Induction safety

[J.P. Hall]

Hi all,

I've been looking into getting a 15kW induction forge and was discussing safety concerns with an electrician friend who would be installing a new circuit for the machine and installing a non-metallic box on the unit. Having not worked with induction before, he brought up some questions regarding safety around the coils themselves and accidentally shorting them. I've seen people shorting coils with a workpiece with no apparent harm aside from the few sparks, but since these are exposed bare conductors, I was curious about what could happen in a worst-case scenario. There are examples of people performing drop-tong welds with induction forges, so it doesn't seem impossible for a tong in each hand to touch the coil, completing a circuit that passes through the heart.

 

I understand that these machines are generally regarded as pretty safe if wired correctly, and I don't see much mention of danger from coming into contact with coils but if I had objective numbers to go by it would be much more reassuring than "it's probably fine". I've heard that the volts/amps at the coils are comparable to a car battery but haven't been able to confirm that.

[George N. M.]

I can't help you with your concerns but to bring up another issue, I'd worry about interference if I had a pace maker or another electronic implant.  I don't know how fast the magnetic field drops off by distance from the induction coils.  That said, we have an induction stove and have not had any problems but the coils are buried in glass in the stove.

"By hammer and hand all arts do stand."

[J.P. Hall]

I have heard mention of pacemeakers, thankfully I don't have one. A more probable issue is if I have any steel  shavings on or in my hand.

[Frosty]

Boy JP, you should talk to people who own and use an induction heater. A coil, wand, paired wands, etc. are ONE CIRCUIT. They ground inside the box and the box is insulated from the exterior. I don't know and I'm not going to do basic research. Are Car batteries rated in KWh?

Induction is what happens when a high frequency ALETNATING magnetic field encounters a magnetic metal like iron or steel. The ferrous atoms literally get slammed back and forth inside the ferrous molecules. First left, then right. Just to pick a direction, please don't ask if they actually move left and right. OKAY? They get slammed, vibrated, I don't know the distance moved, in the heater you're asking about, 15,000/second.

The magnetically induced vibration transfers power from the induction heater to the stock via magnetic induction. The induction wands or whatever shape can NOT short across the coils, loops, etc. If one did it would indicate a failure in the box and it would just go dead. Might let some of the smoke out but all the fireworks should stay in the box.

The reason you're pumping water through the coil is to protect it from radiated heat from the stock being heated.

You won't be holding anything steel close enough to be heated a second times. It doesn't have much range, the handle on a loop is usually way out of range Believe me if you passed a wand over a hand with a sliver in it you'd know AFTER it was all done it would probably turn into plasma and cauterize a cavity before you felt it. Feel it you would though!

I can't believe this is my first post since getting home from the hospital. That is of course if I didn't say it yesterday, I was still really out of it I too often don't know if I did, said, etc. something or just thought of it.

Good to be back all.

Frosty The Lucky.

[George N. M.]

Welcome back, Jerry.  Good to hear from you.  BUT, do not push it.  If you need more time off, take it.

G

[J.P. Hall]

2 hours ago, Frosty said:

Good to be back all.

Welcome back, hope you're feeling better!

Thanks for the rundown, it's good to hear that it's got built-in failsafes. I got the bulk of my knowledge from this video:

 

 

 

From asking around, some folks have accidentally touched a running coil with wet hands and gotten a bit of a shock, but they lived to post about it. I found this example of somebody touching a running coil without much of anything happening:

 

I was a bit paranoid about the minuscule chance of touching the coil with both hands, since shocks are most dangerous if the current flows through the chest area, but it would make sense if the current would just keep flowing through the copper with it having less resistance than the upper half of a human.

[Nobody Special]

Looking around the internet, seems to be a lot of variance - 30 to 40 amps input and yay many hundreds of amps output. 60 milliamps across the heart is what it takes to stop it, right?

Results vary too when touching hot wires. I've touched hot wires plenty of times, even when grounded and been fine. I've even had jerks at the shop when I was young that would charge up a start capacitor and rig it to discharge when caught, then toss it to the next person to walk through the door. But then sometimes people touch regular 120 volt household electricity out of a 10 or 15 amp socket and drop dead on the spot.

I also seem to remember that the first deliberate attempt at execution through electrocution ended poorly. Or you might remember that Ben Franklin survived his kite experiment but one of his associates who tried to recreate the experiment in France wasn't nearly so lucky. While I mention it, ya ever here the one about the time they deliberately electrocuted an elephant at Coney Island?

[Mike BR]

It’s ultimately current that kills, but voltage is what determines how much will flow through your body.  Ever touch the terminals on a 1000 CCA car battery?

Also, the HF itself will tend to protect you, through the skin effect.  The start circuit on a TIG has a much higher voltage, but the HF keeps it from being dangerous. 

[Irondragon Forge ClayWorks]

On 5/30/2024 at 6:42 PM, Frosty said:

Are Car batteries rated in KWh?

Like Mike BR said car & truck batteries are rated in CCA (Cold Cranking Amps). A 1000 CCA is a pretty potent charge.

I can't control the wind, all I can do is adjust my sail’s.
Semper Paratus

 

[Frosty]

Thanks, Randy, Mike. So at 1,000 CCA an automotive battery is 12kw. Yes? You certainly can't put that kind of draw on one for an hour.

Frosty The Lucky.

[Mike BR]

Yep, 12kw.  But CCA is cold cranking amps, so seconds (or tens of seconds?) rather than hours.  Still a lot longer than my life expectancy would be with 1000 amps running through me . . .

[J.P. Hall]

I had planned to coat the coils with some sort of refractory to avoid shorts, but I may cover the straight sections of tubing coming off the machine with something like heat shrink or rubber hose just to be on the safe side.

I also came across this video and it seems that another reason you can touch an induction coil without apparent issue is that the frequency is simply too high to sufficiently disrupt nerve signals.

[Frosty]

Okay, fine I call Uncle, I give up. If you want to believe you can get shocked by touching an open circuit, suit yourself. 

Frosty The Lucky.

[J.P. Hall]

If I came across as argumentative or stubborn I apologize; that wasn't my intent. I'd much rather ask a foolish question on the internet than make assumptions about safety with high-power electrical equipment. I do understand that the induction coil itself is part of a closed circuit, but touching a live uninsulated conductor generally isn't regarded as good practice and I didn't want to accidentally bump something and unwittingly hook myself up  in parallel with the existing circuit.

[Irondragon Forge ClayWorks]

"The only foolish question is the one that was not asked". ~ My grandfather".

I can't control the wind, all I can do is adjust my sail’s.
Semper Paratus