Analog Current Measurement

[DVEntertainment]

Hi guys! I dont know if this is the right place for it but i have a question:

I have power running to my shed, and i cant see the shed from my home, now i want a device that lights a small led (or other source) when the light in the shed is on. I can ofcourse make this with a arduino and a module but i wondered if there were any analog solutions to my problem. If the light in the shed is off, no power is used at all, so there is no need for a ajustable threshold value for the light to go on. It is a workshed so i need the full 16 amps of 230 volt that goes to it.

 

Best regards Daniël!

[Enderman]

You would need to have a third wire going to the shed, cause you can't put an LED in series with the AC line going to the shed.

[Enderman]

If you did have a third line going there, all you need to do is make this simple circuit and have it connected to the same switch that runs the lights in the shed.

So the switch would close both the lighting circuit as well as your LED circuit.

 

But since you want the LED in your house and the switch is in the shed you need a third wire to bring power from the shed to the LED in your house.

[DVEntertainment]

3 minutes ago, Enderman said:

You would need to have a third wire going to the shed, cause you can't put an LED in series with the AC line going to the shed.

ah, thanks. Thats kinda difficult because its 200 meters ( 656 feet) underground. thanks for the answer! i have a solution with an arduino, i have a small board that measures the ac current in series with the fase line goin to the shed. that reports the current to the arduino and the arduino turns a led on. But its not a clean solution and i would love to create a analog solution.

[Enderman]

2 minutes ago, DVProductions said:

ah, thanks. Thats kinda difficult because its 200 meters ( 656 feet) underground. thanks for the answer! i have a solution with an arduino, i have a small board that measures the ac current in series with the fase line goin to the shed. that reports the current to the arduino and the arduino turns a led on. But its not a clean solution and i would love to create a analog solution.

I actually found this, very simple:

https://www.amazon.com/CR-Magnetics-Remote-Current-Indicator/dp/B005CWHDVA?th=1

If you want to try making it yourself you can find schematics if you google "ac current indicator led"

[mariushm]

You could measure the current going to shed but if you're using a 10w led light, the current would be very low

 

There's hall effect sensor ICs like ACS711 for example :

+/- 15.5A : https://www.digikey.com/product-detail/en/allegro-microsystems/ACS711KEXLT-15AB-T/620-1483-1-ND/3868192

+/- 12.5A : https://www.digikey.com/product-detail/en/allegro-microsystems/ACS711ELCTR-25AB-T/620-1371-1-ND/2470595

 

It measures the current going through it and outputs a voltage on a pin that varies with the current so you can use an arduino to do stuff when the current measures goes above some threshold

[DVEntertainment]

8 minutes ago, Enderman said:

I actually found this, very simple:

https://www.amazon.com/CR-Magnetics-Remote-Current-Indicator/dp/B005CWHDVA?th=1

If you want to try making it yourself you can find schematics if you google "ac current indicator led"

Thanks! imma try this!

[DVEntertainment]

8 minutes ago, mariushm said:

You could measure the current going to shed but if you're using a 10w led light, the current would be very low

 

There's hall effect sensor ICs like ACS711 for example :

+/- 15.5A : https://www.digikey.com/product-detail/en/allegro-microsystems/ACS711KEXLT-15AB-T/620-1483-1-ND/3868192

+/- 12.5A : https://www.digikey.com/product-detail/en/allegro-microsystems/ACS711ELCTR-25AB-T/620-1371-1-ND/2470595

 

It measures the current going through it and outputs a voltage on a pin that varies with the current so you can use an arduino to do stuff when the current measures goes above some threshold

i'm currently using this ic icm arduino. it works, but its no clean solution.

[mariushm]

Just now, DVProductions said:

Thanks! imma try this!

That transformer is also available on Digikey for 13.5$ plus shipping : https://www.digikey.com/short/p17wb1

Note that the turn on current is 0.75A ... if you have 110v input, that's around 82 watts. If your shed lights use less than that, your led may not turn on.

[Unimportant]

7 minutes ago, DVProductions said:

Thanks! imma try this!

You can buy ready made units with relay outputs and adjustable trip point like these: https://www.amazon.com/Dwyer-Miniature-Current-MCS-111050-Continuous/dp/B00I9IFJOM

[DVEntertainment]

1 minute ago, mariushm said:

That transformer is also available on Digikey for 13.5$ plus shipping : https://www.digikey.com/short/p17wb1

Note that the turn on current is 0.75A ... if you have 110v input, that's around 82 watts. If your shed lights use less than that, your led may not turn on.

thanks! if it uses less, i will put a glowbulb (is that correct english? In dutch it is gloeilamp) in the shed, than it will use enough power

[Unimportant]

5 minutes ago, mariushm said:

That transformer is also available on Digikey for 13.5$ plus shipping : https://www.digikey.com/short/p17wb1

Note that the turn on current is 0.75A ... if you have 110v input, that's around 82 watts. If your shed lights use less than that, your led may not turn on.

One can always run the wire multiple times trough the loop. Each turn adds to the detected current.

[mariushm]

Yeah, also remember to split the live and neutral wires, don't shove the whole bundle through the hole.  If you insert both live and neutral they cancel out so you'll get no current or very little current.

[DVEntertainment]

1 minute ago, mariushm said:

Yeah, also remember to split the live and neutral wires, don't shove the whole bundle through the hole.  If you insert both live and neutral they cancel out so you'll get no current or very little current.

i understand that thanks

[Vishera]

You can measure the current with a Shunt Current Sense Resistor:

 

[Hugh54321]

there are switches/relays that detect current. All you need to do is find in your house the cable that goes to the shed, cut the external insulation and pull away the live wire, and slap one of these switches on it. e.g. https://www.aliexpress.com/i/33004812581.html

[Vishera]

1 minute ago, Vishera said:

You can measure the current with a Shunt Current Sense Resistor:

 

You can also connect it permanently to a cheap multi-meter as a display.

[mariushm]

@Vishera, it's AC voltage, so you'll have alternate positive and negative voltages on the shunt resistor. Yeah, you could use a diode to block and only have positive voltages but still...

You'd want to have a drop of let's say at least 50mV on the shunt resistor, if you want the ADC on your microcontroller to reliably work... so do the math .. v = ixr  ,,, if you go with 0.1 ohm, you end up with i = 0.05v/0.1 = 0.5A minimum current to detect

However, at 16A you'd have v = 16x0.1 = 1.6v drop and the power dissipated in shunt will be P = IxIxR = 256 x 0.1 = 25 watts.

 

So you'd either have to use an even lower resistor than 0.1 ohm, which will increase the minimum threshold, or somehow short out the current sense resistor with a relay or parallel another resistor with a relay to reduce resistance (like auto ranging)