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In our generation, power supply is very important in our everyday living in the way like our
life will not be complete without it. Thats why they invented the transformer for power
transmission.
Being an electrical engineering student, we have known everything about power transmissionthrough the use of transformer. But will it be proper to know everything about transformer. Not
just the theoretical knowledge about transformer but how to construct a generating transformer.
But first we must know what a transformer is.
A transformer is a device which uses the phenomenon of mutual induction to change thevalues of alternating voltages and currents. In fact, one of the main advantages of a.c.
transmission and distribution is the ease with which an alternating voltage can be increased or
decreased by transformers.
Transformers range in size from the miniature units used in electronic applications to the
large power transformers used in power stations. The principle of operation is the same for each.
Now that we discuss what a transformer is, we will now tackle what will be the paper all
about.
In this paper we will be using laminated core or EI core power transformer. This is the mostcommon type of transformer, widely used in appliances to convert mains voltage to low voltage
to power electronics.
This paper will discuss about power transformers which converts AC to DC supply, and step
down the supply to 19-volts 5-amperes output. It will tackle how the transformers function and
its application, and how to compute the specification to construct such transformer. And tells
what are the needed apparatus and materials for the construction and what will be the step-by-step procedure on constructing this kind of transformer.
Although the transformer is not an energy conversion device, it is an indispensable
component in many energy conversion systems. As one of the principal reasons for the
widespread use of ac power systems, it makes possible electric generation at the most
economical generator voltage, power transfer at the most economical transmission voltage,
and power utilization at the most suitable voltage for the particular utilization device. Thetransformer is also widely used in low-power low-current electronic and control circuits for
performing such functions as matching the impedances of a source and its load for maximum
power transfer, insulating one circuit from another, or isolating direct current while
maintaining ac continuity between two circuits.
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Transformers are needed in electronic apparatus to provide the different values of plate,
filament, and bias voltage required for proper tube operation, and to maintain or modify wave
shape and frequency response at different potentials.
A transformer can convert AC (Alternating Current) to DC (Direct Current) supply
through the use of a rectifier.
Another function of the transformer is to allow AC voltage to be readily converted from
one voltage level to another. This way, the power can be generated at a relatively low
voltage. A transformer is used to step the voltage up to a transmission level close to the usepoint of the power, the voltage is stepped back down, and then routed to the transformer on
the utility pole behind the house or close to the industrial plant. The final step down
transformer changes the voltage to a utilization level. This kind of transformer is called the
power transformer.
Though, this paper will focus on the power transformer which converts AC to DC supply,and for electronic devices which uses low-power low-current supply, this function of
transformer for a high-power distribution is just included for better understanding of thefunction of a transformer.
Transformers are needed in electronic apparatus to provide the different values of plate,
filament, and bias voltage required for proper tube operation, and to maintain or modify wave
shape and frequency response at different potentials.
A power transformer with 19-volts and 2.1-amperes output with 60 hertz operating
frequency are usually applied in the charger of some electronic devices or apparatus.
One of its applications is on laptop or portable computer. Most of the laptop with this
output specification is Netbook, usually small in size and only use for searching and typing..
Another application is on television. Usually apply in wide screen flat televisions which
most of them are using an adaptor to connect to a source.
Any electronic devices or gadgets and appliances with this output specification will be
suitable to use for supplying power to operate.
Occasionally someone asks why electronic transformers cannot be designed according to
curves or charts showing the relation between volts, turns, wire size, and power rating. Suchcurves have appeared in magazines and have been used for small control transformers. The
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idea is that by means of such charts any engineer can design his own transformer. However,
this idea has not been found practicable for the following reason.
(a)Regulation. It regulates 220 Volts to 19 Volts, 2.1 Amperes and 60 Hertz output.This property is rarely negligible in electronic circuits. It often requires care and
thought to use the most advantageous winding arrangement in order to obtain the
proper IX and IR voltage drops. Sometimes the size is dictated by such
considerations.
(b)Frequency Range. It frequency is 60 Hertz fixed. The low frequency end of atransformer operating range in a given circuit is determined by the transformer open-circuit inductance. The high frequency end is governed by the leakage inductance and
distributed capacitance. Juggling the various factors, such as core size, number of
turns, interleaving, and insulation, in order to obtain the optimum design constitutes a
technical problem of the first magnitude.
