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Old 02-03-2009, 06:56 PM   #1
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Default Johnson used to be 2 deg high, now 7?

I have a Johnson analog temp controller on my keezer. I use my 2-point calibrated usb thermometer so I know that it is accurate. When I first got the johnson I found that setting 38 on the dial would get me 40 F in the keezer. I ran another test today and found my keezer to be averaging 45 over two hours with the dial still set to 38. I expected it to be a little bit off, but I don't like that the error is growing. Anyone have any suggestions or know why this is happening?



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Old 02-03-2009, 07:02 PM   #2
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I don't trust my dial at all.

I just place my probes from both the controller and the thermometer in the same spot and once my thermometer reads the desired temp, I dial back the controller just enough to shut it off.

Make sure first of all that your thermometer and controller probe are in the same spot.



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Old 02-04-2009, 08:03 PM   #3
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First thing; you might be able to check and clean the contacts for pitting and wear, if you can dress them that is great. Thet are calibrated at the factory, they usually use paint on the adjusting screw to lock it in this set position.
Second thing; I would do this readjust to the controller if possible to the temperature control unit after it has stablized in a regular refrigerator matching it against a known accurate temp gauge. Once this corrected by the adjusting screw add a little paint to the threads to lock the screw in position. Next have the controller this time control a relay as only the relay coil current which is rather low will go thru the controllers contacts, let the relay take the motors starting surge current amperage that is what a relay is designed for. A small current coil controlling a high current item like a motor or a heating element. This would be a inductive or as a resistive load on the relay. Relays are rated for these types of loasd.
It is better to have the relay contacts take the high current hammering and pitting loads instead of the contacts in your temp controller. The relay coil current will be in miliamps range vs high amps that cause this contact wear and pitting in the first place. Not only the above problems you will have different temperatures that the controller cotacts open due to pitting and sticking contacts.
With this set up you will have dead on repeating temps all the time with the controller contacts not take a beating and sticking from all the pitting and contact buildup. Years ago I installed a relay to a 240 volt hot tub as the contacts in the temperature controller were pitted and sticking causing the temps to vary by many degrees, over 27*F. After purchasing a new temp control at $137 because the old one was totally sealed preventing dressing the contacts I had the controller control a relay coils current. The relay contacts took the high current arcing plus the hot tub temp was always stable and within 0.1*F when set at 102.5*F. Your body can feel a 0.25*F to 0.5*F degree difference.
This resulted from soaking 45 minutes or longer to having to get out after 2 minutes. A narrow happy zone for a good hot tub soak of 35 minutes to get the full benefit of the tub on the sore body muscles.

You got my point above about ading a relay I hope.

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Old 02-04-2009, 09:25 PM   #4
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Quote:
Originally Posted by BrewBeemer View Post
First thing; you might be able to check and clean the contacts for pitting and wear, if you can dress them that is great. Thet are calibrated at the factory, they usually use paint on the adjusting screw to lock it in this set position.
Second thing; I would do this readjust to the controller if possible to the temperature control unit after it has stablized in a regular refrigerator matching it against a known accurate temp gauge. Once this corrected by the adjusting screw add a little paint to the threads to lock the screw in position. Next have the controller this time control a relay as only the relay coil current which is rather low will go thru the controllers contacts, let the relay take the motors starting surge current amperage that is what a relay is designed for. A small current coil controlling a high current item like a motor or a heating element. This would be a inductive or as a resistive load on the relay. Relays are rated for these types of loasd.
It is better to have the relay contacts take the high current hammering and pitting loads instead of the contacts in your temp controller. The relay coil current will be in miliamps range vs high amps that cause this contact wear and pitting in the first place. Not only the above problems you will have different temperatures that the controller cotacts open due to pitting and sticking contacts.
With this set up you will have dead on repeating temps all the time with the controller contacts not take a beating and sticking from all the pitting and contact buildup. Years ago I installed a relay to a 240 volt hot tub as the contacts in the temperature controller were pitted and sticking causing the temps to vary by many degrees, over 27*F. After purchasing a new temp control at $137 because the old one was totally sealed preventing dressing the contacts I had the controller control a relay coils current. The relay contacts took the high current arcing plus the hot tub temp was always stable and within 0.1*F when set at 102.5*F. Your body can feel a 0.25*F to 0.5*F degree difference.
This resulted from soaking 45 minutes or longer to having to get out after 2 minutes. A narrow happy zone for a good hot tub soak of 35 minutes to get the full benefit of the tub on the sore body muscles.

You got my point above about ading a relay I hope.
Well ah...uhhh...I uh...I don't see the button for "add relay"
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Fermenting:.
Conditioning:[Oaked Cider][ESB]
On Tap.........[The Munchner][Spiced Cider][English Cider][Simcoe IPA][Triple Hops Grooved][Cider'n 'gnac]
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Old 02-05-2009, 01:35 AM   #5
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Sorry boss, I was way off base thinking the bulb w/ tube and bellows mechanical temp switch, my mistake still thinking antique temp control.



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