View Full Version : How many fans are too many

10-02-2002, 11:25 PM
Does anyone know what the maximum number of fans that should be run off of one side of the power supply. I am running a volcanoe 7+, 3 case fans, a hard drive and a floppy just off of one connector. I am no math wizard but doesn't the voltage drop each time you split the wires. The reason I ask is that my fans seem to fluctuate a little on the noise and I look at the voltage output in my bios and the voltages are not rock solid. Also my fan rpms seem about 500 rpm slower than they are advertised. My voltages fluctuate about .2 volts. Could my cheap 350 watt power supply be straining, is it just the allowed tollerance built into the cheap pws, or do all pws fluctuate? I always seem to have more questions.

10-02-2002, 11:57 PM
These items are all wired in parallel, so the voltage drop isn't directly related to the number of devices.(Technicly, the longer wire run and heating from the larger current draw have a very small effect.) Your power supply should have a tolerance rating for each power rail i.e. 12v= plus or minus (I couldn't figure out how to make the symbol)3%. Bear in mind that this is only a manufacturer's claim. It's ok for the voltage to be a little different than exactly 12v (or 5v,etc.), but fluctuation is not generally considered good. This would make me think the psu is operating at its high limit.

10-03-2002, 12:08 AM
It's quite possible that it maybe. The PSU's that I use have 2-3 main power conector cables with 3 molex conectors and a floppy connector on 1 or 2 (if 3)cables and 4 molex conectors on the last one which either would be plenty to even out the load even if ya usin' a couple of splitters in there. :smokin:

10-03-2002, 12:14 AM
Investing on a good quality PSU is not a bad idea...even if there is a choice between a good quality 350 psu and a crappy generic 450 i'd rather get that quality 350 watt. PSU's are often overlooked in quality department by a few people. Its just as important as any other comopnent and qualities like reliablilty as well as stability should be considered.

Mr. C
10-03-2002, 01:53 AM
The PSU could be in question, yes.

There are steps you can take to try to resolve the issue before running out to get a new PSU.
You could try moving your power cables around a bit - perhaps using the molex on that circuit going to your HDD to power your CD-ROM instead. As it is surely used a bit less than the HDD I'm sure. That would give you a bit more steady power to the fans perhaps? Basically what I'm getting at, is that your fans will be in constant use - so try to place their power source along with the least used hardware to be drawing from the same circuit. The placement of the fans on the same circuit as the floppy power cable is perfect, you probably don't use the floppy that much.
Unless you tend to use your burner and CD-ROM at the same time, you could use a splitter to power both of them from the same circuit and leave the flow to the fans even less in demand.

Reroute your power cabling in accordance with the manner in which you are most likely to require power throughout your systlem. 350W when used wisely is just as/more effective as 400W used poorly.

And of course, let's not overlook the obvious - are your wiring connections providing good conductivity? I've done a lot of do-it-yourself wiring in my system instead of a lot of storebought connections and it is crucial to have all the connections solid. A less than perfect wiring connection can account for a good deal of fluctuations.

Play around a bit with it and see if you can get some improvement in your power readings.

Good luck, have fun:angel:

10-03-2002, 02:41 AM
Funny you would mention tampering with the wiring. I am a cable splicer by trade and I have access to lots of scotch lock splices. I bought a molex 4 pin connector extender and spliced my fans into that without using molex connectors. The connections are good I know for a fact but I wonder if the splices can handle the current. Phone works off of 23 to 43 milliamps and the scotch locks were designed for that. The splices aren't getting hot so I think they are handling the current ok. Phone works off of around 49 to 53 volts so the voltage isn't too high. I just dont think it is my connections. I do think that it is a cheap power supply. I disconnected my fans and everything else, the voltages fluctuate by about .2 volts. The fans indicate they are fluctuating by about 300 to 500 rpms. I just don't know that I am overly concerned about it. Have you guys looked in your bios and checked your power supply voltages. My guess is that everyone's power supply fluctuates, some more than others.
Also it could be the mobo indicating software. If I was more concerned I could hook up a meter. The fan fluctuation is rather small and If my cpu is ok with it I guess I will just keep a close eye on things.

10-03-2002, 12:41 PM
Yes I check mine often enough but my variences are in the order of .02 - .03 volts on any voltage rail. Not enough to make a difference to any of my 8 fans. :smokin:

10-03-2002, 04:09 PM
lol wiggo, I might be able to start rivaling your 8 fans. I am going to be having: 5 Case fans (80mm's), 2 92mm fans on the hard drive, then the volcano 7+. That makes 8 fans :).