Overloading PSU Cables

[burningrave101]

I havn't done much research into this yet but i thought i would go ahead and see if any of you had some ideas on it.

First off for this rig i'm building now I am using an Antec True Power 430w PSU.

I've came to the conclusion that the reason why people feel the need to buy a 550w PSU because their PC is "special" is because they are overloading one or more of the cables when using smaller 350w and 400w PSU's. A 550w PSU would be able to better handle a cable overload as its maximum loads would be higher.

The hard drives and video card especially must be split up well across the connections and not all be one cable strand.

Have any of you read an article about the best way to split them up? I'm curious as to how many hard drives should be on on strand and what hardware devices are safe to daisy chain and use Y splitters on.

Even though my Antec 430w PSU is more then enough power for anything i could throw at it, it only has 7 4-pin molex connectors. Naturally i'm going to have to split some stuff up considering the case is built to house 6 HDD's and 4 optical drives.

Any suggestions or ideas?

[Ice Czar]

Extension-Cord Basics (http://www.taunton.com/finehomebuilding/pages/h00010.asp)

Im not an EE or an electronics wizard to definitively say where the limit in length and load for guage is...

and since its a dynamic config, not many tutorial exist
maybe you should swing by the cool cases forum and get someone to help you definitively answer for your config

[Snugglebear]

People buy 550W PSUs becuase they have no idea how many amps their equipment pulls at startup, nor how many amps a given PSU will actually provide on a given rail. I'm sure you've done those calculations and realize that most 400-odd Watt PSUs barely provide enough amperes to fire up 5 IDE HDDs simultaneously. Even a 300-odd Watt PSU will keep them all fired, it's just that initial pull that kills.

[burningrave101]

7200rpm hard drives pull around a max of 20w at startup. Normally they only draw 5-10w after that. 5 IDE drives at startup would be roughly 100w off the 12v line.

I've seen alot of people with around 6 HDDs and several optical drives running their system fine on a 300-350w PSU.

My 430w PSU will provide more then enough power, i just would like to figure out the power load each cable should have in order to divide up power usage properly and not stress out one line causing system instability.

[Snugglebear]

You're making the same mistake as the rest. Watts are not the limiting factor, amps are.

One 7200rpm drive will pull 2-3 amps at startup. I just looked again on the label of my Antec 430W, 36A max load on the +5V rail, 20A max on the +12V rail. Please note those max values are derived by testing only one rail at a time, since PSUs don't have completely independent rails, putting load on one rail will lower the max available on others. The machine I've got will fire up fine with 5 7200rpm drives, a floppy, and a celeron 1.1 with 512MB of memory. Other incidentals like nics and controllers don't add much. If I add a 6th drive to the mix, some of the drives will decide not to power up or occasionally it will be a black screen.

[xonik]

Yes, it's not power that matters with wire gauge, it's amperage. That said, an 18 gauge stranded wire will take about 16 amperes depending on who you ask. That would take a large chain of drives to stress the wire limits of such a power supply. Of course, 16 amps would be a significant chunk of any power supply's current delivering abilities, even on the robustly engineered +12 volt rail, where the current draw would come from.

No, the reasons why people buy large power supplies are many. Some do it because they can; others, for bragging; still others, because it will last through many upgrades. I would buy one because the beefier power supplies have better components and larger heatsinks. What's the harm in that?

[Godmachine]

Also a Quick suggestion to those running 5 hard drive+ setups .. try buying only Serial ATA's and use the Serial ATA power connection ..it should cut down a fair amount on the amps needed for start up :)

[xonik]

And why would that be?

