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Converting battery-operated LED Xmas lights strings to run from AC transformer.

Converting battery-operated LED Xmas lights strings to run from AC transformer.

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  #1  
Old 12-20-15, 11:47 AM
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Converting battery-operated LED Xmas lights strings to run from AC transformer.

We have four (outdoor) Xmas wreaths with white LED lights that are battery operated. I want to convert them to run from an AC/DC transformer, because dealing with replacing all these batteries in these each year is such a PITA that we just don't want to do it again (8 tiny screws per each of 8 battery boxes!). But I'm not sure what capacity transformer to get and how to wire it up correctly.

Can someone here can tell me the voltage and minimum amperage each transformer will require and how to be sure I wire it correctly?. I assume that, with that information, I can buy the correct transformers at Frys or on Amazon.

Each of these wreaths has two (2) strings of 20 LED white lights. Each string is powered by two (2) "D" cell batteries in a box. So each wreath has two (2) battery boxes, and therefore each wreath requires 4 "D" cell batteries.

From this, I'm guessing that each string requires 3 volts, but I have no idea what amperage. And if I run more than one string from a transformer, would I need to multiply the required minimum amperage by the number of strings being powered to know the actual minimum amperage necessary to run that number of strings?

These wreaths hang outside on four windows, two of those windows are close to each other on each side of the front of the house. I envision plugging in the transformers inside and running the DC power wires out through the open windows, then closing the windows down on the wires for the season. I have an outside outlet I could use, but I'm concerned that available transformers might not be weatherproof, so it seems better to me to keep the transformers inside the house.

My preference is to have a single transformer provide power to two wreaths (therefore, powering four separate 20 LED strings), but I also could see using one transformer for each wreath (power to just two separate 20 LED strings), if that's simpler. I would prefer not to have to have a separate transformer for each string (therefore, two transformers per wreath).

Hoping to make it easier to understand, I have attached 7 photos showing:
  • one of the wreaths;
  • just a single bulb on that wreath (shows that there are four wires attached to each LED; it does not show that the last LED in each string has only two wires attached to it);
  • the front of one of the battery boxes (each battery box holds two "D" cells);
  • the back of one of the battery box;
  • inside the battery box from one end;
  • inside the battery box from the other end; and
  • the "circuitry" inside the battery box under the plastic shield (I suspect the board is mostly related to the on/off switch on the outside of the box).

Thank you very much in advance for whatever assistance you can provide,
Paul

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  #2  
Old 12-20-15, 12:05 PM
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In the one picture I see an electronic control board. That is probably some type of regulator. That means you'd need to retain those boxes and connect your power supply to the black and red wires that are currently on the battery contacts.


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You need 3v DC wall adapters. Here are a few choices.

Technically a switching power supply is not completely isolated from the AC power line.
3 VDC 1000mA Switching Wall Adapter


This type is the perfect choice. It's a linear power supply which means it uses a transformer. The wiring that goes outside is 100% isolated from the 120v AC line.
Wall Adapter Regulated 3V DC 200mA UL Listed Wholesale Quantities Avail | eBay

A little larger.... current wise but will also work. Is of the transformer type.
amazon/products/power supply
 
  #3  
Old 12-20-15, 08:27 PM
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Do you push the button to get the lights to come on for a certain period? If so, that board is a timer.

If the lights do anything other than just come on, that board controls what the lights do.

Usually each LED light draws about 20 milliamps. These are probably wired in parallel, not series.

You need enough current to drive the number of lamps times 30 milliamps.
 
  #4  
Old 12-21-15, 02:42 PM
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Thanks! The button just turns them on & off. I can't remember whether they stay on for just a certain period of time or until the button is pressed again.

Did you mean 20 or 30 miliamps per lamp? Or are they 20 each, but I should use 30 for calculation purposes?
 
  #5  
Old 12-21-15, 03:10 PM
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You want the transformer to have some headroom, figure 25-30 mA per LED.
 
  #6  
Old 12-22-15, 02:02 AM
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Those are going to be low consumption LED's. They did that to conserve battery power. Any of the power supplies I listed will work for you. It's not critical.

My recommendation is the last one.... 500ma.
 
  #7  
Old 12-22-15, 07:58 AM
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Good point......................
 
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