Induction furnace ratings

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JohnR
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Induction furnace ratings

Post by JohnR » Fri Aug 19, 2022 8:30 am

I am curious about some of the power supplies listed on ebay.
Is there a site where one can go to get information about
requirements such as frequency for various metals?
Also power requirements that can be rated to weight of metals
to be melted .

Thank you

Harold_V
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Re: Induction furnace ratings

Post by Harold_V » Fri Aug 19, 2022 3:14 pm

I don't know that this will answer your questions, but it may help.
page 3 cropped.jpg
Frequency is more dependent on furnace size than the type of metal to be melted. Large furnaces may operate at line frequency, while smaller furnaces require higher frequencies.

The size of the material making up the charge makes a difference, too. If you try to melt chips, for example, higher frequency is required than for melting a solid object of the same mass.

I own a 50kw Ajax Magnethermic induction furnace and power supply. It's a second generation machine (motor generator, not solid state). It operates on three phase power, demanding a 400 amp 240 volt service.. It draws about 190 amps at full output, which is single phase 400 volts @ 3,000 Hz. With it I can melt 70 pounds of steel (or iron) in less than an hour.

H
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rrnut-2
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Re: Induction furnace ratings

Post by rrnut-2 » Sat Aug 20, 2022 9:24 am

Generally, the smaller the furnace and power supply, the higher the frequency. Our "little" 175kw unit operated at 3khz, while the 900kw unit operated at 500Hz. The larger furnaces get closer to line frequency.

Jim B

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JohnR
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Re: Induction furnace ratings

Post by JohnR » Wed Aug 24, 2022 8:32 am

Thank you for all your responses and information .
I know I will have a few questions in the near future.

JohnR

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Re: Induction furnace ratings

Post by JohnR » Wed Aug 31, 2022 11:21 am

Harold
Any chance I could get a copy of the schematic for your unit.
I am investigating going your way with a diesel generator and a used motor generator similar
to your system (german made) but also is water cooled.
I have 480 v 3 phase available but would prefer to keep separate.
Thank you
John

Harold_V
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Re: Induction furnace ratings

Post by Harold_V » Wed Aug 31, 2022 3:50 pm

JohnR wrote:
Wed Aug 31, 2022 11:21 am
Any chance I could get a copy of the schematic for your unit.
It may be possible, but it would not be inexpensive. The schematic I was provided is printed on two sheets, each of which is a D size. They are difficult to read, having been printed from what I suspect is Microfiche. I could have them scanned and printed, but I live 25 miles from the nearest possible source. I drive there only irregularly (often only once per month).
That said, I don't know that the information contained would be of much value to you unless you shared the same motor generator and control system. Much of it is unique to the particular application, which most likely would not be the same as yours, although it may be similar. I should also note that there's two sets. One of them is the schematic, while the other is the mechanical layout, which aids in finding the components. It is an overwhelmingly complex piece of equipment that weighs three tons.
I am investigating going your way with a diesel generator and a used motor generator similar
to your system (german made)
I, too, investigated that option. I could have acquired a 150 kw generator for a reasonable price, but it was obvious to me that operating the generator would be cost prohibitive. And, to add insult to injury, my experience in operating mine suggests that a 150kw generator may not produce enough amperage to start mine (*I'll address that below). Specifications for the 150kw generator suggested 9 gallons/hour for fuel at rated output. With diesel at over $5 per gallon, that would have been prohibitive, especially when I consider that if I keep the output of the power supply at 40kw, I don't experience a demand charge. It makes little difference in the speed of melting, as the furnace can't achieve full power until the charge is mostly fluid. I pay just over 6¢/kwh for power, so the actual cost for melting a charge is in the vicinity of $3. A far cry from the predicted $45. My recommendation to you is to try to operate any equipment from the local power source.

*Startup current, unless the power supply you have in mind has soft start, is huge. Mine draws just over 1,500 amps upon startup, and it does so for almost six seconds (metered by the provider). I have knocked out the fuses on the primary side more than once during startup.

It was not inexpensive getting three phase to my property, but I have several three phase machines and did not want to attempt to operate all of them with rotary phase converters. The size of the service for the induction furnace alone would have made that totally impractical, to say nothing of the cost of acquiring a rotary large enough to operate the motor/generator (approximately 75 hp).

Industry commonly has a backup power system for induction heating, as power loss while the furnace is in operation would lead to the destruction of the furnace, and could also damage the power supply. I live on the dangerous side, as I do not have that backup.
but also is water cooled.
I am unaware of any induction heating systems that are not. Everything in my system is water cooled, including leads, buss bars, capacitors and the high frequency transformer. If the furnace isn't water cooled, it would self destruct almost instantly, as the coil is made of copper.
I have 480 v 3 phase available but would prefer to keep separate.
It's not clear to me what you mean. If you have that service at your disposal, assuming the motor/generator in question will operate properly, that would certainly be in your best interest, due in part to the high current demand when starting. That, of course, depends on if the unit in question has soft start, or not. Mine does not. It also won't operate on 480, as it is designed around 208 volts. It operates acceptably on the 240 volts it is fed.

There's a lot of obstacles to overcome when melting this way. One of them is in transferring the molten metal to the ladle and being able to pour before it has cooled too much. The small volume we deal with makes that difficult. I have yet to overcome the problem, although I have made significant changes. When the weather cools, I'll try again to see if I was successful.

Let me know if you still want copies, and of what. We can work out the details if you really think acquiring them would be of benefit. No guarantee that they will be legible. Mine barely are.
H
Wise people talk because they have something to say. Fools talk because they have to say something.

rrnut-2
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Re: Induction furnace ratings

Post by rrnut-2 » Thu Sep 01, 2022 5:36 am

You will definitely want a back up power source for cooling water for the furnace. A furnace melt down can be very exciting! And yes, Harold is taking a chance without have a backup. The power supply usually doesn't need the backup.

You would be better off trying to find a solid state power supply. I don't have any schematics, but I do have a control board and some parts for a 175Kw unit.

Jim B

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pat1027
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Re: Induction furnace ratings

Post by pat1027 » Tue Sep 06, 2022 9:53 am

If you are on a municipal water service, emergency water can a circuit tied to the municipal source. Of the 8000kw furnaces we installed all but one use the local utility as the emergency water source. The other was well water with a backup generator.

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