I'm using a desktop computer over a power inverter that's connected to a 12V lead acid battery. When the main power supply fails, the inverter switches to battery backup and can power my desktop for 4-6 hours. However, during the transition, my desktop shuts down (the transition time from mains to backup is too large for the desktop).
Is there a circuit / device that'll power the desktop for a few 100 milliseconds till the inverter backup takes over (something like a big capacitor).
An alternative is to connect the desktop to a UPS but that'll cost another $70-$100. I'm wondering if there's a cheaper option at a fraction of that.
Some inverters have a "UPS mode" that has a faster switchover time. The downside of this mode is that the operating input voltage range is narrowed i.e. the inverter switches to backup if voltage is outside a narrow range. This isn't a great solution when power quality is low.