Sensor to detect when a light is turned on

[aurumdeus]

Hi,

I'm looking for something rather specific and I don't know if it exists or not.

I'm trying to plan a system that allows the lighting circuits in a house to be powered by a solar system and a small inverter when the battery has enough power, and will revert to a mains supply if the battery is empty. I have all this designed already.

The light bulbs will all be LED filament designed for mains AC to allow switching between the two.

When the inverter is turned on it still draws just under 5W even with no load. I'm hoping to find something that can detect when an LED light is turned on and send a signal to a relay that will turn the inverter on, that way it will only be powered up when a current is required.

Some inverters have an ECO mode where they will check for current draw every second or two, but that is no use since when the inverter is off the lights will simply draw from the mains.

If it was just normal filament bulbs then something like measuring resistance or continuity across live and neutral would work, but since the LED bulbs will be using a transformer and rectifier in each bulb I'm not sure this would work.

1. Does anyone have any ideas? Is this possible?

All I've been able to come up with so far is measuring current drawn through the circuit and having a relay turn the inverter on when anything is drawn.

2. I can't run the whole circuit (max probably 250W) through the coil in series, so would I need a micro controller connected to an ammeter to measure and activate the relay or is there a more direct way of doing this?

When a light is first turned on it would be powered by mains for a moment before the inverter kicks in and takes over. This might cause a tiny dark flash.

3. Could this be avoided, possibly by placing a capacitor across live and neutral (with a discharge resistor of course)?

Thank you in advance.

 

[Pete999]

To deep for me I'm afraid.

 

[aurumdeus]

A thought relating to question 2. Can I add an AC coil relay in parallel to the live on the lighting circuit? That way the main current will go through the normal wire, and just enough will pass through the coil to activate the relay.
This would of course mean that the wire has to stay live during the switching over process, other wise the relay would turn off again straight after activating.

 

[Pete999]

A thought relating to question 2. Can I add an AC coil relay in parallel to the live on the lighting circuit? That way the main current will go through the normal wire, and just enough will pass through the coil to activate the relay.
This would of course mean that the wire has to stay live during the switching over process, other wise the relay would turn off again straight after activating.

Right, OK , and.

 

[aurumdeus]

Forget that, putting it in parallel with the live wire is just attaching live to both ends, it won't operate the relay coil at all. Me being silly there...

 

[HandySparks]

2: If you want to detect AC current flow in a wire, these might do the job:
EC Products - Building Management, Peripherals and Controls - Hounslow, Middlesex, UK. - https://www.ecproducts.co.uk/productdetail.asp?cat=4&item=1&pid=2144
or
Single Range AC Current Operated Switches - http://www.lamonde.com/acatalog/Single-Range-AC-Current-Operated-Switches.html

You run the wire multiple times through the core if you want to improve the sensitivity.

3: You can't use a capacitor to hold up an AC supply.

 

[Deleted member 9648]

I don't know whether this is an existing lighting system or a new project, if it is yet to be wired it would be a simple matter to include an additional pair wired from each switch or light through a relay arrangement and use this to tell the inverter when a load is switched on.
Seems a lot of effort to save a few polar bears though.

 

[Wilko]

Hi,

I'm looking for something rather specific and I don't know if it exists or not.

I'm trying to plan a system that allows the lighting circuits in a house to be powered by a solar system and a small inverter when the battery has enough power, and will revert to a mains supply if the battery is empty. I have all this designed already.

The light bulbs will all be LED filament designed for mains AC to allow switching between the two.

When the inverter is turned on it still draws just under 5W even with no load. I'm hoping to find something that can detect when an LED light is turned on and send a signal to a relay that will turn the inverter on, that way it will only be powered up when a current is required.

Some inverters have an ECO mode where they will check for current draw every second or two, but that is no use since when the inverter is off the lights will simply draw from the mains.