(c)Voltage. It voltage is 19 Volts. It would be exceedingly difficult, if not impossible, toreduce to chart form the use of high voltages in the restricted space of a transformer.Circuit considerations are very important here, and the transformer designer must be
thoroughly familiar with the functioning of the transformer to insure reliable
operation, low cost, and small dimensions.
(d)Size. Its size is small, the same size with the adaptor of a netbook and notebooklaptop. Much electronic equipment is cramped for space and, since transformers often
constitute the largest items in the equipment, it is imperative that they, too, be smallsize. An open-minded attitude toward this condition and the use of good judgement
may make it possible to meet the requirements which otherwise might not be fulfilled.
The use of new materials, too, can be instrumental in reducing size in some
instances down to a small fraction of former size.
(e)Rectification. A rectifier is an electrical device use to converts alternating current(AC), which periodically reverses direction, to direct current (DC), which flows inonly one direction.
(f) Filter. A device that is designed to physically block certain objects or substanceswhile letting others through. This circuit reduces ripple voltage to become smooth DC
voltage.
Some advantages properties of a power transformer using EI core will be enumerated
below.
Widely available in power ratings ranging from mW to MW Insulated lamination minimizes eddy current losses Small appliance and electronic transformers may use a split bobbin , giving a high
level of insulation between the windings
Rectangular core
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Core laminate stampings are usually in EI shape pairs. Other shape pairs aresometimes used
Mu-metal shields can be fitted to reduce EMI (electromagnetic interference) A screen winding is occasionally used between the 2 power windings Small appliance and electronics transformers may have a thermal cut out built in
Occasionally seen in low profile format for use in restricted spaces Laminated core made with silicon steel with high permeability
Magnetic Circuit is made up of one or more closed loop paths containing a magneticflux.
Power factor is defined as the ratio of the real power flowing to the load to theapparent power in the circuit.
Split bobbin is the method of winding a transformer whereby the primary andsecondary are wound side by- side on a bobbin with an insulation barrier between the
two wingdings.
Mu-metal is a nickel-iron alloy that is notable for its high magnetic permeability. Eddy current loss is the induction of eddy currents within the core causes a resistive
loss.
Electromagnetic interference (EMI) is disturbance that affects an electrical circuitdue to either electromagnetic induction or electromagnetic radiation emitted from an
external source.
Permeability is the degree of magnetization of a material in response to a magneticfield.EI core is a sheets of suitable iron stamped out in shapes like the letters "E" and "I",
are stacked with the "I" against the open end of the "E" to form a 3-legged structure.
Biasing is the method of establishing predetermined voltages or currents at variouspoints of an electronic circuit to set an appropriate operating point.
Filament is a thin heating element. Alternating Current (AC) the movement of electric charge periodically reverses
direction.
Direct Current (DC) is the unidirectional flow of electric charge. Impedance is the complex ratio of the voltage to the current in an alternating current
(AC) caircuit.
RMS Value, In mathematics, the root mean square (abbreviated RMS or rms), alsoknown as the quadratic mean, is a statistical measure of the magnitude of a varying
quantity. It is especially useful when variates are positive and negative, e.g.,
sinusoids.
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AWG (American Wire Gauge) also known as the Brown & Sharpe wire gauge is astandardized wire gauge system used since 1857.
Interpolation means to estimate a value of (a function or series) between two knownvalues; to make insertions or additions.
Transformer is a device used to transfer electric energy from one circuit to another,especially a pair of multiply wound, inductively coupled wire coils that affect such a
transfer with a change in voltage, current, phase, or other electric characteristic.
Voltage Regulation is the change in voltage magnitude that occurs when the load (ata specified power factor) is reduced from the rated or nominal value to zero, with no
intentional manual readjustment of any voltage control, expressed in percent of
nominal full-load voltage.
Wiring is the material, as wire or rope, wound or coiled about anything, or a singleround or turn of the material; as (Elec.), a series winding, or one in which the
armature coil, the field-magnet coil, and the external circuit form a continuous
conductor; a shunt winding, or one of such a character that the armature current isdivided, a portion of the current being led around the field-magnet coils.
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Specification Needed:
Primary Voltage: 220 Vrms
Secondary Voltage, Current: 19 Volts dc, 2.1 Amperes
Operating Frequency = 60 Hz
Step 1:
Compute the total voltage across the secondary:
Esn = 2.35 Edc
Esn = 44.65 Volts
Where:Edc => Secondary Voltage in Volts
2.35 => twice the ratio of the RMS to average value plus
5% regulation
Step 2:
Compute the secondary currents from:
Is = k Idc
Is = 2.226 Amperes
Where:
Is => secondary current in Amperes
k => k factor (see Table 1)
Step 3:
Compute the output power in Watts.
