Edit:

Okay, I've run another few searches on this and it seems that "7-volting" (described below) is a four pin molex trick and not something I can use for the application I have in mind.

But I'm guessing using a resistor is a potential alternative so I guess that's the answer?

Since resistors reduce current rather than voltage, I guess it renders the question moot, but I guess it should be easier. Although it does raise another few questions about resistors...

...for instance, can you use a resistor with a voltage controlled fan where the voltage might change?

Reading about simple series resistors it seems they might not be suitable for use with a fan on a voltage controlled fan-header...

http://electronics.stackexchange.com/questions/127525/reducing-voltage-with-resistors

Oh well, I guess I've got some reading to do :0/

------------------------------------------------------------------------------------

Another "out of left field" question...

Not sure if this is a stupid/easy (or just completely baffling) question or not, but here it is...

The question In short:

If I cut the voltage available to a 12V 32A fan by 58.33% will it cut the current it draws by 58.33%? (i.e. does the reduction to the current it will draw scale proportionally to the reduction in voltage available to the fan?)

https://en.wikipedia.org/wiki/Proportionality_(mathematics)

And the long version of the same question:

If I reduce the voltage available to a device, will it reduce the current which that device draws proportionally to the amount of the voltage reduction?

i.e. If I reduce the voltage available to a device by 25% will it reduce the current it draws by 25% ?

and likewise, if I reduce the voltage available to it by 50% will it reduce the current it draws by 50% ?

and so on, so that if I reduce the voltage available to it by 75% will it reduce the current it draws by 75% ?

Basically what I need to know is this: is the reduction proportional (rather than, for example, logarithmic, exponential, or potentially dependent on some other factor I'm not aware of) ?

The reason I ask is this:

I have a 12V 0.32A fan that I want to reduce to about 21A by dropping the voltage.

I can drop the voltage available to the fan through a (relatively) common process called "7-volting" (i.e. altering the feed so that there are only seven volts available to the 12-volt 0.32A fan).

If 7 volts is 58.33% of 12 volts, and 58.33% of 0.32A is 0.18A, then, if the reduction scales proportionally, it'll bring the current drawn by the fan to within the 21A limit I'm restricted to.

So basically, is it correct for me to assume that if I cut the voltage available to the 12V 32A fan by 58.33% then it'll cut the current it draws by 58.33%?

Basically I imagine it should be a proportional reduction but I know these things are often counter-intuitive and I just wanted to check.

Thanks in advance to whoever might have the answer (and kudos for making it this far). I guess it's a long-shot but you never know. :0P

;0)

Okay, I've run another few searches on this and it seems that "7-volting" (described below) is a four pin molex trick and not something I can use for the application I have in mind.

But I'm guessing using a resistor is a potential alternative so I guess that's the answer?

Since resistors reduce current rather than voltage, I guess it renders the question moot, but I guess it should be easier. Although it does raise another few questions about resistors...

...for instance, can you use a resistor with a voltage controlled fan where the voltage might change?

Reading about simple series resistors it seems they might not be suitable for use with a fan on a voltage controlled fan-header...

http://electronics.stackexchange.com/questions/127525/reducing-voltage-with-resistors

Oh well, I guess I've got some reading to do :0/

------------------------------------------------------------------------------------

Another "out of left field" question...

Not sure if this is a stupid/easy (or just completely baffling) question or not, but here it is...

The question In short:

If I cut the voltage available to a 12V 32A fan by 58.33% will it cut the current it draws by 58.33%? (i.e. does the reduction to the current it will draw scale proportionally to the reduction in voltage available to the fan?)

https://en.wikipedia.org/wiki/Proportionality_(mathematics)

And the long version of the same question:

If I reduce the voltage available to a device, will it reduce the current which that device draws proportionally to the amount of the voltage reduction?

i.e. If I reduce the voltage available to a device by 25% will it reduce the current it draws by 25% ?

and likewise, if I reduce the voltage available to it by 50% will it reduce the current it draws by 50% ?

and so on, so that if I reduce the voltage available to it by 75% will it reduce the current it draws by 75% ?

Basically what I need to know is this: is the reduction proportional (rather than, for example, logarithmic, exponential, or potentially dependent on some other factor I'm not aware of) ?

The reason I ask is this:

I have a 12V 0.32A fan that I want to reduce to about 21A by dropping the voltage.

I can drop the voltage available to the fan through a (relatively) common process called "7-volting" (i.e. altering the feed so that there are only seven volts available to the 12-volt 0.32A fan).

If 7 volts is 58.33% of 12 volts, and 58.33% of 0.32A is 0.18A, then, if the reduction scales proportionally, it'll bring the current drawn by the fan to within the 21A limit I'm restricted to.

So basically, is it correct for me to assume that if I cut the voltage available to the 12V 32A fan by 58.33% then it'll cut the current it draws by 58.33%?

Basically I imagine it should be a proportional reduction but I know these things are often counter-intuitive and I just wanted to check.

Thanks in advance to whoever might have the answer (and kudos for making it this far). I guess it's a long-shot but you never know. :0P

;0)

Last edited: