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What is the difference between the built-in bypass and the external bypass of the soft starter?

Mar 20, 2021

What is the difference between the built-in bypass and the external bypass of the soft starter?

Speaking of the built-in bypass and external bypass of the soft starter, we must first understand: What is the bypass here? Why is there a distinction between built-in and external?


To answer this question, you have to start with the thyristor.



SCR is the core component of the soft starter. Excessive current for a long time will cause a lot of pressure on it. If you rely on the circuit board to trigger the SCR, it is also prone to problems. The soft starter is mainly used in the process of starting the motor, and online protection in the power frequency operation, so you can use the traditional contactor, which is equally convenient and reliable. Therefore, soft starters are used with contactors.


Both the built-in bypass and the external bypass are essentially a contactor that is connected in parallel with the soft starter. The only difference is that one does not use an external contactor and runs directly after starting, which is the built-in bypass. The contactor is outside the soft starter and needs additional configuration, so it is an external bypass.



In a word: the difference between the external bypass and the built-in bypass is: one contactor is outside the soft starter and one is inside. The advantage of the external bypass is that the contactor is outside, so you can drag more than one. However, the disadvantage is that the contactor needs to be purchased additionally, and the soft starter plus the contactor occupies more area. The advantage of the built-in bypass lies in its small size and high cost performance. The disadvantage is that it can only be one-to-one.


In summary, the built-in bypass and the external bypass have their own advantages and disadvantages, and the key is to combine requirements.