Pout = Es Is
Pout = 99.3909 Watts
Where:
Es => Secondary Voltage in Volts
Is => Secondary current in Amperes
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Step 4:
Compute the required input power in Volt-Amperes.
VA =
out
(n)VA = 128.4568 Volt-Amperes
Where:
Pout => Required Output Power computed previously
n => efficiency of the transformer
0.9 => power factor
VA => Power input in Volt-Amperes
Step 5:
Assume a square core area for convenience and compute for the
required area and the size of the EI lamination.
A =
A = 2.0312 in2
Where:
A => cross section area of the core in square inches (n2).
Compute for the tongue width ( tw ) and the stacking height ( g ).
g = tw = g = tw = 1.4252 in
Then use Table 3 to choose the size of the EI lamination required.
g = tw = 1.5 in
The size of the EI lamination also gives the winding length ( wl ), which should
not exceed the tongue width ( tw ) and the allowable winding build-up which
should not be greater than the EI laminations window The details are shown in
Figure 6.
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Step 6:
Compute for the number of the primary and secondary turns Np
and Ns.
Np = Ep 1
f
Np = 473.9506 turns 474 turns
Ns = 1.05 Np ()Ns = 101.0105 turns 102 turns
Where:
Np => number of turns in the primaryNs => number of turns in the secondary
Ep => primary voltage in RMS (22CV)
Es => secondary voltage in RMS
f => frequency of operation in Hz (60Hz)
A => tongue area in square inches
B => flux density in Gauss (Table 3)
Step 7:
Compute for the size of the magnetic wires to be used for the coils.
Ip =
Ip = 0.5839 Ampere
Where:
Ip => current in the primary
Compute for the diameter of the wires for the primary and the
secondary coils.
d = 1.13 * I- login+
1
dp = 0.0246 inch diameter
ds = 0.0479 inch diameter
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Where:
d => diameter of the wire in inches
I => current in the wire in Amperes
Pin => required power in Volt-Amperes
The commercially available wire gauges based on the diameter of
the wire are shown in Table 4.
Primary wire size:
# 22 AWG, dp = 0.0253 inches
Secondary wire size:
# 16 AWG, ds = 0.0508 inches
Step 8:
Compute for the number of turns per layer. Initially compute for
the allowable winding length.
wl = tl2(margin)2(bobbin allowance)
wl = 1.936 inches
Where:
wl => winding length
tl => tongue length
margin => 0.125 inchesbobbin allowance => 0.032 inches
The number of turns per layer:
turns
layer=
wl
diameter of wire with insulation
Primary:
turns
r= 72.7820 turns/layer 73 turns/r
Secondary:
turns
r= 36.9466 turns/r 37 turns/r
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Step 9:
Compute the winding build up of the primary and secondary
winding.
WBtot = 1.1 (WBp + WBs + bobbin thickness + inter
winding insulation)
WBtot = 0.5086 inch
Where:
WBtot => total winding build up
WBp => winding build up in the primary
WBs => winding build-up in the secondary
Bobbin thickness => 0.095
Inter winding insulation => 0.002 number of winding
The total winding build up should not exceed 90% of the EI
laminations window If the computed value does exceed that
amount, choose a larger EI lamination and repeat steps 6, 8 and 9.
Step 10:
Compute for the total length of wires needed for the transformer.
Initially compute for the mean length of turns ( MLT ) of each
winding.
