No contact AC voltage sensing

[lilimike]

Hi to all, I haven't been here in a long time, I have a busy life...

I have this project in mind... actually it is not in mind anymore, it is near completed;
I have a generator that is connected to a breaker in the mains electrical panel with an interlock which prevents the generator breaker from being ON at the same time as the main breaker.

So on a typical bad day I get a power failure, I switch the mains breaker OFF, move the interlock and turn the generator breaker ON and start the gen which restores the power for some of the house.
The problem is, when the mains power comes back I am not aware of it, specially if it happens during the day.

I have programmed an ESP8266 to trigger an email when a gpio sense the voltage near the mains' breaker.
The part where I am unsure is the AC detection circuit, This common circuit is popular but I have seen 2 versions of it and I am wondering if one is better than the other.

I know what a resistor is but what is the difference between those circuits, more specifically the resistors on the Darlington pair?

 

[danadak]

The resistors limit the base drive in T2 and T3 in event
there is strong coupling on the antenna from other
sources like radio stations. They also help to desensitize
the circuit from stray signal; coupling.

Not exactly a robust design, either circuit.

A better choice - https://www.onsemi.com/download/data-sheet/pdf/mid400-d.pdf


Regards, Dana.

 

[lilimike]

Thanks for the quick response Dana.

So my understanding is, the circuit with no resistors would be more sensitive?

MID400 is not really an option as I need to have no contact. The problem is the gen is sending voltage in the mains panel so I need to detect what comes in from the meter and I don't want to mess nor have the right to access that part.

I have taken into account some lever of stray signal, my design gets the signal from the circuit above via an ADC pin and it takes 4 samples in 5 seconds interval.

 

[crutschow]

Add a RC low-pass filter with a 50-60Hz corner and the will attenuate any higher frequency interference.

Wrap a few turns of the antenna wire around the mains cable to get a good signal level.

 

[ronsimpson]

So my understanding is, the circuit with no resistors would be more sensitive?

Not more sensitive, but better at very strong signals.

 

[ZipZapOuch]

Why not just ask a neighbor without a generator backup system to plug the ESP8266 into a USB adapter and plug that adapter into his outlet. You'll get the email when they get power.

 

[lilimike]

ZipZapOuch
That is a good suggestion but I would prefer to keep my stuff on my side of things.

crutschow
I've assembled the circuit, the one with no resistors and definitely not ideal as I get a strong signal from as far as 12 inches away from the breaker panel. I would like to try adding the RC filter, does this makes sense?

 

[ZipZapOuch]

Why not just ask a neighbor without a generator backup system to plug the ESP8266 into a USB adapter and plug that adapter into his outlet. You'll get the email when they get power.

Then connect an inexpensive (expendable) USB adapter between your mains and switch - you can put a breaker in tween if it makes you feel better. It will see the mains power, send the email as soon as power is restored.

 

[lilimike]

Then connect an inexpensive (expendable) USB adapter between your mains and switch - you can put a breaker in tween if it makes you feel better. It will see the mains power, send the email as soon as power is restored.

I am not sure I understand, or maybe I didn't explain properly my setup...
I have an interlock like below, when power goes out I turn off the mains breaker, lift the interlock and turn on the gen breaker which is providing power to he full panel. I want to place my device to sense AC just above the mains breaker.

 

[Nigel Goodwin]

Why not just use a mains voltage change over relay, with the coil powered from the generator input - as the generator starts the relay automatically switches the relay over. It's automatic, nothing manual to do, and you can't get it wrong.

 

[ZipZapOuch]

Why not just use a mains voltage change over relay, with the coil powered from the generator input - as the generator starts the relay automatically switches the relay over. It's automatic, nothing manual to do, and you can't get it wrong.

Such as...

Generac RXSC100A3 100-Amp Automatic Smart Transfer Switch w/ Power Management

Buy Generac RXSC100A3 Direct. Free Shipping. Check the Generac 100-Amp Automatic Smart Transfer Switch w/ Power Management ratings before checking out.

www.electricgeneratorsdirect.com

 

[lilimike]

I cannot go that route for a few reasons, first my generator is not powerful enough to supply the hole house, I have identified important circuits to keep on but some need to be switched off so I need to physically handle this. I understand nothing is impossible and everything is possible but everything have a cost. I believe my solution when properly adapted is the best for its cost.

 

[rjenkinsgb]

I've assembled the circuit, the one with no resistors and definitely not ideal as I get a strong signal from as far as 12 inches away from the breaker panel.

Try changing the 5K6 resistor to a pot or preset - that should allow you to turn down the sensitivity.

You could also try removing the first transistor to reduce gain, and adding eg. a 1nF cap from the input base to 0V, to bypass some noise.

 

[lilimike]

Try changing the 5K6 resistor to a pot or preset - that should allow you to turn down the sensitivity.

You could also try removing the first transistor to reduce gain, and adding eg. a 1nF cap from the input base to 0V, to bypass some noise.

I have not had a chance to apply the low pass filter yet, my post #7 was kind of a question as I was unsure if I had the connections right about if the antenna should connect as showing or if it should be between the cap and resistor. When I was first testing I was using 9V wallwart. I have since added a DC-DC to go down to 3.3V thinking it would give better results but something is wrong, I get a voltage detection even when I get close to a wire that has no voltage (turned off at the breaker) I will try a 1nf cap from base to gnd and also add the low pass filter if I can get confirmation my connections are right. (or will just try connecting both ways)

 

[rjenkinsgb]

If the power supply to the circuit is not grounded, the stray leakage through it will add an AC voltage to the whole circuit, meaning it will trigger near ground.

It senses the difference between the "antenna" and its own ground.

 

[lilimike]

If the power supply to the circuit is not grounded, the stray leakage through it will add an AC voltage to the whole circuit, meaning it will trigger near ground.

It senses the difference between the "antenna" and its own ground.

That made a big difference.
Thanks !