PS from DVR VIP722 - Page 1
Forum section: electronics / beginners

author: jurgyman
author_rank: Newbie
timestamp: January 31, 2013, 06:48:52 pm
content: HeyI rescued a VIP722 from recycling... it has a massive yet silent PS inside.Would like to repurpose it as an ATX computer PS.It has these outputs:And it appears ATX has these power requirements:Could I use this ubec to get the 7.5 down to 3.3:http://www.hobbyking.com/hobbyking/store/__17159__3_3V_3A_UBEC_2_5S_Lipoly_6_23v_.htmlNot sure howto do the -12V however... and I'm not sure about amps required and output.It would be a low-power HTPC / minecraft computer.Thanks!Jurgyman

author: mariush
author_rank: Super Contributor
timestamp: January 31, 2013, 07:20:29 pm
content: You have 12v and 5v on that connector, which is pretty much what all computers nowadays use, besides 3.3v.The problem with that power supply is that it's designed to output low amount of current, I'd say 2-3 A on 5v, maybe a bit more, and about as much as that on 12v.In the DVR, the 12v is probably only used for spinning the hard drive's motor, while the 5v is used for everything else (usb ports, processors on the boards and so on). I have no clue what the 7.5v would be used inside for.-12v on computers is rarely used nowadays, and if it's used it's mostly for serial ports - most motherboards will probably run without -12v connected in the socket.If you want, you can generate 12v from 5v using an inverting converter. MC34063 is a very common and cheap and the datasheet even has schematic showing you how to make it output -12v from 4-6v. Dave also made a video that's on youtube with the formulas for making a step-up (boost) converter using this chip, but you can easily change his formulas with the ones in the datasheet for the inverting configuration and make it generate -12v.You can generate 3.3v using a fixed linear regulator from 5v or 7v - preferably 5v because a linear regulator will heat quite a lot. ICs from the 1117 series will give up to 1.2A on 3.3v and are very easy to use.http://www.digikey.com/product-detail/en/LD1117AV33/497-1485-5-ND/586006all 1117http://www.digikey.com/product-search/en/integrated-circuits-ics/pmic-voltage-regulators-linear-ldo/2556290?k=1117%203.3&ColumnSort=-129&fid=0other fixed output 3.3v regulators you can see here:http://www.digikey.com/scripts/dksearch/dksus.dll?FV=fff40027%2Cfff80182%2Cc00016&vendor=0&mnonly=0&newproducts=0&ptm=0&fid=0&quantity=0&stock=1You can use two regulators or four regulators and output 3.3v to each orange wire in the atx connector separately...so basically yeah, you can make the voltages for the atx, but the point still remains that I don't think the power supply can provide enough current on 12v to power a HTPC.The 5v may be enough to use it for 5v and create 3.3v and -12v from it as the htpc won't use a lot of 3.3v and 5v, but the 12v may not be powerful enough because that's what the htpc will use the most. You can try, worst case scenario the computer would reset itself or freeze or work erratically.

author: jurgyman
author_rank: Newbie
timestamp: February 01, 2013, 04:23:46 pm
content: thx mariush for reply... found this info elsewhere on the ps board:5.1V = 6.2A7.5V = 4.5A12V = 2.5A17V = 0.75A24V = 0.75A100W maxSo if my cpu is 50Watts and video card 40W HD is 5wIt might work... but might be unstable too?Thx JM

author: mariush
author_rank: Super Contributor
timestamp: February 01, 2013, 06:36:54 pm
content: It depends on the motherboard, but usually processors are powered exclusively from 12v.Your cpu is powered entirely from 12v. Therefore 50 watts / 12v = 4A. This is assuming the dc-dc converter on the motherboard is 100% efficient, while in reality it's only about 85-90% efficient, so add 0.3-0.5 A to that 4A value for the processor.A standalone video card is almost entirely powered from 12v - a video card in a pci express slot uses about 5-10 watts from 3.3v and/or 5v and the rest from 12v... but generally it's more cost effective to design a video card to use only one source of power, hence 12v is probably used the most.Let's just say 30 watts on 12v .. that's 30 / 12 = 2 AThe chipset uses about 5-7 watts, but it's probably powered from the 5v. Memory uses about 2-3 watts per module, but this is also most often powered from 5v, less often from 3.3vOnboard soundcards, usb ports etc all use 5v usually.A hard disk uses about 0.5 A on 12v when in use, but up to 2A on 12v when it starts spinning. 5v at about 0.5-1a is used for the electronics on the hard drive.So in total, you have about 4.5a for cpu + 2.5a for video card + 1a for hdd on 12v and about 3-4a on 5v.This is maximum values for 12v, 8-9 amps - on average your computer will use less, let's say 4-6 amps ... but it's still more than the 2.5 A on 12v this power supply can deliver.You *might* be able to play with the feedback circuitry on the power supply to change the 7.5v 4.5A to a 11-11.5v 3A which might be just enough to get the motherboard to accept this input voltage as power for the processor - the motherboard has dc-dc converter to generate the 1-1.1v for the cpu so it will work with less than 12v. You may also be able to make the cpu use less power by undervolting it in the BIOS (enable overclocking but do the opposite, lower the voltage step by step and test stability until the cpu isn't stable anymore, then raise the voltage just a bit to keep it stable)But it's still a really big stretch, and considering you're posting this in the "beginners" section... it's probably over your head.