I want to hardwire some 9v smoke detectors to a wall transformer and was wondering how my detectors i could run from a 12v / 1500mA supply and what kind of resistor(s) to reduce the voltage a bit or will
9v detectors take 12v ok.** Maybe about 25,000.
Average drain is about 40 uA.
More when the alarm goes off though.
** Probably.But use a resistor and 9.1 volt zener to be safe.
...... Phil
-- "Wall transformer"? None.
Maybe. Maybe not. If you want your smoke detector(s) to meet code, you may need to provide a backup power source. Mine use 9V batteries for backup. In addition, they may require some means of alerting the homeowner when the backup supply is depleted.
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ Big business never pays a nickel in taxes, according to Ralph Nader, who represents a big consumer organization that never pays a nickel in taxes. -- Dave Barry
Realize the current drain is non-constant, but is pulsed. That is the smoke detector sleeps about 99% of the time, and wakes up about 1% of the time. The current drain changes with the detector's mode. Also the current drain is *much* higher when in alarm mode.
If you want this to be safe you really should use detectors that are meant to be used either on line voltages, or hardwired to alarm systems, instead of kludging your own.
but if you must, I'd suggest a 9 volt regulator on the output of the
12volt wall wart would do the trick. You should also have a backup battery configured, which negates whatever advantage that the AC power might give you (are you trying to avoid changing batteries?)After all, many fires cause a loss of AC power (especially those that are electrical in origin) and that is not the time when you want your smoke detectors to go off-line!
Don't. You are tinkering with your fire insurance policy. Buy AC powered units and keep the battery units as well.
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