# Adding a Second Power Supply



## Enginr09 (Mar 24, 2009)

Hi all,

I am in the middle of building a slightly old system for practice (being my first computer build). I have done hours of reading on the internet about it, and using the PSU calculator recommended on this website, it gives about 185W required (using the free lite version). I will be powering a 2.4GHz processor with a couple of IDE HDDs, a DVD drive and a small graphics card (64MB).

I have two PSUs of 175W and 180W currently, and this website recommends that I should have another 30% on top of the PSU calculator estimate for expansions and smooth operation. So rather than fork out $50-60 (I admit I am a bit of a tightwad with this computer since it is a practice run for a dual core machine I hope to build later this year), I thought maybe I could have a second power supply running the system. I have researched this idea and it is popular amongst modders. They seem to use one of the following methods:

(As a background, you need to connect the green pin and any black pin on the 20 or 24 pin connector to turn on a PSU)
1. Turn on the second power supply by connecting a relay from PSU 1 to the green and black pins on PSU 2.
2. Turn on the second power supply by simply connecting the PSU 2 green and black wires to those of PSU 1 by scraping back some of the insulation off PSU 1 green and black wires.

Hmmm... I hope I am clear here - see the following websites to see what I mean:

http://www.directron.com/2powersupplies.html

http://deviating.net/photos/2006-06-06-power_supply/

http://www.speedy3d.com/articles/case_mod_p3/01.shtml

What I have a slight concern about is that with two different power supplies, are there two different grounds on the motherboard side of the transformers and would this mess things up? I am thinking that through the black wires on the connector cords, the motherboard will connect both grounds of the transformers together meaning there is a common ground, but I am not sure.

Since none of the websites mentioned any problems with this, I think I might be right, but I just thought I would check before I blew up anything (it's only an experimental computer build anyway:4-dontkno)

Warm Regards, and thankyou so much for your advice in advance!:grin:


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## dai (Jul 2, 2004)

YouTube - How to Put/use Two Power Supplies in Your Desktop


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## speedster123 (Oct 18, 2006)

> There should be no smoke


 LOL . but he is using a compusa supply!
Pretty straight forward lesson.


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