（一）The selection principle of radiator is as follows:
1. Calculate the heating power of the element.The actual heating power P of the element is calculated according to the voltage of the element used and the actual current passed:
P=IT(AV)VTO+[IT(RMS)]2rO
Where: IT(AV): the average current passing through the element
VTO: The threshold voltage of the element
IT(RMS) : The square-root value current passing through the element
RO: The slope resistance of the element
2.Determine the heat resistance Rth of the radiator:
Rth = delta T/P
Wherein: T is the increased value of the element shell temperature, the shell temperature allowed maximum value according to the different use of the element is usually 55 ~ 95℃, usually select 80℃, with this temperature value minus the environmental temperature (according to the specific circumstances of the bad selection, did not explain when 40℃ selection), is △T.
3.Select radiator:
The radiator should be selected according to the following conditions:
(1) According to the actual use of components or customer requirements to choose the way of heat dissipation - water cooling or air cooling
(2) Determine the ambient temperature and △T according to the actual use of components and heat dissipation mode.
(3) According to the component size, customer installation size, in-out line mode, the size of the wind speed, heat resistance of the radiator and other conditions to determine the radiator
（二）Pressure mounting of radiator
In view of the fact that many customers do not know how to properly install the components when they are pressing, we have sorted out the precautions for radiator pressing for your reference:
1. First of all, the power semiconductor components must generate heat loss when they are working.But if the heat is too great, and there is no time to dissipate to the surrounding media, the element will exceed its normal operating temperature and fail.Therefore, it is one of the most important conditions for components to work reliably.
2. The surface of the radiator must match the size of the surface of the components to prevent flattening and bending and damage the components.
3, radiator table must have a high level, finish.The countertops of components and radiators shall be kept clean and free of grease and other stolen goods during installation. Bare hands shall not be allowed to touch the metal surfaces.
4, the installation should ensure that the component mesa and radiator mesa completely parallel, concentric.During installation, pressure shall be applied through the center line of the component to use and evenly distribute the pressure throughout the contact area.It is recommended to use torque wrench for manual installation. Apply alternating and even force to all fastening nuts. The pressure shall meet the specified requirements.
5. When the water-cooled radiator is used repeatedly, special attention should be paid to check whether the table is smooth and flat, whether there is scale and blockage in the water cavity, especially pay attention to whether the table is sunken, if there is an appeal situation should be replaced.
6. When many maintenance customers have component damage, use the multimeter to detect. If there is a bad one, buy a good one and put it in.Actually this kind of hidden danger is very big.Firstly, it is impossible to make quantitative judgment on the pressure resistance of components detected by multimeter. Secondly, the used components do not match the newly equipped components, so it is easy to burn out the new components, which will cause greater loss to customers.(2) Determine the ambient temperature and △T according to the actual use of components and heat dissipation mode.
(3) According to the component size, customer installation size, in-out line mode, the size of the wind speed, heat resistance of the radiator and other conditions to determine the radiator.