MLTp = 2 (tw + g + 4b) + WBp
MLTp = 7.3889 inches
MLTs = 2 (tw + g + 4b) + (2WBp + WBs)MLTs = 8.5306 inches
Where:
MLTp => mean length of turns in the primary
MLTs => mean length of turns in the secondary
g => stack height
b => bobbin thickness => 0.095
WB => winding build up
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The actual length of wires is computed from:
L = MLT N
Primary:
Lp = 3,502.3386 inches
Secondary:
Ls = 870.1212 inches
Where:
L => length of the wire
Step 11:
Since magnet wires are sold by the weight rather by length, thetotal weight of the wires are computed using
W(lbs) =
1
f
1
Primary:
Wp = 0.5677 lbs
Secondary:
Ws = 0.5669 lbs
Where:
W => weight of the wire in lbs
L => length of the wire
f => conversion factor (see Table 4)
Step 12:
Determine the percent efficiency ( ) and voltage regulation ( r )
from:
=out 1
outcore loss(copper loss) = 92.71%
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Vr = Is[ *+
]Vr = 0.024 or 2.4%
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Specification Needed:
Primary Voltage: 220 Vrms
Secondary Voltage, Current: 19 Volts dc, 2.1 Amperes
Operating Frequency = 60 Hz
Step 1:
Compute the total voltage across the secondary:
Esn = 2.35 Edc
Esn = 2.35 19V
Esn = 44.65 Volts
Where:
Edc => Secondary Voltage in Volts
2.35 => twice the ratio of the RMS to average value plus
5% regulation
Step 2:
Compute the secondary currents from:
Is = k Idc
Table 1: Factors K and K for Single- Phase Rectifier Supplies
Capacitor input K K
Full-wave
Half-wave
0.707
1.4
1.06
2.2
Is = 1.06 2.1A
Is = 2.226 Amperes
Where:
Is => secondary current in Amperes
k => k factor (see Table 1)
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Step 3:
Compute the output power in Watts.
Pout = Es Is
Pout = 44.65V 2.226A
Pout = 99.3909 Watts
Where:
Es => Secondary Voltage in Volts
Is => Secondary current in Amperes
Step 4:
Compute the required input power in Volt-Amperes.
VA =out
(n)
Table 2: Efficiencies for Various Sizes Power Supplies
Output in Watts Approximate Efficiency in Percent
20
30
4080100
200
70
75
808586
90
Note 1: The Interpolation
Step 1:
Find the range where the given value falls from the table.
Pout = 44.838 WattsRange available: 4080
Step 2:
Use the formula:
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x1- d1
x1- x=
y1- d
y1- y
Where:
x1is the smallest from the range of independent valuesd1is the given value
x is the highest in the range of independent values
y1is the dependent value ofx1
d is the dependent value of the given value
y
is the dependent value ofx
Computation:
-
-1 = - d
-
(0.969545)(-1) = (85d)
-0.6047585 = -d
2 = 85.969545
VA =
VA =
VA = 128.4568 Volt-Amperes
Where:
Pout => Required Output Power computed previously
n => efficiency of the transformer
0.9 => power factor
VA => Power input in Volt-Amperes
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Step 5:
Assume a square core area for convenience and compute
for the required area and the size of the EI lamination.
A =
A =1
A = 2.0312 in2
Where:
A => cross section area of the core in square
inches (n2).
Compute for the tongue width ( tw ) and the stacking height ( g ).
g = tw = g = tw = g = tw = 1.4252 in
Then use Table 3 to choose the size
of the EI lamination required.
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Table 3. EI Core Data on , Tongue Lamination, and D Core Weight
At 60 Hertz EI Type
Lamination
Tongue Width of
Lamination (inches)
Core
Weight(lb)EI B (gauss)
3.9
5.813.0
17.024.0
37.0
54.082.0
110
145
195525
14,000
14,00014,000
14,00013,500
13,000
13,00012,500
12,000
12,000
11,00010,500
EI 21
EI 625EI 75
EI 75EI 11
EI 12
EI 12EI 125
EI 125
EI 13
EI 13EI 19
0.5
0.6250.75
0.750.875
1.00
1.001.25
1.25
1.5
1.51.75
0.199
0.3610.609
0.8120.966
1.43
2.142.83
3.97
4.92
6.569.75
Since 1.5 is the closest value to 1.4252, choose EI-13.
g = tw = 1.5 inches
The size of the EI lamination also gives the winding length ( wl ), which should
not exceed the tongue width ( tw ) and the allowable winding build-up which
should not be greater than the EI laminations window
W =1
tw
W =1
(1.5)
W = 0.75 inch
tl =
tw
tl =
(1.5)
tl = 2.25 inches
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Step 6:
Compute for the number of the primary and secondary turns Np
and Ns.
Np = Ep 1
f
Np =1
1(1)Np = 473.9506 turns 474 turns
Ns = 1.05 Np
()
Ns = 1.05 (474)
Ns = 101.0105 turns 102 turns
Where:
Np => number of turns in the primary
Ns => number of turns in the secondary
Ep => primary voltage in RMS (22CV)
Es => secondary voltage in RMSf => frequency of operation in Hz (60Hz)
A => tongue area in square inches
B => flux density in Gauss (Table 3)
Step 7:
Compute for the size of the magnetic wires to be used for the coils.
