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back to article Validus backers banking on swing to DC

Validus Systems said yesterday that it will throw a large wad of cash at developing data centre power infrastructure that uses direct current (DC) in the hope of lowering power consumption. It said in a statement that it had raised $10m from Oak Hill Venture Partners, and expects to begin punting its DC technology in late …

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Pirate

One other reason....

DC is not widley used, accidents are more likely to be fatal !

With a powerful AC supply, you may live by being thrown across the room. DC, no such luck, touch and fry !

Not that I've ever touched 240VAC with screwdrivers or bear hands of course, that would be dumb.

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Coat

grin and bare it

@Stu -- if you must touch the 240VAC supply, better to do it with bear [sic] hands than your own. On the other hand, if the bear survives the experience he may not be too happy with you...

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Alert

WTF?

I guess they mean something along the lines of having a shared PSU, instead of lots of separate ones in each system. For what it's worth.

Though there isn't 40% worth of efficiency to be had there. Especially as you'll still need DC-DC converters as the distribution is likely to be 48V.

Doubt you use anything much above 48V as it starts getting dodgy and parts aren't so easy to get; can't imagine anything beyond 120V at a stretch. And of course this means you need big thick cables to handle the current (obviously current goes up compared to 230V/415V AC), which aren't cheap especially with the cost of copper at the moment.

Also might be an issue getting DC from a power plant (or any other form of generator) as the output tends to be... AC! So you'd still have the loss from conversion, plus higher transmission loss.

The bit I really laugh at though is this "it said it has developed a technology that takes the AC power provided by utilities and converts it into DC". So, something new and radical then, like rectifier diodes? Or a switchmode PSU? Or one of the other types of AC/DC converter Can't think of anything new they could have developed.

Personally I smell a company built to spend VC cash, but with no actual engineering content. If they were for real they might not have such fundamentally flawed ideas.

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Jon
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240 V AC

I used to do that as a kid - got electrocuted so many times that my mother told me I should be glowing. However, since computers run on 12V, 5V and 3.3V rails (unless there is something about server power supplies that I don't know) the danger of serious burning should be kept to a minimum. I believe that one of the tech websites has built a DC computer out of consumer parts which was powered by olar and batteries. Not that I am suggesting their solution would scale to the size they're talking about, but the whole thing could be run outside of the national energy grid. That in itself would be extremely beneficial.

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Telephone exchanges run on DC

I don't know what DC voltage Validus is proposing, but telecoms products (e.g. telephone exchanges) usually run on -48V DC power. The -48V supply is converted centrally from the AC mains, and conversion from -48V to lower voltages is done on the logic cards or in the racks. Distributed power conversion is often more efficient than a PC-style PSU system.

Electrocution is not a big risk in a -48V environment but the bus bars do present an energy hazard, so it's common to ban jewellery and metal watch straps.

I wasn't aware of DC being inherently more dangerous than AC - it's really down to volts, body resistance and amps. BTW, I have suffered a full-on 240VAC shock and it's extremely unpleasant - I'm lucky not to be a Darwin Awards candidate!

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> Accidents are more likley to be fatal...

Presumably the best option for most Data centres would be a single unit to take incoming AC and then feed low voltage DC to all the racks. A big transformer/rectifier unit ought to be more heat efficient, and certainly a much better bet for recovering heat energy from. Also there should be in the long term a cost saving from not buying all those transformers for the servers...

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Alert

No, DC not inherently more dangerous than AC

Sounds like an old Edison/Tesla argument. Enough of each would kill you, but it's probably a measurement thing (RMS vs peak AC voltage).

DC power means no individual losses on each server as the AC is converted to DC,.

but the advantage is lost if the single point AC-to-DC conversion isn't highly efficient. Telcos have been DC powered for ages, -48V technology is well understood. What's not well known, is that the 48 volts DC is too high for logic to run on, so DC/DC switching converters (80 to 90% efficient) must still be used in each server to develop the logic supplies.

Not sure if there's a net win here or not, but battery backup sure becomes a lot easier. As always, the devil (and the fun) is in the details...and it's never as simple as it first appears (or as Marketing would like you to think).

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Nothing new here, move along....

