POWER SUPPLY TRANSFORMER
A library paper written by
AMIHAN R. ABELLAR
DANNY A. BABAO
Transformer
is used extensively in electronic products to step down the supply voltage to a
level suitable for the low voltage circuits it contains. In the construction of
a power supply transformer, constructors usually find difficulty because of the
absence of wire estimate in terms of weight. This is an important part of
constructing a power supply transformer especially to the beginners who need
guidance in purchasing the different materials needed. In line to this, we
decided to study on how to compute for the estimate wire needed and the
procedure in making the power supply transformer.
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A transformer (see fig.1) is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's
coils. A varying current in
the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This
varying magnetic field induces a varying electromotive force
(EMF), or
"voltage", in the secondary winding. This effect is
called inductive coupling.
If a load is connected to the secondary, current will flow in
the secondary winding, and electrical energy will be transferred from the
primary circuit through the transformer to the load. In an ideal transformer,
the induced voltage in the secondary winding (Vs) is in
proportion to the primary voltage (Vp) and is given by the
ratio of the number of turns in the secondary (Ns) to the
number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer
thus enables an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped
down" by making Ns less than Np. The windings are
coils wound around a ferromagnetic core, air-core transformers being
a notable exception.
Transformers range in size from a thumbnail-sized coupling
transformer hidden inside a stage microphone to huge units
weighing hundreds of tons used to interconnect portions of power grids. All
operate on the same basic principles, although the range of designs is wide.
While new technologies have eliminated the need for transformers in some
electronic circuits, transformers are still found in nearly all electronic
devices designed for household ("mains") voltage. Transformers are essential for high-voltage electric power
transmission, which makes
long-distance transmission economically practical.
Table 1. Table of copper wire
|
AWG Wire Table, AWG Copper Wire Gauge Chart
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||||||
|
AWG
|
Diam. (mils)
|
Circular mils
|
Ohms/1000ft
|
Current Carrying
|
Fusing Current
|
Feet per Pound
|
|
0000
|
460
|
212000
|
0.050
|
-
|
-
|
1.56
|
|
000
|
410
|
168000
|
0.063
|
-
|
-
|
1.96
|
|
00
|
365
|
133000
|
0.077
|
-
|
-
|
2.4826
|
|
0
|
324.85
|
105531
|
0.096
|
-
|
-
|
3.1305
|
|
1
|
289.3
|
83694
|
0.1264
|
119.6
|
-
|
3.947
|
|
2
|
257.6
|
66358
|
0.1593
|
94.8
|
-
|
4.977
|
|
3
|
229.4
|
52624
|
0.2009
|
75.2
|
-
|
6.276
|
|
4
|
204.3
|
41738
|
0.2533
|
59.6
|
-
|
7.914
|
|
5
|
181.9
|
33088
|
0.3915
|
47.3
|
-
|
9.980
|
|
6
|
162
|
26244
|
0.4028
|
37.5
|
668
|
12.58
|
|
7
|
144.3
|
20822
|
0.5080
|
29.7
|
561
|
15.87
|
|
8
|
128.5
|
16512
|
0.6405
|
23.6
|
472
|
20.01
|
|
9
|
114.4
|
13087
|
0.8077
|
18.7
|
396
|
25.23
|
|
10
|
101.9
|
10384
|
1.018
|
14.8
|
333
|
31.82
|
|
11
|
90.7
|
8226
|
1.284
|
11.8
|
280
|
40.12
|
|
12
|
80.8
|
6529
|
1.619
|
9.33
|
235
|
50.59
|
|
13
|
72.0
|
5184
|
2.042
|
7.40
|
197
|
63.80
|
|
14
|
64.1
|
4109
|
2.575
|
5.87
|
166
|
80.44
|
|
15
|
57.1
|
3260
|
3.247
|
4.65
|
140
|
101.4
|
|
16
|
50.8
|
2581
|
4.094
|
3.69
|
117
|
127.9
|
|
17
|
45.3
|
2052
|
5.163
|
2.93
|
98.4
|
161.3
|
|
18
|
40.3
|
1624
|
6.510
|
2.32
|
82.9
|
203.4
|
|
19
|
35.9
|
1289
|
8.210
|
1.84
|
69.7
|
256.5
|
|
20
|
32.0
|
1024
|
10.35
|
1.46
|
58.4
|
323.4
|
|
21
|
28.5
|
812
|
13.05
|
1.16
|
-
|
407.8
|
|
22
|
25.3
|
640
|
16.46
|
.918
|
41.2
|
514.12
|
|
23
|
22.6
|
511
|
20.76
|
.728
|
-
|
648.4
|
|
24
|
20.1
|
404
|
26.17
|
.577
|
29.2
|
817.7
|
|
25
|
17.9
|
320
|
33.0
|
.458
|
-
|
1031
|
|
26
|
15.9
|
253
|
41.62
|
.363
|
20.5
|
1300
|
|
27
|
14.2
|
202
|
52.48
|
.288
|
-
|
1639
|
|
28
|
12.6
|
159
|
66.17
|
.228
|
14.4
|
2067
|
|
29
|
11.3
|
128
|
83.44
|
.181
|
-
|
2607
|
|
30
|
10.0
|
100
|
105.2
|
.144
|
10.2
|
3287
|
|
31
|
8.9
|
79
|
132.7
|
.114
|
-
|
4145
|
|
32
|
8.0
|
64
|
167.3
|
.090
|
-
|
5227
|
|
33
|
7.1
|
50.125
|
211.0
|
.072
|
-
|
6591
|
|
34
|
6.3
|
39.75
|
266.0
|
.057
|
5.12
|
8310
|
|
35
|
5.6
|
31.5
|
335
|
.045
|
4.28
|
10480
|
|
36
|
5.0
|
25.0
|
423
|
.036
|
3.62
|
13210
|
|
37
|
4.45
|
19.83
|
533
|
.028
|
-
|
16660
|
|
38
|
3.97
|
15.7
|
673
|
.022
|
2.5
|
21010
|
|
39
|
3.5
|
12.47
|
848
|
.018
|
-
|
26500
|
|
40
|
3.14
|
9.89
|
1070
|
.014
|
1.77
|
33410
|
|
41
|
2.8
|
7.842
|
-
|
-
|
1.52
|
-
|
|
42
|
2.494
|
6.219
|
-
|
-
|
1.28
|
-
|
|
43
|
2.221
|
4.932
|
-
|
-
|
1.060
|
-
|
The
following are the methods of computing for a power supply transformer.
