I just got an apcups for cheap. smartUPS 750.
As I often do with electrical equipment I did some measuring about the power consumption. For that I just plugged it in without any consumer attached. It then runned through the night to have the batteries charged to 100%. I then expected to have the UPS consuming only a very small amount of power, because it only have to supply a minimal amount to hold the charge at 100%. I was a bit suprised to found it to drag 13,5W. Switching it of changed that to 12W.
Maybe I'm just an electrical noob, but for me that's not acceptable.
So my question is: Shouldn't it be possible do build a UPS, that consumes a lot less, when in "normal" operational mode?
I know UPS have an additional use, which is to give a stable 230V/50Hz output, even when the input side is unstable.
The main idea is to get it as efficient as possible when it's operating in "power attached" mode, because the running time in battery mode is nearly irrelevant. (e.g. having 1 power off event a year, which shuts down the servers in 30 min is about 0.006% of the operating time)
So my question is: Shouldn't it be possible do build a UPS, that consumes a lot less, when in "normal" operational mode?
The controller could use very little power. Check out these pages - http://www.gammon.com.au/forum/?id=11497 -
The most power loss is related to the efficiency of the internal battery / capacitor.
Maybe an UPS based upon an ultra capacitor is an idea?
Just to make that clear I'm talking about UPS used for servers. I just opened mine and found several tramsformers (one very huge maybe same as in welding machines?) and relays.
And I just touht about it in analogy to PSU. Where now we have PSU which clearly consume below 1W, there where the old ones (with tramsformers) which consume much more just by pluggin them in.
So I thought using that technology in UPS should make them using much less power in "passtrough power mode" than actually do now So the idea was to perhaps do a open hardware project baesed on arduino to get better UPS ...
Note: I'm not a expert in that in any way, but willing to help where I can (e.g my wife works in a PCB producing company).
Just thought an arduino with usb suport could handle all the status messages as fine as the APC with apcupsd ...
Having a pice of hardware, where you can plug in an arduino with the right code and having a full blown, open hard- and software, energy efficient UPS would just be to nice to have. 
I took apart a similar UPS and saw the same inductors you mentioned, so I believe you are not looking at a transformer. Large inductors used to smooth out the output from a UPS to be more sinusoidal. I took apart a variable-speed drive system for a condenser system and found an inductor big enough to put a major dent in the floor.
My APC UPS failed on account of a fried battery pack, not a unusual issue with a SLA battery. I pulled the thing apart and the main OEM PCB filled the length and height of the device. I bought a new set of batteries and am planning on using a picoUPS to provide the charging and switchover, while a board of my own design uses the dimension engineering switch mode power supplies to provide 5VDC for a USB charger and 6.5VDC power supply for our portable phone base station. The external power supply will be switch-mode as well (15VDC @ 1.2A).
I figure my "solution" to be significantly more efficient for my purposes than the OEM solution - i.e. charging a USB device and the main phone base station for the house. Even with a negligible load, the OEM solution lasted less than an hour. I expect the new one to last for hours instead since we'd be looking at a 75-85% conversion efficiency and without the intermediate DC-AC-DC steps.
13W for 750W is only 1.73%.
Power is going to trickle charging battery, and of course there is efficiency of the primary PS.
The way to reduce idle current, would be to put everything in sleep mode, and charge up battery on periodic base. But again, there is a question of waking up time, and it is critical to servers.
I would focus on the end power needed. In the case of a server, you're typically looking at 12VDC for the HDD's and 5VDC for the board. PicoUPS offers all sorts of pre-confectioned power supplies that are DC-DC solutions with very high efficiencies. Makes much more sense to go directly DC-DC with a switch mode than the AC intermediary steps. What's great about the PicoUPS products is that they're based on ITX and ATX power supplies that plug directly into existing motherboards.
Magician:
13W for 750W is only 1.73%.
Not exactly.
First 750VA !=750W (about 680W IIRC)
Second: True if full load.
Another perspective to look at it: 12W input, zero W output (Battery filly charged, no devices on output side, switched OFF!), that would That's not definable (infinitive).
The diffrence then the switched off, compared to switched on (100% Battery, no devices) is 1.5 W which ist incedibly goog for holding the chagre
Constantin:
I would focus on the end power needed. In the case of a server, you're typically looking at 12VDC for the HDD's and 5VDC for the board. PicoUPS .....that plug directly into existing motherboards.
THAT'S really one thing I compleetly missed to think about. Thanks a lot! Just one question: aren't there +12V and -12V for some boards (aka a diffrence of 24V)?
But I like the idea a lot. Use a good PSU as primary converter (which has the additional capability to smoothen the Inputpower) and work with PicoPSU the rest of the way. Only concern to me is the speed of switching to the batteries in case of powerloss. Using some big capacitors for the switching delay, perhaps?
There is no need for the cap you mention - PicoUPS offer a 1.2A charger / switchover board at the low end and higher capacity boards as well to take care of the UPS part. Instead of a lossy diode or other approaches, they use MOSFETs that act very quickly. Read up on the info they have on the site, I was impressed.
The PicoUPS power supplies have wide DC input ranges and plug directly into a standard motherboard plug. So, I am not sure what you need other than to figure out the peak loads, the required components and a credit card...
Oh, I just didn't read carefully enought:
PicoUPS!=PicoPSU
Maybe because I allready knew the PicoPSUs for some time and tought I just forgrt them. But logically someone had take that "shortcut" for a better UPS allready. I will look deeper in that next year, which is only less than 1.5 hours for me 