Ok, here's the situation. I've got 5 Cooler Master 4-LED fans in my case and I want to hook them up to a Sunbeam Rheobus. However, when I hook them up to the rheobus the LED's shine noticably dimmer due to the 12V line droping from 11.96V down to 11.5V coming out of the Rheobus.
I first tried to figure out a way to get closer to 12V coming out of the rheobus, but I figured this would be too hard and I didn't want to fry my whole rheobus.
Next, I decided it would be neat to supply the LED's on the fans with their own dedicated 12V line instead of powering them with the rheobus line. This way I could turn all the LED's on or off with a switch, and they would never get dimmer just from turning down the fan speed. This is when I started reading up on LED's and I'm a bit confused on how they need to be hooked up.
I've read several places that you need to have a resister in series with an LED to help control the current through it. Well, I can't really see the internal guts on my fans well enough to tell if there's a resister hooked up with them or not. What I can tell is that the 4 LED"s are connected in series with one side going to the ground line and the other end soldered to a point on the tiny PCB that is NOT the same as the 12V line runing to the fan. With 11.96V applied to the power line of the fan, I'm reading about 11.5V across all the LED's. This tells me that there probably is a resistor in there. if I measure the resistance from the power line of the fan to the power line of the LED's I get 10.0 ohms.
I'm assuming there's a 10 ohm resister in series with the LED's. So here are the questions I have:
1) If I cut the LED "power" line from the fan and apply my own line of 12V to the LED's, do I need to add a 10 ohm resister?
2) What would happen if I didn't add the resister? Would they eventually fry? (I've put 12V across them for a short time and they lit up nicely, but I'm worried that they'll all fry in a week or so if I'm running too much current through them.)
3) Does a 10 ohm resister sound like too little? The other "LED guide" sites I read seemed to say that 30 ohms was as small as you should go, but they didn't make a whole lot of since because I couldn't find anything talking about this specific situation.
4) Last but not least. Is there a good way to find the type of LED's that are in these fans? ie. what voltage/current they're rated for. I don't want to ruin a fan just to find out and then not be able to put it back together.
Phew, I hope that wasn't too confusing. Thanks for reading this far, and thanks in advance for any advice you might be able to toss my way.
Dave
I first tried to figure out a way to get closer to 12V coming out of the rheobus, but I figured this would be too hard and I didn't want to fry my whole rheobus.
Next, I decided it would be neat to supply the LED's on the fans with their own dedicated 12V line instead of powering them with the rheobus line. This way I could turn all the LED's on or off with a switch, and they would never get dimmer just from turning down the fan speed. This is when I started reading up on LED's and I'm a bit confused on how they need to be hooked up.
I've read several places that you need to have a resister in series with an LED to help control the current through it. Well, I can't really see the internal guts on my fans well enough to tell if there's a resister hooked up with them or not. What I can tell is that the 4 LED"s are connected in series with one side going to the ground line and the other end soldered to a point on the tiny PCB that is NOT the same as the 12V line runing to the fan. With 11.96V applied to the power line of the fan, I'm reading about 11.5V across all the LED's. This tells me that there probably is a resistor in there. if I measure the resistance from the power line of the fan to the power line of the LED's I get 10.0 ohms.
I'm assuming there's a 10 ohm resister in series with the LED's. So here are the questions I have:
1) If I cut the LED "power" line from the fan and apply my own line of 12V to the LED's, do I need to add a 10 ohm resister?
2) What would happen if I didn't add the resister? Would they eventually fry? (I've put 12V across them for a short time and they lit up nicely, but I'm worried that they'll all fry in a week or so if I'm running too much current through them.)
3) Does a 10 ohm resister sound like too little? The other "LED guide" sites I read seemed to say that 30 ohms was as small as you should go, but they didn't make a whole lot of since because I couldn't find anything talking about this specific situation.
4) Last but not least. Is there a good way to find the type of LED's that are in these fans? ie. what voltage/current they're rated for. I don't want to ruin a fan just to find out and then not be able to put it back together.
Phew, I hope that wasn't too confusing. Thanks for reading this far, and thanks in advance for any advice you might be able to toss my way.
Dave
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