Typical UPS setup

A UPS provides stable and uninteruptable power to equipment.

"stable" means a constant voltage that is filtered for interference.
"Uninteruptable" means backed up by a battery (most of the time) in the event of a power failure.

Consider a typical on-line UPS setup for use with computer equipment:

  • Line voltage is converted to DC power to charge a battery.
  • The DC power of the battery is converted to AC linevoltage.
  • The converted AC linevoltage is converted to various DC voltages in the power supply of the computer.
  • The convertors on the mainboard convert this DC supply voltage to lower voltages suitable to the CPU en RAM.

Many conversions, and most of the time very inefficiënt conversions.
I don't want. ;-)

In an off-line UPS, the line voltage is directly connected to the output line voltage, but the battery is always being charged.
Measurement with my own UPS showed around 20W is used for the functioning of the UPS.

Better design

  • Start by filtering line voltage for interference. (Lightning protection, largest ripples, etc...)
  • Use a high efficiëncy converter to convert this to a DC voltage.
  • Use a DC UPS to make the supply uninteruptable.
  • Use high efficiëncy DC/DC converters to generate various voltages.
  • Use a DC power supply to power computer equipment.

The advantages are:

  • less conversions which directly translates in less electricity consumption and less costs, and
  • no conversion to AC line voltage when a power failure occurs which translates to a longer battery runtime.

Looks like an easy choice to me...


It seems mini-box.com manufactures several components that can be used.

  • Line filter (Not shown)
  • Pico UPS with Lead-Acid battery (Rated 10A @ 12V)
  • Multiple USW-525 DC/DC converters (Based on LTC3780 rated 5A @ a wide range of inputs and outputs possible.)
  • Pico PSU inside computer equipment (Not shown)

High available

Offcourse a high available DC power supply can be made as wel with minimal extra cost.

The Y-PWR just takes power from the highest voltage source, or both if they are within certain limits.

In this example a PV panel is used as the second power source.
When the PV voltage is higher, it will be used, but when the sun is not powerful enough the other powersource is used. This way solar enegry is used whenever available, even when there is a power failure.

Off cource it is entirely possible to connect a second AC/DC power converter, preferably connected to another AC phase.

Please read the manuals of all mentioned devices for proper usage and understand the design limits!


I used an old 19 inch rack switch case to house the DC power system.
During installation: