decreasing voltage on LED fan, will leds dim?

[gingo]

If I used a rhoebus to make my LED fans spin slower would the LED's also go dimmer? Also, would it decrease the life of the LED's?

[AntmanMike]

Yes, they would get dimmer. No, it will not decrease their life. LEDs are not that complex.

[rustymaitland]

how come my leds won't dim when i turn the knob down on the rheobus? i have the pcmods version with the 17w/channel.

[MEAT BAG]

my antec led fans dim when i switch them to 7v and it makes them look all ghetto.

[RangerJoe]

it really shouldnt change it that much...if you spin the fan with your fingers hard enough you can see the LED's start glowing...

[gingo]

RangerJoe, that works?

[Liss]

it kinda depends on how much juice your fans suck..
my led fans work fine at 12v.. but at 7v the fans dont spin and the leds a very dim.. :(

[Mpegger]

LEDs are meant to run at thier rated voltage all the time. To reduce brightness, you need to reduce the mA applied to the LED, not the Voltage. Because of this, variable resistors (rheobus) will not operate the LED correctly. As to what kind of circuit is needed to "fade" LEDs, I haven't a clue. I would think some kind of voltage regulating circuit with an adjustable mA output would be in order.

But AntmanMike is correct with the LED Fans. Depending on the LEDs used, they may just shut off after a certain voltage.

[snvpa]

hey thats good to know maybe i can shut these damn blinking leds off on my 2 crystaL case fans if i 7v mod them. annoying pieces of crap. they cool good though and are reasonably quiet.

[800XL]

Mpegger is right. LEDs will dim somewhat in response to voltage, but only in that they are getting less mA. They tend to drop off very fast when they get below a certain voltage and just cut out almost entirely.

An LED fader would probably need to be something like a voltage reg used as a variable current limiter. I think you can do this with an L200 (datasheet link) (http://eu.st.com/stonline/books/pdf/docs/1318.pdf) I recall seeing an example circuit in the datasheet someplace for a current limiter. I may be wrong and there is an easier way to do it though.

Seems like it shouldn't be too hard to wire off the LEDs to another power source and keep the fan connected to some speed control. That way the LEDs stay just as bright (and on) no matter how slow the fan goes.

[Turbokeu]

Originally posted by 800XL
Mpegger is right. LEDs will dim somewhat in response to voltage, but only in that they are getting less mA. They tend to drop off very fast when they get below a certain voltage and just cut out almost entirely.
That's correct.
That "certain voltage" is the LED forward voltage:
Red LED = 1.7V (low brightness) - 1.9V (high brightness,high efficiency,low current)
Green LED = 2.1V
Yellow LED = 2.0V
Orange LED = 2.0V
Blue LED = 3.4 - 3.8V (4.6V for 430nm bright blue)
White LED = 3.4V

Originally posted by 800XL
An LED fader would probably need to be something like a voltage reg used as a variable current limiter. I think you can do this with an L200 (datasheet link) (http://eu.st.com/stonline/books/pdf/docs/1318.pdf) I recall seeing an example circuit in the datasheet someplace for a current limiter. I may be wrong and there is an easier way to do it though. [/B]
You don't need a current limiter regulator to fade a LED. The serial resistor for the LED acts as a current limiter, so all you have to do is to vary the applied voltage.

Originally posted by 800XL
Seems like it shouldn't be too hard to wire off the LEDs to another power source and keep the fan connected to some speed control. That way the LEDs stay just as bright (and on) no matter how slow the fan goes. [/B]
You're right again, see my howto at http://www.turbokeu.com/mycomputer/antecfan.htm to mod the Antec tri-led fans.

CD:)

[macklin01]

Just a quick note -- if your fanbus is PWM-based (not sure if the one you mentioned is), you mostly likely won't notice much dimming at all, since it cycles between 12V (regular brightness) and 0V very quickly, and LED's don't cut out immediately when their voltage is cut. (certainly not on the timescale of PWM). -- Paul

[Nisei]

To get back at this 5.5 year old topic;
I've just got a nice deal on 4 Antec 120mm blue LED fans (not TriCool).
The manual says NOT to connect these to a fanspeed regulated source (e.g. mainboard). I have an Asus P5N32-E SLI and I'm almost certain that it uses PWM to control the fan speeds. I've contacted Antec about it and they say the fans cannot be regulated in any way and they warned me not to connnect them to the regulated mainboard connectors which seems a bit odd to me. Most likely the fans will work just fine but the LEDs could start behaving erratically. Does anyone know who's right here? And can I damage the mainboard trying?

[thideras]

To get back at this 5.5 year old topic;
I've just got a nice deal on 4 Antec 120mm blue LED fans (not TriCool).
The manual says NOT to connect these to a fanspeed regulated source (e.g. mainboard). I have an Asus P5N32-E SLI and I'm almost certain that it uses PWM to control the fan speeds. I've contacted Antec about it and they say the fans cannot be regulated in any way and they warned me not to connnect them to the regulated mainboard connectors which seems a bit odd to me. Most likely the fans will work just fine but the LEDs could start behaving erratically. Does anyone know who's right here? And can I damage the mainboard trying?:welcome: to the forums!

You should have created a new thread instead of bringing this back up :beer:

You can plug them into your motherboard, they may act strange, but they will work.

[Nisei]

:welcome: to the forums!
Thanks :)
You should have created a new thread instead of bringing this back up :beer:
LOL, well usually people get bashed for not using the search function so I searched for a similair thread. Anyway, I thought my post fitted this topic.
You can plug them into your motherboard, they may act strange, but they will work.
Just like I thought. I should have known when the support guy said; "Ive been told they can't be regulated at all". Probably someone who doesn't know anything about it himself :) OK so it's save to try but does anyone have any experience in connecting led fans to a PWM regulated source? Is the result always the same or do different LED fans react differently to this? And has anyone tried Antec LED fans in particular?

[Eclectic]

My OCZ ram cooler has two fans with blue LED's in. With a Zalman fan mate the LED's dim. There seems to be no other adverse effect, other than the fans slowing (which of course was the point).

Im certain you will have no problems.

[JamesXP]

My case has a little spinny thing to change the fan speed, The lights dim a little, But one of my LED fans is a different blue to the other.