Led light voltage

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I have an offroad trailer on which I want to change the existing 12
volt tube lights to accomodate led lights .the led lights run off a
4 volt rechargable battery how/what is the best way to change the
voltage from 12v to 4v on each set of lights there are 4 sets in
different areas I need to change the lights to accomodate the 12
voltage

 

[Caesar Valenti]

All you really need is a simple cheap resistor. Unfortunately I don't
know the current draw on this.... but assuming about 20ma, you will need
to drop 8 volts; so you will need a 300-500 ohm resistor. I would use a
resistor that can handle 1 or 2 watts.

 

[Caesar Valenti]

For 20mA?

A resistor works fine for indicator LEDs but is pretty inefficient for
lighting ones. And when running off batteries this can matter.

Well, I never said this was going to be efficient...just simple. A
DC-DC converter would probably be more efficient, but based upon the
original post, I think that may be overkill. In any case, now they can
decide what is best.

 

[Franc Zabkar]

Well, I never said this was going to be efficient...just simple. A
DC-DC converter would probably be more efficient, but based upon the
original post, I think that may be overkill. In any case, now they can
decide what is best.

It's not clear from the OP's description just how many LEDs are being
supplied from the 4V battery pack, but an old mobile phone charger
using an MC34063 PWM controller IC can output about 500mA. The output
voltage can be reprogrammed by changing one or both of the feedback
resistors.

For very high currents you could use a hacksaw to cut out the Vcore
regulator from an old socket 7 motherboard. I have one that can be
jumpered for 4V.

- Franc Zabkar