Reverse Polarity of Electromagnets.

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The Famous Cash

New Member
HONESTLY. . . I do not wish to offend anyone but I have posted this question many times and get nowhere.

I would greatly appreciate if someone could help.

I know ZERO about electronics and CANNOT answer (the usual) questions about inductance, current et cetera.

1) I will buy two U-shaped electromagnets. (Size at this stage is unimportant. 2 or 3 inches long.)
2) I require to rapidly change the polarity of both magnets simultaneously in a controlled manner between 2 and 50 times a second.

Bearing in mind I cannot be any more specific, can anyone advise of ANY magnets with ANY device which I could use?

In the last forum I was on, I was advised of the Picaxe devices which look promising but I have no clue. . . Help!
 
E

eclectic

Moderator
Welcome to the PICAXE Forum.

I'm sure that a PICAXE could control
an alternating electromagnet coil, (using suitable transistors).

Tell us please,

what's it for?
e
 
B

BeanieBots

Moderator
You won't offend anyone but you probably won't get very far without more detail.
An old quartz watch does what you are asking for at once every second.
The electromagnet suggested eclectic (and many others) could be controlled by PICAXE but would also require drive circuitry.
You need to start somewhere, perhaps if you can give some clues about the application more suggestions will come.
 
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geoff07

Senior Member
A Picaxe can provide the switching signal but it cannot on its own provide the power to control an electromagnet of any size. For that you need additional circuitry most likely including a transistor or two. To design this requires the additional information that has been mentioned.

To quickly switch polarity on a large electromagnet will require considerable energy, so the maximum repetition rate will again depend on the details, and may not be possible at high frequency. The energy in the magnetic field, having been built up, then needs to be removed, dumped, and built up in reverse. The time this will take will depend on the inductance and other circuit characteristics.

Do you mean to reverse the magnetic polarity, or just switch one magnet on and the other off? Most electromagnets are used in an on/off mode, reversal is less common.
 
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bluejets

Senior Member
Sort of makes one wonder why you want to change the polarity...an electromagnet is an electromagnet regardless of polarity.
 
techElder

techElder

Well-known member
What you're are describing depends on size. You are looking at transformer construction with laminations needed at the high end of the frequency you specified. These will have 300 or so turns of copper wire coils to produce the magnetic field.

If you are needing to specify parts to build something like that, look for transformer laminations. These come in various forms, but generally in an "E" shape. These are made of special iron. You would use laminations rather than solid iron to help keep the eddy currents down within the core of the magnet.

This can get quite complicated to design and build. Do some research using keywords like "NDT", "nondestructive testing", "magnetic yoke".

You might accidentally find something, but you really need to specify more details.
 
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Goeytex

Senior Member
Given that the OP has zero electronics knowledge/experience and does not want to disclose any details such as what this is for ... rabbit feeder, motor control, black hole generator, anti-gravity drive, or some kind of 'free energy' experiment... then little practical advise can be offered.

Best I can offer is... that for currents less than 1 amp an L298 can reverse the polarity of two electromagnets. Magnets will likely need to be hand wound. The winding resistance should be such that the current does not exceed 1 amp with a given supply voltage.

Common nails nowadays use such poor quality iron/steel, that they should work OK as a U-core for a small experimental magnet.
 
T

The Famous Cash

New Member
Oh dear. I do feel so guilty. Please accept my thanks for all the kind advice. Unfortunately, as I said, my lack of knowledge about electronics is a heavy disadvantage.
I do not mean to give the impression I do not accept the comments but still cannot come to terms with the fact that no one can say, "Buy X magnets. Buy Y device. Plug it in and the Y device will reverse the polarity you wish to control."
At the moment, that is "all" I require. Size current, power, et cetera will become issues if the initial experiment proves successful.
One of the devices kindly mentioned about is not delievered to UK but thanks.
Yes, the actual polarity needs to be reversed and I do understand the principle and that normally just on/off would suffice.
With grateful thanks for your patience.
 
G

Goeytex

Senior Member
The OP will probably never disclose the actual application. He will remain vague and continue to hide behind his supposed lack of electronics knowledge. Rather than take the time to learn some basic electronics and do some research, he has posted in multiple forums looking for others to provide him a turnkey solution.

As for me, if he is unwilling to disclose the application, and learn some electronics, then I am unwilling to help. I would not want to be responsible for him falling into a black hole & possibly sucking the rest of the Universe in along with him. Oh dear! ... blah ,blah, blah...
 
