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Possible 7v On, 5v Off


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#1 chipD

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Posted 16 February 2008 - 08:42 PM

I want to run my stock delta fans @ 7v while the 360 is on, then 5v when turned off to let some of the air out while cooling down.I know theres some 5v standby sources that are always getting power as long as the power brick is plugged in, but im wondering if its possible to use 5v standby + 12v to get 7v, then when powered off, get 5v?

I have a V2 board (zephyr).

#2 AliasCT

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Posted 16 February 2008 - 10:11 PM

My guess is that you'd probably have to wire in a relay, plus a timer if you didn't want the fans going *all* the time.

#3 chipD

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Posted 16 February 2008 - 10:30 PM

QUOTE(AliasCT @ Feb 16 2008, 04:47 PM) View Post

My guess is that you'd probably have to wire in a relay, plus a timer if you didn't want the fans going *all* the time.


I want the fans to run @ 5v when i turn the 360 off.But when the 360 is running i want the fans to be 7v.My 360 is water cooled, and my pump is externally powered.So I always power on the pump first, then the 360.When im done playing i leave the pump run till the temperatures drop, then i turn the pump off.I always unplug the power brick to prevent my wife from somehow powering the 360 without the pump running.So i figure i could have the fans run @ 5v for a short amount of time till the temps drop then just unplug the power brick as usual.


#4 marmaladeboy

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Posted 17 February 2008 - 04:57 PM

First You will need a 7v voltage regulator (#7807) you can get this from digikey. Power the 7807 from your 12v source to get a regulated 7v supply voltage. In order to alternate between the 7v and 5v sources you can either put in a manual switch or follow rbjtech's "aftercooler" guide or look up my old "automatic voltage switch" schematic (ps. I've been lazy but I plan to post v2.0 of that schematic soon) in this forum. For either of the tutorials you would simply replace any 12v reference with 7v.

#5 chipD

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Posted 17 February 2008 - 06:28 PM

QUOTE(marmaladeboy @ Feb 17 2008, 11:33 AM) View Post

First You will need a 7v voltage regulator (#7807) you can get this from digikey. Power the 7807 from your 12v source to get a regulated 7v supply voltage. In order to alternate between the 7v and 5v sources you can either put in a manual switch or follow rbjtech's "aftercooler" guide or look up my old "automatic voltage switch" schematic (ps. I've been lazy but I plan to post v2.0 of that schematic soon) in this forum. For either of the tutorials you would simply replace any 12v reference with 7v.


I thought of using a regulator, but i was going to use a LM317 and a 220 ohm and 1k ohm resistor to get 7v.Or possibly a 220 and 1.5k for 8v....really depending on how loud each voltage is.I definitly dont want to add a external switch.But can you give me some info on this automatic voltage switch?I make my own circuit boards so difficulty is not an issue.

#6 marmaladeboy

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Posted 17 February 2008 - 11:06 PM

QUOTE(chipD @ Feb 17 2008, 01:04 PM) View Post

I thought of using a regulator, but i was going to use a LM317 and a 220 ohm and 1k ohm resistor to get 7v.Or possibly a 220 and 1.5k for 8v....really depending on how loud each voltage is.I definitly dont want to add a external switch.But can you give me some info on this automatic voltage switch?I make my own circuit boards so difficulty is not an issue.


This is the first version of my switch using an npn, 2 diodes and a 10ohm resistor (R1 is just a stand-in for the load).

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The second version uses just an nmosfet and a single diode, but i haven't finished testing that design completely yet wink.gif

#7 FILTHY J NASTY

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Posted 18 February 2008 - 02:36 AM

I know u can get 7v but wiring 12v to positive end and 5v to the negative end. So maybe if you do the 12v and then the 5v that stays on after the console shuts off, it will work.

#8 marmaladeboy

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Posted 18 February 2008 - 02:50 AM

QUOTE(FILTHY J NASTY @ Feb 17 2008, 09:12 PM) View Post

I know u can get 7v but wiring 12v to positive end and 5v to the negative end. So maybe if you do the 12v and then the 5v that stays on after the console shuts off, it will work.


Unfortunately that doesn't work in this case.. when the console is off and the 12v source goes "off" it doesn't go high impedance, it just dips down to a very low voltage... somewhere in the microvolts.. if you try to drive it with the 5v you end up pouring most of your current into the "off" power supply instead of your load. I wouldn't try this for any length of time as it could have adverse effects on your power brick.

#9 chipD

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Posted 18 February 2008 - 06:01 AM

Also from what grim187 said, is that with the newer falcon boards (most likely zephyr also) when you give the fans 12v and 5v to get 7v it throws an error upon booting.So my only option for 7v is doing the 12v mod, then reducing it with a regulator to get 7v.But this is where im stumped on how to also get 5v on standby mode.Somehow it would have to switch to the 5v standby source.

What would be ideal would be a remote controlled switch to change from the 7v regulated source and the 5v standby source.I would be up for building the circuit board if someone could help with the schematic.I know its possible, but i got an F in EE sad.gif




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