Designing an inverter
transformer can be a complex affair. However, using the various formulas and by
taking the help of one practical example shown here, the operations involved
finally become very easy.
The present article explains through a practical example the process of applying the various formulas for making an inverter transformer. The various formulas required for designing a transformer has been already discussed in one my previous articles.
Designing an Inverter
Transformer with the Help of a Practical Example
An inverter is your
personal power house, able to transform any high current DC source into readily
usable AC power, quite similar to the power received from your house outlets.
Although inverters are extensively available in the market today, but designing
your own customized inverter unit can make you overwhelmingly satisfied and
moreover it's great fun.
At Bright Hub I have
already published many inverter circuit diagram, ranging from simple
to sophisticated sine wave and modified sine wave designs. However folks keep
on asking me regarding formulas that can be easily used for designing a
inverter transformer. The popular demand inspired me to publish one such
article dealing comprehensively with transformer design calculations.
Although
the explanation and the content was up to the mark, quite disappointingly many
of you just failed to grasp the procedure. This prompted me to write this
article which includes one example thoroughly illustrating how to use and apply
the various steps and formulas while designing your own transformer. Let’s
quickly study the following attached example:
Suppose you want to
design an inverter transformer for a 120 VA inverter using a 12 Volt automobile
battery as the input and need 230 Volts as the output. Now, simply dividing 120
by 12 gives 10 Amps, this becomes the required secondary current.
The data in hand are:
Primary Voltage = 230
Volts,
Secondary Current
(Output Current) = 10 Amps.
Secondary Voltage (Output
Voltage) = 12-0-12 volts, that is equal to 24 volts.
Output Frequency = 50
Hz
First we need to find
the core area CA = 1.152 ×√ 24 × 10 = 18 sq.cm
We select CRGO as the
core material.
Calculating Turns per
Volt TPV = 1 / (4.44 × 10-4 ×18 × 1.3 × 50) = 1.96
Calculating Primary
Current = (24 × 10) / (230 × 0.9) = 1.15 Amps,
By matching the above
current in Table A we get the approximate Primary copper wire thickness = 21
SWG.
Therefore the Number
of Turns for the primary winding is calculated as = 1.96 × 230 = 450
Next, Primary Winding
Area becomes = 450 / 137 (from Table A) = 3.27 sq.cm.
Now, the required
secondary current is 10 Amps, therefore from Table A we match an equivalent
thickness of copper wire = 12 SWG.
Calculating Secondary
Number of Turns = 1.04 (1.96 × 24) = 49.
Calculating Secondary
Winding Area = 49 / 12.8 (From Table A) = 3.8 Sq.cm.
Therefore, the Total
Winding Area Comes to = (3.27 + 3.8) × 1.3 (insulation area added 30%) = 9
sq.cm.
Calculating Gross Area
we get = 18 / 0.9 = 20 sq.cm.
Next, the Tongue Width
becomes = √20 = 4.47 cm.
Consulting Table B yet
again through the above value we finalize the core type to be 6 (E/I)
approximately.
Finally the Stack is
calculated as = 20 / 4.47 = 4.47 cm
Table
A
SWG------- (AMP)------- Turns
per Sq.cm.
10-----------
16.6---------- 8.7
11-----------
13.638------- 10.4
12-----------
10.961------- 12.8
13-----------
8.579--------- 16.1
14-----------
6.487--------- 21.5
15-----------
5.254--------- 26.8
16-----------
4.151--------- 35.2
17-----------
3.178--------- 45.4
18-----------
2.335--------- 60.8
19-----------
1.622--------- 87.4
20-----------
1.313--------- 106
21-----------
1.0377-------- 137
22-----------
0.7945-------- 176
23-----------
0.5838--------- 42
24-----------
0.4906--------- 286
25-----------
0.4054--------- 341
26-----------
0.3284--------- 415
27-----------
0.2726--------- 504
28-----------
0.2219--------- 609
29-----------
0.1874--------- 711
30-----------
0.1558--------- 881
31-----------
0.1364--------- 997
32----------- 0.1182---------
1137
33-----------
0.1013--------- 1308
34-----------
0.0858--------- 1608
35-----------
0.0715--------- 1902
36-----------
0.0586---------- 2286
37-----------
0.0469---------- 2800
38-----------
0.0365---------- 3507
39-----------
0.0274---------- 4838
40-----------
0.0233---------- 5595
41-----------
0.0197---------- 6543
42-----------
0.0162---------- 7755
43-----------
0.0131---------- 9337
44-----------
0.0104--------- 11457
45-----------
0.0079--------- 14392
46-----------
0.0059--------- 20223
47-----------
0.0041--------- 27546
48-----------
0.0026--------- 39706
49-----------
0.0015--------- 62134
50-----------
0.0010--------- 81242
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