Electromagnets (Split From Stuart Dynamo)

[Michael GilliganParticipant @michaelgilligan61133]

The best source of information [for ‘the practical man’ rather than the Metallurgist or Physicist] that I have found so far, turns-out to be this little book from 1907, by my new hero

S. R. BOTTONE

https://archive.org/details/magnetosforauto00bottgoog

The impatient can probably jump-in at Chapter III

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

This is astonishing:

https://youtu.be/SGoOu8cPmeM?feature=shared

I need to get some sleep now !

MichaelG.

.

 

[noel shelleyParticipant @noelshelley55608]

An AA battery powers a 50Lb electromagnet ! Amazing ! What would it do with 12V ? Noel.

[Michael GilliganParticipant @michaelgilligan61133]

Now that we’re on a roll with this

… can anyone suggest a good, reasonably simple, design for a small ‘coil-winding machine’

?

MichaelG.

.

Note: Small being [say] capable of being stored in the classic 9L Really Useful Box

[John HaineParticipant @johnhaine32865]

https://www.model-engineer.co.uk/forums/topic/coil-winding-machine/

I can’t speak for exact volume but could run a tape over it!

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, John … I will have a look this afternoon

MichaelG.

[noel shelley]

On noel shelley Said:

An AA battery powers a 50Lb electromagnet ! Amazing ! What would it do with 12V ? Noel.

Once the iron core is saturated more volts won’t make any difference. No idea whether 1.5v is enough in this case to saturated the core.

[david bennett 8Participant @davidbennett8]

Dave if you search Google for “soft iron for electromagnets” (shopping) there is a choice from China via Amazon. The stuff I bought would not pick up a pin after being attached to a neodynium magnet.

dave8

 

[david bennett 8Participant @davidbennett8]

Re above  – via Ali Express, not Amazon. Sorry.

dave8

[Michael Gilligan]

On Michael Gilligan Said:

can anyone suggest a good, reasonably simple, design for a small ‘coil-winding machine’

 

I rather assumed anyone on here had a lathe! Screwcutting system helps layout neat coils, pass wire through slit in piece of wood to adjust friction feed.

Else make a temporary rig with Meccano. Now don’t tell me you have none – oh dear oh dear wasted adulthood.

[Robert Atkinson 2Participant @robertatkinson2]

Pedant alert,

The microwave oven transformer electromagnet is not lifting 50 pounds, it’s holding it. There is no work being done.

As there is practically no gap between the pole pieces and armature /  keeper it takes a very small magnetic flux to hold them together.
If it could lift 50lbs across even a 1mm gap I’d be more impressed.

Robert.

[Bazyle]

On Bazyle Said:

On Michael Gilligan Said:

can anyone suggest a good, reasonably simple, design for a small ‘coil-winding machine’

 

I rather assumed anyone on here had a lathe! Screwcutting system helps layout neat coils, pass wire through slit in piece of wood to adjust friction feed.

Else make a temporary rig with Meccano. Now don’t tell me you have none – oh dear oh dear wasted adulthood.

Let’s amend that to 

can anyone suggest a good, reasonably simple, design for a small dedicated, stand-alone ‘coil-winding machine’

… and before you go making any more assumptions … please do me the courtesy of reading my profile.

MichaelG.

[John HaineParticipant @johnhaine32865]

Someone earlier mentioned the Eureka clock and the belief that modern replicas don’r work well because the original iron isn’t available.  Neville Mitchie’s work certainly confirms that the materials aren’t very suitable, but I think this is really because the original design is flawed, I wrote an article for HSN earlier this year explaining why and if I could work out how to upload docs again to this form (WHY is it so hard?) I’d post a copy or happy to email to anyone interested.  I’m not sure why people are interested in making a replica of a clock that is of fundamentally unsound design!

The static force generated by an electromagnet attracting a piece of iron is proportional to the product of the square of the current and the rate of change of inductance of the coil with distance as the iron moves closer.  Other things being equal when the iron touches the magnet pole, and if the magnetic circuit is closed then theoretically the rate of change is infinite as the flux increases to its maximum possible value.  If the current switches off but the core has some remanence, that’s rather like Robert’s observation.  Of course the very high flux also gives the core some remanent magnetisation.  For Duncan’s sounder, ways to minimise the remanence problem using mild steel include –

• Thoroughly anneal the core after working
• If possible demag the core by passing a diminishing AC current through it
• Design the armature with a stop to prevent the air gap closing – that will help to limit the maximum flux.

I think Duncan also mentioned a “release delay” which might be due to remanent flux, but might be due to using a diode to catch the inductive kick.  If this is done then putting a resistor in series to dissipate the coil energy quicker is useful.

[John HaineParticipant @johnhaine32865]

I wondered about using a lathe but a standard lathe isn’t very suitable as you need to reverse the leadscrew for each layer.  I could have used my CNC one but using the standard Myford leadscrew it has far too much backlash.

