Interrupt circuit help please...

[burbelly]

I am trying to power three 5500 watt elements (HLT, external HERMS, BK) from a 220V 50A supply. I'd like to set up a circuit to interrupt the HLT element when the HERMS and BK kettles fire up. I'd like to put a short delay between the PIDs and the SSRs to allow the circuit to cycle before all the elements turn on.

Any suggestions?

 

[BrewBeemer]

Just an example what you can be applied, prices vary from over $110 on down to less than $20. http://www.surplussales.com/relays/RETimeD-2.html.

 

[burbelly]

This illustrates what I had in mind. Any faults in my plan. I don't know what to use for the 17.5v SSR. That is the voltage that I'd like it to kick in at, approx 50% power per element.

 

[BrewBeemer]

As long as the delay relay has it's proper voltage your only using it's contacts, pick the power supply that makes you happy for the SSR voltage.
There must be a wider range of voltage the SSR can operate under, all the ones i've seen work operate from 3 to 32 VDC.
Check your SSR's as there are AC and DC triggered units.

 

[burbelly]

I'm not following you. The Auber instruments PID I'm going to use has the 3-32VDC outs. 17.5V DC is the PID signal voltage I want to trigger the relays to open the HLT NC relay.

 

[burbelly]

Schematic updated for clarity.

 

[ClaudiusB]

I'm not following you. The Auber instruments PID I'm going to use has the 3-32VDC outs. 17.5V DC is the PID signal voltage I want to trigger the relays to open the HLT NC relay.

How do you manage to get 17.5 V out of the PID, is your model an analog out with a non 0-10 VDC?
The standard Auber modules have a fixed SSR voltage out, 8 V or 12 VDC with a changing duty cycle.

Cheers,
ClaudiusB

 

[burbelly]

I thought that ssr input and the PID output were variable and proportional. If that's not the case then I just need to use two 3-32V SSRs, a 24v ssr and three delays. Is that correct?

 

[Bobby_M]

PID and SSR are binary on or off. You regulate power via duty cycle if the pid supports manual mode.

 

[burbelly]

OK, so here's the final plan, I hope. I found delays that run off the signal voltage. I also found 12v SSRs that consume next to no current. Finally I found a normally closed reed relay. This is what it looks like and if anyone can find fault with the setup please let me know.

 

[BrewBeemer]

Ok, lets throw this out; http://www.patriot-supply.com/products/showitem.cfm/3603

We used them in large refrigeration / deep freeze compressors for Safeway stores. I'm a pack rat collected a pocket full of used ones. 19 to 288 VAC 1 amp Max.
Bad part this is an AC delay vs your DC SSR's unless you trigger your mechanical relay by a Mars delay.
Your mechanical relay will be trouble vs a SSR JMO.

 

[LakewoodBrew]

I have looked at your schematic several times... alas, i am at a loss for what you are trying to accomplish.

As best I can see, you have a 12V source wired in series through 2 SSRs leading to the control on a reed relay, thereby powering the reed relay *only* when *both* of the other SSRs are on.

You are also running your PID signals through a delay between two SSRs wired in series (one of which is controlling a line voltage and the other is in the aforementioned control loop) Unfortunately, with a PID duty cycle type output I think the delay will do one of two things: A. Filter off your control signal and not allow anything to happen, or B. Behave erratically and give you un-intended operational output.

I'd recommend that you write out a thorough description of your requirements and let someone here give you a hand with your electrical schematic. I don't think what you've drawn there is going to get you what you want.

 

[burbelly]

I am trying to make amperage available to the HLT element when the other controllers are on an off duty cycle. When both the HERMS PID and Kettle PID are signaling on duty cycle, the 12v will reach the third, normally closed relay. This will in turn open the circuit and shut off the HLT element. The delay devices allow the SSRs and the reed relay to cycle before applying power to the 240v relays that control the element current and prevent an all elements on situation.

I would then change the PID cycle time to be something like .5 seconds or more. This allows the system to fire the HLT while the mashtun is at temperature and the boil kettle is running full tilt, like in decoction mashing or back to back brews.

This of course is highly dependent on weather the reed relays can take this cycle rate. From my understanding they can take very high cycle rates but "very high" is a very loose term. I could also sacrifice more cycle speed in the PID to alleviate the cycle load on the reed switch. I have also read that a MOSFET chip might work in this situation and be solid state but I have had some difficulty finding a suitable chip.

Thanks again,
Eric

 

[burbelly]

If one of the issues is the PID cannot handle this much current, then I could add one more SSR and use that to control a higher current source like in this pic. This way, the PID is only seeing one SSR and the 12v source can be supplied with more current or voltage.

Edit: added a diode to prevent the kettle 12v source from powering the MLT.

edit edit: that's not going to work. Update coming.

 

[Sawdustguy]

If I read what you want to do correctly your scheme will not work. You will not be allowing the PID to act like PID's if you interrupt and delay their cycle.

 

[burbelly]

Ignore this post, next schematic better.

 

[burbelly]

Here is another revision that would allow me to put the PID in manual mode, flip a DPDT switch, and dump ALL the off duty cycles from the Kettle and the HLT. This would save the HLT PID from analyzing bad data since it expects the heater to be running when it is actually bypassed.

 

[LakewoodBrew]

I fear you are headed down a bunny trail. What is the timing on the delay? If it's anything more than .05 sec you will miss a lot of cycles (.1 sec delay in series with a .5sec PWM cycle will give you a 20% - 80% capability, .05 = 10%-90%).

What you are really looking for (I believe) is a NAND gate connected to the output of the Kettle and HERMS PID outputs with it's output running to an AND Gate along with the output from the HLT PID. Run all of those using a 5-9V Bus and, depending on specs you may, or may not need any buffer to drive the SSRs. If you feel it's absolutely necessary to introduce a time delay, I would just insert a MOSFET buffer, and drive a small RC circuit in parallel with the SSR. The resistor-capacitor circuit will give you an on-delay, but the low impedance of the SSR will give an instant off.

But truthfully, it's all fun and games until someone gets hurt, so unless every word I just typed makes perfect and total sense, please, for the love of god don't try any of this. 220VAC 50A will fry you and every poor soul who tries to pull your convulsing body away from rig if you have even the slightest mistake. You wont even have time to say oops.

 

[burbelly]

Thank you all for your input. It looks like they will be implementing something like this in the Brewtroller platform so all the switching will happen on the software side. My doctor can now sleep soundly... for now

 

[Sawdustguy]

I fear you are headed down a bunny trail. What is the timing on the delay? If it's anything more than .05 sec you will miss a lot of cycles (.1 sec delay in series with a .5sec PWM cycle will give you a 20% - 80% capability, .05 = 10%-90%).

What you are really looking for (I believe) is a NAND gate connected to the output of the Kettle and HERMS PID outputs with it's output running to an AND Gate along with the output from the HLT PID. Run all of those using a 5-9V Bus and, depending on specs you may, or may not need any buffer to drive the SSRs. If you feel it's absolutely necessary to introduce a time delay, I would just insert a MOSFET buffer, and drive a small RC circuit in parallel with the SSR. The resistor-capacitor circuit will give you an on-delay, but the low impedance of the SSR will give an instant off.

But truthfully, it's all fun and games until someone gets hurt, so unless every word I just typed makes perfect and total sense, please, for the love of god don't try any of this. 220VAC 50A will fry you and every poor soul who tries to pull your convulsing body away from rig if you have even the slightest mistake. You wont even have time to say oops.

Good call!! I didn't give it a lot of thought at first but after reading what you have to say I agree with you. Burbelly, I am active on the Brewtroller Site and I think it can be done with a Brewtroller.