Rheostat Baybus

[mcrites]

Ok, I want to build a rheostat baybus to control 2 fans, and I put this little diagram together with some help from the diagram on the caseetc.com article on rheostat baybuses. Now tell me: will this work, or am I a complete dummy when it comes to electronics ;).

[Veland]

That should work!

Just make sure you are using a good reostat, minimum 5 watt I'd say. Anything smaller, and they get real hot and have a short lifespan. If your using it to control your CPU fan, you DON'T want it to burn.

[mcrites]

I am using watercooling ;), trying to kill some noise on my radiator fans, but Im thinking of adding another fan, to try to get the ambient temp in the case down. Right now it hovers around 29C, and my idle temp is 33C-35C. I think it would be better to use the SPST to power the whole fanbus, then chop up parts of the psu wires to hook the SPST to, so when I hook more fans up, all I have to do is hook a rheostat to the fans wires. I was wondering if anyone knew how pcmods did their baybys? Do they use pots or something out of the loop to control the voltage to the leds. I know they cant put the leds in the loop with the rheostat. I was just wondering why they use an led on every rheostat as well, unless of course they use a pot or something. THanks for all suggestions.

[mcrites]

One more question, why does rheostat have more than 2 terminals? I know with a SPDT, you can use both the bottom and top terminals for a different on setting, but I cant figure out why you would split something up 3 times. Maybe for hooking up more than one device? Once again thanks for all answers.

[Veland]

Answers in random order :)

Pcmods use some sort of voltage controller. The one I'm using in my projects, is the LM317T. If you search for LM317 you shold find a lot of projects for this. The beauty here is that you kan use regular pots, since the voltage controller is where extra power is dissipated as heat. But the downside is loosing som power, usually you can not get closer then 1.2 volts from max voltage... Ehh.. That wasn't a good way to say it.. Running from 12 volts you will probably not get more than max 10.8 to you fans!

The two terminals are for the "pot" function. Potentiometer means that you can adjust the potencial between live and ground. So, if you connect the reostat as follows:
1st terminal 12v
2nd terminal multimeter
3rd terminal ground

And the other lead from the multimeter to ground, you can then "dial in" where in the potencial between 12 and ground you measure.

But you only use it as a variable reistor, and don't need the last terminal.


Lastly, there are spelling errors I'm sure, and the only knowledge of electronics are from physics class a long time ago, so don't trust what I'm saying blindly. But I have built a LM317T based fancontroller with it's own power supply, so I have som ideas..

[Veland]

..oh! And you could connect the leds in parallell with the fans, just use an appropriate resistor for the max voltage. Then they would dim (a little) as you reduse fan speed..

Or maybe do something smart with the other reostat terminal? Gotta think about that..

[el]

veland is correct this is the best way and the LM350 is great if you need high wattage.

[mcrites]

I think I will keep it simple and just use the SPST and one led through this. Thanks for all your suggestions, I am a novice at this stuff, so maybe I will implement something more complicated later. :p

[mcrites]

Ok, I built this fanbus like I have in the diagram, havent hooked up to the rheostats yet tho cuz I am testing the fanbus. I need some input. No matter what position the switch is in, the LED is on all the time. Also, I do not get any power to the fanbus at all. I have tested the switch for resistance, and whats weird, or my lack of ignorance, the on side has resistance, and the off side doesn't. Do I have this switch wired backwards? :) Any suggestions at all is extremely appreciated.

[mcrites]

Never mind Im a doof. The led should be on the bottom terminal, and I think I did not have the leads from the fan in properly. :rolleyes: :mad: :D