Model Train Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
420 Posts
Discussion Starter #1
Trying to better understand this process. All/any help much appreciated.
I have some LED lights I want to install on my layout they are 3mm and 5mm white I purchased from AllElectronics. They said they are 3 volt and 20ma.
My power supply I have is output 3V, 500ma 6 w.
1) How would I determine a resistor size with this info?
2) how many of these led's could I use with this supply?

Thanks!!
 

·
Registered
Joined
·
1,286 Posts
 

·
Admin
Joined
·
44,354 Posts
In order to use resistor current limiting, you need to have some headroom. You have an LED with an operating voltage in the 3.0-3.3 volt range, and a 3V power supply. You really want a DC supply around 5V or more to have some headroom to add the current limiting resistors. For 5V, the resistor would be 100 ohms.
 

·
Registered
Joined
·
28 Posts
What about LEDs that have voltage:12V~18V(1000 Ohm resistor in series),Forward current (typ/max): 20mA/30mA. I purchased about 50 of these LED's to use inside houses and such. I just would like to know how to figure out the power supply needed.

Thanks for you help!
Mike
 

·
Registered
Joined
·
26 Posts
I’ve found the LEDs are almost too bright with my power source (old phone charger, cut the end off and figure out which is negative/positive) so I use resistors and combinations of resistors (in series) to get the look I want.
 

·
Registered
Joined
·
2,207 Posts
Coblesan, try a 12 volt wall wart, if that's too bright for you then try a 9v wall wart, maybe even 5. At some voltage they will not light due to insufficient current, you know you went too low then. My control panel lights use a 12 volt wall wart and 1k resistors. The current draw is around .01 ma per led. So a 1 amp wall wart can power a 100 leds, I would use a 50% safety factor and only power 50 or so per wall wart.
 
1 - 11 of 11 Posts
Top