Ex.1.
Compute and design a step down transformer with 220V primary and 6V secondary
with a core thickness of 15in and 13in width.
1. Core area (CA)= thickness x width
ex. 1in x 1in = 1 in2
2. Turns per volt (T/V)= 7.5/CA
ex. 7.5/ 1 = 7.5 turns/volt
3. Turns in primary (TP)= voltage
primary x T/V
ex. 220V x 7.5 = 1650 turns
4. Turns in secondary (TS)= voltage
secondary x T/V
ex. 6V x 7.5 = 45 turns
5. Wattage (W)= 25 x CA
ex. 25x 1 = 25 watts
6. Current in primary (IP)= W/voltage
primary
ex. 25/220V = 0.1136Amps
7. Current in secondary (IS)= W/voltage
secondary
ex. 25/6V = 4.17Amps
8. Size of wire Primary = IP x 1000
ex. 0.1136 x 1000 = 113.6 Gauge # 29 ( refer to Table 1. Table of copper wire)
9. Size of wire Secondary = IS x 1000
ex. 4.17 x
1000 = 4170 Gauge # 14 (
refer to Table 1. Table of copper wire)
The
following are the computation for the weight of wire estimate.
Compute
for the weight of wire using the Ex.1.
1. Perimeter (P)= 2(width + thickness)
ex. 2(1in+1in) = 4in
2. Length of Wire for Primary Winding in Feet
ex. x = [4in(1650turns)/12](2)(.51) =561ft
3. Length Wire in grams
let x = L (lbs/1000ft) (454) refer to table of
copper wire Table.1
ex.
x= 561(260)(454)=126374
4. Length of Wire for Secondary Winding in Feet
ex. x = [4in(45turns)/12](2)(.51) =521ft
5. Length Wire in grams
let x = L (lbs/1000ft) (454) refer to table of copper wire Table.1
ex. x= 26(260)(454)=16564
The following are the materials needed in making a
transformer.
·
Iron
core
·
Magnetic
wire
·
Bobbin
·
Cover
clamp
·
Insulating
varnish
·
Terminal
wiring
·
Fish
paper
·
Solder
The following are the tools and equipment needed for making
a transformer.
·
Rewinding
machine
·
Soldering
iron
·
Electrical
pliers
·
Cutter
pliers
·
Weighing
scales
·
Scissor
PROCEDURE
IN WINDING A POWER SUPPLY TRANSFORMER
The
following are the procedures in winding a power supply transformer.
1.
Prepare
the bobbin
Select an
appropriate bobbin for your transformer.
2.
Weighing
the magnetic wire
Weigh the
magnetic wire base on your computations above.
3.
Winding
the magnetic wire
Make sure
to tighten the magnetic wire while winding.
4.
Joining
broken wires
Solder
broken wires if applicable.
5.
Covering
the terminals
Cover the
terminals with fish paper making it tight.
6.
Assembling
“E” and “I” iron core
Assemble
“E” and “I” iron core alternately insuring not to bend them.
7.
Binding
the core
Bind the
core with a fish paper and a masking tape properly.
8.
Testing
the resistance and connectivity
Test the
transformer with a multi tester for its resistance.
9.
Testing
the voltage output
Test the
transformer with a multi tester for its voltage output.
10.
Varnishing
Varnish
the transformer for a strong hold of its core.
Conclusion
Therefore, transformer is a device
use to step down a voltage power and is extensively used in electronic
products. Core area, turns per volt, turns in primary, turns in secondary,
watts, primary current, secondary current and the sizes of wire should be well
computed to have an accurate output. To lessen the difficulty in purchasing the
materials, weight of wire should be computed. Proper procedures and steps
should be followed.
Book:
Agpaoa,
Feleciano C. 1988.Electrical Transformer Motor Winding, Rewinding and Trouble
Shooting. National Books Store 258 pp.
Online
Materials:
Related
study:
Dalaguit,
Angelo B. 2009. Power Supply Transformer Wire Estimate: Technology Guide
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