DIY temperature controller

Indeed! One of my wife's pet peeves (except ours has OFF, LOW and HIGH ;-)

Provokes the question: Where do you get a probe like comes with my remote meat thermometer? Stainless steel, thus food safe.

...Jim Thompson

Mine new one has three settings, the lowest being, "Keep Warm", which use to really slow cook soup or chili.

Not the Salmonella setting, I hope

martin

Simpler to use a lamp dimmer, open-loop, or even one of those series diode things.

John

No, I've been using it close to a year that way. The food is definitely hot enough when you serve it, but it loses less water while cooking. I takes a couple hours to cook a pot of chili, and I have cooked it as long as eight hours on an electric stove in the past.

I made a slow cooker from a deep electric saucepan a zillion years ago. I used a 72mm x 72mm industrial thermocouple-input controller with a power relay and hid the type J thermocouple inside the prod that used to hold the bimetal thingie. Worked *very* well for stews and such like. Time proportioning with about a 20-second cycle.

It's easy enough to get 3/16" SS thermocouple probes, but I'm not sure you want the probe in your food, just from a convenience POV. It's certainly not necessary from a control POV if the cooking pot is a good quality heavy one.

This one had the original bimetal control in a bakelite plug thingie that unplugged so you could wash the pan without the cord and control. They may not make them that way anymore, I don't know, all our pots are range top type these days.

Best regards, Spehro Pefhany

Farnell have three pages of LabFacility tnermocouple probes, mostly in stainless steel sheaths. For better temperature stability, there's a a page of stainless steel sheathed platinum resistance sensors (again from LabFacility) a couple of pages furhtr on.

snipped-for-privacy@gmail.com scrobe on the papyrus:

Maxim/Dallas have a whole range of parts. Start with the DS1626 standalone thermostat, or for better resolution use the MAX6674 or MAX6675 thermocouple amplifiers with cold junction compensation and an SPI interface.

One concern is that you don't convert a slow cooker to a bacteria incubator.

John

It too long ago to remember the details, but I definitely did consider that danger. IIRC, there's a large margin for error between a good slow-cooking temperature and minimum safe storage temperature*. Of course this was a properly calibrated instrument that we made in volume, and with a one-off homebrew assembly everything, including calibration of the instrument, would be suspect. The sensor will be fine in any case, a thermocouple is perfect for this application (except perhaps system cost for a mass-produced product).

The production of steam at, say, 170ºF is *way* less than near to boiling.

Hm.. I wonder if everyone started to do this if new bacteria would pop up that could live at relatively high temperatures. Temperatures well inside the 'danger zone' are used in some commercial meat cooking, but they heat it up high enough later on to kill whatever has been incubating away.

Aside: I wonder how I managed to look up that kind of stuff before the internet. Library?

Best regards, Spehro Pefhany

I've a very nice Fluke k-type probe, stainless with a very pointy end. Doesn't have a part number on it anywhere.

But why not use one of the Dallas single chip sensors (DS1620)? They even have programmable setpoints and an alarm output, so you can set your own hysteresis points. -55 to +125C.

Take a look at some of the articles at

Cheers!!!

Conceptually: use the resistance of the thermistor to replace (or modify) the resistance of the pot in a lamp dimmer. The dimmer is already set up for line voltage. But (there's always a "but") you need to be sure the wattage of the crock pot is within the rating of the dimmer.

With the warnings others have given you might be better off buying one that has a temperature control built in.

Ed

Do not bother - when i was distillin ..... err ... experimenting with an environmentally sound disposal method for failed wine productions I used a thermostat from a scrapped washing machine. Which worked fine.

One of the mechanical types with a capillary tube and all. That particular device had contacts rated for the load so it was self-containen and also accurate to within 2 deg. C (Good I.M.O.).

A spare thermostat for an oven or washing machine will be easy to get. Much easier than designing one.

I just posted about a analog controller. I need noise free DC opperation.

I would suggest buying this unless you really want to fool around. The cheapest unit I have found, and the price just went up $5, is

greg

Others have offered suggestions for sensing temperature, so I won't.

As for switching AC, I suggest you consider a solid state relay (SSR). They are dead simple to use, controlled by a low voltage and low current signal, and in an easy-to-integrate package. A SSR that can switch 25A costs .... $15 or so? I'm not sure about price because I bought three 25-ampers 15 years ago, put only one into a project (cycling a 1500 watt space heater), and that one is still working just fine.

With an SSR, you need a heatsink capable of keeping the SSR mounting plate temperature at a reasonable temperature while dissipating about

BTW, especially with SSRs, but in any case, you should make sure that any safety cutoffs are not bypassed or eliminated-- especially if this thing is to operate unattended. SSRs generally fail 'on', and even relays have been known to do so on occasion. Solid state control circuits can fail or latch up too (eg. soft failures of microcontroller systems).

Best regards, Spehro Pefhany

Cheers! Rich

No problem - make yogurt! That's just big lumps of rot, after all, isn't it?

Thanks! Rich