# ATX PSU Driving Mixed Voltage Props



## Terrormaster (Sep 27, 2007)

Ok, got a quick question regarding PSU's. I want to use one PSU to drive two different voltage prop components - one +5v and the other +12v. 

I know the PSU is fully capable of doing 3/5/12v. My question is since they all share a common ground is there anything I need to do to either component to protect them or can they share a common ground without modifications?

Thanks,
-TM


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## eanderso13 (Apr 10, 2008)

I wouldn't think there would be a problem, as long as the max current of each individual supply tap is not exceeded. Any slightly complex electrical device will have numerous components inside that run at different voltages and share a ground...possibly a reason why a "ground" connection is sometimes called a "common"...


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## Dr Morbius (Sep 21, 2004)

It should work. I was wondering if the voltages could be combined, say the 5 and 3 to make 8v and so on.


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## Terrormaster (Sep 27, 2007)

Dr Morbius said:


> It should work. I was wondering if the voltages could be combined, say the 5 and 3 to make 8v and so on.


I had thought about that as well... Thats a darn good question.

-TM


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## eanderso13 (Apr 10, 2008)

Ooohhh.....let's see...I'm not sure how the transformer in an ATX power supply is set up, but if it works by having multiple taps off of the same transformer, then you may be able to combine the common of the 5v tap with the high of the 3v and get 8v. But sometimes the smaller voltage tap will just be lower on the transformer winding than the higher voltage tap, and your only options are to use the 3v and/or the 5v as-is. Then there's the possibility that all voltage splitting and regulation is done via circuitry...in which case you would not be able to combine them. You can combine batteries in series to get more juice, but that's because they each have an independent "ground", or "-" terminal and no extra circuitry to fry...


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## Restless Spirit (Oct 27, 2007)

I've combined the +5 and +3.3 before. Just remember the max amps is going to be the smallest of the two. So if the +5 is, lets say, 2 amps and the +3.3 is 0.1 amps, 0.1 amps is going to be your max amps @ 8.3 volts.

Good Luck!


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## slightlymad (May 25, 2006)

Voltage is easy its the amps that will get ya every time


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## Terrormaster (Sep 27, 2007)

Would there be any reason of concern if my PSU is emitting an incredibly high pitched noise? I mean other than driving maybe a few dogs insane? The one I modded was a pretty old one I had sitting around. And quite frankly it's been so long since I had used it last in a PC I can't tell ya if it's something it used to do before modding it.

I think once the yard is up and running with all the other sounds it probably won't be noticeable. But it was even with the AC window unit going almost right next to it.

-TM


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## The_Caretaker (Mar 6, 2007)

sounds like a bad cap, failure in the future


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## Terrormaster (Sep 27, 2007)

The_Caretaker said:


> sounds like a bad cap, failure in the future


Suspected as much. Think I will use this while building Agnes and Beatrix but will pick up a couple prehacked ones from All Electronics before the big night, they had some for around $10 each. Murphy lives at my house and if I count on this baby it's gonna blow right on the 31st.

-TM


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