# LED Forward Current?



## HalloweenZombie (Jul 22, 2007)

Anybody know what the forward current is for monsterguts.com's super bright LEDs? I'm using the LED calculator (http://led.linear1.org/1led.wiz) to figure out resistors. I see some "super bright" LEDs on other sites use 20 mA, but someone told me to use 30 mA. Plus, after some sampling, monsterguts LEDs seem brighter than other super brights. Any ideas?


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## Otaku (Dec 3, 2004)

What's your source voltage? That makes a difference as to the resistor value. All other things being equal, the wizard will tell you to use a higher value resistor as the forward current decreases. Assuming a 20mA forward voltage is safer - you won't blow the LED, but the brightness will suffer. Try dropping a note to Dean and ask for the LED specs. BTW, I've seen "superbright" LEDs with forward voltage and current values all over the map; it's a very broad description.


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## HalloweenZombie (Jul 22, 2007)

Otaku said:


> What's your source voltage? That makes a difference as to the resistor value. All other things being equal, the wizard will tell you to use a higher value resistor as the forward current decreases. Assuming a 20mA forward voltage is safer - you won't blow the LED, but the brightness will suffer. Try dropping a note to Dean and ask for the LED specs. BTW, I've seen "superbright" LEDs with forward voltage and current values all over the map; it's a very broad description.


I'm all set with the voltage (12v) and the forward voltage (monsterguts.com has that listed), just need the forward current. 20mA does seem to be the most common.

I'll drop Dean a note if nobody on the forum knows for sure.


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## Otaku (Dec 3, 2004)

Wow, 12VDC is going to need some beefy resistors. That's a lot of power to waste as heat (assuming you're using one or two LEDs per 12VDC). Are you planning to wire more than one, and if so what is the mA rating of your supply? If you go with a 30mA Vf and have, say, 500mA available you can wire 15-16 LEDs in parallel.


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## HalloweenZombie (Jul 22, 2007)

I've got 12 volt/4 amp power supplies. They designed for commercial building alarms. They are enough to light the whole haunt with LEDs.


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## niblique71 (Dec 2, 2009)

HalloweenZombie said:


> I've got 12 volt/4 amp power supplies. They designed for commercial building alarms. They are enough to light the whole haunt with LEDs.


If you go on MonsterGuts to the LED section and click on "more" button on the far right of each LED selection, you will find the forward voltages for each of the LED's


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## Otaku (Dec 3, 2004)

HZ needs the forward current ratings for the LEDs, I think this info isn't posted on the MG site.


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## niblique71 (Dec 2, 2009)

God I hope I'm wrong, but I'd bet that Monster gusts just added the wrong suffix, and called it forward voltage instead of forward current. The numbers seem to be inline with previous numbers I've always used for LED calculations, calling it Milliamps instead of voltage. Small but still HUGE Mistake if it is true...


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## pshort (May 6, 2008)

niblique71 said:


> God I hope I'm wrong, but I'd bet that Monster gusts just added the wrong suffix, and called it forward voltage instead of forward current. The numbers seem to be inline with previous numbers I've always used for LED calculations, calling it Milliamps instead of voltage. Small but still HUGE Mistake if it is true...


I'm not sure where this is coming from...the numbers that I see on their site are in the vicinity of 2.4V to 3.x V, which is what I would expect for forward voltage. The forward current specs for most ordinary LEDs will be either 20 mA or 25 mA, with some (but not all) 8mm LEDs up to about 100 mA. What numbers are you looking at?


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## Otaku (Dec 3, 2004)

I'm sure the values on the MG site are for the voltage; they don't make sense for forward current values.


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## niblique71 (Dec 2, 2009)

Duh....You guys are right... Damn Beer Goggles.... I wonder why they don't give the values


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## HalloweenZombie (Jul 22, 2007)

The forward voltage is accurate on the site. So we used 330 ohm resistors for a single LED with 3.6v and 30mA current. It works, but I'm not sure if it is as bright as it could be. If I go with 20mA, then the resistor is 470 ohms, which will just decrease the brigtness. But if some of the super bright LEDs go up to 100mA, then I'm not getting full use out of the LEDs. I send monsterguts and email. I'll keep you all posted. Thanks for everyone's help on this.


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## pshort (May 6, 2008)

What is the diameter of the LEDs? If it's 3mm or 5mm (T1 or T1-3/4), then 25 mA will pretty much be the limit (if not lower). Some of the 8mm LEDs will support a higher current, but I would definitely bet against the 3mm or 5mm parts.


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## HalloweenZombie (Jul 22, 2007)

They are 5mm.


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## Otaku (Dec 3, 2004)

HalloweenZombie said:


> I send monsterguts and email. I'll keep you all posted. Thanks for everyone's help on this.


It may take a bit to hear from Dean. His site got hammered with spam a while back and a lot of his legit messages got thrown in the spam folder. He's sifting through them as we speak.


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## HalloweenZombie (Jul 22, 2007)

Dean says I should be using 20mA. He got back to me pretty quick yesterday. What service!


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