Hello all,
I've had a recent surge in needs for usb based cooling such as modems, routers, etc. I had bought a 120mm usb fan a while ago and it was simply a case fan converted from what I could see. So instead of buying more I've decided to make my own as I had some usb cables and tons of 120mm fans lying around.
That said, I've done a few test runs and it's obviously pretty straightforward. My concern comes into play with the amperage of the fans I use. I will say this now, I am definitely not an electrical engineer and will probably be asking a simple question I slept through in school here...
I understand 99% of case fans are 12v. I also understand that USB is 5v. I also understand (please correct me if wrong) that the max amps supplied by usb 2.0 (what I'll be using) is 0.5A / 500mA as often listed in my research.
Now one 120mm fan I tested was 12v .22A. On 5v it started up fine, but barely moved any air whatsoever. I had another fan that was 12v .40A, which is moving around the amount of air I'm looking for. On regular 12v power this was actually quite a loud and powerful fan in general It is also LED if that matters (not a requirement for my needs just happened to have it).
That said, where I am confused is on amperage draw. Now .4A is obviously less than the max output of usb's .5A however from my reading as the voltage supplied goes down doesn't the current (amps if I'm not mistaken in words here) required go up? Would this effectively mean the fan that normally requires .4A on 12v require more to run on 5v? The fan is certainly not spinning at near the speed or strength of when it was on 12v and the wire is certainly not hot nor is the port or any sign of issue.
On the flip side of that, if it does NOT cause the current to go up to compensate, does the current drop or does it remain constant? or go lower For example a 60mm fan I'd like to use with usb is actually showing .12v .70A. Which first off surprises me as the .40a 120mm fan is very powerful as is so I'm surprised this tiny 60mm needs .70A. So like I said, would this, if it dropped current on 5v, mean the current requirements would drop under the .50A limit of USB?
Thanks for all the help as always. My main concern here is safety as these fans will be on 24/7 in some cases and a fire or burnt out usb or even fan is the last thing I'd like to deal with.
I've had a recent surge in needs for usb based cooling such as modems, routers, etc. I had bought a 120mm usb fan a while ago and it was simply a case fan converted from what I could see. So instead of buying more I've decided to make my own as I had some usb cables and tons of 120mm fans lying around.
That said, I've done a few test runs and it's obviously pretty straightforward. My concern comes into play with the amperage of the fans I use. I will say this now, I am definitely not an electrical engineer and will probably be asking a simple question I slept through in school here...
I understand 99% of case fans are 12v. I also understand that USB is 5v. I also understand (please correct me if wrong) that the max amps supplied by usb 2.0 (what I'll be using) is 0.5A / 500mA as often listed in my research.
Now one 120mm fan I tested was 12v .22A. On 5v it started up fine, but barely moved any air whatsoever. I had another fan that was 12v .40A, which is moving around the amount of air I'm looking for. On regular 12v power this was actually quite a loud and powerful fan in general It is also LED if that matters (not a requirement for my needs just happened to have it).
That said, where I am confused is on amperage draw. Now .4A is obviously less than the max output of usb's .5A however from my reading as the voltage supplied goes down doesn't the current (amps if I'm not mistaken in words here) required go up? Would this effectively mean the fan that normally requires .4A on 12v require more to run on 5v? The fan is certainly not spinning at near the speed or strength of when it was on 12v and the wire is certainly not hot nor is the port or any sign of issue.
On the flip side of that, if it does NOT cause the current to go up to compensate, does the current drop or does it remain constant? or go lower For example a 60mm fan I'd like to use with usb is actually showing .12v .70A. Which first off surprises me as the .40a 120mm fan is very powerful as is so I'm surprised this tiny 60mm needs .70A. So like I said, would this, if it dropped current on 5v, mean the current requirements would drop under the .50A limit of USB?
Thanks for all the help as always. My main concern here is safety as these fans will be on 24/7 in some cases and a fire or burnt out usb or even fan is the last thing I'd like to deal with.