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Energy losses in transformers, rectifiers and mains adaptors

The aim is, to see if energy can be saved by using the correct components.

E-I transformers versus toroidal transformers

First I measured the energy losses in two transformers, both with 50 VA power rating.
One transformer is a conventional transformer with a E-I core.
The other transformer is one with a toroidal core. E-I core transformer  2x 24 V  50 VA Toroidal transformer 2x 9V  50 VA

From the transformers, I measured the output voltage at several loads.
The input power of the transformer is measured with my energymeter .
From this data I calculated output power, power loss, and efficiency of the transformer

The efficiency is output power divided by input power.
The power loss is the difference between output power and input power, the power loss is converted into heat in the transformer.

The two transformers have different output voltages, because of that I use for the two transformers different values of load resistors.
The output windings of the transformers are series connected.

Table 1: Losses in E-I core transformer 2x 24 V   50 VA

 Load resistors parallel Output voltage (Volt a.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 9.1 0.000 0.000 9.100 1x 560 Ω 51.0 18.1 4.645 0.257 13.455 2x 560 Ω 50.6 21.9 9.144 0.418 12.756 3x 560 Ω 50.2 25.3 13.500 0.534 11.800 4x 560 Ω 49.8 28.7 17.715 0.617 10.985 6x 560 Ω 49.1 35.5 25.830 0.728 9.670 8x 560 Ω 48.5 42.6 33.604 0.789 8.996 10x 560 Ω 47.7 49.3 40.630 0.824 8.670

Table 2: Losses in toroidal transformer 2x 9 V  50 VA

 Load resistors parallel Output voltage (Volt a.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 1.16 0.000 0.000 1.160 1x 82 Ω 20.1 5.33 4.927 0.924 0.403 2x 82 Ω 20.0 9.97 9.756 0.979 0.214 3x 82 Ω 19.7 14.38 14.198 0.987 0.182 4x 82 Ω 19.4 18.70 18.359 0.982 0.341 6x 82 Ω 19.1 27.70 26.693 0.964 1.007 8x 82 Ω 18.7 35.90 34.116 0.950 1.784 10x 82 Ω 18.4 43.50 41.288 0.949 2.212 Graph 1:
Efficiency versus output power
and power loss versus output power.
1 =   E-I core transformer (see table 1)
2 =   Toroidal transformer (see table 2)

Losses in rectifiers.

The following measurements show the effect of several kinds of rectifiers on power loss.

Rectifier with 4 silicon diodes Circuit diagram 1The toroidal transformer 2x 9V 50 VA is connected in this way to a rectifier circuit. The two 9 V windings are parallel connected, the rectifier consists of 4 silicon diodes (3.7A bridge rectifier). The value of the elco is 4700 μF.

Table 3: Losses in toroidal transformer + 4 silicon diodes, corresponding to circuit diagram 1.

 Load resistors parallel Output voltage (Volt d.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 13.46 1.17 0.000 0.000 1.170 1x 47 Ω 12.26 3.98 3.198 0.804 0.782 2x 47 Ω 11.84 7.22 5.965 0.826 1.255 3x 47 Ω 11.53 10.15 8.486 0.836 1.664 4x 47 Ω 11.28 13.14 10.829 0.824 2.311 6x 47 Ω 10.80 18.67 14.890 0.798 3.780 8x 47 Ω 10.40 23.41 18.410 0.786 5.000 10x 47 Ω 10.03 27.95 21.404 0.766 6.546

Rectifier with 2 silicon diodes Circuit diagram 2. The rectifier is now connected in this way, with two silicon diodes (instead of 4). The two diodes are part of the 3.7 A bridge rectifier used in circuit diagram 1, the two other diodes stay unused. The two windings of the transformer are series connected. The transformer is the same 2x 9V 50 VA toroidal. The value of the elco is 4700 μF.

Table 4: Losses in toroidal transformer + 2 silicon diodes, corresponding to circuit diagram 2.

 Load resistors parallel Output voltage (Volt d.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 13.95 1.17 0.000 0.000 1.170 1x 47 Ω 12.94 4.00 3.563 0.891 0.436 2x 47 Ω 12.47 7.46 6.617 0.887 0.843 3x 47 Ω 12.10 10.60 9.345 0.882 1.255 4x 47 Ω 11.80 13.60 11.850 0.871 1.750 6x 47 Ω 11.23 19.05 16.100 0.845 2.950 8x 47 Ω 10.78 23.86 19.780 0.829 4.080 10x 47 Ω 10.30 28.06 22.572 0.804 5.488

Rectifier with 2 schottky diodes Circuit diagram 3 Now the 2 silicon diodes are replaced by 2 schottky diodes, type MBR360 (3A 60V). The transformer is the same 2x 9V 50 VA toroidal. The value of the elco is 4700 μF.

