Newbie question

[webley445]

Just finished my first homemade jobbie this weekend [see post in cafe]. I scavanged an LED from a keychain light that used two 3v wafer batteries. There was also a resistor attached to the LED. I git it all into a "new" casing and am using 2 AA's to power. Will this cause any damage? Is it good or bad? I didn't measure the resistor for its rating so I have no idea its resistance.

 

[Deleted member 684]

What colour is the LED? If it's white, I think 2 AA batteries should be just about right. The resistor attached to the LED is because 3 volts x 2 batteries = 6 volts. As for your AA battery. 1.5 volts x 2 batteries = 3 volts. Some LEDs can only take so much voltage before it dies.

But back to the main question, what colour is it? White needs 3.6 volts. Somewhat the same for blue and green. Amber and red seems to require much less, around 2 volts? I'm not too sure on the red and amber ones though.

 

[EMPOWERTORCH]

That's the question I would have asked as well.
Recently I've been building a number of direct-drive torches using orange anmd yellow LED's and 2 cell configurations. In most cases I've got the cathode legs of the LED's soldered to a large piece of metal in the torch. The cathode leg is directly connected to the die of the LED (The chunk of gallium arsenide and silicon that actually does the work of converting electrical energy to light energy). Therefore, some of the excess heat is conducted away. These seem to be perfectly happy on direct drive from 2AA's!
In answer to your question though, if you are still using the resistor, you will get hardly any light output at all, as your original keychain torch had a 6V battery supply, and 2AA's are 3V. InGaN green, blue and white LED's will only light dimly, if at all on a 3V supply, even if the resistor is left out.
So, it's down to the colour and the chemistry of your LED!

 

[webley445]

Sorry for the delayed responce. Got caught up with other posts and forgot about this one.

It is a white LED and it is working [lighting]. I will try removing the resistor and see how it goes, if it will get brightter. So far I left it on for over 24hours and the output diminised only slightly. Even with the resistor it seems to be putting out as much light as it did in its original configuration as a keychain light with two 6v button cells. I found a multi-meter I forgot I had in the garage so will be testing to see the resistance of the part.

My next question is can I direct drive 1 to 3 LEDs on a 9v battery? looking to make myself one of those "emergency" lights like I saw in a C-Crane catalogue [can't believe what they're charging price wise for one]. What effect will the 9v have on a LED [using 1 or 2 or 3 of them]. do I need to use a resistor in that set up?

Anything else to add about the 2AA or 9v set up?
BTW, thanks for the input.