Matching Your SCR Clamps with Your Needs
There are different types of SCR devices. The most popular and the most widely used type for applications requiring large, high amperage SCR devices, is what is commonly known as a Hockey Puk SCR device. It is called a Hockey Puk, because of its shape, which resembles a traditional hockey puck. Big SCR devices typically generate large amounts of heat. Heat is a major problem for SCR devices, just as it is for all electronic devices. SCR’s are constructed in a flat circular package, which allows both heat and electrical current to transfer from both the anode and the cathode of the SCR device, with as little resistance, both thermal resistance and electrical resistance, as possible.
The SCR design makes it very efficient for removing heat, but it also makes it more complicated to use. First of all, usually it requires two heat sinks, instead of one, one for the anode and one for the cathode. Then, it requires a special SCR clamp, or heatsink clamp, to hold it all together. This clamp must be calibrated to exert sufficient force to hold everything together efficiently, so as to minimize any resistance, whether it is thermal resistance, or electrical resistance. This is extremely important. It is this clamping force which creates the electrical and thermal connections to the SCR device. Therefore, it is very critical to accurately tighten the clamp and to accurately gauge the proper amount of pressure.
Over tightening of the SCR clamp, or under tightening, as well is failing to maintain a parallel force on the pole face of the SCR device will usually lead to premature failure. Therefore, it is critical that the clamping force applied to the semi conductor pole faces, must be the specified amount of force recommended by the manufacturer of the SCR device. It is also essential that the force being applied is spread evenly across the entire surface of both pole faces and the pole face plane of the SCR device. The SCR clamp must apply the force evenly, so as not to cause any mechanical stress to be transferred to the semi conductor element. It must run smoothly across the entire range of temperatures to which the SCR device will be exposed.
If the SCR clamp is not applied properly, it can cause all sorts of problems. It could crack the semi conductor element. It could also cause current crowding, which could cause the semi conductor to have excessive hotspots, with poor thermal conduction causing overheating of the semi conductor element. On the other hand, when the disc clamps are installed properly along with properly sized heatsinks, they will provide a good electrical contact, with low thermal resistance and this will ensure proper heat removal. This is why it is so important to choose your SCR clamps properly and to get the exact specifications from the manufacturer of the SCR device, in order to know how much pressure should be applied.
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