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soft starter by using thyrister with arduino

Thread starter #1
asalam o allikum

I am planning to start building a soft starter by using arduino which can control inrush current of three phase induction motor.

by using Arduino I don't know how to trigger the thyristor.i don't have any code or relevant data of this project.

can anyone know about it?????????
 

MikeMl

Well-Known Member
Most Helpful Member
#2
Use optical-isolation between the Arduino ports and the gates of the thyristors. Only safe way to do it...
 

MaxHeadRoom78

Well-Known Member
#3
I built one for a Universal motor, but a 3ph one is called a soft start contactor. They can be purchased ready made.
See the Fairchild app note AN-3006 for suitable opto's . you will need a Random phase type for each phase, rather than zero crossing version.
Max.
 
#4
asalam o allikum

I am planning to start building a soft starter by using arduino which can control inrush current of three phase induction motor.

by using Arduino I don't know how to trigger the thyristor.i don't have any code or relevant data of this project.

can anyone know about it?????????
if you have the circuit diagram please share it
 

rjenkinsgb

Active Member
#5
You need to use phase control, so you synchronise with the incoming AC and initially trigger the power devices very late in each half cycle, to give a low current to the load.

Gradually advance the phase timing to increase the current as the load has time to accelerate, until eventually the load is getting full power and you can bypass the electronics with a contactor.

In essence it's a bit like three "light dimmer" circuits working together.
(Or just two - some soft starts directly connect one phase and control the other two).

To isolate the firing signals from the thyristors or triacs, you can either use opto-triacs, made for firing power triacs etc., or pulse transformers.
Pulse transformers are more often used in high power systems.

eg.
http://www.farnell.com/datasheets/97984.pdf

https://www.newark.com/oep-oxford-electrical-products/pt6/pulse-transformer-1-1-1-8-h-1/dp/03M5000

An example of using a pulse transformer (the lower right part of this)
http://lh3.ggpht.com/-qv9-0CilM-Q/TflJ47V2X7I/AAAAAAAABSE/21Nar7kpAmM/28_thumb1.jpg?imgmax=800
 

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