Heating Element Starts to Cool Down After Being On for a While

[Alan in Vermont]

I recently bought a used shotmaker, had to find a way to beat the cost of commercial shot. So far I have made somewhere around 100# and am gradually running the ladle(that's what the pan that makes the shot is called) for longer time periods.

The last time I used it, probably 90 mins. into it it started dripping oddly but that apparently isn't unusual for "something" to change and affect the drippers. So I quit and shut down.

Day before yesterday I had it going again I was well into the second catch pan load when it once again started dripping slower and the individual beads were getting bigger. Also the ingots I was adding to the ladle seemed to be taking longer to melt. This happens somewhere around an hour to hour and a half of "ON" time

I dunked my casting thermometer into the ladle and it was under 600° and dropping fast enough to watch the thermometer winding down.

Yesterday I plugged it back in and it went right to heating.

I had the base apart and cleaned/tightened the terminals. The heating element is an open coil, appears to be the same as an older hot plate. The ends of the element are formed into a loop and the leads are bolted to the element with ring terminals.

Tomorrow I will probably open the base up so I can access the leads while it is energized. I have a clamp on multi-meter which can check AC amps. I hope to be able to see if the amp draw is decreasing when it begins to lose heat in the ladle. If it drops to zero draw, or close to it, it is possible the element is broken and separates after it is thoroughly heat soaked. Seems like 60-90 minutes is a long time for that to happen. It also seems like there should be a serious fireball as the current tries to leap across the gap and THAT should blow a visible gap in the coating on the element.

Anyone have any thoughts about this?

[Valornor]

I wonder if there is a thermal breaker that is kicking off if things get to hot inside of the unit.

I agree, 60-90 minutes is a long time for it to be the coil separating due to thermal expansion, you’d think that would happen within 15-20 minutes of heating up.

I have a shot maker that I used a few times but haven’t used it in years. It will be interesting to see what you find.



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[georgerkahn]

My guess would be a thermal switch -- e.g., a "thermostat" -- of which many similar devices as yours have a simple bi-metallic strip with a contacter at its end. As this heats, the expansion of one of the two attached metals by being heated is great enough to cause its bending -- to open closed (continuity) contact. Upon now being open, it then cools, bends back, and restores electrical contact.
I've had many similar units (as an electronic tech for 40+ years) in for repair, and the quick fix is quite simple, this being to clean oxidation/roughness from the wee spark each time contacts open and close where they do open/close. Bion, my "savior" was a points-file from an old Ford Model-? car kit. Also, bion a "file" which works super is running a US dollar bill slowly run through the closed contacts -- it is just rough enough to do the job...
This may not be the challenge you're experiencing, but -- worth perhaps a look? Best wishes in any case!
geo

[bbogue1]

Ever had an electric oven element or burner coil fail? The direction you are heading is the way to go. Since the unit is used visually check the element and all surrounding metal for burn marks indicating arcing. If that doesn't prove successful in locating the problem check the welded connection where the element attaches to the AC power source. I disassembled a microwave yesterday to get the magnets inside. When I opened it up I saw the stainless steel wires providing power to the capacitor had separated. The idea that the bimetal spring in the thermostat is highly suspect since they do wear over time. Just my 2 cents worth. It will be interesting to see the cause, the fix and how well it runs after.

[JonB_in_Glencoe]

What kind of controller? Bimetal strip as some suggest? or something else?
Other things to check
Are the connections like extension cords...are the plug/receptacle areas getting warm or hot?
a poor connection can start acting like a second load, stealing voltage from your heating element.
Fuse? or circuit breaker? at the power source. If it's a circuit breaker, is it getting warm or hot?

[Alan in Vermont]

I was careless, in my original post, and forgot to point out that there is no thermal relief, circuit breaker, fuse, not even a switch anywhere on this device. The power leads are attached directly to the ends of the heating element with small bolts, no welded ends, no plug-in connectors, zilch, nada, zip.

