5 replies to this topic

[suma]

hi all,
i need power electronic circuits that wark as soft starter of induction motor,using SCRs and TRIACs.

[marke]

Hello suma

The power circuitry is very simple, it requires an AC switch in series with one or more phases to the motor. the AC switch can be a triac, a reverse parallel connected SCR diode or reverse parallel SCR SCR circuit.

Se http://www.lmphotonics.com/sstart.htm
It is that simple, the problems are in the control systems.

Best regards,

[zara]

What rating should be used if the SCR is directly connected to the 220V 50Hz power cord?

[marke]

Hello zara

The voltage rating of the SCR should be at least 3 times the voltage of the AC supply.
For a 230 volt supply, the voltage should be 690 volts.

Best regards,

[zara]

Thanks, marke.
This voltage rating is rms voltage rating, right? How about the current rating should be used if the load is 1000W which is also connected to power cord supply directly? Normally the current rating is rms rating or average rating?

[marke]

Hello zara

voltage rating is rms voltage rating, right?

Correct

How about the current rating should be used

You should calculate the junction temperatures and ensure that the junction temperature of the SCRs do not exceed the maximum rated junction temperature.
The junction temperature is a function of the SCR thermal characteristics and the heatsink characteristics.

Best regards,