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Best way to get 7Volts off molex?!

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Lancelot

Lancelot

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Joined
Feb 12, 2001
Location
the Netherlands
I need to run my Swiftech MCP650 pump at 7Volts cuz at 12V waterflow is so high my res starts foaming up causing bubbles in the loop. I also like the nice and quiet ofcourse! I used to get 7Volts by hooking up between the 12V and 5V lines on a molex. BUT; my new Enermax 660W quad 12V-rail EPS PSU won't start up like this! It probably has much more sophisticated overprotection circuits for server/workstation certification. The MCP650 draws 2A @12V so I've been wondering... I could get eigth 2A diodes and hook these up in series, that way they will take up 0.6V each so I get 7.2Volts, right?! Any other ideas? I need a simple and permanent solution, not rheostats costing a drive bay and lots of wiring...
 
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Could you use one of the resistors like the Zalman reducer does? Looks like it is Green, Blue, Purple, Blank, Gold.
 
Lancelot said:
I need to run my Swiftech MCP650 pump at 7Volts cuz at 12V waterflow is so high my res starts foaming up causing bubbles in the loop. I also like the nice and quiet ofcourse! I used to get 7Volts by hooking up between the 12V and 5V lines on a molex. BUT; my new Enermax 660W quad 12V-rail EPS PSU won't start up like this! It probably has much more sophisticated overprotection circuits for server/workstation certification. The MCP650 draws 2A @12V so I've been wondering... I could get eigth 2A diodes and hook these up in series, that way they will take up 0.6V each so I get 7.2Volts, right?! Any other ideas? I need a simple and permanent solution, not rheostats costing a drive bay and lots of wiring...
Click to expand...

A very simple solution would be to use an appropriate Voltage regulator. :)
You can find them at www.digikey.com

VR's are IC's comprising of transistor pairs and diodes which are monolithically integrated on asingle chip. You could choose from DIP or TO-32/TO-92 package styles. You have one i/p, one o/p and one GND terminal. Thats all !
I have mentioned this several times,but nobody seems to take this approach. :shrug: It is a lot better and stable than having a resistor network.
 
Lancelot said:
I used to get 7Volts by hooking up between the 12V and 5V lines on a molex. BUT; my new Enermax 660W quad 12V-rail EPS PSU won't start up like this!
Click to expand...


his psu wont start with using 5V as the neg.

if you can easily get ahold of a regulator that will handle the current, i would say go that route, but diodes would be easier to get (at least if its like around here, nothing good locally)
 
Those Volt regulators won't take more than 1A and I need 2A with overhead to be safe. I ended up ordering a 3A 0-30VDC Power Supply kit that will work with 12V input...
 
Lancelot said:
res starts foaming up causing bubbles in the loop.
Click to expand...
1-Bigger res.
2-Replace the rez with a t-line (which I did, just to avoid the hassle of a rez.)
 

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A rule of thumb for electronics is the "One Half rule" (you operate the component at 1/2 its rated) Which means that if you are going to run 2A through a component, get one rated for 4A. Applies for Wattage and such as well.
 
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