates the impedance, so hardly any current will flow and the power dissipation in the resistor will be minimal.

[n4te]

I assume you mean the high impedance due to the capacitor causes the snubber circuit to draw very little current, so power dissipation of the snubber resistor will be minimal. That makes sense to me, essentially the snubber barely affects the rest of the circuit, meaning I should see my load (the 546 ohm resistor) heat up just as it does when connected directly to 24VAC.

The pin I thought would sink current to turn on the LED wasn't doing so, as some other code was surprise changing the pin. I hate it when it's my own stupid fault! Sort of, better this than a bum component I suppose. Anyway, my relays are working and my resistor is heating up! Great success!

Thanks everybody! We did it! \o/