Computer - Power Supplies - Your advice please. - Page 1
Forum section: electronics / beginners

author: TymerTopCat
author_rank: Newbie
timestamp: February 15, 2012, 10:09:25 am
content: I built a small PC (Mini ITX Motherboard) for reasons of *low power* usage.The PC, and Monitor when running at full speed (With Monitor on) draws around 27 Watts. On the DC side.And so I can use any Computer Power Supply I want. 1500, 1000, or 750 Watt. Of course these would be overkill, currently it is using a high quality 50 watt power supply.Question:If I used a 1500 Watt (Quality) power supply, would it cause more power usage on the AC side, because of it's larger size?It is my understanding that by using a larger Power Supply it will not affect more energy usage on AC Side. I would imagine there will be some overhead to a larger power supply, but I would guess this to be under 1 or 2 Watts.Please correct me if I am wrong. Your advice is appreciated.-Russ

author: Rerouter
author_rank: Super Contributor
timestamp: February 15, 2012, 10:23:20 am
content: it would be by quite a significant chunk be less efficient than a 250W for the power usage of the device, power supplies are designed to be loaded to about 40-70% of there rating efficiently (when its true and not peak, another story) and as such, it would be stupid to use a 1500W supply with efficiency figures built for 400W+ loads,can be done, just more power consumed, and not exactly practical unless you actually had it lying around,

author: amyk
author_rank: Super Contributor
timestamp: February 15, 2012, 11:34:59 am
content: Here's what a 900W PSU's efficiency graph looks like:http://images.anandtech.com/reviews/psu/2008/cooler-master-ucp-900w/eff-comparison.pngExtrapolate that down to 27W and it looks like it'll be down in the low 50s.A 40-50W supply will be more efficient and draw less power in that range.

author: Simon
author_rank: Unknown
timestamp: February 15, 2012, 12:49:44 pm
content: wow, how did you get a Pc to only use 27 W ? i know VIA did some very energy efficient processors once

author: grumpydoc
author_rank: Super Contributor
timestamp: February 15, 2012, 01:45:50 pm
content: QuoteThere are any number of small form factor computers - with low power draws. Google for nettop or plugtop - I have a Foxconn one which is based on an Intel Atom 525 and probably draws less than 15W when idle, including RAM and SSD seehttp://www.ilgs.co.uk/products.asp?partno=NT-535, some of the plugtop ones are ARM based and draw even less.Edit: In fact in this space "mini-itx" is now pretty large, we now have nano-itx and pico-itx boards to play with.

author: TymerTopCat
author_rank: Newbie
timestamp: February 15, 2012, 08:02:13 pm
content: amykThanks for the chart. Excellent information.Rerouter.Thanks. And you are right, my intention is to keep power usage low. I plan to use a battery and a solar panel to charge the battery. Hence, the reason for low power usage.I just knew there was a good reason for not using a large power supply as they are designed to be used in range of power.-Russ

author: IanB
author_rank: Super Contributor
timestamp: February 15, 2012, 08:37:48 pm
content: It would be logical to use a laptop power brick for this kind of application. Small, cool, no fans.It requires the PC and components to have on-board DC-DC converters for the local voltages needed. It is increasingly common for modern PCs to be designed this way. You give them 12-16 V DC as a main supply and they generate all the secondary supplies they need at the point of use.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 15, 2012, 08:49:31 pm
content: If the motherboard doesn't do DC-DC conversion you can always use one of the pico-psu modules which are basically tiny DC-DC converters glued to a standard ATX power connectorhttp://www.silentpcreview.com/article601-page1.html