Demagnetize a metal with a dc welder?

[Hopefuldave]

I would have thought any ac carrying cable would work...ie power extension cable with a load connected...wrapped around the object?

Then slowly remove the object...should produce a diminishing oscillating magnetic field.

mains cable will have equal and opposite fields from the live and neutral so they cancel out (the reason why coiled up extensions can't carry the same current as extended) - would work if you had just one of 'em coiled and the other straight, or separate coils for L and N though.

Dave H. (the other one)

 

[Pigeon_Droppings2]

mains cable will have equal and opposite fields from the live and neutral so they cancel out

Are you sure....I thought they would have to be carefully entwined for that effect to occur?....but to be honest its been too many years since I did any of this stuff in any great detail!

 

[Brad93]

You can buy proper degaussers from EWM.
First try wrapping the earth round the part a few times.

 

[Hopefuldave]

Are you sure....I thought they would have to be carefully entwined for that effect to occur?....but to be honest its been too many years since I did any of this stuff in any great detail!

Nope, that's to reduce the magnetic field escaping or getting picked up - wound into a coil it's the coil size and turns, the two wires are like windings in a transformer and couple together with opposite-direction magnetic fields which is like putting a pair of magnets north to south - no magnetic "resistance" so both induce a current in each other and you get an increase in the current that heats the coil(s) - I''ve seen a few burnt-out extensions on reels from things as small as (hefty) hot air guns, never mind 3kw heaters - ALWAYS extend the lead fully to avoid letting the magic smoke and flames escape, same with torch and earth on AC welders - mine's Book Of Words even has a diagram of how to coil the two separately (in figure-8s) if the cables are too long...

Dave H. (the other one)

 

[Pigeon_Droppings2]

I dunno...i'd have to think about it.....doesn't that sort of assume that the live and neutral are carrying exactly the same energy?...is that true for an extension with a load on the end?

 

[premmington]

If I get problems - I just switch from DC to AC MMA welding.

Arc blow or arc deflection - is very odd when it happens - you wonder what is going on for a few seconds.


The only things I have had real problem with is making things from car hubs and brake discs (bearings and ABS sensors?).

And a few bits of scrap from the water board yard next door - by all accounts if water runs across or through metal it creates a magnetic field (not sure of this fact?).

Oh... And them silly 90 degree magnetic welding clamps - dumped mine years ago and bought Carver clamps.

 

[Hopefuldave]

I dunno...i'd have to think about it.....doesn't that sort of assume that the live and neutral are carrying exactly the same energy?...is that true for an extension with a load on the end?

Yep, if not the RCD would pop due to the current imbalance - that's what they do, anything over 30/1000 of an Amp.

Dave H. (the other one)

 

[AndVal]

From what I've read AC degaussing is the easiest way to do it. I need to go and find a buzzbox. Thanks for the answers.

 

[voipio]

The problem with reeled-up extension leads under load is more to do with efficiency of heat dissipation (exposed surface area) than electromagnetism.

 

[Hopefuldave]

The problem with reeled-up extension leads under load is more to do with efficiency of heat dissipation (exposed surface area) than electromagnetism.

I don't think so, the same aount of cable in the same space but not in a coil (e.g. zigzag) doesn't get anywhere near as hot, and doesn't blow fuses from the off like a long coiled cable - running a 3 HP single-phase motor on my long extension (25 metre) will pop the MCB
at switch-on if it's coiled, not if it's unwound and thrown all over the shed - before it's had time to heat the cable...

Dave H. (the other one)

 

[Maker]

I don't think so, the same aount of cable in the same space but not in a coil (e.g. zigzag) doesn't get anywhere near as hot, and doesn't blow fuses from the off like a long coiled cable - running a 3 HP single-phase motor on my long extension (25 metre) will pop the MCB
at switch-on if it's coiled, not if it's unwound and thrown all over the shed - before it's had time to heat the cable...

Dave H. (the other one)

A coiled extension lead will behave as an inductor and present a higher impedance to the supply, drawing more current than if it weren't coiled.