Re: PE1950 - EnergySmart - any disadvantages?

michalwd1979 michalwd1979 at o2.pl
Mon Oct 22 07:15:54 CDT 2007


Hello,

Faris,
PE2850 use only 2 voltages +12V (high power on only when server is operating) and +3.3V (only few amps, standby, on all the time). Dell uses very complicated connector to mainboard, problems are not the voltages but the communication and signals.

Kuba Ober and Faris,
Well I am an electronics engineer. I have already designed and build (from scratch!) a few PSUs, the best one has 20V, 100A output and about 95% efficiency. It is fully soft switched to reduce RF noise. Now I am working on 150V, 100A DC-DC converter with reversible output for demagnetization coils used in ships :-). It is now 70% ready with planar transformer, active rectifier and FPGA based control.
I am not afraid of RF compilance, stiffnes, regulation and so on. The problem are the connectors. Reverse engineering the protocol or signals will be __very__ hard. I hope that I will get the schematic of original PSU or something, without this I am not starting this project, I don't want to spend more time on reverse engineering then on real design.

By idle power I mean PSU in the server connected to AC, server is off. Server itself consumes about 4A at 3.3V ~= 14W, PSU losses are dominating. 
Dell PSU has PCF, to meet AC current distortion restrictions it is needed. It in fact works at about 500V, I have 230V in plugs here in Poland.
Some time ago I have made some tests with computers (normal PCs not servers) and RF noise. It seems that main source is the PSU - normal PC has very cheap and not so well designed supply. Mainboard works with low power signals, short tracks and it is quite well screend itself. With multi layer PCS almost always one complete layer is dedicated to ground. I unfortunatelly don't have equipment to check RF noise of my PE with all these holes, but I hope that I will do such tests in future. Anyway I was in server room where most of servers worked with cover removed and there were no problmes with using phone or listening to radion in next room, but keep in mind that even with cover removed PSU units are always in metal case.

Best regards,
Michael W.


Dnia 21 października 2007 23:02 John <jses27 at gmail.com> napisał(a):

> On Sun, 2007-10-21 at 03:36 -0400, Kuba Ober wrote:
> > On Tuesday 16 October 2007, michalwd1979 wrote:
> > > Thanks for the info Faris.
> > >  From my test it turns out that the efficiency of PSU is rather poor. 1 PSU
> > > of dell2850 takes about 40-50W idle. In my configuration no loaded server
> > > uses 180W (3 SCSI drives 2x 3GHz Xeon, 4G RAM). Fully loaded it needs
> > > 240-250W. In fact I could save about 40W just by taking out one PSU. Some
> > > other problem is cooling system.  6 high speed fans can take 70-80W alone
> > > when running on full speed, much less when running on reduced speed. I am
> > > using water cooling and only one PSU so I saved about 100W (0.4A).  Now we
> > > are strongly thinking about making custom DC-DC PSU that will run directly
> > > form 24V battery, thus we will not need UPS, that alone can take some power
> > > just to covert energy 2 times. The problem is the connector to main board,
> > > I need to get documentation somewhere.
> The Main Board connector should be documented. Look for Dell specific
> ATX style supplys with a +12v processor lead and should be a -3v PON
> POFF switch lead. The rest can be figured out with a Voltage Meter +3,
> -3, +5, -5, -12, +12. Maybe just might be on the outside of the power
> supply, (connector pinout).
> > 
> > The power supply likely not only supplies the voltages, but also communicates 
> > with the motherboard somehow (about temperatures at least).
> > 
> > You may try to look at the pins with an oscilloscope.
> > 
> > As for DC-DC converters, you may end up having to do custom PCB design and 
> > whatnot: I presume that those supplies are pretty "stiff" on their 3.3V 
> > outputs, and with the power they transfer you will have to know what you&#039;re 
> > doing.
> > 
> > It&#039;s one thing to make a 1W DC-DC based on an application note. A PC supply 
> > like you want to make will take at least a well equipped lab and someone with 
> > some experience (or otherwise brilliant and really understanding physics). 
> > You&#039;d want it to be CE-compliant as far as emissions go, at least. Not a 
> > small undertaking. As far as the server goes, with all the holes you&#039;ve 
> > punched through the case, it probably already is not in compliance for 
> > emissions. Adding your own power supply will, at first try, likely drown out 
> > most of the long, medium and shortwave radio in the neigboring apartments. 
> 
> Yea sure will, bring out the ferrite and torroids!! Also the capacitors.
> 
> > Not a nice thing to do. Power-efficient DC-DC converters run at lower 
> > frequencies (say 50kHz) and they radiate like hell by default ;)
> 
> I smell a Ham Radio Operator?
> 
> > You may want to look into the power supply and find out whether it has a PFC 
> > (power factor corrector). If it has, and it&#039;s a separate block, then the 
> > DC-DC is designed to run off 300V and isn&#039;t that easy to interface to. If 
> > there&#039;s no PFC, you will be able to power it with 100V DC going directly to 
> > the far side of the rectifier -- those supplies take AC, rectify, and then do 
> > DC-DC.
> > 
> > If there&#039;s a PFC, *and* you&#039;d be brave, you can always rewind the primary on 
> > the high-frequency transformer in the DC-DC converter with 1/3 of the turns 
> > of a slightly thicker wire, so that the DC-DC would run on 100V DC instead of 
> > 300V. A PFC is a step-up converter, and its output will be in 280-350V range, 
> > depending on how it was designed. Getting rid of PFC and doing a DC supply 
> > will save you 10-15% on efficiency (assuming your DC source is 100% 
> > efficient). Measure it all first, of course.
> > 
> > You may just as well use a 9 x 12V batteries connected in series. They can be 
> > on-line-charged using regular, line-frequency transformer-based power 
> > supplies, as those will by default have a primary-to-secondary insulation 
> > that can take a 100V offset. Not pretty, but simple, and way simpler than 
> > making your own supply from scratch.
> And by that means of using batteries, it will filter some of the RF
> Hash. AC is Nothing but High Level RF.
> > 
> > By the way, the power supply should take ~120V DC without any modifications.  
> > Oh, the joys of switching power supplies :)
> 
> I wonder if it is going to oscillate?
> 
> > 
> > Cheers, Kuba
> > 
> > _______________________________________________
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> > Linux-PowerEdge at dell.com
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> -- 
> ~/john
> 
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