Ip =
Ip =1
Ip = 0.5839 Ampere
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Where:
Ip => current in the primary
Compute for the diameter of the wires for the primary and the
secondary coils.
d = 1.13 * I- login+
1
dp = 1.13 * -log1+
1
dp = 0.0246 inch diameter
ds = 1.13 * -log1+1
ds = 0.0479 inch diameter
Where:
d => diameter of the wire in inches
I => current in the wire in Amperes
Pin => required power in Volt-Amperes
The commercially available wire gauges based on the diameter of
the wire are shown in Table 4.
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Table 4: Magnet wire data on diameter, resistance, and Core Weight.
AWG
B & S
Gauge
Diameter in inchesOhms per1000 Ft.
Pounds per1000 Ft.
Margin min inchesBare Enamelled
101112
13
14
15
16
17
1819
2021
22
2324
25
2627
28
29
30
31
3233
34
35
36
37
3839
40
0.10190.09270.808
0.0719
0.0641
0.0571
0.0508
0.0453
0.04030.0359
0.03200.0285
0.0253
0.04030.0359
0.0179
0.01590.0142
0.0126
0.0113
0.0100
0.0089
0.00800.0071
0.0063
0.0056
0.0050
0.0045
0.00400.0035
0.0031
0.10390.09270.0827
0.0738
0.0659
0.0588
0.0524
0.0469
0.04180.0374
0.03340.0299
0.0266
0.02390.213
0.0190
0.01690.0152
0.0135
0.0122
0.0109
0.0097
0.00880.0079
0.0070
0.0062
0.0056
0.0050
0.00450.0040
0.0036
0.99891.2601.588
2.003
2.525
3.184
4.016
5.064
6.3858.051
10.1512.80
16.14
20.3625.67
32.37
40.8151.47
64.90
81.83
103.2
130.1
164.1206.9
260.9
329.0
414.8
523.1
659.6831.8
1049
31.4324.9219.77
15.68
12.43
9.858
7.818
6.200
4.9173.899
3.0922.452
1.945
1.5421.223
0.9699
0.76920.6100
0.4837
0.3836
0.3042
0.2413
0.19130.1517
0.1203
0.0954
0.0757
0.0600
0.04760.0377
0.0299
0.250.250.25
0.25
0.25
0.25
0.1875
0.1875
0.18750.1562
0.15620.1562
0.125
0.1250.125
0.125
0.1250.125
0.125
0.125
0.125
0.125
0.09370.0937
0.0937
0.0937
0.0937
0.0937
0.06250.0625
0.0625
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Primary wire size:
# 22 AWG, dp = 0.0253 inches
Secondary wire size:
# 16 AWG, ds = 0.0508 inches
Step 8:
Compute for the number of turns per layer. Initially compute for
the allowable winding length.
wl = tl2(margin)2(bobbin allowance)
wl = 2.252 (0.125)2 (0.032)
wl = 1.936 inches
Where:
wl => winding length
tl => tongue length
margin => 0.125 inches
bobbin allowance => 0.032 inches
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The number of turns per layer:
turns
layer=
wl
diameter of wire with insulation
No. of Layers =turns
layer
Primary:
turns
layer=
turns
r
= 72.7820 turns/r 73 turns/r
No. of Layers =
No. of Lrs = 6.4932 7 rs
Secondary:
turns
layer=
turnsr
= 36.9466 turns/r 37 turns/r
No. of Layers =1
No. of Lrs = 2.7568 3 rs
Because some figures were rounded off, check if the values still
satisfy the number of turns in the primary winding.
Checking:
turns
layer=
p
o of ayers\
No. of Turns = turnslayer
(No. of Layers)
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For Primary:
turns
layer=
turns
r= 67.714 turns/r 68 turns/r
No. of Turns = (68)(7)
No. of Turns = 476 turns
For Secondary:
turns
layer=
1
turnsr
= 34 turns/layer
No. of turns = (34)(3)
No. of turns = 102 turns
Step 9:
Compute the winding build up of the primary and secondary
winding.
p = o of layers in primary (dp inter layer
insulation)
WBp = 7 (0.0266 + 0.002)
WBp = o.2002 inch
s = o of layers in secondary (dsn inter layer
insulation)
WBs = 3 (0.0524 + 0.002)WBs = 0.1632 inch
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WBtot = 1.1 (WBp + WBs + bobbin thickness + inter
winding insulation)
WBtot = 1.1 (0.095 + 0.2002 + 0.1632 + 2 (0.002))
WBtot = 0.5086 inch
Where:
WBtot => total winding build up
WBp => winding build up in the primary
WBs => winding build-up in the secondary
Bobbin thickness => 0.095
Inter winding insulation => 0.002 number of winding
The total winding build up should not exceed 90% of the EI
laminations window If the computed value does exceed that
amount, choose a larger EI lamination and repeat steps 6, 8 and 9.
