# Electric Candle

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Where I live, we frequently go without power 3-8 hours at a time. It can get annoying and expensive running down batteries for light and burning candles is simply a bad idea. Rummaging through Instructables I found MooseTooths project, and though I liked it, it seemed the efficiency could be greatly improved with an LED replacement, but who wants to struggle with getting the polarity of an LED right in the dark? We'll take care of that.

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## Step 1: The Polarity Problem

The problem of polarity was solved by building a bridge rectifier. We usually think of rectifiers in the sense of converting AC to DC, but they can also be used if the polarity of the source is unknown.

One source of diodes, indeed the source I used is CFL's, instructions for disassembly have been posted by Westfw.

## Step 2: Attachments

The springclips on a lantern battery can be frustrating to attach things to. I decided alligator clips were the best solution. They are imply soldered onto the inputs of the diode bridge and bent to fit the battery.

## Step 3: Voltage Drop

If you want to be accurate at this point, you can measure the voltage drop caused by the bridge to accurately compute the resistor you will need. I didn't and simply put two 68 ohms in parallel to get 34 ohms.

## Step 4: The LED

I have these lovely little 10 mm LEDs from Alan Parekh, which are very bright, but I didn't just want a spot on the ceiling so following guyfrom7up's instructions I diffused the LED.

## Step 5: Finally

I attached the LED resistor combo to the bridge, remember, here polarity matters. Now we have a circuit that we can clip onto the battery, in the dark without regard for the polarity and that will provide somewhere between 10-15 days of light.

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## 31 Discussions

Why bother with the rectifier? If you hook up the LED backwards you will have no light, but it won't be damaged. It would seem "no light" would be a pretty good indication of reverse polarity. Something tactile like a piece of tape on the ground side clip would also seem to be a simple solution. Otherwise nifty!

4 replies

I wondered if anyone ever knew what that was :P Maybe one day I'll put up my lantern. It uses 4 AAs, a 3 watt cree q5 and an 800ma current regulator.

My lantern uses a 12v amber car LED indicator bulb, a modified light fitting, a KP nuts tin, a switch and a 12v plugpack :)

I think the idea here is that you can replace a candle with this in a power outage.

It's safer, it can be left unattended, and it's probably cheaper to boot because it will "burn" unattended for several candles' worth.

You can also get ready-made bridge rectifiers from suppliers like Digi-Key for just over the cost of one diode.

Saves a little when making a bunch, although if you are only building a few you can probably find enough stuff in the olde junkbox.

I'll have to fave this one. I have some 12 volt gells around and I think I need a multi-LED adaptation of this for every one of them. I'll string several LEDs and add an appropriate resister.

Good idea. But I can't think of a more expensive battery to clip this to. I use 9 volt batteries from the dollar store. Do they even sell these monster 6v batteries anymore?

6 replies

Just a little math 9 volts are 2 for \$1, Lantern Batteries are \$7. capacity of a 9 volt is about 250 mah, capacity of a lantern battery is about 10000 mah......

those are probably already dead batteries that they sell for a buck lol i love paying for dead batt.

You say that the 9v is a quarter amp and that the lantern is ten amps? a 9V battery Ranges from 500MA to 900ma, I'm not sure about the lantern though.

Alkaline 9v batteries are 595 mAh An Alkaline 6v lantern battery is 26,000 and 52,000 mAh depending. This information is from the third edition Pocket Ref. And yes they still sell lantern batteries :).