This is not to be plugged into a PC USB port but into a USB wall plug that you get with mobile phones.

I've got 3 5v fans but they are so loud and when the 12v is running on 5v USB it generates enough airflow at the slower speed and is super quiet, perfect for my needs. The only question is.... is there likely to be any type of safety hazed?

 

If you aren't exceeding the current rating of the mobile phone charger then no.

 

The fan I have now is an xbox 360 fan and says the following:

DC12v
0.40A
-9F15

The charger says

Input: 100-240v ~ 0.3A (Max.) 50/60hz
Output: 5.0V ---- 1.5A

 

0.4a will be on the 12V DC supply , so on the 5 v dc usb it will take less current and run slower.

 

OK so am I correct in thinking that the mobile charger can take 1.5A meaning the fan will require less current than the charger is actually able to provide?

 

OK so am I correct in thinking that the mobile charger can take 1.5A meaning the fan will require less current than the charger is actually able to provide?

yes.. you have some room to work with there.. all good

 

Thats great. Thanks for your replies. I'm just starting to learn about this stuff so I'm always over cautious to start. Many thanks.

 

OK so am I correct in thinking that the mobile charger can take 1.5A meaning the fan will require less current than the charger is actually able to provide?

Yes indeed your supply can provide more current than the fan requires.

Two things about this.

Firstly this is true of pretty well all electrical sources - the source determines the voltage (5 in your case) and the load determines the current (probably 0.2 - 0.3 amps in your case).

However an electric motor relies on its speed generating a 'back emf' to limit the current. This is why the stall current is so high.

So you should make sure your fan is kept clean and obstruction free so it never stalls as the 5 volt supply can probably supply enough current to burn it out.

go well

 

Again thanks. I will get a 5v fan but I prefer to "play and learn"

 

I didn't say don't use your 12v fan I said, don't obstruct it.

 

Putting a series resistor with the fan will only drop a few percent of the running voltage, but can greatly reduce the startup and stall currents. If stalling will be an issue.

 

Does anyone know if these new brushless DC fans have internal protection circuitry ?
I have a few 12 volt Pc fans and from the gap I can see some components in it . I don't want to take them apart yet because they are new and >10 bucks each but my curiosity probably won't hold out much longer

 

I would expect that a USB port or charger would have internal current limiting protection circuitry. Have people found this not to be the case?

 

David, you have resurrected a 2-year old thread. The original poster (OP) has probably lost interest by now.
Google "USB current limit".