Outdoor Light Status Indicator

[Robertc65]

I want to mount an LED or some sort of  Lamp on each of my switch plates that control outdoor lights so that I can tell if they are on or not without having to look out the windows. If all of my lights used a single 2way switch this would be easy but all use 3way switches. On te switch which connects to the actual light this is not a problem but what about the other 3way switch that is connected to the power source. It seems that I need some sort of circuit that can sense current draw or voltage drop. has anyone ever done this before?

Thanks in advance

Rob

 

[ante1]

Hi Rob,

That’s not too hard to achieve. With a small toroide core (about 30mm or so) you can make a “transformer”. Let the “mains hot” wire make the primary by winding it through the toroide about 8 to10 turns. The secondary will consist of about 30 turns of a thin insulated wire to which you connect a LED! That’s all you need for each “channel”. Of curse it depends on the load how many turns you might need on each side, but this is a start to experiment with!    8)

 

[Robertc65]

Thanks for the suggestion. I searched for a 30mm toroidal core and found that I could easily buy them in lots of 1000 or more from any number of questionable offshore manufactures, however I just need a few. I checked allectronics.com and digikey.com. All electronics a a few cool toroidal xformers but no cores. Digikey may have them but they don't show the size. Do you have any idea where I may find one.

Thanks

Rob

 

[ante1]

Hi Rob,

They should be easy to find, however the 30mm is not a critical thing. Smaller or larger will also work as long as you can put the wire with enough turns on it. If you don’t have a “junkbox” you could search in a dumpster for old computers and things like that. In many power supplys especially in computers you will find toroids to scavenge! There are many other places to look but as I don’t know your neighbourhood I can’t be more specific!  ;D

 

[ante1]

This is roughly what I mean:

;D

View attachment 37463

 

[Alun]

Ante,

How powerfull is this light?

I think you'll need a lot more than 30 turns on the secondary or more on the primary,  a red LED needs 1.9V to light up and for this to happen the amount of turns on the secondary needs to be a sufficiently high ratio to the voltage drop caused by the current on the primary.

Here's an example:
The mains light requires 500mA.
Suppose the torridial core with 10 turns has an inductance of 100uH (and that's being optimistic), the impedance @50Hz will be:
2pi*50*100*10-6 = 0.0314ohms
The voltage drop on the primary @ 500mA will be just:
0.0314 * 0.5 = 15.7mV
If the secondary has 30 turms the out put voltage will only be:
3 * 0.0157 = 47.12mV - way to low to power an LED!
The voltage needs to be at least 1.9V to light the LED that's 1.9/0.04712 =  40.32 times higher to power the LED so the number of turns on the secondary will need to be:
40.32*30 = 1209.7, off course I wind a few more to ensure the LED will glow birght enough as it's forward voltage needs to be above 1.9V.

If you don't fancy winding this many turns than I recommend you wined more on the primary.

Note:
These calulations don't take into account the fact that the core might saturate or the DC resistans of the turns on the secondary.

 

[ante1]

Hi Alun,

Yes, as I mentioned these numbers of turns is just a start for experimenting! I don’t know if Rob has one 1000W lamp or five 1000W lamps on each “channel” so there is an X in this equation. I have used this circuit for an evacuation fan (2hp) and it works fine.

 

[Robertc65]

Basically each circuit will power either 2 or 4  150 watt flood light bulbs. I do plan to use an LED as the indicator so the 1.9volts is the maximum voltage drop I'll need across the secondary. I work with computers for a living and have plenty of junk around so I'll scavange a few to see if I can find any coils to use.

Thanks for all of the good info.

Rob

 

[audioguru2]

I would make a current transformer with a voltage too high for the LED and use a current-limiting resistor to protect the LED.

