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byronebula
New Member
2 Posts |
 Posted - Jan 08 2013 : 6:03:37 PM
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Hi,
I've just been trying to work on a small and simple project, that of powering a desktop fan by a usb input.
I have a 12V, 0.3A computer fan which i want to utilize.
A USB port only supplies 5V, 0.5A.
I've been trying to think of a simple solution to this small problem.
I thought of using a 9V battery in parallel with the port, but I'm not sure how that may effect the computer.
I came across a simple circuit on this site which steps up a 6V input to 12V. But the circuit requires a 2A input to receive a 0.8A output. With a 0.5A input, I'm certain it would not supply enough current.
I know i could just use two DC batteries, but I don't want to keep replacing batteries. I need something that is sustained by the usb, either entirely, or at least partially.
Is there any way around this?
Your help would be much appreciated.
Thank you! |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - Jan 09 2013 : 01:33:58 AM
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DON'T PUT 9V IN PARALLEL WITH YOUR USB PORT!
You could damage it.
Not all USB ports are the same but I think it's safe to assume your USB ports will not supply a current any higher than 0.5A.
The amount of power that can be supplied from a 5V 0.5A(max.) USB port is 2.5W (5V * 0.5A).
Unfortunately, for your fan to run at full capacity requires 3.6W of power.
You say that you "need something that is sustained by the usb, either entirely, or at least partially". Depending on your computer you could just tap off the 12V rail of your power supply if practical. Is this an option? This solution would be too invasive and impractical for a laptop and there would be no guarantee that it'll work.
I know powering your fan from a USB port is convenient but why not use a 12V power adapter instead?
If these two aforementioned solutions are not doable then your best bet is to use a tiny yet efficient DC-DC converter that boosts your 5V (USB port) to a higher voltage than 5V which you can then supply to your fan. You must experiment to find an output voltage that causes the input current to your DC-DC convert to be no higher than 0.5A.
You need to look for a variable boost converter. They could also go by other names.
This looks like it may do the trick:
http://www.ebay.com.au/itm/3-5-30V-to-4-30V-DC-to-DC-Stepup-Voltage-Power-Converter-Battery-Volt-booster-/140897892403?pt=LH_DefaultDomain_0&hash=item20ce2b3833&_uhb=1#ht_3392wt_1163
Personally I would like to see the efficiency curves but since it's so cheap I would buy it just out of curiosity. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
Edited by - wasssup1990 on Jan 09 2013 01:53:55 AM |
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byronebula
New Member
2 Posts |
Posted - Jan 09 2013 : 1:14:32 PM
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Hi Wasssup!
Thanks for your prompt reply, and for clearing up my thoughts!
Unfortunately, tapping off the 12V rail of my power supply would be a bit too invasive. Also, I need it to be portable, and if possible, universal.
It looks like the simplest solution is the 12V power adapter. Although it isn't quite what I was hoping to do, but it will have to suffice. Thanks for the suggestion.
The variable boost converter sounds like an interesting project itself. I would prefer to make one rather than buy, so I will search for some schematics.
Thanks for your assistance!! |
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Aaron Cake
Administrator
Canada
6717 Posts |
Posted - Feb 03 2013 : 11:34:57 AM
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| How about just using a 5V fan? |
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USB power source
