h. Innovative UPS for small home applications, mini PCs and notebooks
Today mini PCs and micro PCs are often used to run home automation systems. Unlike desktops they only need a small power supply. But unlike notebooks and tablets, they lack batteries that would keep them powered on for hours during a short main power supply interruption, a power shortage or an electrical breakdown. One can use a standard UPS (uninterruptable power supply) to power a mini PC, but this is a very expensive and inefficient solution for a computer that only needs a single voltage DC power supply.
You can easily build your own online UPS that enables a much better protection than a standard offline UPS. The difference between the two is that an offline UPS detects power shortages and switches from the main line power supply to the battery power supply as needed. It usually incorporates a power relay that has to have a short enough switching time to prevent the computer losing power.
An online UPS also has two voltage converters: an AC/DC convertor and a DC/DC or DC/AC converter. But they are always running and no switching between power supply from the mains and battery power supply is needed. This solution is not efficient for desktops that have high power consumption, but it is perfect for a mini PC and other small computers that require a simple DC power supply with only one voltage level.
The trick is to use an AC/DC converter that provides power for the accumulator battery and DC/DC converter that powers the computer. Industrial lead accumulators are perfect for this job, because they can be always connected to a power source and do not require power management.
It is important to consider lead accumulator battery specifications to determine the optimal voltage to which the accumulator battery may be constantly connected/charged without the need for power management.
The DC/DC convertor is connected in parallel with the accumulator battery to be constantly powered on and to provide constant voltage level for the computer. This configuration also offers a better power surge protection for the computer since it is not directly connected to the AC mains.
Click on the picture to enlarge it.
Here is the parts list of my project (UPS parts only):
- TDK Lambda LS100-15 AD/DC converter
- Panasonic industrial LC-R123R4PG lead battery: 12 V, 3 Ah (may be constantly connected/charged at 13.6 V)
- Diotec power diode P1000M (10 A, 1000 V)
- Trust 90W Primo Laptop Charger (DC/DC converter)
Here is the schematic of a home automation system with a home-made UPS:
Accumulator battery and AC/DC converter in operation: Click on the photo to enlarge it.