Converting solar led lights

I

indudio

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Hi,

Since the cool white color is hard to come by this year, I earlier on picked up a few boxes of containing about 50 to 100 packs of the 200 led cool white solar lights. These run at 2-3 volts. I would like to know if I could run these at 12 or 24v if I add a resistor to them. They only have the + and - ( basically 1 channel).

I attempted this with some 1/4 watt carbon resistors however they ended up smoking.

I assume it can be done, maybe with 1/2 watt resistors or higher?

Any thoughts?

(ps if anyone has any cool white big w or Kmart strings I will gladly purchase them off you)
 

David_AVD

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Best bet is to run them at 5V, with a smaller series resistor. I did that in 2011 with battery operated candy canes.

12V or 24V operation is not really an option due to the large amount to power you'd need to waste.
 
I

indudio

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So @ 5volts, be looking at about 50 ohm resistor?
Or less?
 

David_AVD

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indudio said:
So @ 5volts, be looking at about 50 ohm resistor?
Or less?
Some of the solar light sets contained a single AA (rechargeable) cell and a small circuit board. The board contained a specialised IC to charge the AA cell from the solar panel and also act as a boost converter for the LEDs.

Thinking about it now, for a 50/100 string of parallel connected LEDs setting the current with a resistor will be tricky as the value will be critical.

If you assumed 2mA per LED (solar LED sets are often not very bright), 50 in parallel would draw 100mA @ approx 3.2 Volts. That means you need to get rid of 1.8V (5.0V - 3.2V) at 100mA which will require an 18 Ohm resistor, rated at 0.5W or more.
 

AntinOz

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So, to add a totally silly question to the thread and, hopefully, not take it too far off topic. Could I run this off the 3.3v rail on my Arduino (which I could control through Vixen), or would the current draw be too high?
 

David_AVD

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You would need to determine the voltage required and the current drawn by the LED set you want to use.
 
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