[duncan webster 1Participant @duncanwebster1]

I think you’ve got me and Dave mixed up

[John HaineParticipant @johnhaine32865]

Oops!  Apologies to both!

[duncan webster 1]

On duncan webster 1 Said:

Just to make an old man happy, can you repeat your test on a 6″ nail. Zap it with some magnetism, then send if it will pick up a pin.

Hmmm, did the experiment.  Results not as expected.

Apparatus:

Plus a 6″ Nail and, because the nail came out of the box magnetised already, a small twist drill weighing 0.19g selected from a set such that the nail can’t quite lift it off the ground.  It can lift one end.

Method: I laid the nail across the electromagnet and powered on for 30 seconds.  0.8A at 6Vdc not 8A as I mistyped in an earlier post!  I did not stroke the nail across the magnet.  I expected the nail to become more magnetised, not less.

Result:  Now the nail is incapable of lifting the 0.19g twist-drill.  As far as I can tell the nail is demagnetised.

Conclusion:  I don’t understand!!!

What where you expecting to happen Duncan?   Can you cast light into my darkness?

Dave

 

[Robert Atkinson 2Participant @robertatkinson2]

If the existing polarity was opposite to that generated by the electromagnet you will de-magentise.

This brings back memories of repairing aircraft remote indicating tachometers. You had to re-magnetise the generator rotor to get the correct output voltage. Go too far and you had to reverse the field. Used a a capacitor discharge magnetiser. Some of the indicators (synchronous motor driving “speedo” type drag cup or disk) needed similar field adjustment to get within the hairspring adjustment range.

Robert.

[Harry WilkesParticipant @harrywilkes58467]

Talking about generators being de-magentise back in a previous like another Sparkie and myself had to change the  generator on mobile crane as this crane was fitted with a magnet, the weather was was very bad this night heavy snow fall. We changed changed the generator ok but no way would it strike up we tried the old trick of hitting with a hammer but no go, i then tried flashing the field winding from a 24v battery which we carried on the back of the Landy still no go we was around two and half hours into the job and we were wet cold and very pee’d off ! I then ask the driver to move the crane and directed him to park it just inside a 250v DC overhead crane track I then connected the generator fields to the magnet supply of the overhead crane this time flashing the fields with 250v DC holding my breath asked the mobile crane driver to git it another try and I’m happy to say away the generator went so back to the shop for a well earned cuppa.

[duncan webster 1Participant @duncanwebster1]

Just that I think nails are made of soft iron, but if they were magnetic out of the box that theory doesn’t hold. Of course the drill could have been magnetised.

To fully demagnetise something you normally use a decaying AC current in the coil, or move the piece away from a coil carrying non decaying AC.

[duncan webster 1]

On duncan webster 1 Said:

Just that I think nails are made of soft iron, but if they were magnetic out of the box that theory doesn’t hold. […]

That iop link that I gave shows the style of nail which was made of soft iron … Everything since then is open to question.

MichaelG.

[duncan webster 1]

On duncan webster 1 Said:

Just that I think nails are made of soft iron, but if they were magnetic out of the box that theory doesn’t hold. Of course the drill could have been magnetised.

Ah yes.  I think modern nails (since about 1900), are made from Dead Mild-steel, less Carbon, the stuff used to press shapely car panels.

I tested the drill with a relay core, and couldn’t detect any magnetism.   Even this aspect of the problem is hard, because almost everything made of Carbon Steel is slightly magnetic!

 

To fully demagnetise something you normally use a decaying AC current in the coil, or move the piece away from a coil carrying non decaying AC.

If I was serious about testing magnetism, I’d have to build a demagnetiser.  Life is too short!

Dave

[Robert Atkinson 2Participant @robertatkinson2]

Hmm I have a standard coil and a couple of gauss meters but I’ve enough projects on at the moment to start down this rabbbit hole…

[SillyOldDuffer]

On SillyOldDuffer Said:

[…] I tested the drill with a relay core, and couldn’t detect any magnetism.   Even this aspect of the problem is hard, because almost everything made of Carbon Steel is slightly magnetic!

I was going to leave mentioning this until I had played some more … but it may be useful, so here goes:

https://www.kjmagnetics.com/blog.asp?p=kj-pole-id

These people supply permanent magnets, but they have a lot of generally-useful information on the site … Plus a handy little App for the iPhone.

The App doesn’t do much, but it’s free, and it works !

[including telling you if it cannot detect any magnet within its range]

 

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Regarding the Coil-Winder … this is roughly what I was looking-for:

https://www.instructables.com/Make-an-Automatic-Coil-Winder/

… but unfortunately it relies a lot upon 3D-printed parts.

MichaelG.

[Author]

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