[DMarti]

Power Supply wattage calculator (http://www.jscustompcs.com/power_supply/)

[Ice Czar]

re: bigger is more robust
(heatsinks, load drawn to life expectancy ect)

your preaching to the choir when your addressing burningrave101 on that particular issue (http://www.hardforum.com/showthread.php?s=&threadid=703824&perpage=15&pagenumber=3) :p
(and contains my thoughts on voltage regulation & transient resopnse)


Originally posted by DMarti
Power Supply wattage calculator (http://www.jscustompcs.com/power_supply/)

I'll see your calculator and raise you an article & dynamic load test results :p
takaman's Power Supply Calculator rev0.63 (http://takaman.jp/psu_calc.html?english) displays amps per rail and has a much more extensive database ;)
Choosing the right Power Supply (http://www.firingsquad.com/guides/power_supply/)
[H]ardcore PSU info (http://hardforum.com/showthread.php?s=&threadid=702661)

but thanx I'll add it to my links ;)

[gigglebyte]

damn..I guess I should get a bigger PSU for my Shuttle as it is only a 200W...but wait....my XP 2400 with (2) 7200 RPM drives, optical and Radeon 9800 Pro seem to be working fine....guess I don't have a power system anymore :D

As far as I am concerened I think it is more quality than size though size does make a difference...a good friend of mine just got the Antec 550 but is only running an A64 3400+ Radeon 9800XT, (2) 120Gig 7200 drives and (2) optical's...his reasoning was he would rather have too much than too little power for his system AND he didn't want to have to upgrade his case/PSU with his next couple of system upgrades

now burningrave101...you had asked

The hard drives and video card especially must be split up well across the connections and not all be one cable strand.

Have any of you read an article about the best way to split them up? I'm curious as to how many hard drives should be on on strand and what hardware devices are safe to daisy chain and use Y splitters on.

and I would say the simple answer is how ever many connections are on that strand...I saw several referenes to common sence in the other thread and if you think about it...the PSU mfg's are the real experts here...not you...not me...not anybody else on this forum but the people who MAKE and DESIGN the damn things...they are the people who rate the PSU at what ever wattage and also figure out how many devices should be connected to each leg by putting **GASP** the correct number of connectors on that leg.....so lets think about this....if Antec puts 4 connectors on each leg of the PSU and there are 5 legs how many devices did they design it for....mumblemumble and cary the 1 mumblemumble I would say 20 connections

[Snugglebear]

The itty-bitty PSUs seem to be the most robust as far as loads go. I've been working with OEM micro- & flex-ATX stuff for years and they actually handle loads over rating without issues. Haven't seen normal desktop PSUs do that very often. I have a feeling the PSU mfgs have a hunch people with small machines will push a whole lot of crap in them and thus make them a little better than they'd otherwise be. There may also be negligible cost increases in doing so given that they're already working with a minimalist unit.

[O[H]-Zone]

I went to that power-supply calculating page. AMD Athlon @ 1400, 2 sticks PC133 SDRAM, 6 7200RPM drives, DVD Burner, DVD/CD-RW Combo Drive, 4 80mm fans, Sound card, TV card, Firewire card, 2 NICs - sugested power supply: 503 watts. Just dumped my 350 and got a 550...much more stable, and overclocks better too.

[gigglebyte]

and it told me that I needed atleast a 260W so I guess I have one of those "magical" PSU's that make their own power :D (j/k I know it is just an estimate but that goes to show you that they are just that..estimates)

[DMarti]

Excellent links thanks.

Originally posted by Ice Czar
re: bigger is more robust
(heatsinks, load drawn to life expectancy ect)

your preaching to the choir when your addressing burningrave101 on that particular issue (http://www.hardforum.com/showthread.php?s=&threadid=703824&perpage=15&pagenumber=3) :p
(and contains my thoughts on voltage regulation & transient resopnse)




I'll see your calculator and raise you an article & dynamic load test results :p
takaman's Power Supply Calculator rev0.63 (http://takaman.jp/psu_calc.html?english) displays amps per rail and has a much more extensive database ;)
Choosing the right Power Supply (http://www.firingsquad.com/guides/power_supply/)
[H]ardcore PSU info (http://hardforum.com/showthread.php?s=&threadid=702661)

but thanx I'll add it to my links ;)

[Stang Man]

here's some useful equation, from Ohm's law, for finding Voltage, Amperes, Resistance, Power

V=IR
P=IV
P=I²(R)
P=V²/R

V= Voltage, measured in volts (V)
I= Current, measured in amperes (A)
R= Resistance, measured in Ohms (Greek letter Omega)
P= Power, measured in Watts (W)