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

In article
,
wrote:
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.

--
*(on a baby-size shirt) "Party -- my crib -- two a.m

Dave Plowman London SW
To e-mail, change noise into sound.

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.

Dave Plowman (News) wrote:
In article
,
wrote:

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.

In article ,
Caesar Valenti wrote:
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.

--
*Change is inevitable ... except from vending machines *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Caesar Valenti wrote:

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.

On Sat, 22 Nov 2008 09:02:14 -0800, Caesar Valenti
put finger to keyboard and composed:

Dave Plowman (News) wrote:
In article ,
Caesar Valenti wrote:

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.

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
--
Please remove one 'i' from my address when replying by email.

Franc Zabkar wrote:

snip

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.

Good candidate for 'Tip of the Month'! Old VRMs either sawed-out or
on plug-in cards could make great supplies for lots of purposes.

Michael