A Simple
Magnet Motor
in the making
I started with 2 speaker magnets:
a plastic lid cut in half, and glued to one side, keeps them apart.
Being able to pick up 2 free speakers (magnets) at a car stereo shop is good
when you are still experimenting. I also got a flat, soft steel bar (soft iron
is better) at a hardware store 1/8" x 1/2" x 36" for about $3.50 to use for
the electro-magnet. I cut off about a 9" piece of it. 3+" for the magnets on
one side, 3-" for the coil in the middle and, 3+" for the other side. I may
or may not need magnets on the 2nd side.
I discovered the magnetism falls off rapidly as you move out along the 3" on
either end. So, the speaker magnets are inadequate.
In the meantime, I had discovered that Radio Shack had some "large" bar magnets
for about $1.15 each. about 8 or 10 of them are about as strong as the speaker
magnets - and, more compact. They are about .9"x1.9"x.4"
Now, I am planning on 2 stacks of 8 (or 10) with a short 1" coil in between
on a 3" rod, (not 9"). (2 stacks of 4 each are shown)
I am learning as I go ... if you get ahead of me,
let me know your results. ... Send pictures!
("contact us")
Ideas and sources on small electromagnets
|
Lifting Electromagnets
500 lb
|
500 lb with 200 lb
|
inside view
|
see
Experiments with electromagnets - Page 1
- by Rick Hoadley
20-030 Small Magnet: Weighs 2 pounds - lifts 200, due to precision machining.
Uses only one 1-1/2 volt "D" cell battery (not included). 1-3/4" diameter
cold rolled steel core and yoke are ground to within a fraction of 1/1000
inch. Coil has 175 turns of #28 magnet wire, 4 strands parallel (= 1 strand
of 22 gauge). Includes: alligator clip leads, battery holder fastened
directly to magnet for portability, instructions with experiments. Works
best with included yoke, may not work on other surfaces. Wt: 0.8 kg
$49.25 on 7-11-2006 at
www.sciencefirst.com
20-035 Large Electromagnet: Same as above but lifts 500-700 pounds and
requires two 1-1/2 volt "D" cell batteries, not included. Works best with
included yoke, may not work on other surfaces. Wt: 1.7 kg
$83.75 on 7-11-2006 at
www.sciencefirst.com
for the small quantities needed here, Radio Shack sells a kit of three
tiny spools, #278-1345, $5.00, 200ft of #30, 75ft of #26, and 40ft of #22.
( I used the 40' of #22, and got about 240 turns - on my smaller diam. coil )
If you applied 5 volts to them on the spools they came on:
| Length, feet |
Gauge, AWG |
Resistance, Ohms |
Voltage |
Current, I=V/R |
Number of turns |
Ampere-turns |
| 200 |
30 |
20 |
5 |
0.25 |
800 |
200 |
| 75 |
26 |
3 |
5 |
1.67 |
350 |
580 |
| 40 |
22 |
0.65 |
5 |
7.7 |
160 |
1230 |
Note that Ampere-turns is a relative measure of the strength of the magnetic field.
"One other thing we need to keep in mind. When current flows through the wire, it creates heat. Will the coil get too hot? First, find out how many watts will be dissipated by the coil. For the third coil in the table above, the watts = I^2 * R = 7.7*7.7*0.65 = 38 watts. There needs to be enough surface area so that the watts/sq.in. is no more than 0.5. In this case, the watts/sq.in. works out to about 9.5, which is a lot more than 0.5! So, expect the coil to get hot and don't keep in on continuously. It's OK to run it for 10 seconds, then turn it off for 30 seconds to be able to cool."
Rick Hoadley
see
Experiments with electromagnets - Page 2
- by Rick Hoadley
"But a creative scrounger can do better. Think power transformers! If you
obtain an old power transformer, you can pry a couple of laminations free
using pliers and a knife, and the whole stack will then easily disassemble.
You're left with a spool full of wire for free. Besides power transformers,
larger "choke" coils are also a source of free wire. For thin wire, try finding
a transformer with a high voltage secondary such as those used in old tube-type
equipment." -
Bill Beaty
a galery of images of electro-magnetic fields
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