Electric Circuits: please look at this diagram...help!
 

I'm so clueless when it comes to electric circuits. After the CPA exam in a couple of weeks, I'm going to learn...
But for now, I wired up my fans so that I could control them. I am experiencing a few anamolies, which I'd like to have explained.
When I switch either the 92mm fan or the 80mm fans from the 5v line to the 12v line, they slow waaay down. It doesn't seem to affect the 172mm fan that is running on the same line. Should it?
I don't know what the hell I screwed up. You'll probably laugh when you see what I did...
What kind of circuit do I have, anyway? If you plug multiple hard drives into the same power lead from the PSU, what kind of circuit is that? help!!!

oh yeah..

Just to make sure... when the switch is up, as shown, the fan is getting 12v.. right? Down=5v?

If your fans are wired up as you have it in the diagram then throwing the switch from 5V to 12V wouldn't affect the 172mm fan that is on the rheostat. Out of curiousity, how far can you turn down the Rotron and still get it to spin?

As for the switches, if they spin fast at what you think is 5V and slow at what you think is 12V then you most likely wired them up backwards. Got a multimeter? It isn't hard to either measure the output voltage or else to just check the continuity of the switch in either position.

My expierence has been that 3way switches tend to wire up backwards from what you think they will when using them for 12v off 5v.

Ok.. I was just wondering if I had them in series, parallel, or both.. I don't know what kind of voltages I have running through there...

The comair won't spin at all at 5v, even if it is already spinning. Don't know about 7v...
I'm using a 25 ohm rheostat. I can crank it down all the way, and it's fine. It just needs to be turned up some when you start it. At the lower settings, the motor makes a slight 'ticking' sound. Add a little juice, and the noise goes away, and you have a low pitched whirr. Not too bad.

Question: the comair is rated at 24v, and draws .75A. Does this mean it is a 32ohm resistor? Therefore, at 12v, it draws .375A. Now, if you add a 25 ohm resistor to the circuit, how much voltage is flowing through the fan? Or does the resistor just let less current through? What make the fan slow down!?? Use numbers in your answer.. :) (i'm such an accountant.)

Just click here (I am too lazy to make a gif or jpg)

Its just the way a switch works, just a simple little metal lever.

-WireX

Thanks, that answers it. I was concerned that somehow the comair was using up the 12v line, so that when I switched the other fans to use that line, it was actually getting less juice than w/ the 5v line... I'm so clueless.

Still doesn't answer my question about the rheostats, though (see above).

A resistor does not alter voltage. It resists current (amps). Voltage drops occur when you apply KVL and calculate the voltages over every component. But strictly speaking, resistors only resist current. Diodes drop voltage. An ideal drops voltage between .6 and .7 volts.

And to clarify your situation up there, when you split up a line like you did with that 12v line, all the branching lines still have 12v. The only thing that changes is the current.

Ok.. well how much current does the PSU put out? or is that the wrong question?
could you elaborate? What's KVL? How much current does my little 25ohm resist? An Ideal diode? Do I need these diodes in my system?

Is there a good website that has a zillion illustrations?

If I wanted to hook up fans in series, how do I do it? How about parallel? hmmm? :confused:

So do my fans run slower when they're all hooked together?

If someone's bored, they can take my diagram and label it, showing how much current, voltage, etc is going to each. Assume that the 172mm fan draws 1A (rated at 24V), and the 4 smaller fans draw .25A (each rated at 12V).
That would be great.

lol, i drew you up a diagram in windows paint, but i dont have any software to convert the bmp into a jpg (and i aint puttin up a 1 meg pic either ;P ). o well, lol

if your fans are wired in parrallel, they will all run at the same voltage (or current? some-1 more knowledgable please confirm). if your fans are wired in series, all the fans wired after the first will spin slower. damn, i wish i hadnt forgotten all this electronics stuff i learned in HS lol!

dude.. open it in ms paint, and Save As, then select .jpg instead of .bmp. :D paint will save files as jpegs.

not mine.....bitmaps only.

im using the MSpaint that came with win98se....cuz thats the OS i got ;p
i'll look for a newer version of paint on M$' website.....

i searched, there was none i could find. i did have PSP, but it was only a 30-day trial. dammit, i need something that'll last forever lol! (non-warez...)

get IfranView


or you could just get Morpheus or kazaa, and download winxp. no product activation.. you can swap parts around to your heart's content. :evilaugh: ...or so I'm told .. lol

if your fans are wired in parrallel, they will all run at the same voltage (or current? some-1 more knowledgable please confirm). if your fans are wired in series, all the fans wired after the first will spin slower. damn, i wish i hadnt forgotten all this electronics stuff i learned in HS lol! [/b][/quote]

In parrallel they all get the same voltage. In series they all get the same current, this current goes down as you add more components inline (as there combined resistance goes up). In series all the fans will go at the same speed (if they are the same type of fan of cource) including the first one. But the entire line will get slower as you add more.

Edward

ah ok, that makes sense thx :p

Basic electronics here, but please ask more questions if it isn't clear. Hopefully, you can do basic algebra, because that's all you need for this stuff.

1) Basic equation for current, voltage and resistance.
Current = Voltage / Resistance

2) Resistors in series always add together.

-----R1------R2----
Total resistance over that portion of a circuit is R1 + R2

3) Voltage can be "divided" by using two Resistive loads (resistor or fan, or whatever).

If they are equal resistive loads, the voltage in the middle is half of the voltage sent across the divider.
+12V ----R1-----<+6V>------R2---- Ground

Basically, at the mid point, the voltage is equal to:
Voltage = (Input Voltage) * (R2 / (R1 + R2))
= +12V * (R1 / (R1 + R1)) = +12V * (1/2) = +6V

So, for fans in series, things get complicated. However, all the fans are slowers. Not just the first one.

Also, just as a very basic, think of electricity as water. more specifically water cooling (just to make it easy). The tubes are always full of water (or should be) but when you apply a pump (elctricity), all the water (electrons) get pushed along, that is why you can put a resistor on both the positive and negitive lines (I hope?) and it will still act normally.

I don't know if this affected anything, but it makes things easier to put into perspective.

-WireX

rightttt.... hmmm. let's break it down...

is this how you wire fans in series vs. parallel?

parallel....

looks correct to me.

ok.....
so, when fans are run in parallel, as in the fanbus, each fan gets 12v. Since the PSU can supply alot of current on that rail, each fan still can run at its rated amperage. Right?
In series, the fans get the same amperage, but the voltage gets split up according to resistance?

When you run a resistor (rheostat) in series with a fan, you DO?!? drop the voltage going to the fan?

Since the PSU can put out as much current as needed, the only thing that would change in a fan ciruit is the voltage. Right?

Fans run in parallel each get full voltage and run full speed.

Fans run in series do not get full voltage, and each of them runs slower than normal.

The pictures were correct.

Ok... so what's the difference between the panaflo 120mm L1A & M1A fans? http://www.panasonic.com/industrial/...pdf/fba12g.pdf
Does the faster fan just have less resistance? (by my calculations, about 35ohms more resistance) If I added a 35ohm resistor to the fan circuit, I would have a L1A fan, right? If so, I could just get the faster fan, and use a rheostat to slow it down to the speed of the L1A, or even slower.... right?

L = low, M = medium, H = high.
sure, get a high-powered fan tho. that way when you want the extra airflow, its there for you.