Need advice to control power to a device with a relay.
Am making a system that allows me to reset a remote CCTV DVR device using a GSM receiver.
The GSM receiver is working perfectly, but I am having a problem with the control relay.
The relay is used to maintain the mains line ( 220V ) to the CCTV system with the 220V Live wire through the ‘Com’ and ‘NC’ contacts. So under normal conditions the power is supplied to the device.
When the GSM receives a signal, it pulses the relay for 10 seconds. This cuts power to the DVR and 10 seconds later the relay is ‘off’ and the DVR boots up again.
My initial test involved controlling the mains line to the complete CCTV system, but the relay kept failing - dissected the failed relay and the ‘Com’ and ‘NC’ contacts are ‘pitted’ so I assume they are welding themselves together as a result of an arc.
Then discovered that the line is actually for the DVR itself AND all the cameras. Powers each of 3 transformers ( 220V 1.5A converting to 12VDC 5A ) and only 1 required for the actual DVR itself.
So next step is to replace the relay, and use it to power only the DVR power.
But which side of the transformer is best to control to cause the least damage to the relay ? The 220VAC or the 12VDC ?
The relay is marked :
10A/28V = ( DC symbol )
coil symbol 12V = ( DC symbol )