Carrier-grade equipment [big routers/switches, telephone-exchanges] have traditionally run on -48VDC at {mumblethousand} Amps, supplied from vast lead-acid battery-banks and fed through open, exposed copper busbars with a cross-section like a bodybuilder's arm.

True telco-types only talk AC when it comes to providing ringing-current [25Hz] for phones.....

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Go

Hmmm, seems good!

I'd guess that a room based approach based on a (new?) standard might help to avoid all those voltage transformers in each application?

How about computer monitors, desktops, laptops or portables that might be introduced into the workplace?

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Server Rooms

One idea I had was during the winter months to cool down server rooms with outside air that is already cold. I work in a server room and we run two air conditioners non-stop 24/7. I know how much it costs to air condition my house and it is not easy to pay for my own electricity.

There are some alternatives. Building structures with thicker walls and more insullation might help. The problem is getting rid of the hot air coming off of the all cpu and chipset and power supply coolers. Plus the more air you move the more dust you need to filter out of the air. Dust can kill just as much as Heat.

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I can see benefit

If they're distributing +/-12V, +/- 5V and perhaps 3.3V it might be worthwhile. Running on 48V like telcos do is not a requirement, and never has been. The fact that telcos have a large market for 48V power products helps, for sure, but maybe these folks are making 12, 5 and 3 V products of the same nautre?

Either way, now you've got one power source for all your stuff... could be efficient, but what if the rectifiers blow up? Battery power won't keep the data centre running long enough to replace those (likely specialty) parts.

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Rik
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The big(ish) gain can be in the UPS

Couple of points:

Almost all PSUs you'll find in a datacenter are of the switching type; exceptions may be the odd wallwart supply for a modem. Guess what? The very first thing a SPSU does is rectify and smooth the incoming AC. Next step is a chopper at several tens of kHz, then a smallish transformer (the power a transformer can handle is tied to the cross-section of its core, times the frequency at which it operates. Frequency goes up, required core cross-section goes down for a given power rating. If your PC's power supply was using a transformer at 50/60Hz it alone would weigh at least a Jub, and it would require several capacitors the size of a Bulgarian Airbag). Basically a DC-DC converter. I haven't tried feeding DC at the appropriate voltage to a bogstandard PC PSU (mainly because I'm lacking the required DC source), but theoretically it should just work.

If you're going about feeding DC power into your data centre you wouldn't want to run your distribution system at the voltages the systems require (12V, 5V and 3.3V) as that would require three buses (+ground), at several tens of amps per bus, per system. Meaning humongous busbars and connectors if you want to keep voltage drop at acceptable levels. So you choose 48V, which is a Telco standard already. Or 42V, an automotive standard, if you dislike Telco standards. Or 36V if you dislike both. Now what? You need a DC-DC converter, making the PSU exactly like it is now, save the rectifier and smoothing caps, and designed to work from 48V instead of 150..300 VDC (rectified 110V or 230V AC).

So, basically, no gain here so far. But 48V DC is much easier to make uninterruptable as apart from the right bunch of batteries and their charger (as with UPSes now) you just need a beefy diode, saving the DC-AC conversion step.

UPSes can generate a lot of heat too, as I noticed at a previous gig where the power requirements for the computer room was more than adequately met by the UPSes, but *their* cooling was, ah, somewhat lacking. Pulling more than 20% of the rated power tripped the UPS room temp sensor until we got some serious cooling in...

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Alert

WTDF?!

(The 'D' means double)

Especially when it says "...limitations with pumping DC power from electricity plants, as it can only travel for about a mile before the energy supply begins to weaken."

DC power distribution systems exist that send Megawatts for miles at high efficiency.

However, there are many reasons for using AC generation and distribution (look them up on the many websites available, actually Wikipedia is quite good at factual engineering things like this, sorry but it is) so that's why we have AC as the publicly available grid power source.

The advantage these people seem to be suggesting is replacing all the individual mains AC-DC converters (switch mode power supplies and also DC-DC voltage converters) with some kind of giant site based AC-DC converter which then feeds DC power to the server racks, hence to the motherboards/hard drives etc. The idea behind one giant site based 'infrastructure' converter is that it can be made to be more efficient than any much smaller converter that works on the same principles (but only if it operates at near maximum design load all the time). However, existing switch mode AC-DC power supplies are already quite efficient (I believe in the order of greater that 85%) so its hard to see where they can get 40% power saving from. It may just be possible that they mean 'reducing power wastage by 40%' which would be a good thing of course.

