I'm trying to make a backup power supply for a home WiFi router (12V, 0.5A) and observe that the relay release time for a QYT73 relay is around 1 second. That is enough for the router to reboot, which is undesirable.
When AC power switches off (power outage,) I expect the relay to instantly switch power to a battery (5msec. according to the relay datasheet,) but it takes approximately one second for the relay to release contacts, which is enough for the router to lose power and start rebooting.
I have a suspicion about the AC-DC adapter. It looks like it has some capacitance and after the AC is off it takes some time for the capacitor to unload, while the voltage drops enough to switch off the router before the relay coil releases the contacts.
Oddly enough, when the DC power source is back again, the relay switches to connect C-NO instantly, so the router doesn't recognize the switch and does not reboot.
Is there any way to make the voltage/current drop on the relay coil faster so the relay release time will come closer to the datasheet value of 5 milliseconds?
Circuit purpose and description
I'm using a QYT73 relay to switch between the main power source (AC-DC adapter output 12V 0.5A) and a 12V battery.
Relay Datasheet Values Coil Nominal Voltage - 12V Nominal Current - 30mA Coil Resistance 400Ω Operate time (8msec. Max) Release time (5msec. Max) Pick-Up Voltage (Coil Nominal Voltage 75%) - 9V Drop-Out Voltage (Coil Nominal Voltage 5%) - 0.6V
When a DC source is on, it also powers the relay coil and current to the load goes through (C->NO) contacts of the relay. When the DC source powers off, a relay should release contacts C->NO and switch to the power from a battery (C->NC.)