Dear all expert,

I a new member in this forum. Hope will get some suggestion and opinion from you.

I a final year electrical student, and currently need to select the final year project.

I fell very interested to do a simple soft starter for 3 phase induction motor. The soft starter i suggest to

build only have 2 feature: user can select ramp up and ram down time.

since i new in power electronics field, my question is

from your experience, will this project can be easily to do (for just the learning purpose), or need to do a lot

of work and will make life very difficult? because i found that it is really hard (likely don't have) to find the

complete soft starter schematics on website. all website are just introduce the theory of the soft starter.

Do any website have the schematics for references? Do you recommend student to do this type of project?

hope will get the answer from you. thank you very much :-)

Hello KCC

Welcome to the forum.

While the basic concept of the soft starter is relatively simple, there are some complex issues to be resolved if the starter is to perform with stable results under all operating conditions.
I do not know of much information freely available that will help you identify and overcome these issues. Most of the work has been done outside of the public domain and so is not published.
If you just want to get a soft starter operating without concern for optimum results, then the project is relatively easy. If you want to develop the project to be a potentially commercial proposition, then it is not so easy.
The big thing however, is that you are essentially on your own due to the lack of "design" information in the public domain.
Variable speed controllers, are a different issue with a lot of information publicaly available. Although conceptually, these are a much more difficult and complex product, it is probably easier to build one from scratch due to the amount of information and specific modules available.

While you may be able to get some answers here on the forum, do not expect the forum users to do your project "by remote control". The forum users provide answers on a voluntary basis and are not always correct, certainly, they have no responsibility to provide answers.

Have a good day and good luck with your project,

Dear Marke,

Thank for your reply. I have gain more confident after view your answer. Yes, I don’t need for optimum result, but at least the project can function properly. Hope will continue get the support and guides from you along the project.
I have some question regard on soft starter design and hope will get some comments from you.

1)Can I use microcontroller to directly firing the SCR pair without using the pulse transformer. I hope it can reduce my budget and the circuit complexity.

2)How to select the rating for SCR pair if I just want to design the soft starter for 1hp to 5hp, 3phase induction motor. (voltage level=415V line to line, 50 hertz)

3)I wish to control power flowing for each phase of the induction motor. Since each phase is 120o apart, and I wish to use only 1 zero crossing circuit, so how to calculate the time delay for the other two phase in order to get the same firing angle?

Hello kcc



1) Think about the voltages on the SCRs and the voltage on the microcontroller.

2) Perhaps you should talk to the SCR suppliers and look at their application notes.

3) This depends on the architecture you chose to use.

Please remember, this is your project, you need to work out ways of achieving the results based on research that you do.

Best regards,