(this is not a home appliance, but may be a SOHO case)
Quite a long time ago, I had some trouble about keeping my computer room with continuous energy supply. The UPS devices were expensive, used lots of room area and also added up some 15-20% heat to it. They also tend to fail in some emergency cases after the years, and required an eye on them to ensure the batteries were just fine...
As any computer uses a switched mode power supply (SMPS for friends), I wondered why not to feed them straight with simple DC (at 144Vdc, for an instance). This should work, provided the computer's power supply does not expect some AC for some strange function, but should not be the rule in general cases.
Feeding with DC at moderated voltage has two advantages when working in emergency power, both improving energy conversion rate and thus, battery duration: no conversion is required from battery to mains AC (so we remove a 15-25% of energy losses at that stage) and we extend the battery charge range (provided we use a universal computer power supply) because we can work over a wider voltage range (often down to 133Vdc, and up to 320Vdc so we can use several spare batteries). Using a quite high voltage has the advantage of requiring quite low currents, and so standard (and even quite long) cables can be used, and even the DC supply can be isolated from the computer room on an adjacent facility. And the use of standard, low cost, automotive batteries also is a plus for your bucket and allows for over dimension on the capacity, making run times of hours a simpler matter.
Here the point is:
- To feed enough computers so having 12-13 batteries in series is worthy. A dense rack should be enough demand to make it worth.
- Provide some sort of shunt devices so if a battery gets damaged or you want to hot-replace it, the rest of batteries continue supplying power. Using several extra batteries (e.g. 16 batteries instead of 12, and up to 20 if desired), we improve the roughness of the system.
- As the batteries alone (plus the shunt devices, that are independent to each other) are simple devices, this makes this power supply quite resilient to failures.
- A specific charger and pass-through power supply has to be designed. It has an extra advantage: is quite easy to make it redundant by simply (almost) connecting more than one in parallel, as we have a single DC rail to feed.
