Designed and constructed a prototype of a magnetic relay, using electromagnets made of iron bolts and magnetic wire, along with LED indicators.

1. Magnetic Relay
By Elliott Sarich and Brian PrattObjective
• Explore the concept of electromagnetic
fields through the construction and
development of a magnetic relay.
Procedure
• Using the DC power supply, power
one of the solenoids with 1A of
current.
• Power the paper clip with 5V, and
ground everything together.
• The respective powered solenoid will
attract the paper clip via a magnetic
field.
• The metals will come in contact with
each other: completing the LED circuit
• To see the full effect of the relay,
switch the power source to the second
solenoid.
• The tension of the paper clip moves it
back to center position, when it
becomes de-magnetized, and then
promptly comes in contact with the
second solenoid, completing the
secondary LED circuit.
• The basic design is a board with two
solenoids facing each other.
• There is an unraveled paper clip
suspended between these two
solenoids, with enough slack to move
and touch either of them.
• The paper clip is wired to a 5V source.
• When a solenoid is powered, it becomes
magnetized and attracts the clip. It
comes in contact with the head of the
solenoid much like a switch, and
completes the LED circuit.
• The magnetic wire around the solenoid
acts as a separate circuit from the LED,
and the iron cylinder allows current to
flow to the secondary circuit.
Design
Principle
Flow Chart
Name Quantity Cost
Paper Clip 1 $5.00 (box of 100 on
Amazon)
Bolt/Nut
assembly
1 bolt/2+nuts $1.00 (ACE Hardware)
Steel bolt 2 $5.00 (Box ACE
Hardware)
LEDs and
Resistors
2 of each $2.00 (Radioshack)
Wood Block 1 $1.00 (ACE Hardware)
Magnetic Wire 1 spool $5.00 (Radioshack)
Assorted Wire Multiple
Colors and
spools (4)
$5.00 (Radioshack)
Sand Paper 150 Grit $5.00 (ACE Hardware)
Heat Shrink
Tubing
Assorted Pack $5.00 (ACE Hardware)
Electrical Tape 1 Roll $2.00 (Radioshack)
Total
$36.00
Evaluation of Design
• The main principle at work in our project
is the property of a solenoid, which is
that when current flows through a
cylindrical coil of wire, a uniform
magnetic field is created inside. This
magnetic field points in a direction that
depends on the current according to the
right-hand rule, as displayed in the figure
below.
• The magnetic field is very weak outside
of the solenoid, but this changes when
something called ferromagnetic metal is
inserted inside the coil of coated wire.
With an induced magnetic field,
ferromagnetic metal acts like a magnet
with a north and south pole based on the
direction of the induced magnetic field.
Ferromagnetic metal has regions of
alignments called magnetic domains.
These magnetic domains describe
groups of atoms that when aligned with a
magnetic field, increase its strength.
Typically the domains are pointed in
different directions. However, when a
magnetic field passes through the metal
in a specific direction, it aligns the
domains so the magnetic field is greatly
increased in magnitude. How capable a
metal is of amplifying an induced
magnetic field is described by a
measurement called magnetic
permeability μr.
Force Equation: F=
𝜋𝑟2 𝜇 𝑜 𝜇 𝑟(𝑁𝐼𝐿)2
2𝐷2
Solenoid Equation: B=μoNIL
Prototype
Relative permeability of metal cores μr 100
Number of turns of wire N 428
Length of solenoid L (cm) 10.5
Current I (A) 1.02
Radius r (cm) 0.25
μo 4π*10-7
B at edge of solenoid (D = 0) (Wb/m) 5.76*10-5
Distance D
(mm)
Calculated force
(N)
Pulls paperclip?
1 2.49 Yes
2 0.62 Yes
3 0.27 Yes
4 0.15 Yes
5 0.09 Yes
Equipment