Main > Main Forum
Basic electrics question.
(1/2) > >>
jimmy2x2x:
Ive just bought a simple led light cluster

It is powered by 3xAAA batteries (1.5V each = 4.5v)

Could I power this by a 5v supply from a pc molex?

Thanks
MonMotha:
In general, no.

Those LEDs probably don't actually add up to anything near 5V.  The designs are usually really cheap and rely on the resistance of the batteries (fairly high for 3xAAA) to provide the "ballast" that you normally see in series with an LED.  A PC supply is a pretty stiff 5V and will probably blow up your LEDs or at least cause more rapid failure (not that those things seem to last very long, anyway).

A resistor can be used as typical in this application, but the value will require some measurement and calculation to determine (or just try about 50 ohms and see if you're lucky).
ragnar:
Are you sure about that?

5 volts is 5 volts.  The current draw depends upon the resistance of the LEDs.

I'd say, have at it.  Unless the LEDs are expensive.
jimmy2x2x:
Cheap as chips, £1 for a cluster of 24!
Blanka:

--- Quote from: ragnar on August 19, 2010, 11:52:22 am ---The current draw depends upon the resistance of the LEDs.
--- End quote ---

The stupid thing is that LED's are not Ohm's ballasts. They do not work according to ohms law. They are basically no-speed-limit lanes. You need a resistor to prevent them from frying. In cheap battery solutions, the battery is the resistor, but on a PSU, a seperate resistor is needed. There are many led-calculators on the net. Check what you need for 5V with 3 leds. Probably a low-ohm one, 10 ohm or so.
Navigation
Message Index
Next page

Go to full version