variable solid state relay

How does the relay work on resistance.

 

So if the potentiometer was disconnected from relay what would relay do?

 

Hmm interesting... It was my understanding that an ssvr did not do PWM but instead actually varied the output voltage rather than the timing of it by pulsing as done in PWM...

 

^^ bingo. It's essentially a PWM with a sinusoidal envelope. See the first graph below.

 

Ditto. I used an SSVR until I got around to adding a PID to my setup. With the potentiometer disconnected, the SSVR sees basically infinite resistance between the two terminals, so the relay stays open.

I really did like the knob control over my boil, especially at the hot break point when I'm pushing the volume of my system. I'm going to be implementing a switch on my boil kettle so I can switch between full-on, the knob/SSVR, and the PID (for hop stands).

OOPS, edit, I forgot that I picked up a cheap eBay LED dimmer PWM and added modified it to pulse at a lower frequency. I'm not actually using the SSVR.

 

Can you wire an SSVR in parallel on the element side with a standard binary SSR for such control? This way you could control boil either by PID/manual % or via knob control. Any implications to powering one while the other is off or on reduced output PW?

-BD

 

Sorry for a hijack from an electrical noob, but how does a SCR (silicon controlled rectifier) fit into this discussion? Any problems with using one to control a heating element that we should worry about?

 

That would work fine (I think), but it would probably lead to some confusion while

 

You'd want a triac as they are bidirectional.

Since SCR's are one-directional, you'd already be at half power using one unless you full-wave rectified the AC coming into it first, which would require a full bridge (4 diodes).

 

This tells me there's a lot more than I thought that I don't understand. Are you saying that one of these will only give me half power to the element even when turned all the way up? If that is the case, could I use an element at twice the wattage and still get the heating power I'm looking for?


I know there are better options. I'm just trying to figure out how these things work.

 

That looks like it will work fine. Sorry for being confusing, I had my engineering cap on.

(From the Too Much Info dept: If it actually has an SCR inside, it must have a diode bridge to full-wave rectify before the SCR. Or, it actually has DIACs / TRIAC inside)

 

No such thing as too much information, just the ability to comprehend it. Does this mean that the diode bridge will allow full power passed through to the element?

 

Yes.

120V AC power from the wall flows from the nuetral wire (white) to the line wire (black) for 1/120th of a second, then it reverses direction and travels from the line to nuetral for 1/120th of a second. Two directions. the full cycle is 1/60th of a second, so we say we have 60 Hertz.

Since an SCR can only conduct in one direction, half of that cycle would be eliminated completely, and you'd be at half power to start with.

A full diode bridge "rectifies" the current, forcing both halves of that cycle to flow in the SAME direction. Thus, both halves get through the SCR, and no power is lost (though you lose a little, maybe 2 or 3%, in the diode bridge).

A TRIAC allows flow in both directions and thus doesn't need the diode bridge.

FYI, you car has a similar diode bridge in its alternator so the bi-direction power generated by your engine is rectified for charging the battery.

 

As you know the Relay is a electromagnetic switch. For its operation you have to give supply to it and disconnected from it. You can simply do it with the TRIAC. For TRIAC control you have to use the variable resistance, which controls the angle of fire for TRIAC. Using resistor you can control the ON/OFF of relay.

 

Hijack:

I'm planning on using an SSVR with PID (pot wired inbetween). When using the PID function I'll have the knob all the way up. When using the knob I'll just kick the PID over to manual mode so it's always on.

Any issues there? Probably should have researched it more before buying. But I don't see any trouble with it. I think I've seen it done that way before...

 

If you use a SSVR with a PID then basically what you have is a variable power controller. Use the potentiometer to set the effective power of your heating element and the PID to maintain the temperature.

 

It'll work fine (I think). I wouldn't do it though. Once you put the pid in manual mode, it's pretty easy to just digitally dial in your power %, and it's accurate, unlike the non-linear dial of the SSVRs.

I do understand the allure of the dial though. I use a PID for HLT and an SSVR for BK. I like the dial for the boil. I have separate sockets for the HLT and the BK.

BTW, since I only have 30A service in my brewing area, I use a fat DPDT switch to select which outlet is getting power, the HLT or the BK. That way I don't accidentally turn them both on and force a trip to the breaker panel.

 

Yeah on my last two builds I've just used the PID buttons, but figured I'd bling this one out with a knob for boil control. Pointless maybe, but whatever.

 

Why not a separate socket for the HLT and BK?

 

This is a single pot BIAB setup. PID is only there for heating strike water and for the temperature readout.

 

I pictured the power running through the SSVR relay, then through the PID relay. That way would work I think.

 

Yeah you guys are right. I can't control the SSVR with PID's 12v output. Should have caught that. I'll have to think about this some more. Feck. Don't want to do 2x relays. Probably just scrap it and do the buttons afterall...

 

I ran the PID to control one hot leg of the 240VAC and the SSVR with potentiometer to control the other. Works just fine, brewed about 10 batches with it so far. The PID I had was the TA4 so it couldn't do manual duty cycles. It is somewhat unnecessary with a TD4 or comparable PID. The knob is quicker to adjust though. A bunch of button presses on the PID can be frustrating if you're in panic mode to prevent a boilover. I found that keeping a metal pan close at hand and scooping a pan-full of wort will be enough of a heat sink to stop the boilover in most cases

 

That I think you're describing is what I thought iijakii was going to do.

I have a switch on my panel that kills all power to the elements for those OH SH1T events

 

Why not use the $6 led pwm controller with a regular ssr like mentioned earlier? you can just run the ssr control voltage from the pid through it...
I have a bunch of these left over from a led reef tank lighting build... hmm if I build another panel I may have to check this out.

 

So bridge diode before, or after scr?