If it was just normal filament bulbs then something like measuring resistance or continuity across live and neutral would work, but since the LED bulbs will be using a transformer and rectifier in each bulb I'm not sure this would work.

1. Does anyone have any ideas? Is this possible?

All I've been able to come up with so far is measuring current drawn through the circuit and having a relay turn the inverter on when anything is drawn.

2. I can't run the whole circuit (max probably 250W) through the coil in series, so would I need a micro controller connected to an ammeter to measure and activate the relay or is there a more direct way of doing this?

When a light is first turned on it would be powered by mains for a moment before the inverter kicks in and takes over. This might cause a tiny dark flash.

3. Could this be avoided, possibly by placing a capacitor across live and neutral (with a discharge resistor of course)?

Thank you in advance.

Hi and welcome to the Forum !
I think you will need a computer based monitoring system to detect when a switch is thrown. But you might as well have put a bigger battery in and put up with 5W idle current of the inertor. Or have that light switch start the invertor, then the light etc.

 

[snowhead]

Not forgetting that whatever circuitry is used to look for the signal to power up the inverter will itself draw current.

Nothing is Free.

 

[aurumdeus]

Thanks Handy, those look perfect. I think they'll do the job.

I theory I need to be able to pick up 20 mA current (4W (lowest power LED bulb that will be used)/240V = 17mA, plus a little for efficiency.

It's not a new project, it's to be retrofitted to an existing lighting system in a house.
Although it's a reasonable amount of work designing and planning, once that is done there are a few places that will use the same system so I think worth it in the long run. Also power cuts aren't that unusual, especially in winter, so having a lighting system that won't die along with everything else is another benefit.

Although whatever sensor is used to power the inverter will use some current, I think it will be less than the 5W idle draw.

 

[aurumdeus]

I'm also thinking of adding an arduino to monitor energy usage per day that is drawn from mains vs solar, to give an idea of how well the solar capacity is holding up to the demand.

This part is partly an excuse to add an arduino since I'm gradually learning how to program them, but only as needs arise. If I end up using an arduino to activate the inverter via a non contact ammeter, I can add a voltmeter and use that same arduino to do the data logging as well.

 

[aurumdeus]

Is there anything that can be used to keep the AC circuit energised while the relay is switching? It will be likely a max of about 0.5J needed (based on 0.1s switching time), such a small amount of energy but it's not worth going UPS to cover it.

 

[marconi]

Renewable energy policy database and support: France - http://www.res-legal.eu/search-by-country/france/

It seems to me you are in danger of over complicating matters and will have technical difficulties maintaining uninterrupted lighting during switch-over between mains and PV. I think the best solutions are generally the simple ones using tried and tested technology.

Why not use the classic PV installation which has a PV powered inverter feeding into the mains and metered? France has a feed in tariff - see link above. Such systems are available, reliable and safe. And they are maintainable and familiar to homeowners and electricians. Such an installation would feed all appliances not just the lighting.

 

[marc8]

hi
use to install a lot of immersun units few years ago might be worth having a look at using something like one of these although these were used for monitoring PV going back to the grid & then turning on an Immersion heater, might be able to adapt something like this using the current sensor around the lighting supply cables or even have the lights you want to use on one board & clamp the supply tails to that board.
the immersun unit usually turned on at around 500watts going back but in programming this could be altered (lowered).
these units also logged information Kwh used & input & output draws.
might be barking up the wrong tree but might give you a few ideas

 

[PEG]

As mentioned,you run the risk of over complicating/spending,on this project.

If it is your own,or a bit of experimenting,then no problem,i'm keen on a bit of Heath Robinson...

If it is for occasional outages of mains power,your battery capacity,should be sized for the anticipated losses due to the inverter,for the period of any outage.
These would remain charged and at standby,for the greater period of time,which is mains fed.

...I also thought that these many French "outages",were an integral part of their constitution,allowing for jam-jars with tea-lights,to be hung from pear trees,and a day's work to be dumped,with a shrug of the shoulders...