Electric Melter

[Steve Beckwith]

With the assistance of Scott Duhahee I built a furnace that is very similar to the one he uses at Radiant Glass. It incorporates an EC 75# free standing crucible with 9 side fired elements installed in 2600 ifb from Harbesen Walker. The ifb is backed up with 8" of what I believe to be 2300 deg. frax, the lions share came from my old Denver furnace and the balance was a gift from a friend. The problem I am having is that as I brought the temperature up it was going smoothly to 2000 deg. but when I attempted to go up to 2150, it tripped the breaker at somewhere around 2100. I flipped the breaker back on and it stayed on and the controller was calling for power but the furnace would not respond. I thought that I had probably had an element slip off its shelf and short out with another one. I turned off the power and checked the continuity of all of the elements. I disconnected all of the elements from each other and from the power supply and tested with an ohm meter. The only setting on my tester was OHM X1K. At this setting, all 9 elements tested out at 0 ohm, but when I tested any element lead against any other element lead i was getting about 2 ohm. At 1100 deg, the resistance had increased to about 10 ohm, at 850 the meter barely moved at all, if at all. At room temp, there is no reaction on the meter at all. I have visually inspected the elements and they all look fine. I think that all of my controls are ok because I am getting power to the leads that connect to my elements. I have all of the element tails firmly packed in frax and they pass through mulite tubes installed in an aluminum plate to the exterior of the furnace. I am stumped. The only possibility that I can come up with is either the brick or the frax is conductive at 2100 deg. Is this possible? Also, my crucible is now loaded with about 60# of half melted batch. Will it survive a trip back up to working temp? I realize that I am not able to talk electricity that well but I hope you all understand. I don't mind saying that I am really bummed about this and I really need some assistance. Thanks in advance, Steve B

[Scott Dunahee]

What size wire are you running to the furnace? How far is it from the main panel? How many amps is the breaker? You said the breaker was an old one. Is it that same wire and breaker you used to run your Denver on? The wire may be old from that use and if it was close to the amp rating to begin, resistance in your feed circuit may have bumped the amps enough to trip the breaker. The breaker may also be bad. The wire connections into the breaker may be loose resulting in an increase in resistance and a trip.

Everything in your furnace is conductive at furnace temps.

I'd start by checking your feed stuff. Also, it'd be good to know the resistance of the individual elements when you get a better meter. Get one with a clamp on amp meter. It's awesome for checking the furnace draw and which bank has gone out while hot.

I think your furnace is fine and the problem is on your supply side. Without more testing numbers, I am not certain.

BSD

[F Thumb]

What are you using for a controller? Are you using an SCR, or a SSR? Bobby pin and tin foil?

How far is it from the main panel?

LOL! I burnt out my first two control panels this way.

"Am I far enough away yet?" Doh!

:thumb:

[Steve Beckwith]

I am using a new 75 amp ssr, the breaker is a 60 amp GE, approx. 9-10 ft. of 8 ga. copper wire to a receptacle, 9 ft. of 6 ga. copper to the controller. The 8 ga. is original, the 6 ga. is new. This circuit ran an EF240 Denver furnace drawing about 45 amps for 7 years. Maybe the problem is on the supply side but I just don't understand how I get such good (not 100%) continuity from element to element at 2000 deg when they are completely disconnected from each other. Maybe this is normal. Is it? Maybe it's a demon in the wires. Maybe it's the ghost of Denver Glass coming back to haunt me. I used some steel and frax from the old Denver in this build. While I don't consider myself to be superstitious it has come to mind that I might be dragging some of the old Denver Ju Ju along to the new machine. Thanks for the response, Steve B

[Brian Gingras]

what is the "theoretical" draw(amps) of this new furnace?

[Scott Dunahee]

It is (9) 5 ohm elements wired as 3 parallel banks of 3 elements in series. It should draw 48 amps when the elements are new.

The elements are Kanthal A1 and I've wound and used 4 sets off that spool with no unexpected problems.

I'm only thinking it's something in the supply wiring because he had it hot for almost a week and it was working fine until he went to cook his batch. It's a big, constant draw to get wire melters up to temp with a pot full of glass. And that's when he threw a breaker.

I've never had my furnace trip my breaker but I would think that it was a short, increasing the amperage or it was riding close to the amperage limit and getting hot when it went full bore for a while.

