The Shop > Metal Stuff
I bought another deader
John Rudd:
Given the short dv/dt, I’d be surprised it uses a 3 term unit….PI would suffice if really needed….
ddmckee54:
I's definitely got a controller in it. It's one of those Chinese $10 specials. There's not much on the label that I can see and all the controls of this thing will be replaced anyway. It's only got a single set-point in the controller, and the heat is only wide open throttle all the way.
Anyhewwwww... I got as many of the dribbles as I could get cleaned up and started checking things out electrically. Everything checked out to be OK. At least as OK as I could guesstimate with almost less than no information. There was nothing left to do but give it the juice and see what happens. I made sure the switch was off, plugged it in, turned my back, and threw the switch.
This is what happened, just ignore the messy bench:
IT'S ALIVE???...
It was actually rather boring, no boom, no cloud of magic smoke, just the power switch and controller coming to life - just the way electrical startups are supposed to go. But I DO know that this thing's got a mechanical relay for the power contactor to the heating coil - I can hear it click on and off when I cycle the power to the furnace.
This is the mystery metal that I removed from the beast.
The piece in the front was chipped out from the bottom of the furnace itself. The rest were removed either from the base of the furnace or from between the bottom of the furnace and the base of the furnace. (There's an air gap there.)
I did let it start to heat, and the temperature DID start to rise, so I'm pretty sure the heating coil is still functional. There appears to be a factory defect in the ceramic heating chamber liner, probably good enough? Time will tell. It was late when I got to this point so I only let the temperature come up a couple of degrees before I shut it off.
The controller's set-point was 1150 degrees C, which is right around the melting point of silver, so I'm thinking the mystery metal MIGHT be silver?
Tonight I'm going to figure out how to change the set-point of the controller, drop that to about 300 degrees, and let the beast heat to temperature - see how long it takes. It seemed like it took FOREVER for the temperature to change those three degrees, actually it was only about 10 minutes. Ten minutes probably wasn't that bad considering that there's the ceramic heating chamber liner and a steel tube sheath between the heating element and the thermocouple. I let it heat 3 degrees just to be sure I wasn't just seeing the temperature flicker from the 25 to 26 degrees it was claiming as the ambient temperature. My basement is NOT that warm so I know it was lying about that, probably the cold-junction compensation I was talking about. Doesn't matter, for this purpose it's close enough.
Don
tom osselton:
If it stamped “Hi Yo “ it’s silver.
ddmckee54:
There was no "Hi Yo", but the the pieces did say "neigh" to being easily rounded up and herded away.
Over the weekend I figured out how to change the change the controller's set-point. I dropped the set point to 300 degrees, checked the time, then went away for a while so I wouldn't be tempted to stand there watching the process variable display change. I wanted to see how much the temperature would change in 30 minutes. The answer to that was Nadda, Zip, Zilch and Bupkiss. Alas, there was no joy in Muddville.
I tore the thing apart - again, and did a little trouble-shooting. I could hear the relay pulling in after the controller booted up, so I knew that it was at least trying to work. I checked the voltage across the heating coil, that was 120V so I knew the relay contacts were at least sorta good. When I tried to measure the resistance of the heating coil I got NUTHIN' this time, it was an open circuit. That 3 degree temperature rise that I saw last week was probably the last gasp of the heating coil.
I've got a new coil on order. It's going to to be taking a Slow Boat from China, supposedly it will be here about 2-4 weeks from now.
tom osselton:
Just wondering what the thickness of the wire is I’ve got some nicrome wire here that I’ve been wondering if I could try making one although I’ll probably just buy one.
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