Lightbulbs draw about 10 times their rated current when not hot. With an LED connected directly to a current transformer then the LED would conduct 10 times too much current.
Light bulbs also frequently arc when they burn out. The arc draws a huge current that would instantly burn out an LED directly connected to a current transformer. ;D

 

[ante1]

Hi Audioguru,

Well Mr Theory expert! ;D  Sure, it makes sense to put a current limiting resistor in the circuit like you suggest. The led in my circuit has survived several years with fanmotor starts and stops. The start current peak has a much longer duration in the fanmotor circuit than any light bulb circuit. A led can withstand very high current pulses, no problem! A 20mA led will survive 2A pulses! Besides there are some inertia in the transformer and the current will not be proportional from primary to secondary windings with only the short pulse from a cold filament.  8)

 

 

[audioguru2]

A 20mA led will survive 2A pulses!

Hi Ante,
I've seen IR LEDs with a 1A max rating, but I use blue, green and white LEDs with a 100mA max rating.
I blink them very briefly at 90mA and they are extremely bright. I wouldn't dare to operate them with pulses exceeding 100mA. ;DView attachment 37471

 

[ante1]

Hi Audioguru,

You should try with 2A, but only briefly! ;D  I have a circuit description someware, as soon as I find it I’ll let you know.

 

[audioguru2]

You should try with 2A, but only briefly!

No thanks. The 100mA max rating is for 100us which is brief enough. With its 10% duty cycle its average temp won't be very high so I think there must be a fuse (thin bonding wire) in my low current LEDs.
If I find a visible LED with a 2A max rating I'll try it. ;D

 

[ante1]

Hi Audioguru,

OK, this is not the one I was looking for (2A) but anyway Gary thinks it’s possible to send up to 10A through a LED!
LED testing: http://www3.telus.net/chemelec/Projects/Osc/Pulsed-LED.htm

BTW: Gary is Canadian so you can trust him! ;D ;D

 

[audioguru2]

Hi Ante,
Gary doesn't say which LED he used.
I have seen the tiny size of the bonding wire inside my clear LEDs and the case magnifies it.
10A! I wouldn't even put that much current through the dinky little SCR he used. Years ago I used that SCR to drive 40mA relays. ;D

 

[ante1]

Hi Audioguru,

He is using standard LEDs! As I said before; it’s just a brief pulse! Many components can take a lot of over-current if it’s pulses, a 1A diode can in some cases survive 100A or more if it’s pulsed. There are 50mA fuses which will stand for a 10A pulse and they have a really thin wire inside! The 2N5064 however will not support this circuit up to 10A unless it’s a single pulse!
I will post the “2A” circuit as soon as I can find it! ;D

So you don’t trust your fellow Canadian? ;D

 

[Robertc65]

Hey audioguru, Have you never blown anything up just for fun? Are you afraid of a little popping sound or just don't want to blow 20 cents on an LED experiment. You seem a little rigid. Lighten up, The book is not always right.

I changed my spec. I have decided to migrate my 6 outdoor light switches into one 6 gang switch box, with single Pole X10 switches. I'm mounting the 6  switches in a hallway equidistant to the front and back doors.

This greatly simplifies my indicator issue. Now we are simply dealing with how to light an LED with 110 Volts AC  without causing adioguru to get upset at the potential of a popping sound accompanied by a slightly delayed unpleasant smell.

 

[audioguru2]

Hi Robert,
Who is rigid?
My circuits are designed within manufacturer's ratings and work fine without blowing-up.
I have lots of fun blowing-up backwards high-value electrolytic capacitors. When I was young I made capped pipe-bombs that went off like rockets, and open-ended pipe-rockets full of propellant that exploded! I even made a chemical mix with iodine that self-combusted when it dried.
Also when I was young I plugged an NE2 neon bulb directly into 120VAC. It disappeared with a bang and I am lucky to still have my fingers and vision.

I don't have any 150W lightbulbs to test to see how many mains cycles they draw up to 10 times their rated current until they become hot and their current drops to normal. So I can't test my LEDs with their 100mA absolute max momentary current with 10 times their rated max current.
Instead I will test some LEDs with a mains transformer and peak currents 10 times and 20 times their absolute max rated current and let you know what happens. ;D 

 

[ante1]

Hi Guys,

Just remember: "There are old technicians and bold technicians, but there are no old, bold technicians."  ;D