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Hello All,

I was recently asked to start a tread on induction coil design.

I'll open with a link to this three part article on the subject.


Note the "flow" of the current and how stacking the coil can increase heating in areas. This may come in handy when heating unequal parts evenly...say a bolt head and shaft...the head has more mass and takes more time to heat.


Some units may not sense a load unless there is inefficiency in the coil...my larger unit is such..its minimum setting is near 5kw so small items actually require an inefficient coil for it to work at all.





Note also that some simple heating coils need odd contortions to get the power to the area required without cancelation and getting even heating. Some of the smaller induction units work at such a high frequency that they may not heat stock well....in industry efficiency is the name of the game,but in our work it often comes down to ....will it work at all. A 15kw unit at 30,000 or more hertz can do wonderful work, but it is far from an industrial machine and has limitations that can be worked around...but only to a limit. For deep heating a lower Hz rate is far better and may be worth the expense..especially if found on the used market.


I would avoid the motor generator units as they have parts issues.


More later.



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Thanks for this Ric!


Learning about the design of these coils is one of my goals in the upcoming year.


As I mentioned in the other thread, I have on of Grant's machines that I hoped would allow me to forge during the cold, dark Alaskan winters when the temperature dropped in the negative numbers. Unfortunately, since I have yet to get my head wrapped around coil design, I've used the machine very infrequently (even after paying an electrician a bazillion dollars to wire it up . . .the cable to the machine is literally 1.25" diameter!!).


Thanks again.



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Thanks for developing the topic Ric. I'm glad the Sarver unit is still available, and I'll keep a watch out for your updates here.


Take care, Craig

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Thanks for developing the topic Ric. I'm glad the Sarver unit is still available, and I'll keep a watch out for your updates here.


Take care, Craig



I have asked Stanley Zinn (author of the above link) if he was interested in writing a booklet specific to the small shop regarding these high freq lower power induction units. I am not sure he will take on the topic (I do not "know him" per se, but his article is very good and he does consultation work..so..a booklet seems like a big article to me), but if he does not then I will find another more versed than I to do the work.


I envision it something like Dr. James Batson's Hydraulic press booklet.....general info and practical "how-to" about what can...safely...be done with these units. It will not be about building the induction unit, but rather using it well.


topics like

What is induction

How these small units work vs the larger big brothers in industry

General coil design and theory

tube diam and wall thicknesses


water injection

odd shaped coils and how to bend them

what really happens in the field and what other applications it can be used for

Melting, heat treating and control...for when you do not just want to make things hot, but hot with a temp in mind.


that sort of thing.


Such information could only increase the demand for the units...taking some of the mystery out of them. Perhaps Larry Langdon who has taken over the business would be on board with such a thing as well...I have not asked him.



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