I have inverter at my home which always restart my desktop computer when the electricity goes down. What is the solution of this problem? How can I convert my inverter into ups?
Either the switchover time of your UPS is too high or the hold time of your computer power supply is too low.
If your inverter allows battery charging then leave it connected to the AC socket (ON) and the connect your PC through the Inverter output. In an event of power failure, provided that your battery has sufficiently charge, your PC will not experience any downtime because now you have make your UPS and ONLINE UPS which means it is always ON.
You probably charge your battery separately or your Inverter relays might need some replacement.
hasanevanof: As pointed out by Asad, the problem is that of the "transfer time" (aka "switchover time"). As far as I know, many devices that are sold as "inverters" are not suitable for use with computers because of high transfer time. Please check the specification sheet of your device.
Also note that the term UPS is used for a device that comprises of these three basic components: i) battery, ii) charger, and iii) inverter. So your question should be how to decrease the transfer time on your so-called inverter. I could be wrong, but I guess that you will have to make significant changes in the device circuitry which is not for an option for the most of us -- unless you are into electronics.
I heard there is a computer kit available that can be used in desi ups so they won't restart.