I am designing a panel that will handle 2 120V hots running through circuit breakers. I want to use an indicator LED to alert me when the breaker is thrown. I was originally thinking of using a single 240V Indicator LED across the 2 hots, so that if either circuit blows, the LED goes out.
However, this won't tell me if only one or both breakers were thrown (they operate separately).
Does anyone know of a 120/240V LED that would be one color when there is 240V and another color if it is 120V? That way I can tell if just one line or both lines blew.
Also, using a single line for the LED, do I have to cap it to ground? The way it looks in most schematics is line -> resistor -> LED -> line, circumventing the fuse or breaker.
Unless Google turns up something, you will need to design and construct this yourself. Do we understand you plan to use an Arduino to implement it?
You are presumably in the USA. Are both of these lines on the same phase, or opposite phases and thus 240 volts apart?
Did you want the indicator to be off or on when the situation is "normal"? A red/green LED will show yellow when both colours are energised (as in the common message boards); you might prefer it to be green as "normal", and use yellow or red for (which?) fault conditions. You might use an RGB LED.
If you do use an Arduino - it's not such a silly idea though you would have to arrange a transformer to operate it - you can have all sorts of indications - flashing and such.
How about a wall wart that can handle 120 and 240, that puts out say 5 volts. Then you have a small (hopefully safe) signal to sample (maybe use a voltage divider).
Or, maybe a LED with a resistor to allow 240 Volts, and then use a light level sensor to detect differences in brightness.
Or, maybe a optical isolator (analog) that can read up to 240v.
Thanks for the replies! Don't worry, I worked as an electrician for a bit, so I am used to handling mains.
This is to handle power before it goes into the 5v transformer for the arduino. I am controlling relays with it that are protected by a breaker. I want to have a way to see if there is power at all (or if the main breaker is thrown), or if one or both of the legs throws. I considered using these opto-isolators Intelligent Power and Sensing Technologies | onsemi but am trying to reduce part count.
To answer your questions:
I am in the US, so I am working with 2 120v lines in opposite phases.
I didn't find anything in Google for this. I only found stuff like this http://www.newark.com/jsp/search/productdetail.jsp?SKU=93K6625
Ideally, the LED would be green or blue for "all ok", then yellow or red for one or both breakers thrown.
I haven't been able to find a 120v or 240v RGB LED.
As for the LED I posted from Newark, I guess I could just use 2 of those.
I found this schematic online Fuse Monitor Circuit Diagram
Could I just use the LED from Newark, and connect it to the 120v hot on each side of the breaker? The LED already has a resistor. From the schematic, is the capacitor and 4 diodes necessary.
You could use two leds, one for each leg of 120V. But in that simplest form, the leds will light when voltage is present, and they will not light when voltage is missing. That could work for me. Would that work for you?
The Newark LEDs most likely implement an internal circuit equivalent to the second one in Chicago Dave's description. "AC" LEDs are made for the purpose with two elements back-to-back, the capacitor limits the current and the resistor limits the surge when the circuit is suddenly connected whilst the AC is at peak voltage which is going to happen every so often.
An indicator across the supply after the breaker will show when the supply is on. An indicator across the breaker itself will show when it has tripped. The limitation here is that the indicator itself will feed a very small current to the controlled circuit in this circumstance which generally does not matter in the least unless it causes confusion when you start testing things, or if you are about to touch the wiring and presume it has been isolated by the open breaker.
Of necessity, the current drawn to light a LED (at 3V) is much greater than the current required to light a "good old" neon indicator (at 90V) so whilst you could generally get away with connecting yourself in series with the neon indicator (as with the "test screwdrivers" where you put your finger on the end), you would not want to with the LED indicator.
If your intent is to use a multi-colour LED which has a common terminal, then Chicago Dave's first and (modified) fourth diagrams allow the LED terminal to be common with one supply terminal, so you could have one such circuit feeding each colour with one terminal common to both. For your indicator, you connect the common terminal to the outlet side of the breaker, the red circuit to the supply and the green to the neutral. It will show green when the breaker is closed, red when it is open.
Good call Paul__B.
That would give lights when the breakers are tripped. I got it in my mind, what if the whole street went out (but looking back, that was not the idea).
The indicator from Newark incorporates a 1n4004 rectifier diode and a 3.9k resistor. Since I would like for the breaker to turn on when the breaker throws, I would like to connect it across the breaker (if there is a general power outage, then it wouldn't light, but this is not vital in this case). I attached a circuit showing how I think it should be attached (the rectifier diode and resistor are included in the LED itself so I didn't draw them). Is this how it works? The only things connected downstream are pumps which aren't on all the time. Small amp draw won't matter, but will the LED light up when the pumps are off? They aren't connected to neutral, so how would this be?
Chicago Dave - this is the first time I've seen a 0.22u cap in line with the LED. As I saw in the comments, this reduces current, but does it heat up a lot? Also, for a 120v line, I guess I would use a 250v cap instead of a 400v, correct?
You are right, placing the led (red) across the breaker would light the led when the breaker trips, only if there is some load on that line.
If that is the case, then you can add one additional led (green) on that line. It only lights if the breaker is ok. Now that could be strange tho, if there is no load, and the breaker trips, you could get both red and green leds lit. This may be prevented by reversing one of the leds, so one gets lit by the positive part of the ac sine wave, and the other gets lit by the negative part of the ac sine wave.
And be aware, by putting an led across the breaker, there can be voltage even if the breaker is flipped off (going through the led). Not much current tho.
The one drawing I found has a 4,700u cap between line and neutral behind the breaker. Would this give enough load to light the LED? Would this replace the in-line cap in Chicago Dave's schematic?
I personally don't see a need for capacitors on an ac line, but maybe I just don't understand the purpose.
I am still leaning toward using two leds for each breaker.
pekasus:
Chicago Dave - this is the first time I've seen a 0.22u cap in line with the LED. As I saw in the comments, this reduces current, but does it heat up a lot? Also, for a 120v line, I guess I would use a 250v cap instead of a 400v, correct?
Thanks again for all your help!
Should've mentioned... those caps are "X2" caps, and are meant to be connected to 'mains' power. They're "special".
And, you should be able to use a 250v (275v) cap for 120v line, but it shouldn't be an issue to use a cap rated for higher voltage than needed. -- 'Better safe than sorry!'
For the first image (w/ 2 diagrams) I uploaded, the LED will be 240v above earth if the active and neutral are swapped and this represents a shock of over 340v if anything is exposed. The power diode in the first diagram is designed to discharge the 0.22u during one half of the cycle so that the capacitor will charge during the other half-cycle and deliver energy to the LED. The 1k resistor limits the peak in-rush current when the circuit is first turned on and the mains happens to be at a peak.
As second diagram shows, two LEDs can be driven from the same circuit as one LED will be illuminated during the first half cycle and the other LED will be driven during the second half of the cycle. Second LED just replaces the normal "power diode" in first diagram.