I have no way of knowing who made this. There isn't any identifying marks anywhere on it. Not even a wattage rating for the element. It has been around for a while, judging from the uniform, light, rust on all the mild steel parts. There was a sheaf of papers with it, including drawings for the ladle as well as sales literature from Littleton & Better shotmakers. I'm starting to lean heavily towards this being a homebuilt unit.

[Mike W1]

Just a guess but if it's a fuse or a circuit breaker they aren't likely to fix themselves after a cooling off period I wouldn't think.

Post ahead of me wasn't there when I wrote, and those things don't exist on this unit apparently.

[JonB_in_Glencoe]

So nothing on the unit, Got it.

I'll rephrase the second part of my question.
So what about anything between the unit and your House's power distribution panel?
Are the connections, like extension cords and/or the plug-receptacle area getting warm or hot?
a poor connection inside a plug-receptacle area can start acting like a second load, stealing voltage from your heating element.
Does your power distribution panel have circuit breakers(or fuses?), is the circuit breaker in the power distribution panel getting warm or hot?

[Alan in Vermont]

JonB,

The shop has a sub-panel(breakers) that is fed with, IIRC, #6 conductors about 30 feet from the disconnect, into the shed structure. There is about 15' of 12-2/w Grd from the sub-panel to the outlet box. The whole thing was installed circa 1997. Never a hint of any issues with it. The cord from the outlet to the ladle appears to be 12 ga. SO or similar. Black/white/green wires in a rubber jacket. It doesn't seem to be charred or anything, even right at the element end of the cord.

I have not checked for any hot spots yet. I'm not sure how much can be told that way since the whole thing gets extremely hot once it has been running for a while. There is no insulation around the element, not even a drip shield to bounce heat back up to where it could do some good. I will try shooting it with an IR thermometer the next time I have it heated up. I have some 1" thick high temp insulation left over from building my smelting pot. I would love to insulate around the element so that I'm not wasting so much radiant energy trying to burn the steel bench top into slag. If I do insulate around the element, how much is too much? Seems like I remember reading something about stove burners burning up if there was no breathing room around them.

I will go through and check for hot spots at the wiring connections when I fire it up again.

[3006guns]

Just a thought to narrow this down a bit........

With the unit off and cold, check the resistance of the heating coil with a multimeter ON THE COIL CONNECTIONS and make a note of the ohms. Plug the unit in and wait for it to poop out again. Quickly pull the plug and check the coil again. You will be getting a different reading due to it being hot, BUT if you get NO reading at all, you just found your problem. Or, if the coil still has continuity, you've at least eliminated one possibility.

Something else........AC equipment doesn't really "arc and spark" as much as you might think. Now, if it was a DC circuit, yeah. DC gets upset when it gets "interrupted" since it's trying to flow in one direction. AC tends to not spark as much since the current is changing directions 60 times a second.

[wv109323]

I would clean and retighten the terminals where they bolt onto the element. Heat will cause oxidation and small bolrs can stretch with time. An amp meter around the wires feeding the element
should tell you if it is drwawing current.

[popper]

Calrod are a tungsten wire inside a ceramic/steel tube. They are NOT made to be run full on all the time! The wire will separate when the tube expands and no heat. Cool down and they run again. It needs a temp controller!

[Phlier]

Calrod are a tungsten wire inside a ceramic/steel tube. They are NOT made to be run full on all the time! The wire will separate when the tube expands and no heat. Cool down and they run again. It needs a temp controller!

Would a PID type controller be ok to use with this type of heating element?

[popper]

Yes, would work the best but as I don't do shot drippers I don't know how/where the probe/sensor would be connected to the pot. PID also can have initial over/under shoot temp so you have to wait until that is complete before temp stabilizes. It will prevent the burn out of the cal rod. Sister-in-law had a hot tub that was not temp controlled, she'd turn off the pump and I'd get to replace the cal rods.