Calculating which rheostat to use.

[ClarkKent]

I have a lot of fans for my case. I want to build a rheobus so I can control them. Lets say I have a delta ASB0812HH fan with 0.20AMPS of rated current and 2.4WATTS of output power. What (WATT and Ohm) rheostat should I buy to be able to turn the fan from 6V-12V?

 

[Matt761]

A 30 ohm resistor i believe.

 

[ClarkKent]

Do you know the math to find that out? And will it matter what WATT the rheostat is or does it just have to be larger than 2.4? And if I were to use two fans with those same specs on the same rheostat would the ohms have to be 60?

 

[Susquehannock]

Have you seen greenman100's post?
* How to Choose a Rheostat/Variable Resistor *

These might help as well:
* A Rheo Baybus you can't Overload! *
* The Rheostat Fanbus *


Good luck with your project.

 

[ClarkKent]

Thanx they were great guides. But they don't explain the math. They just tell you to buy certain parts and put them together. Basically I need to know if putting 2 fans on the same channel is going to burn out my rheostats. So there would be two fans with a combined 4.8Watts and .4Amps. Does any one know the math or can point me in the right direction?

 

[matttheniceguy]

Go online and learn. Learn about Ohms law (I=V/R) mainly and how to do calculations for simple circuits. Learn about putting things in series or parallel and what this means for everything. A fan is just an electric engine with blades on it, so learn how electric engines work too. It's all really simple stuff, and everything will make a lot more sence once you know it.

 

[archilochus]

Check this out and WELCOME TO THE FORUMS..

http://www.cpemma.co.uk/rheo.html

 

[ClarkKent]

you guys have been great thanks for all the help. I'll show you my mod when I get finished with it. Right now I'm trying to decide wheather to do rheostats of to go with 12V/7V switches. Or could I go with 12V/7V/5V switches couse that would be great?

 

[matttheniceguy]

a lot of fans won't start at 5V. Most of them will have enough power to run at that voltage (if you start them at 12 you can lower it to 5 and they *might* keep going) but most fans won't start at 5V.

 

[ClarkKent]

Ok so they wont start at 5V. But I could just make sure the switches are at 12V to start and then turn them down to 5V right?

 

[archilochus]

Panaflo's don't run under 7 volts...They quit.. Why have a fan if you are going to turn it down to 5 volts? Just curious..

 

[ClarkKent]

My new case (That I'm building myself and you can see here http://www.ocforums.com/showthread.php?t=314393) is going to have a lot of fans and I want to be able to slow them down when i sleep. There will probably be around 10 fans. I have 3 Deltas, 2 Sunons, 1 Thermaltake and a bunch of generic ones.

 

[archilochus]

Are you entering the case into a flight contest? My temps are derived from 6 total case fans..All 92mm fans..I had to get away from those pesky 80mm noise makers..My goal is to have even less fans than I have now, in the future.. Keep your flow up and fan numbers down,

 

[ClarkKent]

Right now I love the way my case is planned to look. I realize that there will be some niose problems but that is why I want the option to turn them down. If you have any suggestions for doing that please help me out. Post here or in the thread for my case. I've asked for help and concidering you are ranked as "THE FANMAN" maybe you can help me out.

Q: What brand of fans do you use? And where are they in your case?

 

[archilochus]

My case fans are NMB: 3610KL-04W-B40/. 2850 rpm @ 48 cfm/ 37 dBA..Those are controlled on my 4 channel rheobus...5x92mm/ 1) top blow hole 2)frt. int. 2) rear exh.
My mobo wall hole mod fan is a 92mm Panaflo U1A:FBA09A12U1A/. 3450 rpm @ 68.80 cfm/ 43 dBA..Also on rheobus..Right side panel..
2x80mm in PSU..inline configuration..

please don't quote my pix.

 

[ClarkKent]

To get 10 fans I added in my PSU fans and my CPU. Which I can see you didn't. So I guess my number would be 7. So thats not too bad then, right? Also I have a question about your mobo wall hole fan mod. So you cut a hole in your mobo tray and put a fan on the back? Does it cool well, how many degree's?

 

[archilochus]

It got me a 2°C drop in cpu, full load temps..Below is a link to MOBY's home page...See all 3 pages of pix, to see the cases evolution..

http://groups.msn.com/MOBYSHOME/mobyscasemodding.msnw?Page=3

please don't quote my pic.

 

[ClarkKent]

Looks great. What did you use for your filter mesh? Did it cut back on air flow?

 

[archilochus]

Very little..I used some weiner grill material from Wal-Mart, $0.94 each sheet..Oscarware: 12" X 16" Grill Topper....The filter media, is washable a/c filter media also bought at Wal-Mart...2 sheets,15" X 24"..$2.00 Cut to fit...
The grill material is soft enough to hand shape.. Expanded aluminum..