How a Controller works

[sicktght311]

So i've read the sticky at the top, and read countless wiring diagrams, parts lists, etc, and i'm like 90% positive of what goes into building a controller, both 120v, or 240v, but i'm still a little hazy on the signal path and what certain parts handle, mainly when it comes to firing and controlling the power to the element.

I'm very well versed in standard 120v/240v household wiring and how to repair/replace/install things, so the whole input/output portion of a controller diagram, with wiring gauges, etc I can follow easily, and everything makes sense and the reasons make sense. I'm trying to figure out the following

----I get that the PID is the equivalent of the computer, reading inputs (temp), and determining when to set output (power to the element). So i see Relays, SSRs, and Contactors in panel wiring diagrams, but sometimes one or two is missing, sometimes all 3, etc.

I guess if someone can just do a quick write up of how the signal path works, and what the individual components actually control, in something like the standard Electric Brewery or eBrewsupply panel, that would make it infinitely easier to follow and plan.

 

[tofuguy]

Short Circuit Brewers has a channel on YouTube where there go through step by step of building and explaining a controller for a HERMS setup. They also use nice animated graphics explaining the circuit diagram. I suggest you head over there and take a look.

 

[sicktght311]

Thanks! I've always followed his stuff, but never realized there was a video that goes in depth. That would be perfect

 

[ajdelange]

It is the job of the controller to determine when and how much heat needs to be delivered to the load and it determines this by examining the temperature of the load and the way the temperature varies with time with respect to a model it contains of the thermal properties of the load. There are many ways to implement the controller function (Delta T, PID, Fuzzy logic etc.) and many ways to translate the controller's heat demand into a signal to a heat source. The usual means used by home brewers is an electronic controller that runs the PID or fuzzy logic (or a combination) and outputs either 0 - 5 V, 4 - 20 mA, TTL PWM or dry contact PWM signal proportional to the heat demand. Certainly the most common hookup is to use a TTL PWM signal to gate an SSR in series with one (or both) legs of a 240V heating element. But I had, for example, a setup in which the 4 - 20 mA signal operated a gas valve and 0 - 5 or 4 - 20 mA signals can be used to vary the firing angles of SCRs or triacs in fancier systems.

Let's be sure you understand the concept of PWM (pulse width modulation). If you have a heater that draws 10 Amps at 240 W it will dissipate 240*10 = 2400 Watts and deliver 8.2 kBTU (2/3 ton) of heat to the load per hour. If you leave it on for half an hour then turn it off for the next half hour it will deliver, in that hour, 4.1 kBTU. While the load will clearly heat up noticeably for the first half hour and noticeably cool down during the second the amount of power delivered to the load in that hour is still 4.1 kBTU. If you hold the heater on for 1 minute and off for a minute, then on for a minute then off for a minute... it is still delivering 4.1 kBTU/hr (half its capacity) but now you probably would not see much of a temperature change over the course of the hour. This is how the PWM (pulse width modulation) output controls heat delivery in most homebrewing setups. The contoller has a cycle time of something like 60 seconds and when it wants 100% power it leaves the TTL output at +5 for the whole 60 seconds and never turns it off. If it wants 90% it holds its output at +5 for 54 seconds and then sets it to 0V for 6 seconds and so on. The TTL signal gates the SSR(s) sending power to the heater during the ON gated time periods. If the controller has a relay output in addition to the TTL output its contacts can be used to switch a low voltage (typ. 24 VAC) to the coil of a contactor with the same result except for noise and short contactor life if the cycle time is short.

PWM systems can work down to the AC cycle level. You can obtain 10% power by firing the SSR for 10 cycles (1/6 sec) and leaving it off for 90 cycles (9/6 sec) or for respectively 1 and 9 cycles but such short cycle times are not necessary with the relatively large thermal masses of even a home brewing setup.

I've addressed what I think you are looking for. If I've missed, tell me what you are after.

 

[augiedoggy]

Its mainly about added safety.
Contactors are just big relays used to actually kill both legs of the power to the element because the ssrs we use normally just control and switch one leg and allow a lot of voltage leakage at that while doing it that can still zap a person good. also many have had ssrs fail most commonly in the on position.
The other advantage of the contactors are that they make it easier to setup a 30a panel that will only allow one element to be on at a timeas far as HLT or BK... I do this myself with 2 NO/NC relays controlling either contactor so I can still use my 240v 1800w rims along with my 4500w HLT element but not my 5500w BK element.

SSRs are non mechanical switches which can turn on and off very quickly without damaging them like a mechanical relay or contactor (the contacts would burn up if you did this with a mechanical relay/contactor). SSrs can control the heat output quickly and provide different levels of surface heat at the element by pulsing the power on and off quickly. as well as just using quick on and off control to hold temps.
SSRs are usually controlled with a low dc voltage between 3-32v which is a control signal outputted from a pid or temp controller like the ezboil.

temp probes,
pt100 probes are a form of rtd and the most commonly suggested type for the hot side applications. there are others like thermisters but generally the rtd is more accurate and has advantages like threaded or TC bases and quick disconnects.

 

[sicktght311]

Ok so now i pretty much get it.

