There is no more false triggering with this value. Before, if you reset the SCR still triggers. The biasing and the blocking diode that was added gives satisfactory results. But as you suggested, I will try to add a resistor maybe a 10K to the cathode of D7 to ground would be suffice.

 

Shouldn't you have a high value resistor from the cathode of D7 to ground to give he leakage currents a place to go?

Final Drawing incorporating your suggestion to give the leakage currents a place to go. Thanks for all the suggestions and the design by Alec_t, eetech00, KISS and many other experts in this forum to make it all possible to finish this project. I found this design to be simple, less components, easy to trouble shoot, reliable and attain what I want to achieved on this project. Keep it up guys and hoping I would return such help you parted on me to others and hopefully they may get something useful for this project. Thank you very much AAC Forum.

 

I suspect D7 and R10 are now redundant, but hey, if it works it works . Good result.

 

I suspect D7 and R10 are now redundant, but hey, if it works it works . Good result.

Yes, Alec_t, it works and it works fine. There is no more false triggering by the SCR. It is stable and perfect for my application. Forget that redundancy between D7 and R10 as long as no false triggering. Thank you very much for your design. I really appreciate it very much.

 

I must admit...
You Guys did a very Good Job.

 

I must admit...
You Guys did a very Good Job.

Thanks R!f@@, the benefit all goes to Alec_t and eetech00 who give a simple design and a workable model and of course your comments and insights on the design. There is one comment though but it was not included in the beginning of the design was that when the alarm is triggered and it goes after some time like a instantaneous earth fault, it should remain an alarm until you press the reset. The idea is to determine what causes the tripping of the circuit breaker.

 

I have added 1 NO Contact to latch the relay when there is alarm and another NO Contact to give supply to the timer. This addition in the circuit will set the alarm to latch even it goes until you press the reset.
My question is, can we change the relay contacts to use transistor instead?

 

You could use another SCR instead of the NO contact to latch the relay. The SCR anode/cathode would be connected between the bottom end of the coil and the ground rail. The top of the coil would connect to +48V, and the SCR gate would connect, via a suitable voltage-divider, to the 'Alarm' input.

 

Alec_t, I have implemented the above diagram and it work fine. The idea is to make the component less and simple to trouble shoot as long as the output satisfy your requirements. I think this design is final and need to design the PCB for possible production. Again, Thank you for all the efforts, ideas and thoughts for this project.

 

as long as the output satisfy your requirements.

They're your requirements, not mine . Glad it does what you want.

 

This is the proto type for this project.