AC voltage sensor

[matkt051]

Hi guys, Im trying to do this project in which there is an AC sensor which will sense the high voltage Mains connection and then give a DC as output.

I know we can use the Relays to do this. but due to the power consumption of the relays, I thought there could be another way.

The circuit needs to be isolated from the mains (for safety reasons).

I even thought of useng a hall sensor to sense the AC and then use its output to conrtol other circuits.

any ideas?

Please let me know if im on the correct path.


Mat

 

[RODALCO]

4n35

You could try an optocoupler IC like a 4N35.

Drive the AC input side via a bridge rectifier and limit the current to 5 - 10 mA.

Output is open collector.

Most opto's are 2 kV isolation rated.

 

[matkt051]

Hey,

thanks for getting back to me.

yea thats a good idea. but are there any other techniques that we can do by using a TRIAC or Thyristor?

Im looking at all the solutions before I make a decission thats why.

Mat

 

[crutschow]

A TRIAC (type of thyristor) or an SCR (another type of thyristor) do not provide isolation.

For isolation you could use a small power transformer (such as a 6V or 12V filament transformer), and rectify and filter its output to give a DC voltage.

What are you intending to do with this signal?

 

[ericgibbs]

Hi guys, Im trying to do this project in which there is an AC sensor which will sense the high voltage Mains connection and then give a DC as output.

I know we can use the Relays to do this. but due to the power consumption of the relays, I thought there could be another way.

The circuit needs to be isolated from the mains (for safety reasons).

I even thought of useng a hall sensor to sense the AC and then use its output to conrtol other circuits.

any ideas?

Please let me know if im on the correct path.


Mat

hi Mat,
As you are a Wanabee, I would go with Carl's post #4, low voltage isolation transformer and simple bridge rectifier/smoothing.

 

[MikeMl]

Even an old cell phone charger puts out a "logic signal high" (5V) when there is AC present.

 

[matkt051]

LOL. I know that

Thanks for the ideas.
but when using a transformer, wont the power consumption be high? Im designing this for my Final year project and one of the aims of the project is that the power consumed by this circuit must be low as this would also affect the standby power consumption of the whole system..

In reply to "crutschow", Once I get the output, I can use this sgnal to control a transceiver to transmit a signal to a reciever and then vice versa. (if u know what I mean).

the main reason why Im interested in this thyristor is because of its continuous output due to a pulse on the gate. Please see the diagram below.

 

[matkt051]

and BTW,

In all the datasheets Ive seen, the Thyristor gate has a DC input and switches AC load.

Is it possible to have an AC input and switch DC load?

sorry if it seems a bit weird. :S

 

[ericgibbs]

and BTW,

In all the datasheets Ive seen, the Thyristor gate has a DC input and switches AC load.

Is it possible to have an AC input and switch DC load?

sorry if it seems a bit weird. :S

hi,
If you use an SCR for switching the DC , how do you plan to turn off the SCR..?

 

[matkt051]

hi,

I plan to put a transistor in between the DC and the SCR with its base connected to the Gate terminal of the SCR.
Therefore, when there is a current on the gate, the transistor (works as switch) will conduct and so will the SCR.

hope I make sense.
M

 

[ericgibbs]

hi,

I plan to put a transistor in between the DC and the SCR with its base connected to the Gate terminal of the SCR.
Therefore, when there is a current on the gate, the transistor (works as switch) will conduct and so will the SCR.




hope I make sense.
M

hi,
Sorry, that will not work...transistor idea.
Once the SCR starts conducting, you will have to switch OFF the DC to stop the SCR conducting, they are not On/Off gate controlled switches

 

[matkt051]

How come? cos if the switch is open then obviously there is no connection between the supply and the SCR. hence wont the SCR stop conducting as there is no DC supply(i.e the DC is not connected to the SCR).

What are your thoughts on this??

 

[ericgibbs]

How come? cos if the switch is open then obviously there is no connection between the supply and the SCR. hence wont the SCR stop conducting as there is no DC supply(i.e the DC is not connected to the SCR).

What are your thoughts on this??

hi,
If you just want to turn on the SCR with a transistor/resistor combination, thats possible.

If you realise once the SCR is on/conducting you have got to disconnect the DC voltage to SCR's Anode to turn it off thats OK.

 

[Reloadron]

Hi guys, Im trying to do this project in which there is an AC sensor which will sense the high voltage Mains connection and then give a DC as output.

I know we can use the Relays to do this. but due to the power consumption of the relays, I thought there could be another way.

The circuit needs to be isolated from the mains (for safety reasons).

I even thought of useng a hall sensor to sense the AC and then use its output to conrtol other circuits.

any ideas?

Please let me know if im on the correct path.


Mat

Hi Mat

Looking back at your original post here I have a few questions. You mention sensing the presence of AC mains high voltage connection then later mention the use of a hall effect sensor which would respond to current. My question becomes are you interested in sensing the presence of AC mains where there is some current flow to a load or merely the presence of a voltage with absolutely no load?

Should there be a load then I would suggest starting with a small device along these lines. You simply pass one of the mains lines through the small coil and any current flow exceeding about 750 mA will light the LED. You can see from the data sheet they come in several flavors but the minimum current (red or white LED) is about 750 mA on the AC line. The LED could be removed and you could drive an optocoupler or using the existing LED fabricate your own optocoupler using an LDR. For that matter you could wind your own coil and fabricate your own device. The concept remains the same. Obviously totally isolated from mains and simple.

I use them to detect open heater elements in large heater arrays (480 VAC at over 10 Amps) per heater and they work fine.

This all assumes there is some current flow in the AC mains.

Ron

 

[matkt051]

Hi thanks for gettin back to me.

I want to know if a switched live signal from a boiler contains any current components. if so, how much would it be? IKm thinking upto 5-6 Amps?????

 

[Reloadron]

Hi thanks for gettin back to me.

I want to know if a switched live signal from a boiler contains any current components. if so, how much would it be? IKm thinking upto 5-6 Amps?????

You totally lost me. Boilers can have dozens of signals from them, thermometer, flame detectors (gas fired), pressure, the list goes on depending on boiler type, fuel, all sorts of variables including blower(s) and air flow.

What exactly do you have and what exactly are you trying to do? Maybe if we get a good handle on the big picture some solutions will come up.

Ron

 

[matkt051]

Hey guys,

thanks for all your valuable support. I have some solutions here.
1. use a rectifier with smoothing circuit to switch a Relay (solid state or electromechanical).
2. use current limiting resistor with regulator connected to optocoupler. tHe output will be Low voltage DC.

do you think there are any other ones that might be suitable for this application?#

thanks a lot.

Mat