Table 5: Losses in toroidal transformer + 2 schottky diodes, corresponding to circuit diagram 3

 Load resistors parallel Output voltage (Volt d.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 14.22 1.17 0.000 0.000 1.170 1x 47 Ω 13.30 4.20 3.764 0.896 0.436 2x 47 Ω 12.79 7.69 6.961 0.905 0.729 3x 47 Ω 12.43 10.86 9.862 0.908 0.998 4x 47 Ω 12.10 14.06 12.460 0.886 1.600 6x 47 Ω 11.48 19.51 16.824 0.862 2.686 8x 47 Ω 11.00 24.32 20.596 0.847 3.724 10x 47 Ω 10.57 28.80 23.771 0.825 5.029 Graph 2:The values for efficiency and power loss from table 3, 4 and 5 are shown in these graphs. The use of 2 schottky diodes gives the best efficiency, and the lowest power loss.

Losses in several kinds of power supplies and mains adaptors

Toroidal  2x 6V 15 VA  I have build this power supply with the following components:
1 toroidal transformer 2x 6V 15 VA
2 schottky diodes MBR360 and an elco of 4700 μF.

The output voltage is not stabilized.

Table 6: Toroidal transformer 2x 6V 15 VA

 Load resistors parallel Output voltage (Volt d.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 9.48 < 0.50* 0.000 0.000 < 0.500 1x 82 Ω 8.95 1.18 0.977 0.828 0.203 2x 82 Ω 8.65 2.11 1.825 0.865 0.285 3x 82 Ω 8.41 3.05 2.588 0.848 0.462 4x 82 Ω 8.20 3.98 3.280 0.824 0.700 5x 82 Ω 8.01 4.63 3.912 0.845 0.718 6x 82 Ω 7.84 5.56 4.497 0.809 1.063 8x 82 Ω 7.50 6.94 5.488 0.791 1.452 10x 82 Ω 7.23 8.07 6.375 0.790 1.695

* My energy meter cannot measure power below 0.5 W. Switch mode mains adaptor Brand: HQ Model: P.SUP.SMP1-BLThis adaptor is adjustable between 3 and 12 Vdc. The output voltage is stabilized, so constant. But I did notice this adapter can cause interference if connected to e.g. radio's or telephones. This adaptor is tested at 9 volt output voltage.

Table 7: switch mode mains adaptor

 Load resistors parallel Output voltage (Volt d.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 9.06 < 0.50 0.000 0.000 < 0.500 1x 82 Ω 9.05 1.87 0.999 0.534 0.871 2x 82 Ω 9.04 3.01 1.993 0.662 1.017 3x 82 Ω 9.02 4.40 2.977 0.677 1.423 4x 82 Ω 9.00 5.56 3.951 0.711 1.609 5x 82 Ω 8.98 6.72 4.917 0.732 1.803 6x 82 Ω 8.97 8.14 5.887 0.723 2.253 7x 82 Ω 8.95 9.30 6.838 0.735 2.462 Non stabilized mains adaptor. Brand: MW Model: MW79GSThe output voltage is adjustable between 3 and 12 V, and tested at 9V. The maximum output current is 800 mA. The adaptor has internal a small E-I core transformer.

Table 8: non stabilized mains adaptor 800 mA

 Load resistors parallel Output voltage (Volt d.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 12,42 2,22 0,000 0,000 2,220 1x 82 Ω 11,56 6,68 1,630 0,244 5,050 2x 82 Ω 10,99 7,58 2,946 0,389 4,634 3x 82 Ω 10,50 8,25 4,034 0,489 4,216 4x 82 Ω 10,08 8,97 4,956 0,553 4,014 5x 82 Ω 9,74 9,63 5,785 0,601 3,845 6x 82 Ω 9,40 10,21 6,465 0,633 3,745 Stabilized mains adaptor. Brand: Skytronic Model: MW300GSThe output voltage is adjustable between 1.5 and 12 V, and tested at 9V. The maximum output current is 300 mA.

 Load resistors parallel Output voltage (Volt d.c.) Input power (Watt) Output power (Watt) Efficiency Power loss (Watt) - 9.40 1.60 0.000 0.000 1.600 1x 82 Ω 9.35 6.44 1.066 0.166 5.374 2x 82 Ω 9.32 6.82 2.119 0.311 4.701 3x 82 Ω 9.29 7.93 3.157 0.398 4.773 Graph 3:
Efficiency en power loss for:
6 = Power supply with toroidal transformer (see table 6)
7 = Switch mode mains adaptor (see table 7)
8 = Non stabilized mains adaptor (see table 8)
9 = Stabilized mains adaptor (see table 9)

Conclusion:

By using toroidal transformers, energy can be saved in power supplies.
Especially at low output current, the toroidal transformer is much better then the E-I core transformer.
Also by using schottky diodes and rectifiers with 2 diodes (instead of 4), energy can be saved.

Every reduction of losses, can save at long term quite some energy.
Every Watt saving, gives per year a saving of 8.76 kWh.

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