Aluminum radiator for LEDs

It is known that the service life of LEDs directly depends on the quality of the material used in the semiconductor, as well as the ratio of the device current to the amount of heat generated. The light output gradually decreases, and after it is half of the original value, the service life of the LED will begin to decrease. The duration of the devices can be up to 100 000 hours, but only on condition that it is not affected by high temperatures.

To cool devices that produce heat, radio electronics use a device such as a radiator for LEDs. The removal of heat from aggregates to the atmosphere is achieved by two methods.

The first way to cool LEDs

This method is based on the emission of thermal waves into the atmosphere, or thermal convection. The method relates to a discharge of passive cooling. Part of the energy enters the atmosphere with a radiant infrared stream, and part goes through the circulation of heated air from the radiator.

Among the technology for LEDs, the passive cooling circuit has become most widespread. It does not have rotating mechanisms and does not require periodic maintenance.

The disadvantages of this system include the need to install a large heat sink. Its weight is large enough, and the price is high.

The second method

It was called turbulent convection. This method is active. In this system, fans or other mechanical devices that can create air currents are applicable.

The active cooling method has a higher level of performance than the passive method. But the unfavorable weather conditions, the presence of a large amount of dust, especially in the open space, do not allow installing such schemes everywhere.

Manufacturing of radiators

When choosing a material, the following rules should be observed:

• The heat conductivity index should be not less than 5-10 W. Materials with a lower value can not transfer all the heat that the air takes.
• The level of thermal conductivity above 10 watts from a technical point of view will be redundant, which will entail unnecessary cash costs without improving the efficiency of the device.

As a rule, aluminum, copper and ceramics are used for the production of radiators. They produce devices based on plastic that dissipates heat.

Aluminum accessories

The most popular LED radiator is made of aluminum. The main disadvantage of the device is that it consists of a number of layers. This inevitably causes transient thermal resistances, which can be overcome by means of additional heat-conducting materials: substances on the glue, insulating plates, materials for filling air gaps.

Aluminum radiator for LEDs is used more often than others. He is prone to pressing and copes well with the removal of heat.

For an active cooling level, as a rule, a flat sheet of aluminum is required, the size of which is not larger than the size of the luminaire. The sheet is blown by a fan.

A suitable temperature for the operation of the LED is 65 ° C. However, the lower the temperature, the higher the efficiency of the device and the greater its resource. The optimum surface temperature of the radiator is 45 ° C, but not higher. For a diode with a power of 1 W, it is necessary to install an aluminum radiator. The area of the radiator is 30-35 cm ² . The LED 3 W radiator will require doubling the area and will be 60-70 cm ² .

As the radiator is best suited device from aluminum as the easiest and relatively inexpensive. When calculating the device for LED matrices, a ratio of 35 cm to 1 W is taken.

For cooling systems of an active nature, the area of the radiator may be smaller by a factor of 10. The LED 1 W suffices 3-3.5 cm ² .

For example, consider a radiator "star" for LEDs. The device is used to divert heat from the LED and is a small radiator. It is based on a plate made of a composite material - aluminum is used, which removes heat from the LED, and copper foil with contact pads. The radiator is mounted on LEDs with a high power rating (1-3 W).

Radiators from copper

The devices contain a copper plate. Copper has a higher thermal conductivity than aluminum. Its inclusion in the scheme is justified.

But in general, the metal is inferior to aluminum in terms of weight and technical characteristics. Copper is not a ductile metal. The manufacture of a device from copper by pressing is economical. A sharp treatment leaves a lot of waste of expensive material.

Radiators made of ceramics

A successful model is a ceramic radiator for LEDs, which are initially applied to traces that conduct current. Directly to them, the LEDs are soldered. Such a design leaves heat twice as much compared to devices made of aluminum.

Radiators made of plastic

Heat dissipating devices made of plastic are of some interest. And this is understandable, since the cost of this material is lower than the price of aluminum, and the level of manufacturability is higher.

But the level of thermal conductivity of ordinary plastics is not higher than 0.1-0.2 W / (m · K). Achieving an acceptable indicator is possible with the help of different fillers. When replacing the heat sink from aluminum to a device based on plastic (of equal value), the temperature in the temperature range is raised by 4-5%. Proceeding from the fact that the heat conductivity index of heat-dissipating plastics is lower than that of aluminum (8 W / (m · K) versus 220-180 W / (m · K)), we conclude: plastic can compete with aluminum.

