Back again for another instalment of ‘I built this thing and here is how I did it’. This is how to build a PID temperature controller for a mushroom steriliser barrel and, in fact, for any aspect of mushroom growing that needs high-amperage temperature controlling such as your PC and dehydrators.
A legal preface: I’m not an electrician, therefore you should take this information as a rough guide rather than firm plans. Speak with a qualified professional before you undertake any electrical works. Look both ways before you cross the street and don’t take sweeties from strangers.
This post compliments my previous post on ‘how to build a mushroom steriliser barrel’ which you can read here – https://archersmushrooms.co.uk/how-to-build-a-drum-steriliser-for-mushroom-growing/
The premise of a PID controller is almost the same as a thermostat, that is holding temperature between a certain range. Where a PID differs is its efficiency and accuracy. A thermostat will work within a range of X degrees. Turning off when it reaches target and turning on when it drops below.
A PID calculates how much power it needs to allow to flow to hold the value. This may sound the same but it’s much more efficient. PID’s release short blips of power rather than running the element for another 30 seconds. As the cycle progresses and the bags absorb heat (acting as a heat sink) the PID will need to introduce less energy to maintain that temperature. Compare this to a thermostat which is still following a range, a PID is much more energy efficient.
For mushroom growing, this means a much more consistent sterilisation temperature, a much more efficient use of electricity, less water used and some PID’s even have timer features which tell the unit to start a timer and then cut off at the end of the cycle.
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A PID kit. It’s a bit more expensive as a kit but comes with all the bits you’ll need such as the controller, heat sink, SSR (solid state relay) and a thermocouple* See below.
The thermocouple, which is type K meaning it has 2 terminals, which comes with the kit is perfectly adequate. However, it is quite a short length and doesn’t allow for a quick release, rather you have to use a spanner and un-screw it from the steriliser. I suggest these ½” NPT (They still fit ½” BSP) thermocouple which have a cannon plug for easy disconnecting. When used with a 3/4” to 1/2″ reducing bush they can fit into the pre-tapped holes in most barrels.
An enclosure of some sort. I prefer plastic to metal but it’s dealers’ choice. The depth of the enclosure is important PID controllers, SSR’s and their heatsinks are quite tall things so the box needs to be deep enough to allow the full-length in. Mine is 240*190*90mm.
Cable with a suitable rating for your element size. I use 4mm H07RN-F rubber cable. This gives flexibility up to about 20amps. I run at about 15 amps so I’m well within safety. This is one of the few places online, however, it would be cheaper to go down your local electrical merchants and ask if they have anything suitable. You want it to be flexible, solid core isn’t suitable. It must also have a durable insulation, again, solid house wire isn’t suitable.
Suitable plugs – depending on your element size I suggest 16amp or 32amp 3 pin plugs. Even though a UK spur is rating to 3000~w, if you run a 3000w element on that line I guarantee a standard plug will weld itself in eventually.
Ring terminals, Wago connectors, cable ties, DIN rail and cable glands
How To build it
The process of making the controller is very simple. First, mark the bottom of your enclosures with 3 holes. Make sure the back side is clear of any box structure and has enough room for the cable gland nut to go on the back.
I use a q-max knockout punch to make two 25mm holes and one 20mm hole. I wouldn’t suggest spade bits or forstner bits as they bite and crack the plastic. A cone drill is probably the best solution if you don’t have a q-max, I haven’t yet tried hole-saws but I would imagine they would just bite too.
Next, I measure the size of the PID itself and cut a square-ish hole out for the controller to pass through. For this I used a Stanley knife and a lot of swearing. I then passed the controller through the hole and secured it using the white clamp provided.
I then measured and cut some DIN rail the width of the boxes mounting holes. I secure the SSR and heatsink using two m6 bolts and nuts and capped them with some rubber. It’s worth noting that you can mount the heatsink on the DIN rail directly using the lots but the fitting is loose and I couldn’t find any way of clamping it tight.
After that I secure the DIN rail to the enclosure using 4 short screws.
Next, I began wiring up the unit. Below is a wiring diagram of how I did it. Consult a trained professional before you undertake and electrical work on your own. This is just for reference only and should not be taken as the correct way of doing things.
I made the loom in 2 rather than splicing into one continuous cable. I should have omitted 1 live Wago and just connected the outlet straight to #2 on the relay. But when you aren’t an electrician these things happen! I made the diagram correct so there may be discrepancy between the diagram and my actual work, but the diagram is correct.
You can see the sequence of photos below of how the actual wiring looks in the enclosure and how I made it secure.
I finished it off by securing all the loose cables down and then, using some hot glue, I insulated the exposed terminals to minimise risk of the TC cable coming loose and arcing between the #1 and #2 SSR terminals. Ask me how I figured this out. LOL.
After, simply close the box up and attach your plugs to the inlet and outlet. Follow this video guide on how to set-up a PID as it would take too long to explain. Don’t be scared, PIDs can do a lot more than what we will use them for, so a lot of the functionality is not used. Any questions drop me a message but just remember. This is a guide only and should be used just for reference and not as firm plans.
A lot of work goes into these blogs, if it helped you out and you can afford it, then you can support my work by buying me a pint! Cheers!