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208 V single phase?

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T. J.

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#1
I recently acquired a muffle furnace in an auction. The nameplate specifies 208 volt single phase input. Am I going to fry it if I use standard 240 volt input? If so, is there an economical way to convert 240v to 208v?

IMG_0553.JPG IMG_0550.JPG
 

ttabbal

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#2
Most US homes have 220V. I'd bet it would be fine. You could use a suitably rated variac to adjust the voltage.
 

jim18655

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#3
Buck transformer if you're worried. It will make more heat on the higher voltage.
 

aliva

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#4
If you use 220v your current ( amps ) will drop a bit. I wouldn't worry about it
 

higgite

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#5
If you use 220v your current ( amps ) will drop a bit. I wouldn't worry about it
If it is a resistance heater, which it appears to be, the amps will not drop, they will go up by the ratio of the voltages. And the heat output will go up by the ratio of the voltages squared. So, as someone said earlier, yes you will get more heat, but for how long before burning out the elements is anyone's guess. The manufacturer can probably answer your questions without guessing. ;)
Thermofisher Scientific 1-866-984-3766

Tom
 
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Smithdoor

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#7
This was used were three phase Y only using 2 of 3 wires
Safe is to use a buck and boost transformer some time it can be wire for 240v but not label

Dave

I recently acquired a muffle furnace in an auction. The nameplate specifies 208 volt single phase input. Am I going to fry it if I use standard 240 volt input? If so, is there an economical way to convert 240v to 208v?

View attachment 272442 View attachment 272441
Sent from my SAMSUNG-SM-J320A using Tapatalk
 

T. J.

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#9
Thanks for the replies. After a brief examination, it looks like 2 of the 4 heating elements are probably shot (no continuity). I may just the replace them with elements made for the higher voltage. More disassembly and research are in order...:cool:
 

Bi11Hudson

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#10
Running it on 220-240 will not hurt it, short term. But long term, you will be looking for the heating elements to fail faster. A buck-boost arrangement to pull 240 down to 208 is the simplest solution. Since a buck situation is involved, the KVA rating will only involve the difference of each leg. Thereby saving you a few bux. But, there must be an old timey electrician doing the hook-up. The transformer will have eight leads. Find someone that knows transformers. A "bulb snatcher" won't cut it.

Some folks will comment you need a variac or some such. While a variac will work, and work well, the cost of one big enough to meet your needs will drive you to setting up bank jobs instead of machining.
 

Logan 400

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#11
If you change the heat strips to 240 volt like you mentioned above be sure to check the control transformer. You may be able to simply change the line supply connection to 240 volt. Depends on what transformer was used.
Jay
 

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RJSakowski

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#13
You only need a 7.5 kva since the transformer only carries part of the load. Still about $125.
The muffle furnace is rated at 3.8 kva. I calculated the power requirement for a bucking transformer from the bucking voltage x the rated current draw; 32 volts x 28 amps = 896 watts.
 

Bi11Hudson

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#15
I'm a little more awake now. And I know I ain't supposed to do this .... Go to www.hudsontelcom.com There will be a link to an article on "Home Shop Electrics" that will contain the diagrams / schematics for a buck-boost transformer.

This article will be for boosting 208 volts to 240. The same connections will be used, but the connections will be on the inside rather than the outside. The article is long, nearly fifty pages. Look toward the back end for buck-boost usage.

Correction: It is a little over half way in.

I realize I'm being a little cryptic here, I apologize. The article was written over 15 years ago and I've had a few strokes since. I would trust the article more than I would trust me now.

Bill Hudson​
 
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RJSakowski

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#16
Firstly, the nameplate shows an operating voltage of 208 and a current of 28 amps. This would calculate to 5700 watts. The nameplate also states 3800 watts. Looking at ThermoFisher specifications for current products, it appear that the 5700 watt rating would be correct. I thought at first that the current rating may have been maximum inrush current but most of the common resistance heating alloys have resistance increases of less than 10% at 1200ºC. I would assume that the current specification was the correct value unless additional information proved otherwise.

My idea was to have a separate 32 volt transformer running from the 240 volt line and wired in series with the muffle furnace so the 32 volts was out of phase with the 240 volt line voltage. According to Schneider's selection guide, their transformers are rated as isolation transformers and a transformer operating in buck/boost mode can service a load of 7.5 times the name plate rating (240/32, in this case). A 1 kva 240/32 volt transformer should do the job.
https://www.schneider-electric.us/en/faqs/FA91925/
http://download.schneider-electric....1570.78723956.1532274532-224319235.1532274532
 

mksj

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#17
The heating elements voltage is specific to the model, so the 1738 is the 208V version and the 1740 is the 240V single phase version. They both have the same oven dimensions, but the replacement heating elements are different. The elements are in series, so when one fails the other will not function. The 1738 takes two pairs of EL9X5/EL9X4 elements the 1740 takes two pairs of EL9X3/EL9X4 elements, top and bottom elements and a pair of side elements. What may be the overriding factor is the replacement cost of the elements range between ~400-800 each. So at a minimum if you were to replace all 4 elements to 240V type, you are looking at ~$2000 to replace 4 elements for 240V operation.
Models and specifications:
https://store.clarksonlab.com/FA1738.aspx
 

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T. J.

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#19
I haven't had time to digest all of the good info y'all are providing this morning, but I have tinkered with the furnace some.

I started by sanding the oxidation off of the heating element leads and rechecking them. It turns out that only one is bad. The other three all have a resistance of 7.8 - 7.9 ohms. The bad one is melted in two where the lead comes thru the firebrick at back of the furnace. I'm going to pull it out and see if it's possible to repair it. I've read that it's possible to solder this type of wire with special flux and solder. I'm asssuming this is Kanthal wire.

The reason why the replacement elements are so expensive is that they are embedded in a thin refractory brick. So they are not directly exposed to the interior of the heating chamber. If replacement is necessary, I think I will try using an inexpensive "regular" element. I would just need to find a way to support it.
 

T. J.

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#20
Here's the inside of the furnace. The bad element is on the left.
IMG_0555.JPG

I just got it pulled out. This is a pic of the back side.
IMG_0556.JPG

I checked the element and the portion embedded in the brick seems good. I just need to attach enough wire to the broken lead to reach all the way through the back of the furnace.
 

higgite

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#21
A 32 volt bucking capable of carrying 28 amps will be around 900 watts. A substantial transformer. New cost would be close to $200.
http://www.newark.com/hammond/1182u30/transformer-toroid-60v-1kva/dp/54X7560
You only need a 7.5 kva since the transformer only carries part of the load. Still about $125.
The muffle furnace is rated at 3.8 kva. I calculated the power requirement for a bucking transformer from the bucking voltage x the rated current draw; 32 volts x 28 amps = 896 watts.
If you check out the transformer recommended by the calculator (1S46F), you'll find that it is a 1 KVA transformer capable of bucking or boosting a 7.5 KVA load. It is not a 7.5 KVA tranformer. RJS's calculation is correct. A 1 KVA buck/boost transformer will handle the OP's application.

Tom
 

jim18655

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#23
My mistake for using the calculator. I misread the size from the actual load listed on the first page instead of looking at the specs on the transformer. I haven't done these calculations in about 7 or 8 years.
Proves the old saying "All of us are smarter than one of us."
 

higgite

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.......... Proves the old saying "All of us are smarter than one of us."
Or "Two heads are better than one." ....... especially when you're taking about draught beer. :beer mugs:
 

higgite

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