Quick Question

kahless78 · Post by **kahless78** » Wed May 05, 2010 9:22 pm

Ok I have a 6.0 volt power supply I want to run two led with a drop of 3.0 @20 ma Are 1/4 watt 150 ohm resistors to much?

brt · Post by **brt** » Thu May 06, 2010 8:27 am

http://www.quickar.com/noqbestledcalc.htm

kahless78 · Post by **kahless78** » Thu May 06, 2010 10:14 am

I know this lol Its says I need a 1ohm resistor. However last night I hooked it up using a 150 ohm resistor and it worked I didn't notice any drop in brightness in the leds but the main thing is will this hold up or will this burn out. I don't want to do this and have the model together then not be able to fix it you know what I mean?

USS Atlantis · Post by **USS Atlantis** » Thu May 06, 2010 11:40 am

Using the 150ohm vs the 1ohm will reduce the brightness - not by much if it's a "superbright"

Added benefit - since the LED isn't running at full brightness, it will actually extend the lifespan - no burnout

kahless78 · Post by **kahless78** » Thu May 06, 2010 11:53 am

Thank you Ken God you have been great help to me with this project!!! They are super bright leds, I guess thats why i didn't notice and difference. but just to be clear on what I am doing i will be going from the power hub to the first led then that led will will be hooked up to another led then to the 150 resistor then to the negative hub

walter · Post by **walter** » Thu May 06, 2010 1:29 pm

I have 2 3mm white leds with 1k ohm resistors runing on a 6v power supply thats deen on from December and are as brite as when first pluged in.

kahless78 · Post by **kahless78** » Fri May 07, 2010 11:04 am

Do you have a resistor on each led or just one? I was going to hook them up in a series with one resistor.

USS Atlantis · Post by **USS Atlantis** » Fri May 07, 2010 12:06 pm

The pair of 3mm LEDs with 1k resistors sounds like 1 resistor per LED

All this will do is decrease the brightness by a percentage

And I'm not surprised that you haven't seen a decrease in intensity in 6 months - LED lifespans are measured in years (100,000 hours of MTBF is 11 years at 24/7 operation) - by reducing the output with the 1k resistors vs 150 ohm (my calc), you're probably adding a few years to that

kahless78 · Post by **kahless78** » Fri May 07, 2010 12:27 pm

So to put it simply so my little brain can understand is yes it will work?

walter · Post by **walter** » Fri May 07, 2010 12:51 pm

kahless78 wrote:Do you have a resistor on each led or just one? I was going to hook them up in a series with one resistor.

Yes one resister on each led.

kahless78 · Post by **kahless78** » Fri May 07, 2010 1:29 pm

Ok But I need to know if one 150 ohm resistor will be ok for two leds? I have hooked up two in a series with a 150 ohm resistors and on each the brightness dims alot. However when I just use one resistor for two leds the brightness hardly dims and that is what I need to know before i seal up the model if I can use two leds in a series with a 150 ohm resistor?

USS Atlantis · Post by **USS Atlantis** » Fri May 07, 2010 1:57 pm

Yes, running the two LEDs in series with one 150ohm resistor will be fine

And since you're getting this all hooked up/assembled - I'll say it first

(grin)

kahless78 · Post by **kahless78** » Fri May 07, 2010 2:20 pm

I will take some this week end bud thanks again!!!!!!!!!

The pics will be in the star trek forum