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Not sure what your electrical skills are like but building a PID controller with a solid state relay is pretty simple and just a case of buying some parts and connecting them together.Just a word of warning with using an Inkbird 308 to control the mash and boil. I have been using one for about 12 months now to control my RIMS system which uses a 2.2 Kw element as the main heater with a 1.5Kw in the RIMS tube. (Always used independently never on together ) Everything has been fine until a couple of brews ago. The inkbird socket melted after a 60 min boil with main element and welded itself to the plug of the element !
I’m currently just using the inkbird to control the smaller element only until I can find a plug and play PID option (if anyone has hot any ideas please let me know as I can’t see anything much cheaper than £1000.)
I have been told that I may have experienced a voltage drop which could have caused the 2.2Kw element to draw more current exceeding the 10amps max of the inkbird hence it melting. I’m not sure what happened though.
Just saying be careful when using the inkbird controller on its limit .
Here's an example of one YouTube video taking you though it...I'm sure there are many more.
Going back to the OP's original question I'd not get too panicky yet...I get a very similar affect with my PID controlled RIMS tube in that it sometimes jumps upto 80 degrees before dropping down. There is no way in the world the mash is responding that quickly and measuring the mash temp confirms that...however my theory is more around the RIMS tube configuration:
My RIMS tube is configures as standard or at least as I've seen them configured before...so a tube....heating element coming up from the bottom....temp thermowell and thermocouple coming in from the top.
There is an air gap in the very top of the RIMS tube as the tube outlet is a bit below the top of the tube so you need a thermowell and probe long enough to get past the air bubble and into the flowing wort.
The thermocouple is directly above the heating element and probably quite close to it...so I suspect when the temperature appears to run away you're actually picking up some of the heat directly from the element. Of course the heating element is running quite hot but the flowing wort over it means the wort doesn't get as hot as the element but if your thermocouple is picking up the radiated heat of the element then you're getting a false reading.
I'm looking to reconfigure my RIMS tube in one of two ways:-
1. Turn it upside down...heat rises so maybe if you just turn the tube upside down then the thermocouple wont pick up the radiated heat from the element....potential downside to this is that the wort will heat up as it flows over the element so you might have a difference between the measures wort temp and the wort temp at the outlet of the tube.
2. take a T-piece off the top of the RIMS tube so the wort turns through 90 degrees out of the top of the tube. In the other end of the T-Pice have your thermowell and thermocouple so the probe is measuring the wort temp on the output of the tube. With the flow rate of the wort that should be, near as makes no difference, the same temp as the wort in the tube.
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