Lowering min voltage on Nexus controller...?

Being directly related to cooling, I thought this the best spot to post.

To start, I bought a Vantec Nexus (3.5" version) to allow for better cooling during the day and silence while sleeping, as opposed to all fans at 7v the whole time. I was happy when it came, happy when the LED's were just the right brightness for me...then I plugged a previously-hardwired@7v fan the controller...wtf? I could easily tell it wasn't running 7v...at 7v the 80mm Stealth was dead silent, but when I put it on 'low' on the nexus, it was running at least 9v. Does anyone know what min voltage they really put out?

I'm interested as to which resistors I'd have to swap out and what resistance they'd need to drop the min 2 volts. Does anyone have any insight? All I can find elsewhere in seaches are reviews and the like. Thanks.

Mine tested as low as 7v when using a multimeter.

Maybe you should look into a fan controller with 0-12V adjustment.

i'm sure you can mod the nexus w/ resistors... but in case you do feel like avoiding a project, i avoided the problem nicely with my sunbeam rheobus

Another simple change is to put a resister or rheostat in line with the fan. That will lower both the min and the max though.

If your going to start modding electronics I suggest you get a multimeter. I bought one at the local megalomart for $15 and have been using it for five years now.

As far as what resisters to use, I don't know. I might be able to figure it out if you give me some information about it. First, what chips are on it. Most chips will have a part number printed on the top. Next, a picture showing the layout of the controller would help if you can get a clear sharp picture. Make sure you use a camera with optical zoom, otherwise it will just be a blur.

No offense, but I don't think you'd figure this controller out that easily. It uses a seperate IC for controling/powering both the fans and the LEDs, and to top it off, they sanded off the markings from the IC.

I have a multimeter, two actually (and access to some very high-dollar ones too), but the problem is that mine doesn't do well with measuring switched DC sources well. I can't find my other one which probably would, but I can tell you right now that contoller isn't close to 7 volts on low. My 80mm stealth is running 7.59v (haven't installed the antec 350w psu) and its much more quiet on the +5/+12 volt lines than on the Nexus lines.

I got it more as a "maybe I can use it" item. I guess sound from my PC isn't so much of an issue now since I got my logitech z-5300 speakers D ). Thanks for the suggestions, mabe I'll just mod the controller to use rheostats in a while. Better yet, maybe just junk the pcb it came with and make a few LM317 circuts. It's just that...I hate spending money on stuff, then having to mod it just so it works right.

Thanks for all the suggestions.

The reason you are showing greater than 7V is because the Nexus line uses a PWM, pulse width modulation, circuit. So instead of reducing the voltage it changes the amount of time that the voltage is on.

I understand the pwm concept, that's why the only multimeter (the cheap wallet-size one) I can find in my house atm can't read the voltages right. I'm saying the fan puts out more noise on the Nexus's claimed 7volts than when its hooked up to a true 7.49 volts. It could be that on the lower voltages it's just the typical 'squealing' from the pulses being so few (expensive R/C motors & speed controls do the same under 10% max rpm)...but as you crank it up, it just gets louder. Another thing is their circut seems to not be very linear - it's like it has 5-7 distinct steps.

I've decided on cutting the traces to the knobs and putting various resistors in place, then adding LM317 circuts that are controlled by the knobs. That way I'll have both fixed outputs and adjustable ones too, although I'll probably 'reuse' the fan connectors they have on there. The pots on there are 4.5-10k ohm, and I'm guessing very low watt capacity, so using them in a LM317 circuit is my only option. I've decided on using a 2500ohm/10500ohm combo for R1/R2 using a standard LM317 circuit (time 3 or 4, might use one LM350), which would give 11.5v with the knob at 4 ohms, and 6.5v with it cranked to 10k. The reason my R1/R2 are so high is because to get 12v w/the pot at 10k, you need another 10k of resistance. Since R1 must be high to support that 10k pot, a value of 4ohms (pot turned down), you need at least 10k ohms for 7 volts.


If anyone ever wants to try this in the future, this link gives the best formula for finding the resistance you'll need for R1/R2 when you input a certain voltage; the normal forumla usually just outputs voltage and assumes you know R1/R2 already.

http://www.interq.or.jp/japan/se-inoue/e_ckt21_2.htm