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I have a CO/Natural Gas meter that requires a backup battery to be able to function (without beeping), even if it is plugged in. I find that I am replacing batteries every couple of months (I have 4 in my house). I am wondering if I can use a wall wart for the 9v supply. I know that the 'backup in case of power failure' function would no longer be present, but that is not a concern of mine.

Better yet, can I hook up the 9v supply that comes with the unit (9v 400mA) to the 9v battery connector, so that the supplied 9v adaptor effectively runs both the unit's main power and it's backup? I have opened up the unit and the soldering would be incredibly easy.

Thanks in advance for any options that may be forthcoming.

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  • \$\begingroup\$ Please provide details of the "meter" (or do you mean "monitor"?). \$\endgroup\$ – Andy aka Nov 28 '16 at 15:18
  • \$\begingroup\$ This is the monitor: homedepot.ca/en/home/… \$\endgroup\$ – Fed Nov 28 '16 at 16:04
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Not knowing the circuit sensitivity to overvoltage and knowing wallwarts will be unregulated at 50% higher voltage with no load, 40% from rectified rms and 10% for DCR loss in transformer at full load, you can certainly choose your own appropriate supply if you understand the risk of overvoltage and need for reasonable regulation 10%.

Why do you have 4 gas meters? You mean Carbon Monoxide smoke alarms. How many hours of power loss per 2 month? You could run a 9 V LDO at each meter from a 12V SLA and feed from spare wires in telephone jack if only using 1 line. The monitors may need low ripple so measure both Dc and AC V to ensure proper performance with self test.

Another battery solution is 9 V Lithium which last 2-3 years or more from online sources. $10 approx. or use 3x CR123A Lithium in series @$1 each in bulk online.

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From rough analysis in comments I calc. 1.6mA drain on battery backup for 8 mos life being powered from internal AC-DC supply due to automated battery test, (guess) Lithium 9V , 3x to 5x capacity of Duracell depending on specs . avail at Lowe's $11. **I might consider 1k to 330R to internal 9V dc supply but measure to null current drain from battery over a period.*

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$ – Dave Tweed Nov 30 '16 at 14:10
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If the unit already comes with an AC power adapter then you should use that to power the unit via its normal connection point.

If your backup 9V batteries are failing every couple of months it would seem that you have rather unreliable AC mains power source. In this case the unit becomes non functional at loss of AC power if the backup battery is dead. If the problem is not a bad mains supply then it would seem that you should talk to the supplier instead and find out why their back up battery solution is not working so good.

If it is really the beeping that is the problem in the case of the backup battery being dead then trying to defeat that is a safety consideration. You can choose to disable the safety warning but a far more effective scheme to do that would be to put tape over the piezo device sound resonator hole.

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