electric question.

warlock110 · Apr 7, 2005

Say if my fan at 12V is taking in 9 watts of power, when i put it on a fan control at 5V, would it consume less power, or does the extra power transform into heat? Because if at 5V the fan is taking in less power, then the PSU should be less on load. Same question but with light, when the light is switch off, does it still consume power?

Electron Chaser · Apr 7, 2005

warlock110 said:
Say if my fan at 12V is taking in 9 watts of power, when i put it on a fan control at 5V, would it consume less power, or does the extra power transform into heat? Because if at 5V the fan is taking in less power, then the PSU should be less on load. Same question but with light, when the light is switch off, does it still consume power?

In this instance the "fan" will consume less power and will not produce any excessive heat though it will run warmer since you are running at slower then it's intended speed. However the fan controller will still draw slightly more power to control the fan at that speed since no circuit is 100% efficent. No not even close to the entire 9 watts. NM I really don't want to go to far into it and confuse you.

When a light is off the circuit is broken and therefore it canot consume any power.

warlock110 · Apr 7, 2005

Electron Chaser said:
In this instance the "fan" will consume less power and will not produce any excessive heat though it will run warmer since you are running at slower then it's intended speed. However the fan controller will still draw slightly more power to control the fan at that speed since no circuit is 100% efficent. No not even close to the entire 9 watts. NM I really don't want to go to far into it and confuse you.

When a light is off the circuit is broken and therefore it canot consume any power.

sounds confusing already but i'm gonna give it one more shot to make it clearer, I have a nexus 301 that can adjust fan from 0-12V. And i have a few 3 blade deltas that's rated for 9watts (well that's what on the label anyways). So here are the senerios

Fan @ 12V = 9 Watt
Fan @ 07V = ???????
Fan @ 05V = ???????
Fan @ 00V = ??????? total stopage, but is that bad for the fan?

Between 7 and 5V what's recommeneded, and how much of the fan's life span will get reduce? i never thought that running the fan slower will damage it...

yeha · Apr 7, 2005

the fan will last longer when run at a lower voltage. less motor wear and all. the only way i can imagine it harming the lifespan is if it were a hydrowave design which was made specifically for a certain rpm, and anything less than that doesn't cycle enough lubricant. but that seems pretty doubtful.

as for where the power goes, if you get the 5 volts directly from the psu's 5v rail, then the fan will draw 3.75 watts instead of 9 and the psu will output/draw less overall power than running the fan from the 12v rail. the formula here for power (watts) is voltage times current, so for the fan at stock 12v it's 9 watts = 12 volts * ? amps, which we can solve as the fan's current draw being 0.75 amps. the fan will draw 0.75 amps (well, at low voltages it'll actually a bit more depending on its circuitry) at any input voltage, so if you lower the input voltage to 5 volts, you have 5 volts * 0.75 amps = 3.75 watts.

now then, if you're supplying the 5 volts from a fan controller, odds are that controller isn't transforming the 12 volts its supplied with to 5 volts, it's getting lower voltages by resistance (a potentiometer i assume in the nexus). thus, if it's drawing 12 volts at 0.75 amps to power the fan, but only outputs 5 volts to the fan, then that 7 volt drop is being transformed into heat in the fan controller. call me crazy, but i'd say the amount of heat being dumped into the fan controller in that case would be 5.25 watts (9 watts drawn - 3.75 watts to fan). at 7 volts, the power would be 7 * 0.75 = 5.25 watts.

this is all just from a loose understanding i've pieced together over time. probably wrong on some/many points, i'd love to be corrected so i could straighten out some terms in my head.

warlock110 · Apr 8, 2005

yeha said:
the fan will last longer when run at a lower voltage. less motor wear and all. the only way i can imagine it harming the lifespan is if it were a hydrowave design which was made specifically for a certain rpm, and anything less than that doesn't cycle enough lubricant. but that seems pretty doubtful.

as for where the power goes, if you get the 5 volts directly from the psu's 5v rail, then the fan will draw 3.75 watts instead of 9 and the psu will output/draw less overall power than running the fan from the 12v rail. the formula here for power (watts) is voltage times current, so for the fan at stock 12v it's 9 watts = 12 volts * ? amps, which we can solve as the fan's current draw being 0.75 amps. the fan will draw 0.75 amps (well, at low voltages it'll actually a bit more depending on its circuitry) at any input voltage, so if you lower the input voltage to 5 volts, you have 5 volts * 0.75 amps = 3.75 watts.

now then, if you're supplying the 5 volts from a fan controller, odds are that controller isn't transforming the 12 volts its supplied with to 5 volts, it's getting lower voltages by resistance (a potentiometer i assume in the nexus). thus, if it's drawing 12 volts at 0.75 amps to power the fan, but only outputs 5 volts to the fan, then that 7 volt drop is being transformed into heat in the fan controller. call me crazy, but i'd say the amount of heat being dumped into the fan controller in that case would be 5.25 watts (9 watts drawn - 3.75 watts to fan). at 7 volts, the power would be 7 * 0.75 = 5.25 watts.

this is all just from a loose understanding i've pieced together over time. probably wrong on some/many points, i'd love to be corrected so i could straighten out some terms in my head.

this is what i'm thinking too. How the hell do i make the fan draw power for the 5V rail? lol.

schismspeak · Apr 8, 2005

warlock110 said:
this is what i'm thinking too. How the hell do i make the fan draw power for the 5V rail? lol.

You just change the wires around on the fans connector, in the volt mod section there is a fairly recent thread that should have a link to do it.

warlock110 · Apr 8, 2005

schismspeak said:
You just change the wires around on the fans connector, in the volt mod section there is a fairly recent thread that should have a link to do it.

The wire method actually cancels out the electric rail i believe, so it's still drawing the same ammount of power at full blast, it just got canceled out to reach the desire voltage.

yeha · Apr 8, 2005

warlock110 said:
The wire method actually cancels out the electric rail i believe, so it's still drawing the same ammount of power at full blast, it just got canceled out to reach the desire voltage.

i'm not sure what this means, perhaps you're refering to the 7-volt mod..

to run a fan at 5 volts instead of 12 volts, you just swap the 12v and 5v lines on the molex connector that you're plugging the fan into. no crossing lines or anything, the fan's ground line still goes to ground but the dc input draws from 5v instead of 12v. ergo, the fan's running at 5v now, straight from the psu.

here's how the molex connector lines are:

the 12v and 5v lines can be manipulated (use the 5v as ground) to get you 7 volts while dumping power back into your psu - this is generally recommended against. however if you just swap the 12v and 5v wires, anything you plug into that modified molex that used to draw from the 12v line will now get 5 volts instead.

there's a little article about it here with some more pics.

warlock110 · Apr 8, 2005

yeha said:
i'm not sure what this means, perhaps you're refering to the 7-volt mod..

to run a fan at 5 volts instead of 12 volts, you just swap the 12v and 5v lines on the molex connector that you're plugging the fan into. no crossing lines or anything, the fan's ground line still goes to ground but the dc input draws from 5v instead of 12v. ergo, the fan's running at 5v now, straight from the psu.

here's how the molex connector lines are:

the 12v and 5v lines can be manipulated (use the 5v as ground) to get you 7 volts while dumping power back into your psu - this is generally recommended against. however if you just swap the 12v and 5v wires, anything you plug into that modified molex that used to draw from the 12v line will now get 5 volts instead.

there's a little article about it here with some more pics.

u're right, thanks, hehe this save me alot of trouble.

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