>> 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

> Do a Google for LED drivers. There are ones around which will work over a
> wide range of voltages. Ready made and circuits you can build yourself.
> But for maximum efficiency you might have to go back to basics rather than
> adapt your existing ones.

> But if all you want is working light stick with fluorescent. It's more
> efficient than LED at the moment.

>> 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.

> For 20mA?

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

>>> 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.

>> 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.

> 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.