Further, having generated local infrastructure sourced DC, at various different voltages (or else you'll need local multiple DC-DC converters in the server racks) you then have to distribute it around site on meaty copper busbars, due to the high currents involved when using low voltage to deliver power. (Lets not get into the consequences of shorting flashes with DC power, I once blew a hole in sheet aluminium with a powerful DC source.)

"..it said it has developed a technology that takes the AC power provided by utilities and converts it into DC."

Well, that was done a long time ago (think rectifiers, capacitors, and er, switch mode power supplies), so unless they've developed something truly new and wonderful that has a conversion efficiency in the late 90's percent for a compete system, I can't see what they are offering.

"Validus then pumps the converted supply out to servers specifically designed to run on DC power."

Hmmm, all servers are designed to run on DC power, that's why they have switch mode AC-DC power supplies bolted inside them somewhere so they can obtain their required DC power from the universally available AC grid supply. We're back where we started with Validus providing a massive infrastructure DC power source. (See above).

I think I'll stop now.

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Err...

I was under the impression that you could already get servers that run on -48vDC (or at least servers with DC power supply modules). I'm pretty sure that there are some Proliants that do and I seem to remember that there are some IBM Blades that do also, specifically for use in Telcos. You do the AC-DC conversion centrally or at the individual rack, so many machines can be powered by one supply.

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@Jon

"I used to do that as a kid - got electrocuted so many times..."

If you got electrocuted, then I assume there is e-mail access beyond the grave, because electrocuted means executed!

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Stop

Efficiency and safety

A couple points:

First off, it is quite likely that the efficiency numbers they are quoting are total efficiency, not efficiency at each individual server. As has already been mentioned, in any serious datacenter, the UPS systems tend to be of the AC-DC-AC conversion style, so you always - at all times, even when connected to grid power - are converting the power twice. Next, the AC is distributed through the datacenter, where it it is then converted by the individual computer power supplies into DC. By using a DC distribution system, you seriously reduce the number of power conversions, which in turn increases your total datacenter efficiency.

HOWEVER, DC distribution is more dangerous - regardless of what commentators here may believe. The reason for this is quite simple, actually. In AC power, voltage (and thus, current) in the circuit drops to zero 100-120 times a second. This makes it much easier to break a circuit - whether this is from your own muscle contractions, a switch, or an accidental short. Either is just as likely to kill you if, for some reason, you take the shock right across the heart, or if you can't let go, etc., but when it comes to the likelihood of a sustained event, DC is clearly the greater danger.

-daniel

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Anonymous Coward

Nice Try - No Cigar

The concept of supplying Data Centres with DC power is one that is starting to gain momentum. Unfortunately, the perceived benefits are unrealistic. Here's a link to an article which summarises it nicely...

http://www.apc.com/wp?wp=63

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Coat

Pedanticity

"If you got electrocuted, then I assume there is e-mail access beyond the grave, because electrocuted means executed!"

I think you mean internet access beyond the grave, as you don't need email to post a comment.

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Joke

Wow, neat new development..

"To work around that problem, it said it has developed a technology that takes the AC power provided by utilities and converts it into DC."

Wow, that's amazing. I do hope they patented that idea in case anybody else steals it.

Really, this has happened for years. All it needs is for server vendors to dish our more kit that runs at -48v and we can all quite easily do DC in the DC..

We have had a completely DC datacenter for about 4 years now, the good folks at SUN have various DC offerings.

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Bronze badge
Boffin

Big deal

Feed the computers an AC square wave with rounded edges. This will provide a better power factor without disabling TRIACs and voltage doublers. All that changes is the UPSes. Sure, some wall-warts will go up in smoke but you're not using them if you're trying to be energy efficient, right?

Of course this plan doesn't suck enough money out of the "Green Movement" to be a product. Even if a UPS manufacturer did it, computer manufacturers would claim all warranties voided unless new certified computers were purchased.

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Does anything really need AC?

As most devices contain circuitry (either onboard or via an adapter) to convert AC to DC anyway so why are we still using 240V AC?

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