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I bought another deader

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I recently scored my second non-working electric jewelry furnace.  My first was brand new, but had a factory FU.  Imagine that, a cheap Chinese knock-off that doesn't work.  That one was an easy fix, it had a solid state relay that had the 2 input wires to the relay reversed.  Polarity does matter in DC electronics.  This is my second one.

I haven't opened the second one up yet to see what's wrong, but there's not much on the inside of one of these things.  This thing useta work, you can tell it HAS been used.  I'm suspecting a bum power switch, but I'll know for sure when I crack it open. 

I don't plan on using most of the electrical guts of this thing anyway.  The plan is to modify this guy and turn him into a flask burn-out oven for lost wax or lost PLA investment casting.

I like radio control, and I'm especially interested in RC construction type stuff.  I've been building a stash of Bruder construction equipment that I plan on converting to RC.  I'm planning on casting some parts out of ZAMAC to get some extra weight.  I can make flasks that will work with these small electric furnaces, especially if I can get this latest deader working and modified the way I can see it in my head.


I cracked it open.  I'm still not sure what the problem is - but I'm pretty sure I know what caused it.  I believe that the previous owner had a crucible failure.  I've got metal dribbling down into the guts of the furnace. 

I don't see any obvious electrical arcing, so whatever happened probably wasn't a short circuit.  The plastic around one of the spade lugs on the 120V power socket appears to be melted, and the crimp-on wire terminal for that same spade lug seems to be welded to the lug.  There's enough connections into whatever it is that controls the power to the heating coil that I'm pretty sure they used a mechanical relay instead of a solid state relay - but there's no numbers on any of the sides I can see.

I got a little deeper into the guts of the beast last night.  I've got to remember to take some pictures tonight, after all...  Without pictures, it didn't happen.

I did discover that other than "120V AC"  and the terminal numbers, there is NOTHING written anywhere on what I'm assuming is the power contactor for the heating coils.  The power goes from the switch, through the "contactor", then to the heating coil/s.  The PID switches a normally open contact to turn on/off the heating "contactor" coil.  If the "contactor" had screw terminals and/or a heat-sink I might think it's a solid state relay, but this guy has all spade lugs and no heat-sink, so I/m leaning towards it being a mechanical relay.  The PID controller must have quite the dead-band to keep that contactor from banging on and off all the time once the temperature reaches its' set-point.  Or maybe it does bang on and off, until I get this thing turned on I won't know.

That 120V power socket wire terminal that I thought was welded to the socket's spade lug definitely is welded on.  I tried moving it from several different angles with different tools and no-go.  I've got to remember to take my meter back down to the shop tonight so I can determine is it's safe to plug this thing in, or if all the magic smoke has already been let out.  I'm not smelling the typical fried electrical parts smell, so I've still got some hope.


I forgot to say that the PID connections LOOK like there's a dry contact in the PID that will turn the relay on and off.  The PID says it's 120V, and that matches where those wires go on both ends.  I've got 2 wires that go from the PID to the relay.  If the label on the PID is to be believed they are going to a normally closed contact in the PID.  The other 2 wires from the PID go to the thermocouple.  Those are NOT thermocouple wire, so unless this $10 Chinese PID has built in cold-junction compensation my temperature won't be accurate - there'll be an offset.  But in the hotternhell temperature range required to melt gold and silver, that offset can probably be ignored.

I'm surprised it uses a pid controller. A simple thermostat would probably suffice for most casting operations surely?

In fact if only uses a contactor or mechanical relay, it is unlikely to be PID


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