DC vs AC

I recently heard someone say that they heard someone say.

"They say our computers will perform better if we use DC power".

I think what he meant was. the powersupply may not clean up the dirty AC power as good as say: A UPS with DC output to a computer power supply which has DC input. Or maybe a power supply which has a battery and its DC output comes directly from the battery.

Has anyone ever heard this, and would it be logical to do something like this?

I understand that this may lower the temp and make the devices work better and last longer, but how much? Not enough to see a faster CPU benchmark?

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Quote :

I recently heard someone say that they heard someone say.

"They say our computers will perform better if we use DC power".

I think what he meant was. the powersupply may not clean up the dirty AC power as good as say: A UPS with DC output to a computer power supply which has DC input. Or maybe a power supply which has a battery and its DC output comes directly from the battery.

Has anyone ever heard this, and would it be logical to do something like this?

I understand that this may lower the temp and make the devices work better and last longer, but how much? Not enough to see a faster CPU benchmark?

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If I understand this post, you seem to be asking if the inbound current to a power supply unit was DC instead of AC would it make a difference in performance?

I don't see how. The current coming into your house is AC. It has to be converted to DC at some stage for a computer to work. In a computer that 'stage' is the PSU. If the PSU was to work with DC as input current, then it has to be converted to DC before entering the PSU. So all this accomplishes is putting the AC/DC conversion process earlier in the chain of events.

If the goal is to get clean input for the PSU, here's a better way:

Convert the incoming AC to a UPS to DC, then regenerate a new AC signal. This is what online or dual conversion UPS's do, such as the Tripp-Lite SU1000XL, and medical- grade UPS's.

I have a dual conversion UPS and there is no performance difference with it as compared to running my computer directly from a wall AC outlet. If this type of UPS has any advantage over other types of UPS's it might possibly be in longer life of the computer components, particularly the PSU.

Or have I misunderstood your post?

-Bob

Reply to BobA

Yes you go it. However what if instead of taking that DC power directly from the UPS battery and converting it back to AC, you run DC directly to your powersupply. Technically, wouldnt DC power be cleaner than converting DC back to ac then back to DC?

Reply to flex411

I think people are thinking of converting whole houses to DC power, which would not work at all due to some of the amperage requirements of A/C, Heater, Refrigerator whatnot, but would be better for nearly everything else.

Either way, the reason we have PSU's are for clean stable DC power. If we have say, an industrial grade transformer to turn AC to DC i.e. a rectifier: http://en.wikipedia.org/wiki/Rectifier then the PSU wouldn't need its own internal rectifier. But there wouldn't be any cleaner power, or more stability, since PSU's are already using high quality parts. It might live longer and give off less heat since its not going from AC to DC, but other than that, there is no big point.

I doubt we'll lose the AC -> DC characteristics of PSU's, its just not feasible at this point. We don't want to lock consumers into a PSU that doesn't convert AC into buying a standalone transformer.

Reply to Doughbuy

Quote :

Yes you go it. However what if instead of taking that DC power directly from the UPS battery and converting it back to AC, you run DC directly to your powersupply. Technically, wouldnt DC power be cleaner than converting DC back to ac then back to DC?

Not cleaner, but more efficient.

There has been a lot of talk about this lately in regards to data center power. The conversion of AC to DC or DC to AC results in lost power being converted to heat. At your home this is negligible, but to a large data center this could mean millions of extra dollars in energy costs, directly due to lost energy, and indirectly due to increased cooling costs.

Reply to PhilFrisbie

I understand how a UPS works, I was refering to the Tripp-Lite SU1000XL bobA was talking about. But it looks like theres a transformer in there and it doesnt use the battery for its power either?

I'm just trying to figure out why someone would say this assuming they knew what they were talking about. It looks like they dont know what there talking about considering everyone's reply's. "It doesnt't improve performance" End of story?

Reply to flex411

Quote :

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There has been a lot of talk about this lately in regards to data center power. The conversion of AC to DC or DC to AC results in lost power being converted to heat. At your home this is negligible, but to a large data center this could mean millions of extra dollars in energy costs, directly due to lost energy, and indirectly due to increased cooling costs.

