LEDS from 4.5V Batteries to 5V USB conversion

[magda]

A little bit off topic, but apparently there is no off topic forum...

I have a Led Xmas tree for the office
https://www.lemaxcollection.com/vil.../chasing-multi-light-spruce-tree--large-74265

It uses three batteries (4.5V - 65mA) and I want it to be powered by the PC USB port. Adapting the current cable to an USB cable is pretty simple. I suppose I can just plug it in, but I want the leds to last. My question is should I use a resistor? And if so, what ohm value should I use?

thanks

 

[The Mad Atheist]

IIRC, a bit rusty, 20 years out of the field, you could throw a couple of diodes in series and that'll drop it down to .4 volts, doubt .1v will kill em.
Er, correction, regular diodes will have .7v drop, so just use 1.

 

[Brian_B]

Doubt the extra 0.5V would hurt them at all but the diode idea is a good one.

 

[magda]

IIRC, a bit rusty, 20 years out of the field, you could throw a couple of diodes in series and that'll drop it down to .4 volts, doubt .1v will kill em.
Er, correction, regular diodes will have .7v drop, so just use 1.

You mean a diode

or another LED?

 

[Brian_B]

You mean a diode
View attachment 120852

or another LED?

Electrical they amount to the same thing. One just emits light.

 

[BinarySynapse]

Fresh alkaline cells put out 1.6-1.7v for a bit. So you'd really be getting 4.8-5.1v from the battery pack. I dont think 5v from the USB port is going to hurt it