Its seems that more and more brewers are looking into and building their own brewery controllers. We have had some great chats with other brewers regarding CraftBeerPi and the Automated Brewery Guide for the hardware. Some of the questions that we receive and we find on the forums are related to the SSR. What type to get, how to wire them and how to install them.
So i thought we would offer our two cents on this.
The basics of an SSR is quite simple. Some form of signal is used to close or open a circuit. (that is the very very simple concept) For the purpose of using a Raspberry Pi to control the SSR, we use a 3-32VDC control SSR. Using the SSR with a Raspberry Pi is quit easy since the Raspberry Pi`s GPIO pins will send out a 3.3V signal, enough to control the SSR. So, think of your GPIO pin and wire as your positive, and then connect the other to Ground. When you activate one of the pins via your CraftBeerPi software, it will connect the two points and complete the circuit.
For the connecting to hardware, all we need is to take your example L wire from your power input and connect it to one of your SSR terminals. The other terminal will have a similar L wire to your hardware. The N wire will go straight from power to the hardware. And thats how we make the software control the hardware.
One thing to remember is that there are also some very poor SSRs out there. These will “claim” to be 3-32VDC controllable, but in fact, you need close to 5V to be able to open/close the SSR. And some are just poor in build quality. Use what other people are using and recommending, thats the best advice.
What about Ampere? Yes, well.. its down to what you connect to them. 5500W or more heating elements will quickly reach the limit of a 25A SSR. Remember, when open, it will generate a lot of heat and if you need to run your element full force, it puts quite the load on your SSR. We like to think of it this way, 25A will be more than sufficient for your pumps and other accessories. 40A will cover most heating elements. But please, do check and do some calculations before installing your own. We do however recommend a heatsink on your SSR. And while heatsinks often come with the SSR, we recommend putting some thermal paste underneath for the best heat transfer.
The heatsinks above (and most of the ones that come with SSRs) will fit directly onto a DIN rail. Otherwise, you can easily mount them with screws inside your controller box. Please remember to keep a plastic cover on them, or lock the controller when in use, as you will have an exposed connection here.
Below are two 40A Fotek SSRs being mounted in our controller on a DIN rail.
On the 3-32VDC control terminals, we can share the Ground between them, leaving less wires clogging up your box. If you go for the same IKEA box we have, you are insulated quite well in terms of electrical shock from equipment failures. If you do have a metal cabinet, please remember to ensure a solid ground connection to your DIN rails and other parts e.g. door and the cabinet itself. And one important thing to note, we are not electricians, we should always consult with competent people before putting power on equipment like this.