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Molex mod? Need help!!

post #1 of 19
Thread Starter 
Hey overclockers!! Ok, so as the title states, Im thinking of running something that uses 2 AA batteries off of molex.

First, is this possible?
and Second, Do I need to get any resistors or anything?

Answers would be much appreciated!! Hopefully there are some experienced OCNers who have done this before or have a electrical engineering degree
    
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post #2 of 19
The orange wire on a SATA connector supplies 3.3v. That should be safe to power your device.
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post #3 of 19
Quote:
Originally Posted by Philbar71 View Post
The orange wire on a SATA connector supplies 3.3v. That should be safe to power your device.
Most ATX PSUs lack +3.3V on their SATA connectors.


A device that takes two AAs probably takes 1.5V-3.0V. To run it off an ATX PSU you'd have to find a way to regulate the +5V down to that voltage. That would need (in order of increasing difficulty, cost, and effectiveness) a resistor (not just your ordinary one either, this will have to be a low-resistance, high wattage one), or a Zener diode, or a linear regulator, or a buck converter.
post #4 of 19
Quote:
Originally Posted by Phaedrus2129 View Post
Most ATX PSUs lack +3.3V on their SATA connectors.


A device that takes two AAs probably takes 1.5V-3.0V. To run it off an ATX PSU you'd have to find a way to regulate the +5V down to that voltage. That would need (in order of increasing difficulty, cost, and effectiveness) a resistor (not just your ordinary one either, this will have to be a low-resistance, high wattage one), or a Zener diode, or a linear regulator, or a buck converter.
It would have to be the correct resistance for the load, but not necessarily a low resistance...
post #5 of 19
Quote:
Originally Posted by the_beast View Post
It would have to be the correct resistance for the load, but not necessarily a low resistance...
Resistors are generally intended to limit current, not voltage. You'd have to induce a very large load to get the intended voltage drop.
post #6 of 19
OP: What is it that you want to power, because it depends on how much current is required.
Edited by snorbaard - 4/13/11 at 10:01am
post #7 of 19
Quote:
Originally Posted by Phaedrus2129 View Post
Resistors are generally intended to limit current, not voltage. You'd have to induce a very large load to get the intended voltage drop.
Only if the resistance is small - if the resistance is higher then the voltage drop is much higher for any given current.

Hence the reason why the right resistor is required (and why this is a bad way to go for the whole project) - the correct resistance value needed will change for different loads. A much better way is a simple linear regulator (with a couple of caps if required).
post #8 of 19
Thread Starter 
Quote:
Originally Posted by snorbaard View Post
OP: What is it that you want to power, because it depends on how much current is required.
I want to power a small discrete gps tracking device. There has been a rash of thefts in my neighborhood and I wanted to be able to track my computer whenever it was on. Some of the things I'm looking at run off of 2AA's... Or even something like this? But I still have to look around... +1 to everyone for helping
Edited by PixelFreakz - 4/11/11 at 11:16pm
    
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post #9 of 19
Where do you intend to mount this GPS? Remember that, unlike a car with lots of windows, your PC is pretty much a solid metal box. And they are usually used inside buildings, rather than out on the open roads. Which means no decent satellite signals in, and no GSM signals out.

I think you'd be better off putting your money into theft prevention (cable ties or steel cages) rather than GPS tracking.
post #10 of 19
Quote:
Originally Posted by Phaedrus2129 View Post
Most ATX PSUs lack +3.3V on their SATA connectors.


A device that takes two AAs probably takes 1.5V-3.0V. To run it off an ATX PSU you'd have to find a way to regulate the +5V down to that voltage. That would need (in order of increasing difficulty, cost, and effectiveness) a resistor (not just your ordinary one either, this will have to be a low-resistance, high wattage one), or a Zener diode, or a linear regulator, or a buck converter.
Pardon the ignorance, but every PSU Ive bought in the last decade (With SATA) has 3.3V on the connector. (The orange wire???)

We are talking about the same thing right?
Edited by Philbar71 - 4/12/11 at 9:28pm
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