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Step 10:
Compute for the total length of wires needed for the transformer.
Initially compute for the mean length of turns ( MLT ) of each
winding.
MTp = (tw g b) WBp
MTp = (1 1 ()) ()
MLTp = 7.3889 inches
MLTs = 2 (tw + g + 4b) + (2WBp + WBs)
MTs = (1 1 ()) ( () 1)
MLTs = 8.5306 inches
Where:
MLTp => mean length of turns in the primary
MLTs => mean length of turns in the secondary
g => stack height
b => bobbin thickness => 0.095
WB => winding build up
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The actual length of wires is computed from:
L = MLT N
Primary:
Lp = 7.3889 474
Lp = 3,502.3386 inches
Secondary:
Ls = 8.5306 102
Ls = 870.1212 inches
Where:L => length of the wire
Step 11:
Since magnet wires are sold by the weight rather by length, the
total weight of the wires are computed using
W(lbs) =
1
f
1
Primary:
Wp =
1
1
1
Wp = 0.5677 lbs
Secondary:
Ws =
11
1
1
1
Ws = 0.5669 lbs
Where:
W => weight of the wire in lbs
L => length of the wire
f => conversion factor (see Table 4)
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a. Winding resistances (From Table 4)Rp =
p
1
11
1
Rp =
1
11
1
Rp = 4.7106
Rs =s
1
1
1
Rs =11
1
1
1
Rs = 0.2912
Where:
Rp => winding resistance in the primary
Rs => winding resistance in the secondary
b. Copper lossesCp = Ip2 Rp
Cp = (0.5839)2 (4.7106)Cp = 1.606 Watts
Cs = Is2
Rs
Cs = (2.1)2 (0.2912)
Cs = 1.2842 Watt
Ctot = Cp + Cs
Ctot = 1.606 + 1.2842
Ctot = 2.8902 Watts
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Where:
Cp => copper loss in the primary
Cs => copper loss in the secondary
Ctot => total copper loss
c. Core loss (From Table 5 and Table 3)Core loss = (Approx. Core loss) (Core Weight)
Table 5: Core characteristics data at different operating frequencies.
Freq.
inHertz
Lamination
Thickness(inches)
Core
Material
Core Flux
DensityBm in Gauss
Approximate
Core Lossin Watts/Lb
25
6060
400800
0.025
0.0140.014
0.0040.004
2.5% silicon
4% siliconGrain-oriented silicon
Grain-oriented siliconGrain-oriented silicon
14,000
12,00015,000
10,0006,000
0.65
1.01.0
4.54.5
Core loss =1 att
1 lb(4.92 lb)
Core loss = 4.92 Watts
Where:
Core loss is inatt
lb
Core weight is in lb
d. Voltage DropVDp = Ip Rp
VDp = (0.5839) (4.7106)
VDp = 2.7505 Volts
VDs = Is Rs
VDs = (2.1) (0.2912)
VDs = 0.6115 Volts
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Where:
VDp => voltage drop in the primary
VDs => voltage drop in the secondary
Step 12:
Determine the percent efficiency ( ) and voltage regulation ( r )
from:
=out 1
outcore loss(copper loss)
= 1
() = 92.71%
Vr = Is[ *+
]
Vr = (2.1) [ *+ ]Vr = 0.024 or 2.4%
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Summary of Design Computations.
Winding
DC
Voltage at
ratedcurrent
AmpereNumber of
TurnsAWG#
Weight
Needed
Primary
Secondary
220 V
19 V dc
0.58 A
2.1 A
474
102
22
16
EI lamination to be used is EI-13
The Output Transformer
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Step 6:
Immerse the core and the windings in a can of varnish for 10 to 15 minutes. This
is an insulation also. Remove and let the transformer dry
Step 7:
To complete everything, bake the transformer in the cover for about four hours or
let it dry for a couple of days to let the varnish dry and remove its sticky nature.
Step 8:
Now your transformer is ready for testing.