trying to adapt warm white LED to candles

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If you like the flicker effect of candles try mixing some orange neons , perhaps overdriven, fed from DC rather than AC.

Reminds me of the fad for mock leaded glass windows - strips of lead laid over plate glass. Missing the point entirely , that the visual effect of leaded glass windows is not the lead itself but the multi-facit reflections off the individual small panes.

These original candles don't flicker (they have a standard incandescent) and the hopeful LED replacements won't work from DC, which is why I am asking the best way to power them.

First, & very importantly, LEDs are INHERENTLY DC devices. You have a string that uses 120v AC because there is a rectifier built into the string, or each bulb has 2 LED's, in opposite orientation.

So, you need to determine which it is. Here's how: get a DC supply of more than 3.1v. You can use 3 AA or AAA batteries, end to end, or a 6v DC wall wart. Connect a 100 ohm resistor in series with the supply. This limits the current to 30 ma, so as to not burn out the LED.

Then connect the supply to the LED, both ways (both polarities). If the LED lights with both connections, there are 2 LEDs in your bulbs and you'll need an AC supply. If it only lights on one polarity, there is just 1 LED and you'll need a DC supply.

Report back with your findings and we'll go from there.

Bob

Ah, the walwart I initially tried wasn't plugged in completely so that's why the LED's wouldn't light. My findings are that each bulb has 1 LED as it only lights the one way.

Looks like I should just be able to use a cheap walwart to power these if I'm not mistaken. Should I include the 100 ohm resistor to each LED?

Thanks, Bud

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Do you want just one bulb in each candle? Are these individual candles, or are they the "8 candles in a row" of 4 ascending and 4 descending height?

"Do you want just one bulb in each candle? Are these individual candles, or are they the "8 candles in a row" of 4 ascending and 4 descending height?"

Thanks, one bulb per candle. I'll have two candles per room and I hope to use a separate power source for each candle pair as there are 3 rooms.

OK, here's the next thing about LEDs: they're current devices. I.e., you design your circuit for the current through them, rather than the voltage across them. And LED brightness is a matter of how much current you put through them. For your lights, I would use the .027A (27 ma). The .067 is bogus: how can a bulb draw more than is going through the whole string? Although the .067 might be a maximum current.

So, assuming a 6v DC supply and 3.1v dropped across the LED, there has to be 2.9v dropped across the resistor. With .027A needed, a 2.9/.027 =

107 ohms. 100 ohms is a common value - use that. .027A & 2.9v gives .08 watts dissipated by the resistor - it will not heat up the candle stick. And you can use the smallest resistor (1/8W).

Each LED will need a resistor.

BTW - it you want to use a separate wallwart for each, you can get them for $2.59 each (shipped) here:

If you want to carry this further, you can experiment with the brightness by changing the 100 ohm resistor. Smaller resistor equals brighter LED. But shorter life. Too small means zero life. If the .067A LED rating is a maximum current, you couldn't use a resistor smaller than 2.9/.067 = 43 ohms. And at that, the life would probably be very short. IME

Have fun, Bob

There are a bunch of issues here.

Have you verified that the optical properties are acceptable? Light comes out of a LED in one direction. It's non-trivial to adapt an incandescent fixture to LED. You might need to do some grinding on the LED plastic or use more than one led to get the look you want. Those lamps look like the right stuff, but can't be sure from the picture. Try it.

This project appears to be all about aesthetics. Make sure you like the look before you invest in a bunch of power supplies. Even number of LEDS means you can use AC.

Your power choices depend more on what power supplies you can get. Without going into all the gory details... Go to a couple of garage sales and pick up some 25-cent cellphone chargers. Use a 5V charger and a resistor at least 68 ohms 1/2W. Larger resistor for lower brightness is no problem. For the nitpickers reading this, you're probably gonna put the resistor in heat-shrink without heat sinking inside some plastic thingie, so a higher wattage resistor is warranted. At 100 ohms, 1/4W should be big enough. When you're done with the prototype, run it a while and make sure nothing gets hot.

READ THE LABEL. Not all cellphone chargers are 5V. Some are 5.4V and need larger resistors. Check the current rating on the label. One charger should easily supply two LED-Resistor combinations...or more...check the label.

You mentioned smaller wire. The size of the wire is relatively unimportant. BUT You want something that won't be damaged and shorted by flexing, slamming the window on it, cat chewing on it. If it shorts and your wall-wart is plugged in behind the curtain... have your fire insurance paid up. Chances of a short AND just the right combination of PS factors to cause overheating are very small, but the consequences are catastrophic. Save your good luck for something else.

Sounds like a good plan, thanks, except I'm a little concerned about one thing: actual wallwart voltage. Very often, they're marked as 6V, but output will be a volt or two higher. In that case, I'm assuming I'd just need to increase the resistance slightly to each bulb, correct? If 7V, then

3.9v dropped across the resistor so 3.9/.027= 144 ohms (I would use the closest standard resistor, probably 150 ohms). So power would be a little more, but I could still use a 1/4 watt resistor. Please correct me if I'm wrong. Been years since I've done much with electronics calculations, but they're coming back to memory somewhat.

Bud

That's all correct.

Bob

Working out good so far. I've had whatever walwarts I've had in the junk box and have had to readjust the resistance accordingly. You'd be surprised how much more some of the actual voltages are than are stamped on the units. One I have said "12 volts", but in actuality, it was 19.5V! Makes me wonder how much electronics in general burn out because of mislabeled adapters.

Bud

Some over-voltage is to be expected: it's the compensation for the supply bogging down under load. But 19.5 vs 12 is a bit much. If you're curious, you could load it to its rated current & see what happens to the voltage.

If you are going to be using 12v supplies, you might need higher wattage resistors. E.g., (12 - 3.1) * .026 is just a 1/4 watt, so using 1/2 might be a good idea. Of course, if that "12v" supply is really 19.5, you'd need an even larger one.

Bob

Yes, I used resistors up to 1 watt today. I aimed to use double the wattage required as a safety margin. All the candles are now in the windows and are lit nicely. My only concern now is LED life. I understand it varies greatly according to manufacturer. I had really hoped I wouldn't have to touch these for years. Perhaps so, but I'm not sure.

Bud

mislabeled adapters.

It's 12 volts at specified amps.

Greg

Oh, ok, well that makes sense now. Didn't think about it that way. Thanks. In other words, the label is correct when the unit is, say, plugged into whatever device it was made for, and the device drawing the same current as on the label. Bud

I'm sure that life does vary with mfg'r. It also varies greatly with the current used to drive them. But that affects the brightness, too. You could try this: use larger & larger resistors until the bulbs are too dim. A pot would be the easiest. It might surprise you as to how low you can go & still get the desired affect.

Bob

Today, I went back and measured the current for all the lights. All were from about 20-27 mA. I then increased resistance for each one until current was from about 13-16 mA. There was slight dimming, but I think still acceptable. I'll find out for sure after dark.

It has been fun modifying the original incandescent candles into these. I've also had a chance to revisit electric circuit study, something I haven't done for nearly 15 years.

Bud

That's really good. If the dimming was only slight and it's acceptable, your bulb life will be greatly extended. How much, exactly, I couldn't say.

Bob