power for LEDs
- Thread starter bukster
- Start date
Not a heck of a lot 
Even if you wire them all in parrallel you will only use 20x.03 = 0.6 Amp.
But if you wire them series / parrallel it is much more efficient. You can probably run 3 x LEDs in each circuit. That way you could run 7 strings of 3 LEDs each with one resistor on each leg. That would cut your power down to 0.21 Amps from a 12volt plugpack.
Cheers
Ian
Even if you wire them all in parrallel you will only use 20x.03 = 0.6 Amp.
But if you wire them series / parrallel it is much more efficient. You can probably run 3 x LEDs in each circuit. That way you could run 7 strings of 3 LEDs each with one resistor on each leg. That would cut your power down to 0.21 Amps from a 12volt plugpack.
Cheers
Ian
sorry like i said it's been a long time since i've had to mess with anything like this. would it matter if i had a 5v or a 12v power supply? i mean i know there'd be different resistors, but would the amperage be the same? sorry for the dumb questions
If you wire each LED with a resistor and connect it to the power, then the current will be the same for 5v or 12v. But at 12 volts that actually wastes most of the power.
If you wire them series / parrallel then you can have one resistor for 3 or 4 leds on the 12volt supply and draw less current, use less resistors and waste less power.
I know it's not a lot of power, and resistors are cheap, but it's silly to just waste them.
Have a look at this page, it will do the calculations, draw you a little diagram and even tell you what colour resistors to get
http://led.linear1.org/led.wiz
Cheers
Ian
If you wire them series / parrallel then you can have one resistor for 3 or 4 leds on the 12volt supply and draw less current, use less resistors and waste less power.
I know it's not a lot of power, and resistors are cheap, but it's silly to just waste them.
Have a look at this page, it will do the calculations, draw you a little diagram and even tell you what colour resistors to get
http://led.linear1.org/led.wiz
Cheers
Ian
This is the answers I got for you - use 21 LEDs, it's more elegent
Solution 0: 3 x 7 array uses 21 LEDs exactly
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
The wizard says: In solution 0:
each 120 ohm resistor dissipates 48 mW
the wizard says the color code for 120 is brown red brown
the wizard thinks ¼W resistors are fine for your application
together, all resistors dissipate 336 mW
together, the diodes dissipate 1386 mW
total power dissipated by the array is 1722 mW
the array draws current of 140 mA from the source.
Solution 0: 3 x 7 array uses 21 LEDs exactly
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
+----|>|----|>|----|>|---/\/\/----+ R = 120 ohms
The wizard says: In solution 0:
each 120 ohm resistor dissipates 48 mW
the wizard says the color code for 120 is brown red brown
the wizard thinks ¼W resistors are fine for your application
together, all resistors dissipate 336 mW
together, the diodes dissipate 1386 mW
total power dissipated by the array is 1722 mW
the array draws current of 140 mA from the source.
Depends how much Moonlight you want I guess...
It's only 1.3watts of light, so it's not going to be very bright compared to flouro tubes.
Easy to disconnect a few if it's brighter than you want.
Cheers
Ian
It's only 1.3watts of light, so it's not going to be very bright compared to flouro tubes.
Easy to disconnect a few if it's brighter than you want.
Cheers
Ian