I'm just guessing until we have numbers from a better meter. How did the copper look in your element hookup area? Was it discolored or crispy at all?

BSD

[Steve Beckwith]

I need to add a correction here. From the breaker to the receptacle it is about 14 Ft using #8 copper wire. Also, I have used the same #8 wire to run from my mdr to the elements. I did notice that as the ssr kicked on that the breaker would hum loudly enough that I could hear it from 4-5 ft if the room was quiet. Also, I had it at 2000 for two days before attempting to run up to 2150. That is when this problem occurred. All of the copper looks ok where each one connects to the element tail. I have not examined the connection where I brought the power to the rear of the furnace and then split each one into three to connect to the separate banks of coils. Thanks again to all for responding. S

[Brian Gingras]

replace the breaker, and put a clamp on amp meter on the line while running and check the actual draw.

[Steve Beckwith]

At this point with other obligations today I will have to postpone reassembling everything until tomorrow. I made a run to Home Depot and for the paltry sum of 140 bucks walked out of there with a new breaker, 6 ga wire and a new clamp on amp meter. I have replaced the wire from the panel to the receptacle with the 6 ga and installed the new breaker. As soon as I can put everything back together I will let 'er rip at about 20 deg/hr because of the full pot. The nagging question that I still have is the conductivity between the elements at 200 deg. even when they were completely disconnected from one another. I understand that heat makes some things conduct electricity that would not conduct if they were cold but in this case, is it normal? Apparently, I am just going to have to run it up again and see if the same problem happens again. S

[Brian Gingras]

200 degrees should not be enough to make the refractory conductive. Are you 100% certain that everything is wired right? How are you grounded? you made sure no pigtails are touching anything at all?

I had my furnace blow the breaker 3 months ago. It was becuase I had 2 low resistance elements that at 1200 sent it over 80amps when it's normally 65 amps. It took me a while to track that issue down with the furnace hot.

[Paul Thompson]

Originally posted by Scott Dunahee
{snip snip}
Everything in your furnace is conductive at furnace temps. How conductive? I'm guessing (hoping, actually) that refractory matls (the IFB?) aren't going to get down to 5 ohms. Now that those materials are conducting, will there be any kind of electrolysis effect between the coils and the IFB, or is that one of those "you've got other things to worry about" diversions?

[Pete VanderLaan]

Steve, the pot should be OK but go at 30F per hour and go thru quartz inversion very slowly. From 1000F to 1100 F, take six or seven hours. Once its glowing , just bring it up.

[Steve Beckwith]

[QUOTE]Originally posted by Brian Gingras
[B]200 degrees should not be enough to make the refractory conductive.

OOPS! I missed a zero there...it is 2000 degrees. So much for proof reading. Regarding the conductivity of the elements, I was using a POS $15 meter to check the continuity of the elements which it does just fine but I definitely had some strong readings between any and all of the disconnected elements. I just purchased a true RMS meter today so I will be able to talk amps and ohms a LITTLE more professionally (I hope) the next time this happens. Or...maybe I am just smokin' rope and what is happening is no big thing and I am making more out of it than it really is. I can connect various electric components together successfully as if it were a kit and do OK but I am not knowledgeable enough as of yet to trouble shoot these things. Thanx to all again for the input. This is really a great forum! Steve B

[Brian Gingras]

are you using low iron brick?

Considering I've actually seen iron stain on IFB before that MAY be the issue, it could be actually shorting across the elements at 2000

I'd still change out the breaker as well.

[F Thumb]

Does the controller have an output limit function? I use 12 - 5.5 ohm elements (three elements in series, four groups in parallel) and have my power limited to 50% maximum output.

:thumb:

[Steve Beckwith]

I don't know if the brick is low iron or not. I explained exactly what I was building to the person I spoke with at Harbesen Walker and this is what they quoted and sent. The invoice is back at my retail space, I will check it tomorrow. As far as the output limit, I don't know. I am using a Fuji PXR4. I am still learning this thing but I have enough of a drift of it to program a ramp and soak cycle but that is about it. The only thing that I can really do now is fire it back up and see of the problem reappears. Unfortunately, I have shows the next two weekends and I want to be around as the furnace comes up to temperature so I probably will not even start to heat it up until after Thanksgiving.