Heat treat oven

[Bob D.]

Those connectors are typically used at the probe for a process tank but not at the instrument itself. Have never seen them used on ovens or furnaces. Also used often to monitor test loads in furnace surveys for the temporary wiring.

Bob D.

[Steggy]

Nice score, a Variac is a brand name for a rheostat...

Actually, Variac® is a brand name for a variable autotransformer, not a rheostat. A rheostat is a variable resistance of the same general type as a potentiometer.

[stephenc]

So... plugged it in and no heat .

I'm open to suggestions except any that require spending more then a couple bucks .
Right now my fun fund is dedicated towards a milling machine .

After dinner I'll try my luck at getting some decent pictures of the controllers guts .

[Bob D.]

Steve
Without the T-couple connected the controller will not turn on the power relay. This is a failsafe for T-couple failure so the oven doesn't run away. Need a pic to help you out.......
Bob

[Bentworker]

Variac = variable autotransformer... Check

Glad to see the horse did not survive.

There are some neat programmable controllers with solid state switching that can be had pretty cheap on eBay. They are mystery import in origin. The nice thing about them is some are fancy enough that you can program a stepped heat cycle. I have one on a $30 Craigslist kiln and it comes in handy.

Measure the resistance on the heater coil, if it isn't open you can start tinkering with the existing controller or just go and swap it out. Wild guess on the coil is it will be 5-10 ohms.

Also that Variac is a handy tool. That plus a rectifier can make for a handy D.C. source for parts cleaning with washing soda. Also great for making a pickle light.

[stephenc]

Sorry it took so long to get back here , I got caught up in some woman drama .

Anyhoo .. maybe these pics will help . On the second pic you will see the red and yellow wires of the temperature probe .
I tried them there simply because they was the only two lose screws .. great logic lol
But alas it didn't work .
I went to check resistance on the heater coil and learned that my meter has a blown fuse so no help there until I get to town tomarow

[John Hasler]

You've got the thermocouple in the right place. That jumper doesn't look right, though. Where does the wire coming off the upper right terminal go? It isn't factory. The splice near the relay is proof that someone has hacked the thing up.

[Bob D.]

Steve,
From what I can see things are wired ok. Can't confirm the common connection to the relay though. That relay was added by someone. It looks like a Dayton 10 or 20 amp double pole power relay. Not sure it is rated for resistive loads though.
Leave the elements unplugged. With the controller plugged in try moving the set needle below and above the thin temperature indicating needle. Does the relay click in and the indicater come on? Looks like one lamp is for power to the controller and the other is for heat on. Did you try heating the T-couple tip with a match or lighter to see if the needle went up? Who knows, the controller output may be toast and they used it for temperature reading only and were using the variac to limit the elements to a desired temp. That would take some trial and error and limit how fast of a heat up you get.
The 3 connections where it says load, the center C is common,(bare jumper for hot) is ok. The wire looks to be connected to the N/C, normally closed. Thats wrong, it should be on the N/O, normally open.

Bob

[John Hasler]

Is that the tip of the thermocouple in the photo of the meter?

[rrnut-2]

This is a block diagram of what you should have to control the oven. This does not include the safety circuit which will shut down the oven
in case of overtemp.

[Bob D.]

The pic showing the meter and T couple is so fuzzy....... if the tip is seperated it won't work. Should be a little ball where the legs are fused together. You can use a torch and fuse them back together. The two legs are different materials. The fused junction creates a millivolt generator when heated.

Bob

[SteveM]

The pic showing the meter and T couple is so fuzzy....... if the tip is seperated it won't work. Should be a little ball where the legs are fused together. You can use a torch and fuse them back together.

I don't think they need to be fused.

I have a pyrometer that uses type K thermocouples and I made a new probe by just twisting the wires together. They are pretty stiff and have held together for 20 years.

That may differ by thermocouple.

Also, the connectors have "polarity". I say that in quotes as it is less a plus/minus thing than a material thing. The parts on each side of the connector are materials that match the different materials in the wires. If you introduce a different metal-to-metal junction in the path, you have another thermocouple (a thermocouple is just two different materials joined together).

For a type K thermocouple, the materials are Nickel-Chromium and Nickel-Alumel.

Steve