I have a sprinkler timer in the garage that is both connected to ac and a 9v battery. The 9 volt battery fails a lot. It actually powers the memory of each sprinkler station and run times. When the 9v battery is too weak to power the memory , the entire sprinkler system shuts down and reboots but will not run. How do I rewire the memory unit so that it runs on ac instead. I have an old 9v power pack that puts out 9 volts and 450 mA. Can I safely just connect it to the 9v connectors on my sprinkler timer?
9V BATTERY SOURCE IN THE SYSTEM IS THE BACK UP POWER TO THE SYSTEM MEMORY WHILE AC POWER WAS INTERRUPTED ( LOST ALL AC POWER IN WHOLE HOUSE ) . THIS 9V BATTERY SHOULD NOT CONSUME POWER INTO SYSTEM WHILE AC POWER IS NORMAL. SOME BAD DESIGNED SYSTEM DOES DRAINING OUT THE 9V BATTERY SLOWLY BECAUSE 9V WAS CONNECTED DIRECTLY TO THE SYSTEM MAIN 9V POWER SOURCE COMING FROM AC CIRCUIT. TO SOLVE THIS TROUBLE IS QUITE SIMPLE, JUST ADDING A BLOCKING DIODE IN BETWEEN BATTERY +9V TERMINAL AND SYSTEM. THIS WAY, 9V BATTERY IS NO MORE DRAINING BY SYSTEM LOAD WHILE AC POWER IS ON , AND 9V BATTERY SHOULD LAST AS LONG AS ITS LIFE. NEVER REPLACE 9V BATTERY WITH ANOTHER 9V POWER SOURCE THAT COMING FROM ANOTHER 9V POWER ADAPTER, DO THAT CAUSING THE SYSTEM IS NO MORE ABLE TO RECOVER WHILE AC POWER IS INTERRUPTED BECAUSE BOTH 9V ARE FAILED.
Current drain from a keep alive battery should be minuscule. A good quality 9 volt battery should last a year or so in that kind of operation. Are you sure you are using a good quality battery?
If you have a well regulated 9V converter that converts 120 vac to 9 vdc, that should work fine. You could also get a battery charger with rechargeable 9 v battery, however this will actually exceed 9 vdc so you would need to make sure that your controller will work safely with the peak output of the battery charger with battery connected.
Possibly not safe, as it may produce as much as 12 volts when the memory unit uses only one or two milliamps. How about connecting an extra 9 volt battery in parallel, and change the 2 month old battery about once per month.