Power input--->Switch to power unit on--->PID (control temp)--->SSR (Fire element)--->Contactor (failsafe)--->Element

PID's low voltage output connects to the SSR which opens and closes the high voltage output to the element depending on when the PID tells it to

Only question is the contactor then. What is controlling whether the contactor stays Open or closed to let power flow through. What would cause it to interrupt the circuit in the event that the SSR gets stuck in the on position.

I'm doing all of this to plan an eventual build of a 240v panel when i upgrade my system down the line, but i'd also like to take a crack at a simple 120v controller for my 3 vessel 120v system instead of running multiple inkbird IPB16s

 

[augiedoggy]

contactor is usually turned on by a manual selector switch. this way you can easily turn it off as changing the temp to 0 on the pid every time is a tedious process. plus you can still monitor temps with the element off.

 

[ajdelange]

The basic power flow would be

PowerInput ---> Breaker/Switch/Contactor --> SSR --->Heater

The "Signal" flow would be

Thermister/RTD/Thermocouple/1-wire Temp sensor ---> Controller --->SSR gate

There really isn't much reason to have a contactor unless you want some type of logic in the system which, for example, might prevent an HLT from receiving power when the kettle is operating (and/or vice versa) or if you wanted START/STOP pushbuttons and/or remote emergency STOP buttons. IOW if all the contactor does is respond to the setting of a manual on off switch it is functionally just a switch and you might as well use a switch or circuit breaker instead.

 

[augiedoggy]

On top of that, as mentioned above the other reason is the contactor is a dual pole switch that also turns off both hot legs of power otherwise theres power going to the elements at all times when the panel is on. depending how a persons workflow and hardware is setup some like to disconnect things and move things around or start cleaning while the panel may be in use. its just safer and it less likely to result in gfci breaker trips to do this if the power has been removed from the wires before someone might unplug something with wet or damp hands. Theres just more potential an electrical mishap when theres always one hot leg at every 240v element. The extra switch or switch controlled contactor comes in handy for other things too like when your about to get a boilover.. You can simply manually kill the element power momentarily and then turn it back on.
Contactors are not needed but they do add safety measures and make accidents or issues less likely. especially if a person uses things like bargain knock off foteks for ssrs and repurposed spice shakers for element electrical enclosures in a potentially wet enviroment..

 

[sicktght311]

Got it now. Contactors/Relays are powered directly from one side of the 240v circuit, and the other side comes from the output of the SSR. It acts as the final say before power goes out to the elements, and is controlled by a 3 way switch (Boil, Off, HLT). When you select off, then absolutely no power is going to an element since both legs are controlled by the Contactor/Relay and are off. When you select an element to on, it completes the signal path of the output of that SSR, and the output from the hot bus, to the 2.

I guess now that i understand each component and how it works in a 240v Kal style controller, i'm still struggling to convert that wiring diagram to 120v to build a smaller 120v only Herms system. Is it still as simple as wiring exactly like a 240v panel, with contactors/relays after the SSR, but substituting the 2nd hot wire in a 240v system for the neutral wire in a 120v system, and just swapping out components for their 120v counterpart?

 

[doug293cz]

Got it now. Contactors/Relays are powered directly from one side of the 240v circuit, and the other side comes from the output of the SSR. It acts as the final say before power goes out to the elements, and is controlled by a 3 way switch (Boil, Off, HLT). When you select off, then absolutely no power is going to an element since both legs are controlled by the Contactor/Relay and are off. When you select an element to on, it completes the signal path of the output of that SSR, and the output from the hot bus, to the 2.

I guess now that i understand each component and how it works in a 240v Kal style controller, i'm still struggling to convert that wiring diagram to 120v to build a smaller 120v only Herms system. Is it still as simple as wiring exactly like a 240v panel, with contactors/relays after the SSR, but substituting the 2nd hot wire in a 240v system for the neutral wire in a 120v system, and just swapping out components for their 120v counterpart?

I prefer to design with the contactors upstream of the SSR's (unlike PJ who liked to put them downstream, as you describe.) The reasoning is that if you want to cut off power, you should do it as close to the source of power as possible, as that leaves fewer components/shorter wire lengths at line voltage when things are supposed to be off.

Contactors can also be wired in self latching configurations that allow implementation of "safe start" circuitry. A safe start circuit prevents the panel from fully powering up if any of the element enable or pump switches are on. They can also be used to implement interlocks, that do things like prevent a RIMS element from being powered if the RIMS pump is off.

And yes converting to 120V is usually as easy as you said. Complications come into play if you have 120V loads in a 240V system that are powered from different hot legs (for current balancing.) Also, if you have any 120V loads, you have to make sure the neutrals are connected to the hot that has been repurposed to neutral. If you are unsure at all about how to do the conversion correctly, ask for help from someone qualified. There are some things you don't want to learn by trial and error.

However, if you want to run your panel from multiple 120V circuits, things get more complicated, as the neutrals for the different 120V feeds must be kept separate from each other, as well as the hots. If you don't understand what I just wrote, you should NOT attempt to implement a multi supply circuit panel by yourself.

Brew on