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RESISTOR PROBLEMS

 
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precisewitem
HG Master


Joined: 07 Dec 2006
Posts: 130
Location: NY

PostPosted: Tue Dec 19, 2006 1:13 pm    Post subject: RESISTOR PROBLEMS Reply with quote

Found these great LEDs I'm going to put in my wireless 360 controller:
The Led light http://www.theledlight.com/pdf/YM5mmGreen.pdf

Now for foward voltage it says: 3.1V +/- .3V
so for running the LEDs: min=2.8 norm=3.1 max=3.4 right?

current rating is: 30mA

I will be running 6 of these off the battery pack, which is 3V.

so FV=3, C=30, 6 LEDs in parallel - plug those numbers into the resistor calculator and you get a 1ohm resistor with a rating of 0W. Does this mean that I will not need a resistor, or that I need to find a resistor with a rating of 1ohm 0W?
Resistor calculator http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

Any info would be appretiated,
Chris
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Nginuity
HG Ruler


Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Tue Dec 19, 2006 3:49 pm    Post subject: Reply with quote

No, it doesn't mean that you don't need a resistor.
Since you are (somewhat) matching the input voltage with the LED voltage, then the resistor is not being used for voltage, just to regulate the current going into the resistors.

For example:

r = (v1 - v2) / (a*ln/1000)

(3v-3v)/(30*6/1000) = 0/.180 = 0 ohms

since there is no 0 ohm resistor (well, that would be a vacuum), they give you the next value up, which is the 1 ohm. It is recommended you always use a resistor to keep the LED's from burning out faster from current exposure.

I am kind of concerned that your forward voltage is a little more than your circuit input voltage though, because the LED will not let current pass without the required forward voltage, and when your batteries start slightly dying, I can guarantee you the lights wont work, because the battery pack will have considerably less than 3 volts for use. The LED's probably wont even work unless you always have a fully charged battery pack.
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precisewitem
HG Master


Joined: 07 Dec 2006
Posts: 130
Location: NY

PostPosted: Tue Dec 19, 2006 7:14 pm    Post subject: Power supply Reply with quote

Well the LEDs will run on 2.8 to 3.2V, so I figured I would run them at 3V rather than trying to step up the current. I'm hoping not to run into problems with battery life, do you have any suggestions on what I should do?
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Nginuity
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Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Tue Dec 19, 2006 8:04 pm    Post subject: Re: Power supply Reply with quote

precisewitem wrote:
Well the LEDs will run on 2.8 to 3.2V, so I figured I would run them at 3V rather than trying to step up the current. I'm hoping not to run into problems with battery life, do you have any suggestions on what I should do?


My point was that the specs say 3.1 +/- .3 V

That doesn't mean that it will run in that range, it means that the forward voltage will fall somewhere in between that range...might be 2.8, might be 3.4. If it is on the low side, the lights will light up, but if it is on the high side, you wont have enough voltage provided, or they will be dimmer than usual. Using batteries might run the voltage on the high side, but characteristically, as they start using the stored power, the voltage drops. (A good example is that a car battery that is rated for 12 volts will show 14.4 volts when it is fully charged, but will show less than 11.5 volts when dead)

I don't know what you might do short of using a voltage doubler. I was thinking an opamp, but first you don't have 5 volts to drive it, and your output can't be more than the supply voltage anyway.

Let me know how you decide to do it and I will point you in the right direction.


Last edited by Nginuity on Tue Dec 19, 2006 10:42 pm; edited 2 times in total
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precisewitem
HG Master


Joined: 07 Dec 2006
Posts: 130
Location: NY

PostPosted: Tue Dec 19, 2006 8:15 pm    Post subject: Power supply Reply with quote

Thanks again for your help, what I could really use is a link to a place to get 3v green leds with an mcd over or around 5000. I can't seem to find anyhting but parts lists, anyone got any good led sites ?
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Nginuity
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Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Tue Dec 19, 2006 10:46 pm    Post subject: Re: Power supply Reply with quote

precisewitem wrote:
Thanks again for your help, what I could really use is a link to a place to get 3v green leds with an mcd over or around 5000. I can't seem to find anyhting but parts lists, anyone got any good led sites ?


Well, this isn't really my area, but I would assume that as they get brighter, the voltage requirements increase.

Alan has a great store. Here is the link to his green led:

http://alan-parekh.vstore.ca/product_info.php/cPath/4_6/products_id/17

It's 8000 mcd's
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precisewitem
HG Master


Joined: 07 Dec 2006
Posts: 130
Location: NY

PostPosted: Thu Dec 21, 2006 8:20 am    Post subject: Thanks Nginuity Reply with quote

I found some yellow LEDs at 5000 mcd 2.4V through superbrightleds.com. I will use these in my controller along with the proper resistor depending on how many I will be installing. I was able to find low wattage resistors through electronics plus. Thanks for all your help
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