Induction Furnaces and Phase Converters - Okay? Or not okay?

Researching purchase of an induction furnace and the question occurs to me that if we choose one of the larger units that runs from 3 phase, will there be any issue running it from RPC generated power? Native 3 phase is not available here right now, and we are moving soon anyway. New shop will most likely have 3 phase, but even if it doesn't, I'd like to know if this is an issue for our current situation.

Thanks.

"Induction furnace" is not just one thing..... It will depend somewhat on what is actually done with the power coming in. is it used directly (not likely for anything small), is it rectified, does it drive a motor -generator, etc. What kind of converter is intended? And, what is "large"? Then there is whether you mean an induction "furnace" or heater. The "furnace" is usually used for melting metal, the "heater" for heat treating.

First issue is the size/power. A large induction furnace would need a big converter. The cost would be substantial if large is in the couple hundred kW area or larger.

If a converter can provide the power needed, and the output waveform and voltage are adequate, it should work fine, the setup just might be large and expensive.

More details about what is intended/needed, power level, etc?

Thanks JST. I was hoping that you would see this.

I should have been more clear. My apologies.

We already have a few RPCs. In use. Power supply is not an issue. ( the whole shop runs on them ) My concern is whether or not that power is suitable for use by the induction unit, since it uses IGBTs and my ignorance regarding them and most things electronical. Thinking on that now, I'm guessing it should not be an issue since the WEDM has some in it and it's been running fine for a decade or so, now...

Proposed use will be heat treating and brazing applications. I only require about 5KW at the moment, but given that these things are imported, I'm considering an overkill approach and going for a 25KW - 30KW size unit.

Thanks.

What is the diameter of the heated item? I am using a 15kw Chinese induction heater.....it’s actually 7.5 kw.....but it’s single phase in.

snowman said:

What is the diameter of the heated item? I am using a 15kw Chinese induction heater.....it’s actually 7.5 kw.....but it’s single phase in.

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It will vary, depending. This immediate task is a 1" shaft that needs a small disc of 1/8" material brazed upon it, a few inches from one end. My plan is to make a coil for the job. Good to see my research and suspicions confirmed about the power output. Thank you. According to various "calculators" and an engineer acquaintance, we need about 1.5 - 2KW for this specific task. Some other heat treat scenarios have it going as high as 5KW. So, I figure the 25KW unit should work. The 15KW is still single phase, but once you get to the 25KW units they are 3 phase. Hence, my query. Thanks much for the info.

Zahnrad Kopf said:

It will vary, depending. This immediate task is a 1" shaft that needs a small disc of 1/8" material brazed upon it, a few inches from one end. My plan is to make a coil for the job. Good to see my research and suspicions confirmed about the power output. Thank you. According to various "calculators" and an engineer acquaintance, we need about 1.5 - 2KW for this specific task. Some other heat treat scenarios have it going as high as 5KW. So, I figure the 25KW unit should work. The 15KW is still single phase, but once you get to the 25KW units they are 3 phase. Hence, my query. Thanks much for the info.

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The 15 kw ones are popular with blacksmiths. Due to ease of single phase power hook up. I have spoken to Gene and want to get a 25 kw unit from him when I have a project that can justify it.
Link to site with good info there:
The Mettle Works, Induction Forges and heating machines

Here are some links Grant Sarvers (RIP) youtube using them, he had a lot of these, and imported & sold them.
YouTube
YouTube
YouTube
These vids are a few he has up there are more. He has the power turned down on the ones for production, timed so the piece is hot when he is ready for it. They will heat faster than in the tong vids.

Zahnrad Kopf said:

Thanks JST. I was hoping that you would see this.

I should have been more clear. My apologies.

We already have a few RPCs. In use. Power supply is not an issue. ( the whole shop runs on them ) My concern is whether or not that power is suitable for use by the induction unit, since it uses IGBTs and my ignorance regarding them and most things electronical. Thinking on that now, I'm guessing it should not be an issue since the WEDM has some in it and it's been running fine for a decade or so, now...

Proposed use will be heat treating and brazing applications. I only require about 5KW at the moment, but given that these things are imported, I'm considering an overkill approach and going for a 25KW - 30KW size unit.

Thanks.

Click to expand...

OK, induction heaters are pretty much similar internally to a VFD.... the power is rectified, then controlled by IGBTs or in some cases power vacuum tubes, to get an output frequency suitable for the job. (output is usually single phase)

In general there is no issue, with one exception. The manufactured leg is always a bit weaker than the others, because it goes through the idler, and the other two are direct. So that leg may not be as effective at charging the DC supply. The idler adds impedance and rectified supplies draw power in relatively short pulses, so they tend to be a tougher load, and the pulses from the generated leg may be weaker. With three phase input, the pulses are usually not as severe, but the effect is there..

I would be generous with the RPC sizing, to minimize the weakness of the generated leg. Aside from that I do not see any issues. My suggestion would be similar to a hard-starting motor load... use 2x and not 1.5x power for the RPC.

Ok...you will be able to heat 1” with no problem with 15 kw and the right coil.




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If buying one of the Chinese ones...make sure to order extra nuts for the coil connection. It’s an 8mm metric flare iirc. I use 5/16” copper tubing, which I have to order from McMaster.

What you can heat is all about how good you are at winding coils.


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snowman said:

Ok...you will be able to heat 1” with no problem with 15 kw and the right coil.

Click to expand...

snowman said:

What you can heat is all about how good you are at winding coils.

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Thanks. Have seen a few examples by now and came to the same conclusion. I feel pretty confident about it and actually have a fair amount of experience making coils in the past. Actually found my old stash of copper line and flare nuts while looking for something else over the weekend. Looks like I do still need to order some cover for the line though. If the customer green lights the project, we’ll be ordering the 25Kw unit. Still on the fence on whether to use a spare Tig cooler we have, or if I should purchase something better. Maybe refrigerated...

Zahnrad Kopf said:

Thanks. Have seen a few examples by now and came to the same conclusion. I feel pretty confident about it and actually have a fair amount of experience making coils in the past. Actually found my old stash of copper line and flare nuts while looking for something else over the weekend. Looks like I do still need to order some cover for the line though. If the customer green lights the project, we’ll be ordering the 25Kw unit. Still on the fence on whether to use a spare Tig cooler we have, or if I should purchase something better. Maybe refrigerated...

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I would use the spare tig cooler. I have a spare tig cooler I actually bought used from a buddy just for when I get the induction. If you look at the stats in the first link I posted above the cooling spec is the same for the 25 and the 15. My thought is that if the little bernard can not keep up a bigger resevoir and/or a second radiator (heater core) can easily be added to help. Keep an eye on water temp if you are planning to run it non stop for hours at a time.