Discussion Forums > Technology
Help me diagnose this shit
Pentium100:
--- Quote from: kitamesume on December 01, 2012, 01:38:06 PM ---is that 2x10A continuous or pulsed? because pulse rating is approximately 3-4times higher than continuous, and it should be obvious that a switching powersupply is pulsed with a certain duty cycle.
if it was a quality PSU, even if you overload one rail it shouldn't send off a magic smoke, the OCP sensor could get fried when repeatedly done though.
--- End quote ---
Continuous. Pulse rating is only applicable if the duty cycle is low (so the average current is not very high). If the output current is continuous 30A then the diode current will either be continuous 30A or pulsed, but much higher, so it would still overload the diode. Some diodes are actually rated in "average rectified forward current", but I am too lazy to find the datasheet of the failed diode.
And yes, if the PSU is high quality, it would shut off on overload. If it is cheap it will release the magic smoke or just blow up.
--- Quote from: kitamesume on December 02, 2012, 03:16:31 AM ---not really, you have to compute by amperes not wattage, ignoring the 5v and 3.3v loads(they're too tiny to be of concern), you'll need to compute all the total wattage of components then divide it by 12v(this is to include all the loses induced since you're factoring in the efficiency with this setting), once you get your final amperage you'll need to distribute them to rails, load balancing as well.
--- End quote ---
Also, if you have the choice, buy a single rail PSU instead of the multiple ones - no need to load balance.
If you want the power supply to be the most efficient, buy one that is twice as powerful as your load, because these power supplies are most efficient at around 50% load. Adding margin is also good because over time the power of the supply will drop because of aging capacitors. Higher margin is more time until you need to replace the caps.
--- Quote from: buchno on December 02, 2012, 01:29:48 AM ---I just added together 4 FX-8350 and 4 Geforce 690 in the PSU calculator, and they didn't reach 1500W.
Who needs such a PSU...?
--- End quote ---
People who run the computers at 1kW or more. Not running a component at maximum load increases its life and a switching PSU is most efficient at 50% load (so that 1.5kW PSU would be great for a computer that uses 750W).
kitamesume:
--- Quote from: buchno on December 02, 2012, 01:29:48 AM ---
--- Quote from: rostheferret on December 02, 2012, 01:15:40 AM ---I know that for peak efficiency 20% is a good margin to use. Else it seems to depend on the quality of the PSU. I've seen cheap 1500W ones which I bet suck balls. Just go with a reliable brand. I mean, they aren't expensive, and do you really want to quibble over a few quid when buying the one component capable of frying every other? :P
--- End quote ---
I just added together 4 FX-8350 and 4 Geforce 690 in the PSU calculator, and they didn't reach 1500W.
Who needs such a PSU...?
--- End quote ---
ah yes yes, i7 hexa core extreme OCed to over 4Ghz can consume a little over 200watts, pair that up with a dozen harddrives with a hefty quad HD7970GE(yes these things are so inefficient), set capacitor aging at 20% (roughly 3-5years down the road) and it will reach over 1.5KWH
(click to show/hide)
--- Quote from: Pentium100 on December 02, 2012, 03:51:06 AM ---
--- Quote from: kitamesume on December 01, 2012, 01:38:06 PM ---is that 2x10A continuous or pulsed? because pulse rating is approximately 3-4times higher than continuous, and it should be obvious that a switching powersupply is pulsed with a certain duty cycle.
if it was a quality PSU, even if you overload one rail it shouldn't send off a magic smoke, the OCP sensor could get fried when repeatedly done though.
--- End quote ---
Continuous. Pulse rating is only applicable if the duty cycle is low (so the average current is not very high). If the output current is continuous 30A then the diode current will either be continuous 30A or pulsed, but much higher, so it would still overload the diode. Some diodes are actually rated in "average rectified forward current", but I am too lazy to find the datasheet of the failed diode.
And yes, if the PSU is high quality, it would shut off on overload. If it is cheap it will release the magic smoke or just blow up.
--- End quote ---
depending on the diode usage, if the two diodes are in use at alternate load(eg each has 50% duty cycle) they can theoretically handle up to 20-30A(depends on the diode's specs) each.
but since its a cheap PSU, i won't be expecting a pretty diode anyway, most likely it's 60% duty cycle pulse rating is merely 20A or so.
--- Quote from: Pentium100 on December 02, 2012, 03:51:06 AM ---
--- Quote from: kitamesume on December 02, 2012, 03:16:31 AM ---not really, you have to compute by amperes not wattage, ignoring the 5v and 3.3v loads(they're too tiny to be of concern), you'll need to compute all the total wattage of components then divide it by 12v(this is to include all the loses induced since you're factoring in the efficiency with this setting), once you get your final amperage you'll need to distribute them to rails, load balancing as well.
