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Detecting 240VAC

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qtommer

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hi

I would like to detect the presence of 240VAC flowing in a power strip. If 240VAC is present, I would like to trigger out a 5V output. Is there anyway to do this without using a transformer? An IC perhaps?

Thanks!
 
this may sound daft but why dont you just plug a something like a old 5v mobile phone charget into the strip, when there is 240v present then the charger or wallwart will give you 5v ?? or am i missing something???
 
Do you want this to be a portable meter? you can probably use a 9V battery to power it and a set of op amps and resistors to divide the 240 safely down, then use a 5V regulator and an op-amp as a comparator ( with the 5V regulator as the thing to be compared with) to trigger 5V when a thresh hold is reached....

Just throwing some ideas out..
 
Don't you need isolation from the 240V? In other words, dont you what something like an opto-isolator which has no common connection between the line side and the output side?

An opto-isolator with a capacitive drive on the line side would not dissipate hardly any power, provides +-1500V isolation (at least), and produces a logic output when the 240V is present.
 
Off the top of my head; 4N35
 
thank you all for your replies and ideas. =)

sorry for not making myself not clear enough. I actually have a power strip with 3 outlets which I will integrate with automated control from a micro controller (via SMS). Hence, whenever either socket has been activated manually from the push of a switch, I would like to let my micro controller know that the 240VAC flow is going through that particular socket . (Hence, I would need 3 detectors for the respective 3 outlets)


Off the top of my head; 4N35

Hi Mike, from the datasheet, it seems that the IC is unable to detect AC voltages as it has a DC input...how do we rectify this? Or did you mean to append this IC to the output of the set of op amps as edman222 said?
 
I've not time to find one, but I know if you look at the optoisolators page in the digikey catalog you can find an opto with AC input in a heartbeat. You can then use a capacitor (make sure you get one spec'ed to handle atleast 240VAC peak voltage, 340VAC I believe) to limit the current based on the capacitors AC impedence using Xc=1/wC.
 
The one I posted just has an LED emitter, you would just have to use a 1000piV diode to prevent the LED from seeing reverse voltage, and a series resistor to limit the peak current to about 25mA. The resistor would be dissipating a fair amount of power.

Another way is to use a capacitor as the series current limiter which uses a big high-voltage capacitor as suggested in the post above, but dissipates almost no power.
 
sorry for not making myself not clear enough. I actually have a power strip with 3 outlets which I will integrate with automated control from a micro controller (via SMS). Hence, whenever either socket has been activated manually from the push of a switch, I would like to let my micro controller know that the 240VAC flow is going through that particular socket . (Hence, I would need 3 detectors for the respective 3 outlets)

Sounds like maybe the OP whats to detect current flow not voltage present? Witch is it?
 
A very simple way is to use those little neon bulbs to trigger basic photo resistors or transistors. Each socket would have its own indicator bulb that also triggers a photo sensor that in turn relays the signal back to the controller telling it that the circuit is active.
 
hi everyone thanks for the replies

MikeML
Another way is to use a capacitor as the series current limiter which uses a big high-voltage capacitor as suggested in the post above, but dissipates almost no power.

ADWsystems
You can then use a capacitor (make sure you get one spec'ed to handle atleast 240VAC peak voltage, 340VAC I believe) to limit the current based on the capacitors AC impedence using Xc=1/wC.

Im assuming the capacitor would be connected in series with the power line. Am I right?
Conventionally, AC stepdown from 240VAC to lower is achieved through transformers.(which I dont wanna use) . What are the advantages/disadvantages of using a cap instead?

MikeMl

The one I posted just has an LED emitter, you would just have to use a 1000piV diode to prevent the LED from seeing reverse voltage, and a series resistor to limit the peak current to about 25mA. The resistor would be dissipating a fair amount of power.


As the input from the LIVE would be 13A, the resistor to limit the peak current to about 25mA would be one which has a high power rating?

ADWSystems

I've not time to find one, but I know if you look at the optoisolators page in the digikey catalog you can find an opto with AC input in a heartbeat.


ADW systems,thank you for your recommendation. I found quite a few..

https://www.electro-tech-online.com/custompdfs/2011/02/0900766b808e044f.pdf
SAT400 pdf, SAT400 description, SAT400 datasheets, SAT400 view ::: ALLDATASHEET :::
https://www.electro-tech-online.com/custompdfs/2011/02/ps2605.pdf

Am i on the right track with the above selection?

tcmtech

A very simple way is to use those little neon bulbs to trigger basic photo resistors or transistors. Each socket would have its own indicator bulb that also triggers a photo sensor that in turn relays the signal back to the controller telling it that the circuit is active.
that is indeed a clever way..however, I would be leaning more towards the optocoupled method due to academic reasons;) thanks!=)




4pyros
Sounds like maybe the OP whats to detect current flow not voltage present? Witch is it?

Im sorry but Im not so sure what you're going about. Wouldn't both be present if LIVE is detected?

thanks everyone. really appreciate it.
 
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