Calculation of power supply for 12v LED strip
LED lighting equipment consumes much less power than traditional incandescent or halogen lights. But many LED devices, including strips, are powered from 12...36 volts. At lower voltages, even moderate power causes quite large currents to flow. Therefore, it is necessary to approach the choice of power supply for the LED strip consciously.
Pulsed or transformer
For many decades, network power supplies were built according to the scheme: step-down transformer - rectifier - filter. This principle has not become obsolete today, and in many cases this is the best way to go about it.. But with the development of electronics, switching power supplies have been used more and more often. Despite the complexity of the circuitry, they have undeniable advantages:
- lightness;
- small size;
- High efficiency, which in theory could be equal to 100%.
The disadvantages include the generation of high-frequency noise into the network (which can lead to malfunctions of sensitive devices powered from the same network) and into the load. To combat the first problem PSUs are equipped with filters at the input (inexpensive sources are performed by a simple scheme or are absent). The second problem for LEDs is not important. Therefore, the choice is made - lightweight and powerful switching power supplies are used to power LED devices.
Choosing a power supply by electrical characteristics
The calculation of the power supply for any LED strip should start with the voltage. It must match the power supply voltage of the strip. If the voltage is higher, the light will fail quickly. If it is lower, it will shine at half-voltage.
The second important parameter is the maximum power. It is calculated by the following formula:
Rist=Rood*Lens*Kzapwhere:
- Rist - is the minimum power of the power supply;
- Ore - specific power consumption (power consumed by 1 meter of webbing);
- L tapes - total length of web sections;
- Kzap - is a safety factor, it can be between 1.2 and 1.4.
Some values should be considered in more detail.
How to determine the power consumption of one meter of tape
The easiest way to determine the power consumption per meter of webbing is from the technical specification. This parameter is explicitly stated there. If it is not available, but you know the type of tape, you can find this characteristic in various sources.
If this is also not possible, in many cases the specific consumption can be determined with a ruler. To do this you have to measure LED dimensions and determine its form factor. From this characteristic you can find the power consumption of one LED, count their number per meter and multiply.
| LED | 3528 | 5050 | 5630 | 5730-1 | 5730-2 |
| Dimensions, mm | 3,5х2,8 | 5х5 | 5,6х3 | 4,8х3 | 4,8х3 |
| Power consumption, W | 0,06 | 0,2 | 0,5 | 0,5 | 1 |
| Current consumption, A | 0,02 | 0,06 | 0,15 | 0,15 | 0,3 |
The only problem is that some LEDs are available in different versions - with one crystal or with 2-3. In this case, the power will differ by 2-3 times. And the only way to find the required parameter is to take the smallest section of the strip and feed it from a source of knownly higher power. Measuring the current in amperes and multiplying it by the supply voltage (12 V or other), you can get the specific power of the segment (W). By counting the number of sections in a meter you can get the desired value.
If you do not have an ammeter, you can measure the resistance of the resistor mounted on the segment before connecting it to the power supply (or count it if the markings are available). After the power is applied, measure the voltage across it and find the current using the known ratio: I=U/Rwhere I - is the required current in amperes, U - is the supply voltage in volts, R - is the resistance of the resistor.
Why we need a safety factor and what it takes into account
If you select a power supply without a safety factor, it will operate at the limit of its capacity. This mode has its own disadvantages:
- "The Chinese watt may be less than a normal watt.. In all seriousness, this means that the actual maximum wattage of inexpensive power supplies from Southeast Asia is often less than declared.
- Some of the electronic components at maximum current (and maximum heat) have a shortened life span. This is especially true for winding parts (transformers, chokes), which in low-cost power supplies are handmade from thin wire with low-quality insulation.
- If a power supply has poorly soldered contacts (this is quite common), then at maximum current they will heat up and the quality of the connection will deteriorate. This will cause even more heat, and so on all the way to failure.
- If the room temperature rises slightly, the electronic unit goes to its limits and its service life is unpredictably shortened.
- The power consumed by the lighting system depends on the circuitry (although not critically). The configuration of the illuminator may contain: dimmer(s), RGB controller, driver (or several), an amplifier (possibly more than one), other devices.
All these devices consume currents for idling and for their own needs (power for internal circuitry, etc.), their efficiency is not 100%. Compared to the currents consumed by LED-lights, they are small. But if the PSU operates in the "on the edge" mode, this small addition can become critical.
Based on these considerations, the real situation is to add to the calculated power when 20 or 40 percent.
Other features of the power supply
After calculating the electrical characteristics of the power supply for LED strips, it is necessary to pay attention to other parameters.
Design (degree of protection)
Power supplies are available in different versions:
- sealed - Recommended for outdoor installation, as they are protected from precipitation;
- non-hermetic - it is better to install them indoors, because they are cheaper.
In addition, PSUs of sealed version are less cooled, which means that they will be prone to overheating indoors.
Type of cooling
In this category, voltage sources are subdivided into devices:
- with free cooling;
- with forced cooling.
Forced ventilation of the internal space of the unit is carried out by installing a fan, which is switched on and off by the built-in temperature sensor. Such a design has sufficiently powerful sources, and relatively low-current are performed without fans.
The use of a hood reduces the size of the unit by reducing the size of the heatsinks, but the fan is noisy. The closer to the end of the service life, the louder the noise. Therefore, such sources should not be installed in living rooms, as well as in rooms with people (office, etc.)
Example of switching-mode power supply power calculation
As an example of how to choose a suitable power supply for LED strip, you can set the conditions:
- Apeyron 00-12 RGB outdoor RGB strip is used as a lighting fixture;
- supply voltage - 12 V;
- Power consumption - 14.4 W/m;
- Length of segments - 12 m.
We will also need a RGB controller, and to it (for such a length of the tape), and the amplifier.
We calculate the required power according to the above formula:
- L ribbon = 12 m;
- Ore=14,4 W/m.
The installation is outdoor, so the cooling will be good, but there are two additional consumers in the scheme. You can take a safety factor of 30% or 1.3.
Pист=Руд*Lленты*Кзап=14,4*12*1,3=224,64 Вт.
Rounding up should only be done upwards. There are sources for 250 W on wide sale. You have to choose such a device with IP68 rating to install it outdoors.
Another option. You have to power Apeyron SMD2835-60LED monochrome tape, designed for 12 volt. All you need is 1.5 meter of tape with power consumption of 9.6 W/m. Dimmer is not needed, other additional devices are not needed. The power supply can be installed so as to provide a good airflow. There should be no other sources of elevated temperature nearby. The safety factor can be taken at the lower level, equal to 1.2. The power is calculated:
Pист=Руд*Lленты*Кзап=9,6*1,5*1,2=17,28.
A 12-volt power supply with a capacity of 25 watts will do. Devices with natural cooling are made for such power, hermetic design is not needed.
Important! Sometimes power supply manufacturers specify the highest operating current instead of the power rating. It must be converted into power according to the formula Rist=Uslave*Imaxwhere Urap - is the power supply voltage, and Imax - is the highest operating current.
At the end of the video example.
To the question of calculating the load capacity of the LED strip power supply must be approached responsibly. A mistake to the lesser side can cost the loss of an expensive unit, and to the greater side - to unjustified financial costs.