Problem
Avid readers will recall a previous post My Mains Monitor, which described a simple circuit designed and built to alert us to mains power failures.
Every so often, the mains power circuit breaker in the van trips for no apparent reason. Sometimes, it even trips for a good reason (air-conditioner + hair dryer + microwave oven + etc. >15 amps). Keeping an absorption fridge at temperature in very hot weather can be challenging. We went to bed one night expecting the relative cool overnight to help get the fridge temp down to something reasonable but woke the next morning to find that the van and hence the fridge had lost mains power sometime during the night.
You may also recall a number of limitations of that design:
- If you leave the monitor turned on when travelling, it flashes and buzzes continuously. If you turn it off but forget to turn it on when you are next connect to mains power, it is a waste of space.
- Depending on the internals of the AC-DC adapter you use, there may be a delay before loss of mains is indicated by the monitor (mine takes about 30 seconds).
- When the input signal is not present, LED1 may be dimly lit.
Needless to say, My Mains Monitor 2.0 solves all of these problems.
- It alerts us to the loss of mains rather than the absence of mains. Whilst the lights indicate the presence or absence of mains, the audible alarm is triggered when previously present mains power becomes absent and can be muted by pushing a button. The mute is then disabled the next time that mains is present so that the next loss of mains will again trigger the alarm.
- The delay before loss of mains is indicated by the monitor is reduced to 2-3 seconds.
- There are no erroneous glimmering LEDs.