If an inverter is running during the summer, the temperature of its casing may become high to the point of feeling hot to the touch. So, is it good or bad for the inverter casing to be hot? And why does the casing feel hot? Below, we will analyze and answer these two questions in relation to inverter cooling.
Common Metal Thermal Conductivity Coefficients and Radiator Material Selection
Main Contents
Selection of common metal thermal conductivity and radiator materials. The table below shows the thermal conductivity coefficients of common metals:
|
Metal Material |
Heat conduction coefficient |
|
Au |
317W/mK |
|
Ag |
429W/mK |
|
Cu |
401W/mK |
|
Al |
237W/mK |
|
Fe |
48W/mK |
From the table above, it can be seen that silver has the best thermal conductivity, followed by copper and gold, then aluminum. Radiators are usually made of aluminum because aluminum is lighter in weight, cheaper in price, corrosion-resistant, and can be processed into various complex shapes using processing equipment. It can meet the many requirements of the electronic and power industries for radiators, making it the best material for making radiators.
|
Key devices |
Rated operating temperature(°C) |
|
Inductance |
120 |
|
Current sensor |
85 |
|
relay |
85 |
|
Electrolytic capacitor |
105 |
|
diode |
175 |
|
IGBT |
175 |
The components in the inverter have their rated working temperature. If the inverter has poor heat dissipation performance, the heat generated by the components cannot be transferred to the outside as it continues to operate, causing the temperature of the components to increase. High temperature will reduce the performance and lifespan of the components. In order to maintain the working temperature of the internal components of the inverter within the rated temperature range and ensure its performance and service life, it is necessary to use thermal conductivity materials to transfer the heat generated by the inverter to the outside.
From the perspective of heat conduction, the more balanced the temperature inside and outside the inverter, that is, the closer the temperature of the internally heating components, heat sink, and casing is to the outside temperature, the better the heat conduction. If the outside of the inverter is cold and the inside is hot, it means that the heat dissipation performance of the inverter is not optimal. This is similar to the relationship between a thermos and a regular cup:
As we all know, when cups containing water at the same temperature are compared, a regular cup loses heat faster than a thermos and its walls become hotter than those of the thermos. This is because there is a vacuum between the inner and outer walls of the thermos, which acts as an insulator and prevents the heat from escaping, thus achieving its insulation effect. On the other hand, the walls of a regular cup are made of a single layer of material which can transfer heat better, so the walls become hot but the temperature of the water decreases faster than in the thermos.
The principle of heat dissipation in an inverter is similar to that of a regular cup. It allows the heat generated by the internal components of the inverter to be quickly dissipated, thus achieving the goal of rapidly reducing the temperature of the internal components of the inverter and improving its performance and service life.
As we can see from the above, good heat dissipation performance is very important for the inverter. The basic principles of heat generation and dissipation in an inverter will be explained in detail below.
Inverter Heat Dissipation and Design
In an electrical circuit, active components generate heat whenever electricity flows through them. The main heat-generating components in an inverter are the switching transistors (IGBT, MOSfet) and magnetic components (inductors, transformers). Therefore, in order to ensure that the components can operate at their rated temperature, the system’s heat dissipation ability is crucial.
It is inevitable for inverters to generate heat during operation. For example, a 5kW inverter generally generates heat equivalent to 1.5-2.5% of its total power output. The heat loss is about 75-125W. Therefore, cooling is very important for the system. In the case of small household systems, the industry usually uses natural cooling methods.
To achieve excellent cooling performance, the following points can be implemented:
① The larger the cooling area, the better the effect.
For example, for a 5kW inverter with a heat output of 125W, the cooling area should be at least 0.25m2 based on the maximum heat flux density of 0.05W/cm2 for natural cooling at 60℃. To keep the volume unchanged, the surface area of the heat sink can be increased by adopting a multi-finned and corrugated design, which increases the contact area between the heat sink and air and facilitates rapid cooling.
②Enclosure-Radiator Tight Coupling Structure
The inverter enclosure is made of aluminum alloy, which has good thermal conductivity. As shown in the figure above, the integral enclosure structure is adopted, and the radiator is directly and closely connected to the enclosure through a large area, so that the heat generated by the components can be directly transferred to the aluminum alloy enclosure through the radiator, forming a heat dissipation path of component-radiator-enclosure-air.
In addition, the heat generated by the components can also be conducted to the enclosure through the internal air of the inverter, and then dissipated to the external air through the enclosure, forming another heat dissipation path of component-internal air-enclosure-external air.
If a non-integral enclosure is used, the shell and the radiator need to be connected twice, and the contact is not tight. Therefore, only the radiator and a small part of the intermediate shell participate in the heat dissipation, and the upper shell does not participate in the heat dissipation, which greatly reduces the overall heat dissipation performance.
It can be seen from the above that the integral enclosure structure is adopted, and the radiator is directly and closely connected to the enclosure, allowing the aluminum alloy enclosure to participate in heat dissipation through two paths. Because more heat dissipation is involved, the temperature of the inverter enclosure is relatively high. The benefit of this phenomenon is that the good thermal conductivity of the enclosure can quickly transfer the internal heat of the inverter, thereby reducing the internal temperature of the inverter and the component temperature, ensuring longer service life of the components and the inverter.
Reasons for inverter casing heating and hotness
In order to better and faster reduce the temperature of components, ensure a longer service life of the components, the design of the integrated casing in close contact with the heat sink is adopted to make the casing an important part of the system heat dissipation, enhance the heat dissipation performance, and increase the temperature of the casing, which is a normal phenomenon during inverter operation.
Body temperature: The human body’s temperature sense is around 36℃, which will have a warm feeling; at around 45℃, there will be a hot feeling; at around 50℃, prolonged contact will cause a burning sensation; at 60℃, prolonged contact will cause burns.
Due to the need for inverter heat dissipation and the special nature of the working environment (direct sunlight outdoors), safety standards stipulate that the inverter casing temperature should not exceed 70℃. When the external environment temperature is 40℃ in summer, the casing temperature is generally between 55℃ and 60℃. Therefore, when people touch the inverter casing, they will feel hot.
Conclusion
From the two main perspectives of the relationship between component temperature and lifespan, and the principle of inverter heat dissipation structure, the casing has become a part of the system heat dissipation device, which can share part of the heat generated by the components. Although the casing temperature rises and generates heat, the temperature of the internal components of the inverter will decrease more and faster! This ensures longer lifespan and normal operation of the components and inverter.
In summer, when the outside temperature reaches 38℃, the temperature of the inverter casing is generally around 60℃ (the safety standard for inverter casing temperature should not exceed 70℃), and touching the inverter casing will feel hot. However, even if there is heat generation, it will not cause burns.
