Well I need to create a reasonably powerful electromagnet and I am in


by Gurinder R
Tags: electromagnet, powerful
Gurinder R
Gurinder R is offline
#1
Mar24-12, 12:26 PM
P: 13
Well I need to create a reasonably powerful electromagnet and I am in Gr. 12. I havn't been able to find a proper guide/book to create a electromagnet.

I plan on using a ferrous core and 38 gauge wire. I am going to wind the wire around a spool.

My questions:

What should be the diameter and length of the spool?
How many turns should I wind up?
What should I use as my power source?

Thank you for reading this, your help is appreciated :)
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OldEngr63
OldEngr63 is offline
#2
Mar24-12, 02:48 PM
P: 343
Roughly speaking, the more ampere turns you have, the more powerful your magnet will be. So, more turns and more current are the name of the game.
Bob S
Bob S is offline
#3
Mar24-12, 03:29 PM
P: 4,664
Electromagnets made in the solenoid geometry are relatively weak compared to magnets in the "C" geometry or "H" geometry, because the field lines in air are relatively long. Electromagnets using ferrite rather than soft iron are relatively weak because of the relatively low permeability of ferrite. Ferrite is used at high frequencies where a laminated iron design is not suitable. For dc magnets, solid iron is fine.

This shows a C geometry electromagnet (but not an efficient design). The two grey boxes represent the coil cross section.

http://www.google.com/imgres?imgurl=...wBzgK&dur=4829

The magnetic field is proportional to the number of amps I and the number of turns N, or NI (amp-turns). Available power supplies are usually in the 1 amp to 5 amp range, with a wide range of voltages. A good conductor for a small magnet is probably 18 Ga enamel or formvar coated, because its current rating is about 2.3 amps. Larger magnets should use a lower gauge (larger diameter). 38 Ga. is a very poor choice (22 milliamps rating). See Table at

http://diyaudioprojects.com/Technica...an-Wire-Gauge/

In the end, the current limit will be lower than in the Table, because the real problem will be getting the heat from resistance (I2R) losses out.

In the image of the C magnet above, if the height of the gap is g, then the magnetic field in the gap is (from Ampere's Law)
[tex] B=\frac{\mu_{o}NI}{g} \space \space \space Tesla [/tex]
where μo = 1.26 x 10-6 in mks units.
How big a volume of magnetic field do you need?

Gurinder R
Gurinder R is offline
#4
Mar24-12, 03:53 PM
P: 13

Well I need to create a reasonably powerful electromagnet and I am in


Quote Quote by Bob S View Post
Electromagnets made in the solenoid geometry are relatively weak compared to magnets in the "C" geometry or "H" geometry, because the field lines in air are relatively long. Electromagnets using ferrite rather than soft iron are relatively weak because of the relatively low permeability of ferrite. Ferrite is used at high frequencies where a laminated iron design is not suitable. For dc magnets, solid iron is fine.

This shows a C geometry electromagnet (but not an efficient design). The two grey boxes represent the coil cross section.

http://www.google.com/imgres?imgurl=...wBzgK&dur=4829

The magnetic field is proportional to the number of amps I and the number of turns N, or NI (amp-turns). Available power supplies are usually in the 1 amp to 5 amp range, with a wide range of voltages. A good conductor for a small magnet is probably 18 Ga enamel or formvar coated, because its current rating is about 2.3 amps. Larger magnets should use a lower gauge (larger diameter). 38 Ga. is a very poor choice (22 milliamps rating). See Table at

http://diyaudioprojects.com/Technica...an-Wire-Gauge/

In the end, the current limit will be lower than in the Table, because the real problem will be getting the heat from resistance (I2R) losses out.

In the image of the C magnet above, if the height of the gap is g, then the magnetic field in the gap is (from Ampere's Law)
[tex] B=\frac{\mu_{o}NI}{g} \space \space \space Tesla [/tex]
where μo = 1.26 x 10-6 in mks units.
How big a volume of magnetic field do you need?
I need to a pull a magnetic ball 15cm away; ball is 1 cm in radius.

What type of power should I use? 9V battery would be sufficient? what else can we use?
Bob S
Bob S is offline
#5
Mar24-12, 05:23 PM
P: 4,664
In your case, a solenoildal geometry is best. See magnetic field formulas at
http://www.calctool.org/CALC/phys/el...etism/solenoid
Us a 1/2-inch diameter steel rod or bolt, about 6-inches long.
I would use 20 Ga. wire (10 ohms per 1000 feet), which is good for 1 amp. I would use 2 "D" cell batteries in series, and a 300-foot long wire (1 pound), available on eBay for $20.00. If you are really lucky, you could buy a 1-pound coil of 20 Ga. "magnet wire" on a plastic spool like this one,
http://www.ebay.com/itm/Magnet-Wire-...t_778wt_931and find both ends of the wire accessible. In this case just stick the steel rod inside.

[added] Ths formula is more accurate
http://www.netdenizen.com/emagnettes...oids/?solenoid
Gurinder R
Gurinder R is offline
#6
Mar24-12, 05:28 PM
P: 13
Quote Quote by Bob S View Post
In your case, a solenoildal geometry is best. See magnetic field formulas at
http://www.calctool.org/CALC/phys/el...etism/solenoid
Us a 1/2-inch diameter steel rod or bolt, about 6-inches long.
I would use 20 Ga. wire (10 ohms per 1000 feet), which is good for 1 amp. I would use 2 "D" cell batteries in series, and a 300-foot long wire (1 pound), available on eBay for $20.00. If you are really lucky, you could buy a 1-pound coil of 20 Ga. "magnet wire" on a plastic spool like this one,
http://www.ebay.com/itm/Magnet-Wire-...t_778wt_931and find both ends of the wire accessible. In this case just stick the steel rod inside.
umm the one you listed as a spool how would i be able to find both ends? and how many 2d batteries should i put in series? i can buy one off local store which is 0.683433013 in a spool would it be sufficient?
Bob S
Bob S is offline
#7
Mar24-12, 05:38 PM
P: 4,664
I was referring to quantity 2 of standard "D" cells (1.5 volts each). Sometimes, when the wire is wound onto the plastic spool, they let both ends stick out. You want several hundred feet of wire.
See
http://www.netdenizen.com/emagnettes...oids/?solenoid
Gurinder R
Gurinder R is offline
#8
Mar25-12, 11:10 AM
P: 13
Quote Quote by Bob S View Post
I was referring to quantity 2 of standard "D" cells (1.5 volts each). Sometimes, when the wire is wound onto the plastic spool, they let both ends stick out. You want several hundred feet of wire.
See
http://www.netdenizen.com/emagnettes...oids/?solenoid
Thank you Bob. I was wondering how long would 2 D cells last?
Bob S
Bob S is offline
#9
Mar25-12, 12:50 PM
P: 4,664
This Table (see last one) gives the amp-hour rating of NiMH D cells as 9.5 amp-hours.
http://www.allaboutbatteries.com/Energy-tables.html
So 9.5 hours at 1 amp. Don't try to drain an amp from an AA cell.
salzrah
salzrah is offline
#10
Mar25-12, 08:03 PM
P: 79
This is really easy to do.

diameter- atleast .5 in.
length- 3-4 in.
power source- atleast 9V

The main thing is to wrap the wire as tightly as possible and to get as many turns around a single point of the base of the spool. The more you have the stronger it will be. Also, make the base of the spool hollow and fill it with either nails or a bolt, which will enhance the magnetic field strength.


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