# 12V fan on 5V?



## {LSK} Otacon

Quote:


Originally Posted by *crazydj* 
Hi. Is it possible to run a 12V DC fan on 5V? What modifications must i do? Because I'm intending to add 12V fans to my laptop cooler is it is possible. Thanks.

They pry wont turn. They might try to turn, but they wont. If they do, it will be like 2rpm. Unless you had alot of amperage, which you pry dont. You would need alot of amperage to make up for the loss of voltage. Which would be really no different than just running 12v, in the end they both will consume about the same amount of power considering you have the amperage to make up for the lost voltage.


----------



## The Pook

Some fans will, some won't. Depends on the fan itself. Some motors will run fine with 5v, others won't start.


----------



## crazydj

So how do i know which fans can turn and which cant? Are these written on the fan itself?


----------



## DuckieHo

Quote:


Originally Posted by *{LSK} Otacon* 
They pry wont turn. They might try to turn, but they wont. If they do, it will be like 2rpm. Unless you had alot of amperage, which you pry dont. You would need alot of amperage to make up for the loss of voltage. Which would be really no different than just running 12v, in the end they both will consume about the same amount of power considering you have the amperage to make up for the lost voltage.

Incorrect... having a lot of current does not mean anything since it won't be drawn. Also, fans running at 5V still spin at a few hundred RPMs.

Most fans will not start up at 5v but many will run at 5v. The start up voltage is how much voltage the fan needs to overcome interia and begin to move the fan blades. Once the blades get up to speed, the fan can run on much less voltage. Most fans list the start up voltage is around 7v. Give yours a try at 5v. If you see your fans "twitch" but not work, then the start up voltage is too low.


----------



## mashersmasher

yes it's fine. don't know about the wireing in a laptop though. use a voltmeter


----------



## TestECull

If they twitch, spin the impellor, it should start. If it doesn't, the magnet is too powerful to run on 5V.


----------



## a1161979

Quote:


Originally Posted by *DuckieHo* 
Incorrect... having a lot of current does not mean anything since it won't be drawn. Also, fans running at 5V still spin at a few hundred RPMs.

Most fans will not start up at 5v but many will run at 5v. The start up voltage is how much voltage the fan needs to overcome interia and begin to move the fan blades. Once the blades get up to speed, the fan can run on much less voltage. Most fans list the start up voltage is around 7v. Give yours a try at 5v. If you see your fans "twitch" but not work, then the start up voltage is too low.

Correct me if im wrong duckie but a fan will not draw more watts at start up than running it will however draw more current am i not correct? Having thought though i guess increasing Amps are really the same as increasing wattage assuming the resistance is the same


----------



## hvacgaspiping

Quote:


Originally Posted by *a1161979* 
Correct me if im wrong duckie but a fan will not draw more watts at start up than running it will however draw more current am i not correct? Having thought though i guess increasing Amps are really the same as increasing wattage assuming the resistance is the same









Any fan, either A/C or D/C, will use more wattage on startup until the rotor comes up to speed.


----------



## DuckieHo

Quote:


Originally Posted by *a1161979* 
Correct me if im wrong duckie but a fan will not draw more watts at start up than running it will however draw more current am i not correct? Having thought though i guess increasing Amps are really the same as increasing wattage assuming the resistance is the same









True, due to the additional energy it requires to start up a fan. However, if there isn't enough voltage then the fan won't start. Fans are never current starved unless you have less than 1A avaliable on the line. You can have a fan on a 100000A line but if there is only 3-4v, the fan won't start.


----------



## alk

Quote:


Originally Posted by *DuckieHo* 
True, due to the additional energy it requires to start up a fan. However, if there isn't enough voltage then the fan won't start. Fans are never current starved unless you have less than 1A avaliable on the line. You can have a fan on a 100000A line but if there is only 3-4v, the fan won't start.

Yup, it's all down to *Electro Motive Force* which translates into the voltage accross the coils within the fan. The current is related to the number of turns on the stator coils. More turns = more resistance. V=IR, so more current for the same emf.

OT: I have found that the majority of fans DO start at 5V even when they are rated to start up at higher voltages.


----------



## mastercontrol

I was able to run an 80mm case fan (thermaltake, fairly powerful and stiff to turn by hand) by inverting the wires on it because it was too loud. so it is possible.


----------

