# Connecting LED lights directly to 12v source

Discussion in 'The Projects Forum' started by boneman818, Aug 23, 2009.

1. ### boneman818 Thread Starter New Member

Aug 22, 2009
1
0
I was wondering... I purchased some under-counter LED lights from Ikea. There are 4 individual lights that all wire back to a box with 4 connectors. Behind the 4 connector box is a power supply. The power supply lists "Input: 120v-60Hz 0.1A, Output: 12VDC 5W Max.". So if the output is 12v can't I simply connect these lights directly to a 12v source and eliminate the power supply?

I am trying to convert these lights to be used in an RV instead of a residental home. The RV will use only 12v not 110v. I tried to connect a light directly to a car battery and got an unpleasant puff of smoke.

Thanks

2. ### bertus Administrator

Apr 5, 2008
15,534
2,300
Hello,

Do you also know what is inside the box between the lights and the 12 V powersupply?
It can be there is some current regulation inside the box for the leds.

Greetings,
Bertus

3. ### rspuzio Active Member

Jan 19, 2009
77
0
> So if the output is 12v can't I simply connect these lights directly
> to a 12v source and eliminate the power supply?

LED's need a constant current source, not a constant voltage
source. To be sure, they won't light up unless you apply enough
voltage but, once their lit, even a tiny increase in voltage
will make for dramatic increases in current, so your supply
needs to limit the current.

> I tried to connect a light directly to a car battery and got an
> unpleasant puff of smoke.

That's why you need to limit the current --- you found out
the hard way

The easiest way to limit the current is with a dropping resistor.

For more information on ways of regulating current for LED's.
please see the tattoo machine light discussion:

4. ### jj_alukkas Well-Known Member

Jan 8, 2009
751
5
Which way do you guys think is more efficient?

To use ~1k resistors per LED and drop directly ~9V as heat on each resistor? or
To use a single 7805 and drop 5V to Vf using resistors per LED?

7805 is a very lossy regulator at 12v as well as the resistors at 12v.

5. ### Fragger New Member

Aug 21, 2009
5
0
Its just a thought but you could add a 120v power inverter to your rv and run your led's and any other appliances you wish, would be handy in a rv.