Converting battery LED strings to 12V

David_AVD

David_AVD

Grandpa Elf
Community project designer
Joined
Jun 12, 2010
Messages
4,717
Location
Victoria Point (Brisbane)
I bought a bunch of battery powered sets (of 10) LED mini lanterns on eBay. You can get them in various designs for as little as $1 to $2 a set if you hunt around and wait for them to be on special.

Of course I want to use them on 12V, not waste money on batteries each time. So I did up a page (on da-share) to show how to mod them and put a standard (for my display) 2-pin connector on.

mini_lanterns5.jpg
 
Now, if you want to dim or flash those LED strings, you can use a $1 dimmer module off eBay.

Here's one that I've added 2-pin connector tails to so I can put it inline with whatever lights I want.


12v_mini_dimmer2.jpg
 
If I understand correctly, the LEDs on those light sets are all wired in parallel to each other. Couldn't you halve the light set and put the two halves in series with each other? That way you'd have two parallel sections of 5 LEDs in series with each other and you could use the voltage more efficiently with a smaller resistor.

Great simple hack though.
 
You could, but then you'd need to feed the string from the middle if you know what I mean.

The resistor value I chose was a nice compromise between power dissipation and brightness.
 
nice David,


I have 4 strings of those pumpkins, replaced the battery pack with a buck converter and ran them off a dc controller
 
Yeah, I had some of the $0.60 buck converters but wanted to keep these passive so there were no ill effects from being dimmed by a controller.

For kicks I did try it on one string and the dimming was erratic as expected. The buck converters really want to see a constant DC input.
 
I haven't tried this but it might work if the negative wire for the light set is connected to the DC controller and the positive is wired to the output of a DC-DC convertor wired to the same power supply as the controller.
 
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