Questa è una vecchia versione del documento!
UPS Hack
The UPS in object is a TRUST 750 VA (360W) model PW-4075T.
This hack started just for adding a fan blower. The article I wrote said:
My economical UPS dies every two years. Yep, the battery has to be changed but I noticed signs of overheating.
Adding a fan blower may help just a little bit. I removed two plugs and the telephone-surge-protection, opened a hole, and mounted a 60×60 fan blower.
Wiring is shown in photo, only one transistor and one 4k7 resistor to turn on the fan blower with the ups.
But then I saw a predisposition for serial port… some checks and it worked!
Warnings
This is a hack onto shock hazardous circuits. 230VAC (300VDC) are present everywhere also when everything shut down.
Also, keep in mind that low voltage control circuits are actually connected to Mains circuits.
Do not connect Oscilloscopes to main-powered circuits. Isolate them, and connect a safety ground wire.
'This hack is not 100% safe'
Adding the Fan
Note. Fan wires ARE actually connected to MAINS.
Adding the RS-232 interface
Note. Opto-isolators separate RS-232 circuits (SAFE) from ups ttl circuits (NOT SAFE, connected to MAINS).
Solving a "problem"
Initially it did'nt work. This is what I got.
Yellow is the rs232 (from pc to ups). Green is ttl (from pc to ups).
The cause is a capacitor. Two ways: (1) use a TTL/CMOS circuit instead of “pull-up” one. (2) remove that “worthless” cap. I preferred the latter.
