LED “fiber optic” Xmas tree repair/upgrade?

Slayer2003

Newly Enlightened
Joined
Oct 9, 2015
Messages
8
I’m not certain if this is where I should post this, but it seemed most appropriate here.

I’m looking to repair and upgrade a small light up table top Christmas tree that holds rather high sentimental value. The circuit is extremely basic and searching around online these trees seem to all suffer the same fate, flickering of the LED and sputtering of the small motor before not working at all. Well, this happened to mine in December and I’ve put off looking into it until now.

An example of the tree. They come in a ton of different styles but all seem to be the same manufacturer.

At first i thought it was the motor as it was making a terrible grinding noise, so i replaced it but no go. No more grinding however the LED still flickers sporadically.

I then attempted just redoing the solder joints as they were rather sloppy but still no go. Replaced the wiring in case that was an issue and nope.

I was unable to find a match for the unknown brand wall wart, but given the in/output figured i could convert it to USB since i have a plethora of old phone chargers collecting dust, and that gives me a future upgrade path. So i added a USB-C pigtail, plugged it in and still no change in flickering. Bah.

Ok, now I’m about 2 weeks in after waiting for parts to arrive and figure i can just make this thing better instead of trying to track down the LED replacement (which i found and they have terrible reviews for blowing and overheating at even below the listed specs :| ), and the SMD resistor decided that it didn’t want to be a thing anymore wherein it suctioned itself to my iron upon reattachment, becoming a crispy charred speck. Neat.

So, I’ve been pouring over diagrams and calculators and hatching ideas and looking at my array of torches, can i use or make something similar to what is in my lights within this tree?

It wouldn’t have to be insanely bright as I’m certain heat buildup would be an issue(but i do have small fans that could…nonono i don’t need that ;) ), it would have to be able to run for hours on end and I’d preferably like to still use these old USB phone chargers i have for power since they are low draw and low profile like the original power brick. I tested the fiber elements in the tree with a few of my flashlights and anything in the range of 200-500lm would be plenty.

What do you folks think, does this project not have a chance? Or should i just bite the bullet and keep replacing the original bits when they pop?

Original psu output: 5v 0.5A
Updated psu output: Samsung 5v 0.7A or 1A, prefer the 1A ones but have a few in the 0.7A variety
Motor: 3-12v DC toy motor
LED: What i believe the LED is based on the original psu and SMD resistor used
Resistor: 3r0 - 3Ω SMD
 

Dave_H

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Joined
Nov 3, 2009
Messages
796
Location
Ottawa Ont. Canada
Product link gets choked up, is there another? Is this a fibre-optic tree with a colour wheel rotating in the base?

LED you point to looks like two in series (and two parallel) which needs at least 6v so it could not run directly from 5v unless there is a boost circuit somewhere (doubt it). You'd need LED with only one in series typically around 3v, then figure out correct dropping resistor based on current for brightness you need (and within LED spec)

Dave
 
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Dave_H

Enlightened
Joined
Nov 3, 2009
Messages
796
Location
Ottawa Ont. Canada
BTW is the LED actually bad or just the resistor (or wiring)?

Suppose you replace it with single 3W LED and run at 2W (good to derate) which is about 0.67A.
At 100 lumens/watt you would get 200 lumens. Modern LEDs should be able to achieve this.

To drop from 5v to around 3v, use (5-3)/0.67 = 3 ohms (3.3 or 2.7 close enough). Don't count on a small SMT resistor. At 0.67A, a 3.3 ohm resistor dissipates roughly 1.3W, best to use at least 2-3W (or 5W) wire-wound , not uncommon or expensive.

Use 5v, 1A (or higher) power adapter.

Dave
 

Ken_McE

Flashlight Enthusiast
Joined
Jun 16, 2003
Messages
1,686
What do you folks think, does this project not have a chance? Or should i just bite the bullet and keep replacing the original bits when they pop?

Perfectly good project. Hard to give any kind of advice since I don't known how the innards are put together.
 
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