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PID Temp Controller Box

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Finally got around to finishing up the panels and wiring for this tonight. Still have to do the fans though.

Basically, I wanted something to control a small snack oven for SMD reflow soldering, but I also want to try some of that sous vide cooking stuff. I saw something on Hackaday I believe, where someone just put an output socket on the back, and thought it was a brilliant idea. Rather than going for a full custom microcontroller based system, I grabbed an off the shelf PID controller. It's a standard 1/16 DIN unit made by Sestos. Grabbed it off ebay for about $40 including a 25A Solid State Relay, and a thermocouple.

Full parts list:
$40 Sestos PID Controller + 25A SSR + thermocouple
$5 SSR heatsink
$20 Multicomp ABS case
$6 K Type Thermocouple Socket Panel Mount
$3 IEC Socket and Fuses
$7 12V 1A DC psu
$5 dual outlet power socket
$free assorted cable, switches and some fans I had laying around

Works pretty well so far in my testing with a lamp and a lighter on the temp probe  ;)

This is what I plan on mounting in the oven from the back: http://www.goodluckbuy.com/thermocouple-k-type-probe-temperature-sensors-100mml-2m.html with a standard k-type plug on it instead

I might do a fancy microcontroller based system later on. Shouldn't be too hard as the SSR is switched by 5-12V DC, and I already have a 12V DC power source in there.

One thing puzzles me: a PID controller is an analog device, but I don't see where you have analog power control? A relay is a digital on/off device.

Is the PID controller doing PWM on the solid state relay or some such?

Yep, you got it. I recently built a similar set with a very similar controller. Mine has a 50 step sequencer built in so i can do pre-soak and ramp-up to liquidus and then back to room temp all automatically. Works like a charm. Maybe this one has similar stuff. I also built a small circulating fan inside to minimize hot spots.
So, the output of the controller is meant for solid state relay. While the controller does PID, the output is not really pwm, unless you count a very slow one :) They say the controller is a "fuzzy PID" so it "intelligently controls the relay". The shortest on time i have seen is something less than 1 sec. I use a small Toshiba 8 amp device in a TO-something 4 pin package, fixed to a 200 x 200 mm aluminum plate fitted in the original controller space. The normal soldering cycle does not really heat it up, the plate just warmsup enough to notice. So you don't really need an SSR capable of tens of amps. The Toshiba is also zero crossing switching so operation is nice and quiet, no pops or dimming the lights when it switches on and off.

PID controllers are able to drive either an analogue , digital or relay output, depending on the model. Some allow all three as output options, some only one. The better ones have control over the digital outputs so as to handle controls that require specific delay times between operations ( I am using one on an airconditioner so adjusted to give a 5 minute minimum delay on switching, and am using another on a fridge with the same delay) or you can use the SSR output and get a cycle by cycle switching.

Yeah the version I got was the 220V AC input, SSR output version. They come in a variety of versions, and yes, some of the more expensive ones can be configured for different outputs.

There's 12-24V DC/AC versions, as well as output options for a relay, SSR digital out, and 4-20ma current output.

This is the seller I got mine from: eBay auction: #220888955443

I would have liked one of them with the built in set points, but all the ones I could find were 3x the price.


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