9v LED's 12v Power supply

[Acorn]

Hi All,

I have a project where I am using 9v LED bulbs & 12v LED Strips that are all on the same circuit.

The LED bulbs have built in resistors. I tried to light it all via a 9v battery but it would not light the 12v LED strips.

In order to light the 12v LED strips i would need to use a 12v DC adapter.

What i would like to know is, if I use a 12v adapter will it damage / burn out the 9v LED bulbs that are in the circuit?

Many thanks

 

[kinarfi]

add a resistor in series to the 9 volt LEDs and run them at 12 also

 

[Acorn]

Thanks for your reply

The 9v LED bulbs were pre-wired and have a resistor built into each bulb, would this do the trick?

 

[ronsimpson]

Putting 12V on a 9V LED is not good. Probably good for 1/2 second.
Because we don't know how much power the LED uses, or any vital information we need to experiment.

Put a meter across the 9V LED and add a 100 ohm resistor to the 12V source. The meter probably will read 6V and the light will be very low. Try 51 ohms, 22 ohms, 10 ohms. Play this the resistor until the meter reads about 9V. (8.5 to 9.5) You might try a 100 ohm power "pot" and dial in the value. If the meter reads high and the light is bright cut the power now! and try a higher value.

 

[ben7]

Uh, is your 9V battery good!?

 

[ronsimpson]

Likely 9V will not create any light form a 12V LED.

 

[ben7]

Likely 9V will not create any light form a 12V LED.

Yes but sometimes LEDs can be amazingly efficient. I have had some light up from a 9v battery just by the resistance of my skin ... it wasn't all that bright, but it lit up!

If there are 3 LEDs wired in series then yeah they might not light up. Usually the LED Vf is around 3V to 3.3V for white and also blue LEDs.

 

[ronsimpson]

In this case, for a 9V "LED" there are probably 2 - 3V LEDs in series with a resistor that drops 3 volts.
It is a bad idea to use 3 - 3V LEDs and apply 9 volts. There is nothing to limit the current.

 

[kinarfi]

https://www.dropbox.com/s/qa3lc3ukf36l7d6/20121212_111859.jpg
https://www.dropbox.com/s/r5q2wk14tx5yg6r/20121212_111910.jpg
Hi Ron,
I know this goes against most practices of putting a resistor in line with LEDs but these 2 photos are of 6 strings of 4, 3 watt LEDs in series with no resistor, powered by the battery of my off road vehicle and then by the alternator when the engine is running. I have many hours of operation on them and have had no failures, and man, do they light up the road.
https://www.dropbox.com/s/bshhtco1wjaz4ha/At Night.png
Kinarfi