How To Find Power Efficiency

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Power supply current efficiency

Ability supply current efficiency

Electric current efficiency of the power supply is the maximum electric current the power supply should supply to the load, while maintaining all the parameters specified in the information sheet (output voltage, power etc.) and operating within the operating conditions (temperature, humidity etc.).

As per the SI system of units, the current intensity is expressed in amperes (A). The current can also exist expressed in milliamperes (mA).
i mA is 1/1000 A, i.e. 1000 mA = one A (e.m. 600 mA = 0.6 A).

Fig. 1. The human relationship between the power supply and the load
	2 - Load U - Voltage I - Current R - Load resistance P - Power generated past the load

Diagram (Fig. ane) shows the human relationship between the power supply (1) and the load (2). The source of electric ability (power supply), supplies the ability which is absorbed by the load. The load shown in the diagram with a resistor symbol has a resistance (R) and generates a power (P). The load can convert the electric power into another form of energy, e.g. light (light bulb) or heat (radiator).

The current efficiency is the maximum electric current, which may be supplied by the power supply to the load and is related to the power generated by the load. It results from a key law that governs all electrical circuits, i.e. the Ohm'due south law. It defines the human relationship between voltage (V), current (A), resistance (R) and ability (R).

Full general formula of Ohm's law:

A more useful formula of Ohm'southward law to calculate the maximum output electric current of the power supply:

After transposing, the formula for the maximum output power of the power supply is:

where:

I – output electric current in amperes (A),
P – ability in watts (W),
U – output voltage in volts (V),
R – load resistance.

Below is an example calculation (Ohm's law awarding) for the power supply with 12 V voltage and 5 A current efficiency.

Fig. 2. Ohm'south law applications (example calculations)

Power

Resistance

Current

Voltage

Other examples:

Power supply with 12 V output voltage and 10 A power efficiency. We will now calculate the maximum power:

Ability supply with 12 V output voltage and 150 W ability. We will at present calculate the electric current efficiency:

If the power supply is intended for continuous operation (24h), the rated electric current should not exceed 80% maximum current. Information technology is closely tied to temperature. The current efficiency (or power), must always relate to the operating temperature, i.eastward. ambient temperature of the power supply.

The temperatures exceeding l°C (preferably forty°C) should exist avoided, withal, some manufacturers may allow operation at higher temperatures. Maximum temperature specified by the manufacturer for some devices is 70°C; please refer to the specification. There are, however, devices available designed for operation at up to 30°C.

Example 1.

High quality modular power supply 12 V/12.5 A/150 W. Operating temperature: -10°C to seventy°C. The data sail includes a (Fig. three) load vs. operating temperature characteristic.

Fig. 3. Load vs operating temperature feature

The power supply may supply the load at total power up to 50°C. At an ambient temperature of 70°C, the device can be supplied at l%, i.e. at half of the maximum current. It means that at an ambient temperature of 70°C, the current efficiency of the power supply is halved. In this case it is reduced from 12.5 A to 6.25 A.

Case 2.

Modular power supply 12 Five/five A/lx W. Operating temperature: -10°C to forty°C. The data sheet includes an commanded output current (I_North) of the power supply vs. ambient temperature (t_amb) feature (Fig. four) (for momentary load).

Fig. four. Allowable output current (I_North) of the power supply vs. ambient temperature (t_amb) (for momentary load).

The power supply may supply the load at maximum electric current, merely upwardly to 30°C. At an ambient temperature of 40°C, the device tin be supplied at seventy%.
In that case:
– ambience temperature (t_amb) thirty°C – maximum current 5 A,
– ambient temperature (t_amb) 40°C – maximum current 3.v A.

Loftier quality power supply usually characteristic high operating temperature and loftier maximum rated current. Depending on its efficiency, some energy supplied to the device is converted into rut. If a low-efficiency power supply is installed in a airtight enclosure, the components that go heated may increase the temperature inside the enclosure. Which in turn may significantly reduce the current efficiency of the ability supply.

A temperature examination (Fig. 5) using a thermal imaging camera of a cheap 12V/10A modular power supply at different load currents at 25°C is shown below.

Fig. 5. Test temperature of a cheap modular ability supply using a thermal imaging camera
	A - Load 10 A B - Load 8 A C - Load 5 A

Some power supply components may get very hot, i.e. the output filter reactor. The power supply has a depression efficiency and a great amount of energy is lost due to heating.

For power supplies with the output voltage control, its current efficiency, i.e. the maximum electric current supplied to the load is specified by the manufacturer for the rated output voltage. If the output voltage is increased, the output current must exist reduced.

Example 3.

Power supply with 12 V output voltage and 500 W power with output voltage control (11.half-dozen to 16.2 Five). The current efficiency is calculated for 12 V rated voltage.