APC lawyers covered this...
https://www.apc.com/us/en/faqs/FA158607/
pushes APC way down on my stack of companies whose products i will consider buying.
Bumping this old thread. I once saw a set of .pdf schematics for an APC UPS made in the early 1990's.
The basic architecture of a single-stage 12V DC to 120V AC inverter can be deduced from this old schematic. The circuit design is so old that there is no MCU chip. It contains only standard digital and analog IC chips. This type of UPS contains a very large heavy 12V-120V transformer (this transformer is usually bolted to the case of the UPS).
in contrast, nearly all modern UPS back-up power supplies (past 5 years or so) are "two stage" units:
The first stage is a high-frequency DC-DC switching converter with a 12V DC (or 24V DC) input. It has a single DC output between 100-250V. The switching transformer is the typical ice-cube sized or slightly larger ferrite-core transformer as found in high-frequency DC-DC switching power supplies of similar total wattage rating. The difference is this transformer is wired to step up from 12V to 120V, rather than to step down from 120V to a lower output voltage. The 100-250V DC output from the DC-DC converter is then converted to AC by a "full bridge" of MOSFET transistors. This is the inverter section. It converts DC to AC but does not change the peak voltage. The MOSFET switching transistors are pulse-width modulated (PWM) to generate a simulated sine wave output. The DC-AC inverter is followed up by a low-pass filter, consisting of a high-current series inductor and a 10uF 400V metallized film capacitor.
Modern UPS units additionally contain a small 120V to 12V high-frequency switching DC-DC converter section. This is entirely separate from the "step-up" section which goes from 12V to 120V (or higher) DC. The 120V-to-12V section supplies 12V charging current to the battery and also provides power to the internal logic-level circuitry which runs on 5V or 3.3V. The circuit design of this section is similar to a "wall wart" switching power supply brick. These sometimes fail, but repair usually consists of replacing the failed MOSFET (or the dedicated IC chip which internally contains the switching MOSFET). These are generally industry-standard parts which are easy to find and cheap. Occasionally an electrolytic capacitor will also need replacement.
Modern UPS units almost always contain a small MCU which performs most of the logic functions.
In summary, most of the faults in UPS units, both old and new, consist of failed capacitors or shorted MOSFET transistors. But the MCU, as well as the other IC chips which operate at low voltages, rarely fail.
Home
Help
Search
Login
Register