Yes, what's been in the rags lately is talk about switching Data Center systems to all DC, to avoid the lost efficiencies and heat of conversions. The savings in server farm environments could be considerable.

Reply to jtt283

Quote :

Yes you go it. However what if instead of taking that DC power directly from the UPS battery and converting it back to AC, you run DC directly to your powersupply. Technically, wouldnt DC power be cleaner than converting DC back to ac then back to DC?

Not cleaner, but more efficient.

There has been a lot of talk about this lately in regards to data center power. The conversion of AC to DC or DC to AC results in lost power being converted to heat. At your home this is negligible, but to a large data center this could mean millions of extra dollars in energy costs, directly due to lost energy, and indirectly due to increased cooling costs.

Ahh, the guy who said it runs a data center, so thets prolly what hes refering to, saving energy. Although that doesnt improve performance much?

Reply to flex411

It is very difficult and costly (from an engineering standpoint) to get DC current from a power plant all the way to the consumers. When using AC current, you can use transformers to creat high voltage - low current power for transmission across long distances; and then use another transformer close to the consumer to convert it back to low(er) voltage and high(er) current.

This is why we use AC current in our homes and businesses.

True enough, just about every single piece of electronics uses DC current exclusively... thus all those big heavy "brick" plugs that take up too much space on our power strips. It may very well make sense to have a whole house transformer to convert the AC signal from the power company into a DC current, and distribut that throughout the house (w/ a different shape socket so nobody gets confused, of course). But that would require a huge political initiative and the will of the people to conform to such an effort. Building codes and the like would need to be updated, electricians and inspectors would have to be trained, etc etc etc. If it truely is a good idea, then it may just happen one day... but it won't happen overnight.

Reply to SciPunk

I think what there were referring to was that a power supply in a normal home pc converts the AC to DC onto rails. There are a bunch of rails that it converts to. Each time you convert to a different rail you loose more effientcy. And he was talking about using just 1 rail instead of the many that current power supplys use at the moment.

Reply to branson

Thomas Edison's Pearl Street Station had a service radius of about a mile and a half, because it used DC. DC does not propagate like AC does, so it is not practical over distance.
Conversion to DC before entering a climate-controlled data center removes a zillion little heating elements called transformers from the data center itself, so not only are you saving money on lots of conversions, you are saving it on reduced cooling costs. There is typically a large transformer in or near large businesses anyway, converting incoming 480 (or more) down to 240 or 120 needed by the building's circuits. It may also be in an area that doesn't need to be cooled, so the heat doesn't matter.

Reply to jtt283

As a former Power supply and UPS design Engineer here is my two bits; First, a computer uses a switching power supply that converts the AC (alternating current 50 to 60 cycles per second) into DC. This DC voltage is chopped up into a very high frequency where it feeds into a transformer that converts it into several different voltages. Each of these voltages are converted into DC using a rectifier (or diode).
A switching power supply has numerous advantages over a conventional linear supply. However, the chief element of a switching supply is that they all can operate on a DC voltage. If fact they all require rectifying the AC voltage into DC.

As for PFCs. These are Power Factor Correction circuits. AC has one drawback in that it has a nasty habbit of knocking the voltage and current out of phase when powering inductive loads. When the voltage and current are out of phase, the effective power is reduced, reducing the overal efficiency of the supply. A PFC circuit provides a method of placing the voltage and current back into phase making the power supply more efficient.

So full circle here. For optimum efficiency, a low impedance DC power source for a switching power supply. Next in efficiency A PFC integrated into the power supply. BTW- Europe is ahead of the USA, as they are mandating PFC be placed into all switching power supplies. This is a good thing for efficiency, but these supplies will cost a few dollars more.

Regards,

Rickey Horwitz

Reply to rick_h

PSU's would almost never improve performance. Stability yes, the amount you can OC, maybe, depending on how crappy your old PSU is, but if you have a high end PSU with plenty of cooling, the PSU wouldn't effect it at all. I would say our computers would perform more efficently, not better if we use DC, but then the PSU wouldn't be doing the converting.

Reply to Doughbuy

Rick, who did you work for? I sell psu's, power conditioners, transformers & ups systems for the industrial enviroment. Mainly Sola/HD.