--- End quote ---
Also, if you have the choice, buy a single rail PSU instead of the multiple ones - no need to load balance.
If you want the power supply to be the most efficient, buy one that is twice as powerful as your load, because these power supplies are most efficient at around 50% load. Adding margin is also good because over time the power of the supply will drop because of aging capacitors. Higher margin is more time until you need to replace the caps.
--- End quote ---
considering that the PC won't be hovering at 100% peak usage 90% of the time... well hitting a capacity target of 10-20% over the peak usage would be plenty, the PC would spend it's time at 50-60% power usage even during rough encoding, mostly benches are the only things that seems to push power consumption to peak power usage.
Pentium100:
--- Quote from: kitamesume on December 02, 2012, 06:59:52 AM ---depending on the diode usage, if the two diodes are in use at alternate load(eg each has 50% duty cycle) they can theoretically handle up to 20-30A(depends on the diode's specs) each.
but since its a cheap PSU, i won't be expecting a pretty diode anyway, most likely it's 60% duty cycle pulse rating is merely 20A or so.
--- End quote ---
Well, if the two diodes are in use at alternate load (which they are - they make a full wave rectifier). each half can only supply 10A average. So, put them in parallel (or in alternate load) and you get 20A. 30A goes over the spec. The duty cycle does not matter because the shorter duty cycle will be the more current it will generate to produce the same output current (the inductor just averages the current, it does not step it up).
--- Quote ---considering that the PC won't be hovering at 100% peak usage 90% of the time... well hitting a capacity target of 10-20% over the peak usage would be plenty, the PC would spend it's time at 50-60% power usage even during rough encoding, mostly benches are the only things that seems to push power consumption to peak power usage.
--- End quote ---
I do not like failed power supplies - they are time consuming to replace (especially if I tidied up the cables and especially if I do not have a spare of sufficient power) and can produce weird intermittent problems before failing. So, I'd rather buy a bigger PSU and have it be more reliable than save a few euros on the PSU now and curse a few years later. Besides, I never know when I'll decide to add a few hard drives or another VGA.
kitamesume:
there is a technique to bypass the limits of the diodes, thats when you overlap the two duty cycles, the overlapped part would have theoretically double the current capacity. if lets say two 10A continuous when ran at 75% duty cycle would be able to handle 15A repetitive output, the overlapped max current would be 30A.
this would mean that 50% of the time the max current would be 15A while the other 50% would be 30A, with this you sacrificed 25% of continuous amperage for a boost of 50% for 50% of the time, although this causes power sags over the inductors and the imbalance in this can be seen in the harmonics of the output.
although as i've said, i wouldn't expect such a topology on a cheap powersupply.
no you misunderstood my claims, im not saying you should buy a lower capacity PSU, what im saying is that you don't need to get such overly exaggerated headroom for two main reasons.
1) your PC will only hit a certain peak power consumption during stress tests on all components. unless you stress test your PC 24/365 then i doubt you'll need anywhere near twice as much PSU capacity to hit the 50% mark where it is the best efficiency.
2) unless you're adding enthusiast cards in it you shouldn't even need anywhere near 300watts of headroom (i've yet to see one draw anywhere near 300watts is what i'm saying).
as for these two reasons, your PC would spend at 40-60% of it's max power consumption during heavy use(encoding and gaming), while it'll hover at 20% or even less during playback and surfing(unless people claim lies, hahaha) and less than 10% during idle.
if you had like 2x the max load then halve those power usage and you'll be seeing horrible efficiencies since you're practically under 30% of the PSU's capacity.
---
as for the durability of the PSU, capacity has nothing to do with it really, unless you're cutting close to the max PSU rating(PSU has it's own wriggle headroom, depending on manufacturer and model). what you'll need to consider about durability of the PSU is it's reliability, hey a cheapo 650watts like the Corsair VS650 wouldn't be as great as their Corsair TX650 right?
mgz:
--- Quote from: Ixarku on December 02, 2012, 01:27:14 AM ---Yah, really. If I'm going to spend the money and go to the trouble of building a PC myself, my philosophy is to spend money on quality parts, or don't bother with it at all. I've personally had good experiences with Corsair PSUs, although I'm not as exacting about my system requirements as some people.
--- End quote ---
yea i switched to corsair for my last 4 PSU's and i love them. Have not had a corsair psu die yet had other brands die.
And the corsair units you can find really cheap and are solid performers.
currently have 4 corsair 750 supplies running 3 of them 24/7 for the past couple years
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