Design features of radiators

Many people are asking: Which radiator for a LED is better?

There are two groups of modifications:

• Needle-like;
• Ribbed.

For example, a radiator for a 10W LED is represented by a ribbed LED-device.

The first type is usually used for the natural method of cooling LEDs, and the second - for forced. With the same dimensions of the passive needle device is 70% higher than the efficiency of the ribbed view.

Radiators for high-power LEDs are needle-shaped. They are designed for high-power LEDs, but this does not mean that ribbed plate-based devices are only suitable for functioning with a fan. Depending on the geometric parameters, they are also used for cooling of a passive nature.

The radiator for LEDs of any configuration can have a square, rectangular or circular shape.

How to calculate the area of the radiator. Methods for obtaining precise parameters of device parameters

In this case, a number of important factors are taken as a basis:

• Indicators of ambient air;
• Level of dispersion area;
• Radiator modification;
• Features of the material from which the heat exchanger is made.

But all these nuances are needed for the designer who is developing the heat sink.

As a rule, amateur radiators are used as a rule. All that is required is the knowledge of the maximum power dissipation factor of the heat exchanger.

The first method

The area is calculated by the formula F = a x Cx (T1 - T2), where Φ is the heat flux and S is the surface area of the radiator (the sum of the areas of all the edges or needles and substrate in square meters), T1 is the temperature indicator of the discharge medium Heat, and T2 are the temperatures of the heated surface.

When calculating the area, you should pay attention to the fact that the rib or plate has two surfaces for heat dissipation.

Calculation of the surface of the needle is made along the circumference of the circle (π × D), multiplied by the height index.

For surfaces not polished, the heat transfer coefficient is 6-8 W / (m ² · K).

The second method of calculation

There is another simple formula, which is obtained by experiments.

S = [22 - (M x 1.5)] x W, where S is the area of the heat exchanger, W is the power supplied (W), and M is the unused power of the LED.

For a ribbed type of radiator made from aluminum, you can use the data provided by engineers from Taiwan. Data does not have accuracy, as indicated in the ranges with a large run-in. In addition, the definition is suitable for the climatic conditions of Taiwan. They can be taken as a basis only for preliminary calculations.

How to make a radiator with your own hands?

Radio amateurs are rarely accepted for the manufacture of heaters by their own hands, since this element requires special responsibility. After all, this device has an effect on the long-term service of the LED. But it happens that the masters resort to the manufacture of a heat exchanger from improvised means.

First option

The design is unified. It is a circle that is cut from aluminum. There are incisions in it. The resulting sectors are slightly bent. The result is a detail that looks like a fan impeller. On the axes of the device, four antennae are bent, serving as the attachment device. The LED can be fixed with thermal paste and self-tapping screws.

Option 2

The radiator for LEDs can be made with your own hands from a fragment of an aluminum pipe with a rectangular cross section.

Materials you need:

• Pipe measuring 30x15x1.5 mm;
• A press washer whose diameter is 16 mm;
• Thermal adhesive;
• Thermal paste KTP-8;
• Ш-shaped profile 265;
• Self-tapping screws.

To optimize the convention, three holes are drilled, the diameter of which is 8 mm, and in the profile - holes with a diameter of 3.8 mm for fastening by means of screws.

LEDs are glued to the pipe - the main part of the radiator - with the help of thermal glue. In places where the radiator parts are connected, a layer of thermal paste KTP-8 is applied.

Then proceed to assemble the structure using self-tapping screws with a press washer.

Methods of attaching LEDs to the radiator

LEDs are attached to the device using two methods:

• Mechanical;
• Gluing.

Glue the LED with thermal glue. For this purpose, a little glue is applied to the surface of the metal, then the LED is put on it. To obtain a good connection, the LED is pressed down by the load until the adhesive is completely dry. But most masters prefer to use a mechanical method.

At the present time, special panels are produced, through which it is possible to make a diode installation in the shortest possible time. Some models provide additional clamps for secondary optics. The installation is very simple. On the radiator is set LED, then on it - the panel, which is attached to the base with self-tapping screws.

Conclusion

The cooling radiator for high-quality LEDs has become the key to the durability of the device. Therefore, choosing the device, you should be extremely careful. It is better to resort to the use of factory heat exchangers. They are available in radio shops. The cost of devices is high, but the installation of LEDs on them is easy, and the protection is different in quality and reliability.