Now Rick was right on with what he said. There are power conditioners that will clean up the ac sign wave going into the psu. Most "home level" ups systems have a so called pc in them, but are not as efficient as a seperate pc.
Most of the industrial ups have a pc built right in.

I provided a good link that talk about powercondioning.

power conditioning

Reply to Hicks121

Quote :

I understand how a UPS works, I was refering to the Tripp-Lite SU1000XL bobA was talking about. But it looks like theres a transformer in there and it doesnt use the battery for its power either?

I'm just trying to figure out why someone would say this assuming they knew what they were talking about. It looks like they dont know what there talking about considering everyone's reply's. "It doesnt't improve performance" End of story?

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Just to clarify, a dual conversion ("on-line" ) UPS always draws from the battery. Wall AC is converted to DC and is used only to keep the battery charged. The DC from the battery is then converted back to an AC pure sine waveform, noiseless, and very tightly controlled in Hz and voltage. There is no switch over when the wall AC fails, the attached devices just continue to draw from the battery, for as long as possible.

This type of UPS is not very common among home computer users because they cost more than double a top quality conventional "battery backup" type.

-Bob

Reply to BobA

Quote :

A PFC circuit provides a method of placing the voltage and current back into phase making the power supply more efficient.

I was always under the impression that the the reactive component was negligible when measuring power loss (due to component heat), and PSU manufacturers rate consumer ATX units as such because it yields a higher efficiency rating as well as a number the consumer will see since they are not penalized for their "apparent power" usage (essentially getting reactive power for free )

PFC does reduce the power consumption in VA so it does make the AC network it is connected to more efficient, so the UPS or utility company definitly benefits from power factor correction.

Reply to doolittle

Doolittle,

Most people equate innefficiency with heat and rightfully so. However, power phase loss is an innefficiency that also substantial. As you mentioned, VA is a term to express relative power (voltage x current= watts). An AC power signal is sinesoidal, so the voltage and current go up and down exactly at the same time. When the voltage leads the current (such as an inductive load) the amount of power available is restricted, as V and A are not going up and down at the same time anymore. So, the loss again is heat, as the measured voltage across the load is lower because of the lack of current.

As mentioned before, all new switching power supplies sold in europe will require a PFC circuit, as to increase efficiency. BTW- If you look at a power substation, pay attention to the huge cube shaped devices on the power lines. These are huge capacitors that are intended to assist in placing the voltage back in phase with the current.

Rick

Reply to rick_h

I 100% agree that vector addition of mulitple devices with a poor power factor creates a huge inefficiency in the AC network, and results in a poor waveform that hardly resembles a sine wave, and creates dozens of unwanted harmonics in the line. Reducing the phase angle between voltage and current is not a bad idea on a per-device basis if you are in a situation that bad, be it active PFC on your PC's psu or huge caps on large motors.

I was just stating the standard methodology used to measure and calculate AC / DC conversion efficiency as component loss and calculating the ratio of real and apparent power are intentionally kept seperate. The AC/DC conversion loss calclulation only includes the AC real component because the DC side has no reactive component, so a ratio of the two can be compared on level ground.

Quote :

silentpcreview[/url]"]PFC Myths

There are myths about power factor correction that continue to be propagated by well-meaning people. Let's tackle the two most common ones:

Does higher PF reduce my electricity bill?
No, if you are a home user. If you are an enterprise running hundreds of PCs and pay not only for power but also VA, then yes. For more details, see PFC discussion above.

Does PFC make a power supply more efficient?
Not in the normal way that power supply efficiency is defined, which is the power loss (to heat) as a percentage of total AC input in AC-to-DC conversion. However, in the sense that Apparent AC power (VA) is lowered, PFC does reduce energy consumption.

Power factor correction is applied by an input circuit which uses a small amount of input power. With two PSUs that are identical, equipping one with PFC will cause a typical efficiency drop of 2~4%. Many PSUs that have Active PFC also have high efficiency, as APFC is usually found on higher quality PSUs, but the two are not intrinsically related.

PFC does improve the efficiency of the AC network it is connected to, not the device itself.

Reply to doolittle

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