The Control Box

The control box is the brains of the system. It houses the PID temperature controller, the thermocouple (which is connected to the PID), the Ground Fault Circuit Interrupter (GFCI) for the system (very important), and the solid state relay (SSR) that controls power to the Heat Exchanger heating elements. I am no electrician and I managed to embarrass myself substantially by frying a little relay on the PID circuit board the first time I plugged it in. Luckily, the part was replaceable with a little begging, but I made sure that I got input from my electrically inclined friends before I fired it up the second time. I would strongly suggest some help in wiring this up.

The key element is the PID temperature controller. The desired temperature is entered into the PID. The PID then reads the process temperature (in this case, hot wort) via the thermocouple on the exit of the Heat Exchanger coil and compares it to the set temperature. It actually performs calculus to determine if the heating elements need to be on or off to attain and hold the desired set temperature. This allows you to just set the desired mash temperature and then let the PID do all the work. For a good explanation of how PID's work, visit Keith Royster's RIMS site.

The SSR is necessary because of the current draw of the Heat Exchanger heating elements (16-17 Amps). The PID can only handle a small amount of current (200-300 milli Amps). The SSR gets a signal from the PID which closes one set of low amperage contacts. This in turn closes another set of high amperage contacts on the SSR. This allows the high amperage to pass through the SSR instead of the delicate electronics inside the PID.

In ALL instances, ABSOLUTELY, POSITIVELY, USE A GFCI! You are dealing with enough current and voltage to kill you, so do not get complacent.

The enclosure was made from a small plastic tool box to house all of the hardware. Without wiring anything, I placed all the items in the box so that I could get a feel for the layout. Plus, since the solid state relay and the SSR heat up a bit in operation, I also put in a little fan to keep the air moving inside the box. Since each system will be unique, you need to pick a suitable enclosure and lay out the components so that they all fit into a nice workable package.

On the front of the box is a standard outlet for the Heat Exchanger to plug into. The temperature controller controls power to this outlet using the wort exit temperature at the Heat Exchanger coil (read via the thermocouple). Notice that this plug has an on/off switch. This acts as an emergency shut-off for the power to the heat exchanger. I highly recommend this.

Mounting all the stuff into the control box is just a matter of cutting, drilling, and screwing to get everything to fit and stay in place. Since the box houses a significant amount of electricity and we are dealing with water in large quantities, the box should be somewhat water resistant.

The Control Box itself must be powered. I used a standard 3-prong plug with the proper gage wiring to handle the current load to the Control Box.