Resistor help

[Venom Jedi]

Hi guys! I have a problem to find the right resistor for a led. http://forums.thecustomsabershop.com...e-to-Ohm-s-Law I have already read this post, but, I don't know where I can find the voltage of the led. In the shop, the description of the led for example is, typical voltage and maximum voltage. So, witch voltage i have to use for a seoul p4 or a cree xp-e2 or a luxeon? I wanna try with a 18650 3.7 volt battery. I hope you can help me guys, is my first building.

[grumblehound]

in most descriptions for leds you get a minimum voltage, maximum voltage and sometimes a typical voltage

example ..... for a green led you could have 3.2v min 3.8 v max 3.6 v typical
3.2 volts will run nice and cool and should last nearly forever but will be less bright
3.8 volts nice and bright but running hot and probably shorter life
3.6 volts probably the best compromise maybe not as bright but you probably wont notice it

but don't forget a fully charged 18650 gives out about 4.15v initially (source voltage) soon drops to 4.1/4.0
so I would use something about 0.2v under the maximum rating for the led

so 4.1v source
3.6v led
and whatever the milliamps are

hope this helps

[Venom Jedi]

in most descriptions for leds you get a minimum voltage, maximum voltage and sometimes a typical voltage

example ..... for a green led you could have 3.2v min 3.8 v max 3.6 v typical
3.2 volts will run nice and cool and should last nearly forever but will be less bright
3.8 volts nice and bright but running hot and probably shorter life
3.6 volts probably the best compromise maybe not as bright but you probably wont notice it

but don't forget a fully charged 18650 gives out about 4.15v initially (source voltage) soon drops to 4.1/4.0
so I would use something about 0.2v under the maximum rating for the led

so 4.1v source
3.6v led
and whatever the milliamps are

hope this helps

Thank you so much man! So, you mean when i calculate the resistor i have to put 4.1v for the battery? Witch milliamps i have to use? I mean, if i use a forwars voltage 3.40v for a luxeon rebel green, can i use 700mA or the current i want give to the led is not important according to the volts of the led? Sorry, i hope i explained myself.

[grumblehound]

yes about 4.1v for the battery(source voltage) you can use less 3.7v to 4 v but the led will run over its rated voltage until the battery voltage drops
if you have the luxeon rebel star in green in mind then looking at the description it seem its rating is 700mA at 3.4v the run at 1000mA must be its maximum rating which I guess must be at about 3.6/3.7 volts
what you need is a 2watt 1ohm resistor a 3 or 5 watt resistor will do the important bit is the 1ohm

[NanoRex]

We usually drive cool-coloured Rebel LEDs at 1000mA (or 1A). As stated in the store description, the green Rebel has a forward voltage of 3.4V when driven at 1000mA. So your equation would look like: R=(3.7-3.4)/1

[grumblehound]

don't think I have used one of these rebel leds but have always found that about 3.7v or 3.8v was needed to get up to 1000mA on all others I have tried ..........would try some of these if the shipping cost to the uk wasn't $60 $10 led +$60 shipping???????? was going to buy a NB3 sound board but shipping costs as much as the card will have to keep using Hasbro boards for now and save up for a big order with some blades later on just hope things will still be in stock

[Venom Jedi]

Ok i have try manually and i have obtained 0.3 ohm and 0.3 watt. In the online calculator (led.linear1), i've obatained 1 ohm and 2 watt. Witch one is the best? Maybe a round up the resistor obtained manually? I use the green rebel just for a example, if I want try with a seoul p4 or a cree xp-e2, where i can get the forward voltage and the mA? I mean with a different current 700mA or 350 or 1000, the forward voltage remain the same?

[darth_chasm]

don't think I have used one of these rebel leds but have always found that about 3.7v or 3.8v was needed to get up to 1000mA on all others I have tried ..........would try some of these if the shipping cost to the uk wasn't $60 $10 led +$60 shipping???????? was going to buy a NB3 sound board but shipping costs as much as the card will have to keep using Hasbro boards for now and save up for a big order with some blades later on just hope things will still be in stock

You can go directly to Plecter Labs for sound boards out your way. I believe Erv just stocked some.

EDIT: and apparently they are selling faster than you can say I Love Star Wars.

[grumblehound]

darth_chasm ...............I LOVE YOU...................g


I check plecter labs web site most days had started to give up as most things are always sold out
don't think I have checked it in a few days
was 3 left when I looked ordered 2 by the time I had logged in and got to checkout I could only order 1
think it works out a few pound more when you convert euros to pounds but shipping so much cheaper and with any luck it may avoid customs charges

will now start work on a new saber hilt its being built in memory of my GSD Sammy who passed away Thursday going to build it inside a bone if I can find one the right size now can add barks and growls as sound fonts

[darth_chasm]

darth_chasm ...............I LOVE YOU...................g

Haha glad to help out