R

rossko57

Senior Member
Electromagnet
http://www.fisher.co.uk/1/1/4598-electromagnet-u-form-4v-d-c.html

Transformer
http://www.ebay.co.uk/itm/12VA-Transformer-3-4V-2-94Amps-4-3V-0-465Amps-230Vac-input-/261445452438?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item3cdf5d0296
Get an electrician to safely put that in a box and attach mains lead, 3-pin plug etc. , and bring out wires for the 3.4V secondary.

You can then connect ~3.4VAC to the horseshoe electromagnet for a magnetic field reversing 50 times a second.
 
B

Brian M

Member
G

geoff07

Senior Member
Presumably because repulsion is required, between either the two electromagnets or one em and a permanent magnet, or a moving magnetic field is to be produced. Which is suggestive of a two-stroke actuator or a motor.
 
A

AllyCat

Senior Member
Hi,

The Famous Cash said:
..... still cannot come to terms with the fact that no one can say, "Buy X magnets. Buy Y device. Plug it in and the Y device will reverse the polarity you wish to control."
Click to expand...
You haven't said anything about the required strength of the magnetic field, it could be to just twitch a magnetic compass needle (for a school demonstration) or to do serious physical work! So we can't say if it can be powered by a couple of AA cells or needs a bank of car batteries (or worse).

Also, magnetic effects tend to be very "short range" because the fields don't "travel" at all well in air. However, IMHO magnetic field theory (saturation, hysteresis, eddy currents, etc. of the materials) is far more difficult than basic electronic circuit design, so I don't hold out much hope for you.

Cheers, Alan.
 
D

Dippy

Moderator
Like other Forumites here and in other Forums I'm a little confused...

Eclectic supplied a link showing a U-shaped electromagnet, but their suitability was not commented upon.
Others here , and on other Forums, have mentioned H-bridges and chips. Again, no useful response.

However; the statement "Buy X magnets. Buy Y device. Plug it in and the Y device will reverse the polarity you wish to control." leads me to think you want something off-the-shelf and free from effort (and free from PICAXE? Remembering this is a PICAXE forum).

I suspect a hobby DC motor speed controller (H-bridge style) is the closest cheapest COTS item but the frequency would be way off.

TFC: Would I be right in assuming you want a boxed solution with no electronic or coding effort from you?

Depending on your application and expectation you will probably have to experiment.
Assuming there is some PICAXE involvement we are bursting to help.
 
Buzby

Buzby

Senior Member
From : http://cr4.globalspec.com/thread/88928/Rapidly-Reversing-polarity-Electromagets

Re: Rapidly Reversing Polarity Electromagets
04/04/2014 1:26 PM

Thank you for your advice.

Unfortunately, you do not appear to have been too accurate in your calculations.

I retired at the age of 31 which is 37 years ago having run a casino and owning a number of businesses.

My IQ is 127 so I should be able to instruct a friend how to knock me unconscious as I twitch on the ground.

Joking apart, I believe the solution will be found following earlier kindly advice to explore picaxe. This is what I am currently doing.

Thanks to all for your input. Greatly appreciated.
Click to expand...

TFC is right, he really has posted on lots of forums.
 
hippy

hippy

Technical Support
Staff member
The Famous Cash said:
I do not mean to give the impression I do not accept the comments but still cannot come to terms with the fact that no one can say, "Buy X magnets. Buy Y device. Plug it in and the Y device will reverse the polarity you wish to control."
Click to expand...
It may be necessary to come to terms with the fact there is no such device available off the shelf which will do what you want, that no one manufacturers or sells the device you require.

You cannot construct such a device yourself because you do not have the necessary electronics knowledge. You would have to gain those in order to do it yourself and understand what needs to be done.

You could commission the construction of a suitable device but you would have to find someone willing to build it and negotiate with them to do that. You would likely need to provide a more detailed specification than you have so far.
 
T

The Famous Cash

New Member
rossko57 said:
Electromagnet
http://www.fisher.co.uk/1/1/4598-electromagnet-u-form-4v-d-c.html

Transformer
http://www.ebay.co.uk/itm/12VA-Transformer-3-4V-2-94Amps-4-3V-0-465Amps-230Vac-input-/261445452438?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item3cdf5d0296
Get an electrician to safely put that in a box and attach mains lead, 3-pin plug etc. , and bring out wires for the 3.4V secondary.

You can then connect ~3.4VAC to the horseshoe electromagnet for a magnetic field reversing 50 times a second.
Click to expand...

In hundreds of posts, this is the very first direct answer so I thank you for your assistance and am setting about investigating more.
 
