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I need help urgently with this.

Feel free to reply on whichever forum.

Thanks!

 

What value resistor in your gate circuits? For that high-power SCR you are probably not supplying enough gate current to turn it on, nor is there enough anode current with just an LED on 5v for it to latch on.

 

What value resistor in your gate circuits? For that high-power SCR you are probably not supplying enough gate current to turn it on, nor is there enough anode current with just an LED on 5v for it to latch on.

Thanks for your reply.

If you look through the other forum, you will see that I have tried with numerous different resistors and also tried to use a dc motor on it.

Also I have just tried to put a 12v dc motor connected to 12v - then other end connected to K of thyristor and 12v + connected to A of thyristor then 3.3V dc into Gate of thyristor. Still does not work.

Thanks again, and any ideas would be much appreciated!

 

This is what I am trying to do.

Once this works, I will be using the thyristor in a much larger high power circuit.

 

The LED is in backwards in that circuit.

Also needs a dropping resistor.

 

The LED is in backwards in that circuit.

Also needs a dropping resistor.

Yep, realised that!!! Any ideas as to why it's not working? (I have put the LED in the correct way!!!)

What is a dropping resistor?

 

Try this circuit:

 

Try this circuit:
View attachment 345283

Will try that now. Thanks!

 

Dropping resistor is "R2" in the circuit above. (post #7)

It's a current limiter for the LED.

 

Thanks, the circuit above works!
How can I run 400V DC through the thyristor using that circuit above?

Thanks again, we seem to be getting somewhere!

 

Did you read the image that you posted? That thyristor could require up to 270 mA to trigger. The trigger supply must be able to source that much current.

 

Did you read the image that you posted? That thyristor may require up to 270 mA to trigger. You must supply that much current from your low voltage supply.

How could I get that much current to trigger when it has a maximum gate voltage of 1.5V?

 

I also NEED to be able to run 400V DC through it. So not sure how to connect that up with the circuit above.

 

I also NEED to be able to run 400V DC through it. So not sure how to connect that up with the circuit above.

 

View attachment 345284View attachment 345285

Thanks, will try it out in the morning!

 

How do you plan to switch it off once it has latched on ?
Les.

 

How could I get that much current to trigger when it has a maximum gate voltage of 1.5V?

Assuming a 5V supply and the worst case 270 mA to trigger and utilizing Ohm’s law:

R= (5-1.5)/0.27= 12.963 ohm
Use a 13 ohm standard value resistor.

 

How do you plan to switch it off once it has latched on ?
Les.

Thanks for your question. Once it latches on, all that happens is the capacitors will fully empty and then it should switch off. Once it is off, I can then recharge the capacitors and cycle again.

I have not yet tested the new circuit, but will also require a diode to stop back current from blowing the thyristor.

Does this look good? If so, what size diode do you think I would require to stop the back current? I have put in two diodes.

Thanks all!

 

View attachment 345284View attachment 345285

Ive just tried this out, but it does not work. For testing purposes I tried it with 12v as the 400V with a 12V dc motor as the LOAD and the thyristor does not trigger.
Do you know what could cause this?

 

Ive just tried this out, but it does not work. For testing purposes I tried it with 12v as the 400V with a 12V dc motor as the LOAD and the thyristor does not trigger.
Do you know what could cause this?

It may be because of current interrupting in brushes system.
Connect incandescent 12 V bulb parallel to motor,
and see how it will works.