If the wall wart is a switcher (most newer wall warts will be
switchers), I would expect it to "try" to keep the voltage up in a
brown out situation, until it could not, at which point what it
did would be based on the design of the wall wart.
If the wall wart is just a plain rectifying wall wart (no regulation), I would expect its output to be proportional to the line voltage (i.e., if line voltage is a nominal 120VAC, and the brown out is a nominal 60VAC, then the output would be roughly 50% of the line voltage.
In either case, I think (I don't know, Forrest is the authority here), the load provided by the sense on the SiteMonitor has got to be very low. The voltage held would be somewhat dependent on the filter capacitor (or lack thereof) on the output of the wall wart.
To make it a clean go/no-go indication, maybe using a relay to power the sense using a relay that requires some known level of line voltage to maintain a "power on" sense would be indicated. Say have a relay that opened the circuit when line voltage goes to 100 VAC or less?
bp
<part15sbs{at}gmail{dot}com>
Apologies in advance for the lengthy explanation, but hoping the hivemind can help explain what might be happening here:We use packetflux sitemonitors to monitor utility power status and battery voltage at many sites. Pwr1 is wired into a 12V wall wart power supply plugged into utility power. Pwr2 is wired to batteries of UPS. Pwr1 typically reads ~12V if the power is on and 0 when utility power is lost and we know we are running on batteries. The other day is started reading 8V so we new something was not right with utility power. The battery voltage started falling, confirming utility power issue, so a tech went to the site and plugged in a generator. As soon as the generator was plugged in Pwr1 went back up to 12V (even though utility power was still funked). A meter on the AC confirmed only 60VAC. Ever since then Pwr1 (AC) has followed the same readings as Pwr2 - nearly 12V when the generator is running but once the generator quits the voltage reading of Pwr1 drops and starts descending as the batteries discharge. Attached is a screen shot of our monitoring of these events. Had the tech unplug the wall wart and Pwr1 went to 0V. I thought Pwr1 and Pwr2 were isolated from each other and not sure why Pwr1 would start acting this way? Thanks in advance for any thoughts. -Rob
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