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Old 11-25-2012, 01:30 PM   #1
beerFacedotkom
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Default PID Temp controller

Hi,

I've got an electric HLT with a 5500 W element being controlled by a cheap little PID (1/16 DIN dual digital) and an Amico 25W SSR. At 5500 W, the current is 25A, 100% of the SSR rating. Now, I previously had a 4000W element, so I had some current head room.

The problem I'm having is the heating element not turning off when the controller turns it off. The PID seems to work while heating up to the set point (heater doesn't appear to be running open-loop). In fact it regulates fine for a minute, then always starts to overshoot.

It seems like the relay is latching up. The controller is putting out near 0 volts to the control pins on the SSR (measured with DMM), but 220V is still powering the heater. Any hints besides getting a bigger relay?

Jeff

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Old 11-25-2012, 04:56 PM   #2
meadmazer
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Have you tried turning the temp down on controller when the element is powered? This should fully stop any controller output/ssr input, helping to check if ssr is really sticking on.
You could also try a fan on the heatsink.

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Old 11-25-2012, 08:13 PM   #3
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I have turned it down during use and I think that might be working. I'll have to check to be sure. However, I have measured close to zero voltage difference between the SSR output terminals, indicating heater on, even though controller voltage measured 0 (actually floating at ~0.5 V).

I'm wondering if I'm just using the wrong relay with the wrong PID. The SSR was $10 on Amazon, rated to 400 something volts, 25A. The PID produces a +12V control signal. I'm going to take your advice and try a better fan on the heatsink.

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Old 11-25-2012, 11:22 PM   #4
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It was the fan. BTW, I have the 40A SSR. Heat sink is installed with thermal grease. Fan needs to blow continuously on heat sink, no problems after that.

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Old 11-26-2012, 12:17 AM   #5
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Good to hear, I see u r in SLC I am an hour north of you.

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Old 11-29-2012, 08:14 PM   #6
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Deweyville, never heard of it but wiki tells me you're almost in Idaho! What's your line of work if you don't mind me asking? How long you been brewing? Thanks for the answer on the SSR btw.

When I get time, I want to put pics up of my system. I've been working on it for several years if you count the room in the basement I built just for a brewery. Of course, the house was being re-built, re-wired, and re-plumbed, so I worked it in. Small space but all my stuff is right there and I have a hybrid natural gas/electric HERMS-type a thing going on.

Jeff

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Old 12-01-2012, 02:09 AM   #7
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I sent you a PM

Eric

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