R

rossko57

Senior Member
The Famous Cash said:
In hundreds of posts, this is the very first direct answer so I thank you for your assistance and am setting about investigating more.
Click to expand...
In other forums, people have suggested degaussing gear. It's a much better idea really, with a tape head demagnetizer you can just plug in and go. That is limited to 50 reversals a second, but you have not specified that you want the rate to be variable.
http://www.conrad-electronic.co.uk/ce/en/product/304856/Electrical-tape-head-demagnetizers

In other forums and this one, people have suggested loudspeakers. You will have to do work to cut away the paper or plastic cone to expose the business end of the electromagnet and extract it from its permanent magnet casing, but you will get the reward of variable frequency (rate) depending on the "sound" or tone you play through it.
 
A

AllyCat

Senior Member
Hi,

Surely in most loudspeakers the primary magnetic field is caused by a permanent magnet (with a highly constrained field)? The "variable" part is just a tiny coil moving within this strong field. Can't see how the electro-magnetic part would be any more useful than winding some turns of copper wire around a magic marker or piece of dowel.

Cheers Alan.
 
techElder

techElder

Well-known member
What the hell is the op talking about? Great imaginations? A riddle? A big joke? Speakers? Demagnetizers? Magnetizers?

This is the dumbest thread that has ever been on this forum.
 
S

srnet

Senior Member
AllyCat said:
Hi,

Surely in most loudspeakers the primary magnetic field is caused by a permanent magnet (with a highly constrained field)? The "variable" part is just a tiny coil moving within this strong field. Can't see how the electro-magnetic part would be any more useful than winding some turns of copper wire around a magic marker or piece of dowel.

Cheers Alan.
Click to expand...
In the absence of any further information, I took the original post literally;

'Any Magnet' 'Any Device'
 
S

SAborn

Senior Member
Have i missed what the magnet is for, or even a reason of what this is about, it would seem lots of ideas, but almost equal to a topic of how long is a piece of string, And that might even be more interesting or even more helpful.
 
A

austfox

New Member
SAborn said:
equal to a topic of how long is a piece of string, And that might even be more interesting or even more helpful.
Click to expand...
Speaking of which... I just received my first bit of 32 gauge Nichrome wire today, which I will be using in my latest project.

My question is how long should I make it? What I am using it for and how it will be powered is unimportant. I just need to know the optimal length?

Steven.
 
I

inglewoodpete

Senior Member
austfox said:
Speaking of which... I just received my first bit of 32 gauge Nichrome wire today, which I will be using in my latest project.

My question is how long should I make it? What I am using it for and how it will be powered is unimportant. I just need to know the optimal length?

Steven.
Click to expand...
That question is about as useful as the originator of this thread. Why do you want to use nichrome wire? What current is it to pass? What voltage is it to drop? ...or... What is it to heat?

The last nichrome wire that I bought was a roll of 100 metres. Is that long enough?
 
S

SAborn

Senior Member
So how long is your wire as then i can use my crystal ball to tell you you to a sub millimeter of the total length required.

IWP, a 100m roll is good, mine come in 1m sections and a right bugger to join together with 3000c solder.
 
hippy

hippy

Technical Support
Staff member
SAborn said:
Have i missed what the magnet is for ...
Click to expand...
I think that was an unfortunate typo / confusion in the original post; should have been "electromagnet" rather than "magnet".

While the spec was almost completely open ended and the application not disclosed I am pretty sure most of us here could have created something which would have met what specification there was. The problem wasn't that per se but giving the OP what they had asked for, especially considering they had no electronic skills.

I read the second requirement as needing to variably control the polarity reversal between 2 and 50 times a second, rather than it being a device which switched polarity somewhere in that range. That's why I thought there was no ready made solution whereas a mains transformer plus electromagnet does seem to have matched what was wanted.

Full marks to rossko57 for a solution which appears to have matched what the OP wanted, who also seems to have gone away happy with that solution. All-in a happy resolution all round.
 
T

The Famous Cash

New Member
rossko57 said:
In other forums, people have suggested degaussing gear. It's a much better idea really, with a tape head demagnetizer you can just plug in and go. That is limited to 50 reversals a second, but you have not specified that you want the rate to be variable.
http://www.conrad-electronic.co.uk/ce/en/product/304856/Electrical-tape-head-demagnetizers

In other forums and this one, people have suggested loudspeakers. You will have to do work to cut away the paper or plastic cone to expose the business end of the electromagnet and extract it from its permanent magnet casing, but you will get the reward of variable frequency (rate) depending on the "sound" or tone you play through it.
Click to expand...
Thanks for your contribution.
Problem is, as I explained my lack of knowledge in this field, I would not know how to vary the polarity reversal accurately.
In other words, if I wanted to reverse the polarity twice a second then wished to change to (say) 17 times a second, I have no clue how I could achieve that.
 
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