About a year ago, a neighbor's tree interrupted our power service for the better part of a day. Since the APC power supply that was supposed to keep the phone lines and cell phones charged had several annoying features, I decided to cast out for my own UPS for the house phone as well as the cell phones. The APC UPS is built for a totally different purpose - Lots of circuits, inductors, etc. to produce the semblance of a sine wave from a DC power source. The crazy thing is of course that for most applications all that AC power is turned back into DC, with the added bonus of an annoying recurring beep, vast inefficiency at lower power operation, and hence very short runtime despite the use of two 7Ah 12V SLA batteries inside (cabled in series)
So I decided to take a different route, electing to use a PICO-UPS charger board
(green) for the battery and a small 5x5cm board (blue) of my own design to distribute power to the phones. The black phone jack on the left of the board is for the house phone (6.3V) while the dual USB jack provides 5VDC and
features the resistor divider that adafruit was so kind to document
to enable Apple users to recharge their iPhones. All outputs are protected with individual PTCs, feature individual LEDs (to alert me to a PTC shutting down a circuit) and two Dimension Engineering DC-DC power supplies provide the respective DC outputs. An external wall wart provides 15VDC @ up to 1.6A to charge the battery and provide power to the phone board.
I really like the Pico-UPS board so far thanks to its small size and very cool operation. My only improvement suggestion would be to change the power inlet from a .187" blade design to something compatible standard wall warts (i.e. 5.5mmx2.1mm center positive jack). But that is a totally minor issue. I am also super happy with the Dimension Engineering DC-DC converters (here
), among others. They are well-designed, stable, and allow excellent adjustment of the output voltage. Yet to be implemented is a safety feature (i.e. 2A inline fuse on the battery line) and an enclosure.
Yes, there cheaper ways to do all this. Our friends at Dimension engineering have since released more power supplies, etc. But the 3A charger has ample capacity to charge two iPhones at 1A each while also allowing the house phone base (DECT) to continue to operate. Unlike the APC approach, there is no beeping in UPS operation (just some silent LEDs), the conversion efficiency is on the order of 75%, and the battery will be super easy to replace as needed in the future. FWIW, Pico UPS also offers units with programmable outputs, allowing enterprising users to run devices like routers off a similar setup with a stable voltage.
Lest it come across that way, I am not trying to bash APC and their lines of of products. Rather, I believe that there is a market for UPS's that provide efficient power at a regulated 12VDC and 5VDC output to complement what is already out there. Unfortunately (and this will likely kill the idea) industry in turn would have to agree on (a) standardized connector(s) to allow direct hookups and hence for devices to bypass the need for AC-DC-AC conversion. However, imagine the benefits for all sorts of electronic devices, from lower potential EMI to longer run time for the same size battery.