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Consider the normal desktop PC with a UPS unit.
ac is converted to dc and used to charge the battery. In the more expensive units, the dc is continuously converted back to ac, and then supplied to the PSU. The PSU then converts back to dc +/-12V, +/-5V etc.
So why the double conversion?
If
the battery was moved to the output of the PSU, then only the dc-dc convertor stage would be needed. Furthermore, if the battery was contained in the PSU, and was enough to "get you out of trouble", i.e. brown-out over-ride, or long enough to finish shutting down, then this would be something that I would want to have.
A rear connection could be provided for those that wanted an expansion battery. But the main idea is that it is all contained inside the PSU.
Solarcraft DC UPS
http://www.solarcraft.net/dc-ups.html
AC input, 12/24 V DC output. [kropotkin, Oct 04 2004, last modified Oct 05 2004]
(?) Purcell DC UPS data sheet
http://www.purcells...Attachments/RPM.pdf
Similar product to the above; PDF format. [kropotkin, Oct 04 2004, last modified Oct 05 2004]
UPS for DC-only environment
http://www.jtecheng...ples/dcupsstub.html
From JTech Engineering. [kropotkin, Oct 04 2004, last modified Oct 05 2004]
cypherpunk's link as a link
http://www.ups2.com/
[Ling, May 26 2006]
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I'm not sure you can get arround the double conversion, seeing as how the supplimental power is coming from batteries. |
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I've seen these baked several years ago, but they never really took off. Cost too much, perhaps? |
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There seem to be a few DC uninterruptible power supplies around, either taking an AC input or DC input. (See links.) However they're not exactly in the small and cheap sector of the market. |
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None of those are in the right form factor to mount inside a PC case, though, [krop]. |
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The UPS systems shown in the links are a little on the large side. Seems that the pc would be going inside the UPS, and not the other way round, which is what I had in mind - see the last line: " But the main idea is that it is all contained inside the PSU ".
[LBAF], one conversion can be removed: from battery dc volts back to mains ac.
I don't see why they should cost as much as any other UPS, provided the manufacturing quantities are similar. |
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If you can set the battery voltage to be that of the PC, you'll get rid of all conversion except the original AC to DC, which now both units can share. These should be standard on high-end PC's. + |
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Yes, the battery voltage should be similar (ie 12Volts), but it isn't that straightforward since -12V & +/- 5V are required also. It's not a good idea to have a 24 Volt battery, with tap offs at the right points since the supply current at the different voltages is different, and discharging of some of the cells in series wouldn't be consistent.
So a dc-dc stage would be needed. |
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Had the same idea the other day. So, + :) |
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Actually my design had a socket in the PSU so that an optional UPS module (battery, dc/dc etc) could be plugged in. The module would be mounted somewhere in the case (drive bay(s) etc). |
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Yes, this ia good idea and it's time has come. |
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The only voltages required are +12 +5 and + 3.3 (or is that 3.5?). The negative voltages are not required except for by some (antique?) ISA devices and some internal modems. At that least that is my understanding. |
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One big reason for the UPS has been to provide the volts required for the VDU but with LCD displays low volts will do for them too. |
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Three batteries and a three voltage power supply to charge them is all thats required. I think I will build one tomorrow :) ! |
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[KiwiJohn] - some non-antique sound cards require -12V. |
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http://www.ups2.com/ has what youre looking for -- a hybrid psu + ups ...theyre selling it for $200 for the ATX 350W model. |
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