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Q & A: replacing batteries with a power supply

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Most recent answer: 12/11/2015
Q:
I have a LED spotlight that works off of 3 "C" batteries (4.5v). I'd like to use a power supply to avoid replacing batteries in time. I have several power supply adapters with 5v outputs. Do I need to use a 4.5v power supply or can I use the 5v without a problem?
- Vortec (age 20)
Boston,Ma USA
A:

If the power supply were really a regulated 5 V, my guess is that the LEDs could take it, with slightly increased brightnes and reduced lifetime. That's not guaranteed! I'm more worried that the supply might be one of the highly unregulated types that only gets down to 5V when it's connected to a big enough load. 

There's probably a way to make this work, but it's best to find out some specs first. Does the supply give a current (e.g. 500 mA) at which it puts out 5V? Do you know about what the current draw of the LEDs is? If those match up ok you could just put a resistor in series picked to have about an 0.5V voltage drop at the operating current, just to be safe. That only wastes about 10% of the power, so it still should be more efficient than replacing batteries frequently.

Mike W.


(published on 12/11/2015)

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