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help with 1st LED setup

lfcreds91

Mar 14, 2011
2
Joined
Mar 14, 2011
Messages
2
i will be setting up my 1st LED base.....

this is how it looks.

5686480651_7bb9560ab0_z.jpg


the LED will be a 5mm spectrum or rainbow LED.......those that changes color every 0.5 sec.

battery will be 27 V, by joining 3 9V battery together.

resistor will be a 1/4 470 resistor.

the problem is i dont really know the LED forward voltage/current.

judging by the above setup, do you guys think its good to go?

or is it gonna BLOW!!!!!!!!!
 

Mitale

May 8, 2011
4
Joined
May 8, 2011
Messages
4
If you're worried then start with just 1 9V, then move to 2 9V, then 3. It may or may not even start with just 1 9V though.
 

serious coinage

Mar 26, 2011
13
Joined
Mar 26, 2011
Messages
13
Look at the information on driving LEDs in series here.

edit: after some quick calculations, assuming these LEDs are standard red ones with a voltage drop of ~2V and a current draw of 20mA, those resistors should be about 1K. You could run 2 470R resistors in series to get the right resistance if you don't want to buy more, but a 0.25W resistor is too small, you'll need 0.5W ones.
 
Last edited:

nbw

May 8, 2011
48
Joined
May 8, 2011
Messages
48
Do you really need the 27V? If you have 4 of those at 2V forward drop, that leaves 19V to get dropped across the resistors. You could probably get away with 2, maybe 1 if you're lucky. The resistors will need to change.

If you're using blue LEDs that run 2.9 - 3.5V, that's different of course - but 2 batteries should still be ok.
 
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