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How to make an electromagnet

shutter
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How to make an electromagnet

I need to make a small, ( about 2" long) electromagnet, controlled by an "on-off" switch device. but it needs to be quite powerful.

 

I have checked out several pages, and a couple of videos on youtube... it seems that the way to increase the magnetism power, is by increasing the power supply amperage.. 

 

or by increasing the number of turns on the metal core.

 

 

In the first instance... increasing amperage, I assume that using AA batteries in parallel, would do this,... i.e. 1.5 volts output but increasing the amperage by increasing the number of AA batteries connected .  ? ?     right or wrong?

 

In the second instance... To increase the number of turns.... with the "initial" coverage of wire along the length of the 2" bolt, as one layer with the turns touching... what happens at the end?  If I carry on winding BACK down the bolt overlaying the first layer, then back again overlaying the second layer.. back to the top, and back again to the bottom,...

would this work, or would the current be opposing each other in the turns that are overlayed?

OR

 should I cut the wire at the end of the first layer... and start a second layer at the bottom, (joining the ends at the bottom together).  with all the turns in the same direction.... and cutting the wire at the top end of the second layer..( joining the top ends together )... then start the same again for a third layer... and so on ?

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VileReynard
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Re: How to make an electromagnet

If the turns are all clockwise or all anti-clockwise, they will reinforce each other.

Use a "soft" iron core - steel will tend to get permanently magnetised.

If the resistance of the wire is R, current is I & voltage is V then

V = I x R

So choose your voltage to be sufficient to push the desired current through the coils resistance.

Batteries in parallel: available current adds

Batteries in series: available voltage adds.

Note that all batteries have a certain amount of internal resistance. Cheesy

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Baldrick1
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Re: How to make an electromagnet

@shutter

As @VileReynard says, providing you keep winding in the same direction you can layer the coils. If you want the maximum field you should wind as close to the soft iron core as you can. To get the maximum number of turns on the coil it would be best to use as thin as insulation as possible, which is why enamel coated wires is used for transformers. I would recommend putting batteries in series so that you can drive more turns then put batteries in parallel as parallel batteries are unlikely to share the current evenly, resulting in shorter battery life.

If your switching device is a transistor or low voltage switch you should connect an overswing diode across the coil to stop it emitting a high voltage spike when you switch off.

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shutter
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Re: How to make an electromagnet

@Baldrick1 & @VileReynard Thanks for the replies..... so,... keep a continuous wire, and the "return" windings back down will be the same direction as the first layer, then another layer up (  third ) and another down ( fourth ) all in same direction will give an improved "power" or "pull" attraction than a single layer.  I shall be using 0.01mm enamelled copper magnet wire to wind on the core.

 

The idea is to make a "home made morse sounder"  (rough pic below ! ! )

 

002 home made sounder.jpg

 

as used by the old railroad telegraphists in USA  ( clicking sound as opposed to a tone sound).

 

 

it will be "switched" on /off  via a morse key.. so it would be quick successive on off actions...

VileReynard
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Re: How to make an electromagnet

Would an old relay make enough noise?

It would save much winding...

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shutter
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Re: How to make an electromagnet

Haven`t got one  ! !!    and this will be fun to make !... doesn`t need to be LOUD ... just so it clicks !.. Cheesy

picbits
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Re: How to make an electromagnet

Your wire will have a maximum current it can handle before melting or getting too hot.

 

It will also have a resistance per meter. You can work out how many meters you need to wind to get the minimum resistance required for the maximum current.

 

Of course if you are only pulsing it briefly (as in the morse sounder) then the above isn't as vital. A good source of thin enamelled wire is from an old speaker cone - in fact it is already wound for you on a former which may be good enough to just put on a soft iron core .....

Baldrick1
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Re: How to make an electromagnet


@shutter wrote:

@Baldrick1 & @VileReynard Thanks for the replies..... so,... keep a continuous wire, and the "return" windings back down will be the same direction as the first layer, then another layer up (  third ) and another down ( fourth ) all in same direction will give an improved "power" or "pull" attraction than a single layer. 

Yes. If say you are looking from the top of your bolt and start winding clockwise just keep winding in that direction. Don't worry about neat layers, you just need to get the turns on as neatly as you can. The more turns you put on, or put another way, the longer the piece of wire you use, the least the current draw will be from your battery but potentially the more batteries you will need in series. If you wind a length on and don't get a strong enough field then increase the number of batteries.

The strength of the field is determined by Amps X Turns so twice the amps with half the number of turns will produce the same magnetic field. The trick is to have enough turns so that the battery current is not too high. You will find that the airgap will have a large effect on the number of ampere.turns you need.

This project takes me back over 60 years when in short trousers I made a morse key and receiver. In those days the armature was made of a stripped down tin can and the coil was bell wire wrapped around a couple of nails (it used two coils to maximise the pull). This was driven from a carbon zinc U2 battery. It worked!

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7up
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Re: How to make an electromagnet

Pull one out of an old car!

Either go down the scrappy or "improve" your local nuisance neighbours car next time they leave it unlocked (eg when they take the vacuum cleaner back inside).

Heck you could even pull one out of your trusty Skoda - that must be ready for the scrappy now surely? Wink

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shutter
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Re: How to make an electromagnet

@7up 


@7up wrote:

Pull one out of an old car!

 

Heck you could even pull one out of your trusty Skoda - that must be ready for the scrappy now surely? Wink


 

Hmm... interesting concept !.... however... the trusty Skoda... that gave me excellent no breakdown service for 10 years, covering over 230,000 miles for me ... was traded in 4 years ago, for a top of the range, 3 yr old Skoda Fabia 1.6.. and it is a wonderful car, giving me pleasure to drive every day.  

 

so I won`t be nicking the solenoid from there... ( do Diesels have solenoids  ? ?   )   Roll_eyes

Mustrum
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Re: How to make an electromagnet

You could take a trip round the car showrooms, get the sales peeps to turn on the indicators, find the one with the most pleasing click, the buy a indicator relay - probably cheaper on a well known auction site, but from your retail of choice 😉

HTH 

Baldrick1
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Re: How to make an electromagnet

All this talk of starter solenoids and indicator relays (aren’t these actually combined/timer relays and therefore unsuitable?) is missing the point that @shutter is planning to use AA batterie(s) as the power source,

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Mustrum
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Re: How to make an electromagnet

But he also mentions "quite powerful", maybe he has  yet to realise that AA batteries would be better suited to driving a simple electronic device to create a noise on a speaker, rather than the need for more power, perhaps from a much bigger battery to deliver the power needed to operate a relay type device?

VileReynard
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Re: How to make an electromagnet

How about a transformer for the electromagnet; since it only gets intermittent use it could be connected to a mains supply.

It would be quite powerful.

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shutter
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Re: How to make an electromagnet

@Mustrum  By "quite powerful"... I was really talking about something stronger than seen on You Tube vids that just managed to pick up a few paper clips...as you can see,  the "power" would be needed to energise the 3" bolt sufficiently to counteract the spring or rubber band to enable the sounder to work.

@VileReynard as regards the speaker idea... yeah.. it would work... but would not be "the same as " seeing an old telegraph sounder working and sounding. ... and as for mains power... it should be "safe" to use, as a demo, and not rely on mains power, making the whole thing undesireable

 

Here is a short video of an original sounder dates from about 1900  The morse key is about the same age....

 

https://www.youtube.com/watch?v=Lki3jxNLVCI

Note, these sounders were at the end of miles of wire, and powered by wet cell batteries, hence the double coils of the electromagnets

 

Correction to the original post... wire size would be 0.1mm  not 0.01mm ! ! .... Embarrassed