Forrest - thank you for the explanation! -Rob
On Wed, Jan 20, 2021 at 7:35 PM Forrest Christian (List Account) < [email protected]> wrote: > The explanation of what I think is going on is a bit hard to describe: > > The base unit draws power from the highest voltage supply attached to the > device using diodes to select between them. Where two supplies are roughly > the same voltage it is sort of random which it considers the highest > voltage since there are some diode tolerances involved - and if they are > really close there is a possibility that it will pull from both. > > When your power source failed, the wall wart was still most likely > providing intermittent bursts of 12V, which the base unit was trying to use > 100%, which would force the wall wart to drop power since it didn't really > have much power available. I'm guessing if you had connected something > like an oscilloscope to the wall wart input you would have seen voltages > alternating between some low voltage and 12V fairly rapidly. The > sitemonitor averages this long enough that you probably were seeing 8V > because that was the average. Or stated differently: The wall wart would > put out 12V, the base unit would try to use that since it was higher than > your battery voltage, which would cause the wall wart to fail because it > didn't have adequate input voltage, which would cause the base unit to > switch back to the battery which would cause the wall wart to produce 12V > again, which the base unit would use again, and the cycle would repeat, > with an average voltage of ~8V. > > I'm guessing what is going on now is that the same thing is going on > except that for whatever reason the wall wart is not dropping down below > 12V like it was. Another mode that a wall wart with insufficient power > can get into is that it raises it's voltage to just at the point that it > provides some of the power to the sitemonitor and the battery provides the > rest. If it tries to provide more, the sitemonitor will pull more power > from it, causing the voltage to drop. So at this point, it seems like the > wall-wart has switched to this 'tracking' mode for some reason - maybe > there's a bit more or less power. > > I guess the executive summary would be that what you're seeing isn't 100% > unexpected in the case where the wall-wart isn't being powered correctly > but hasn't completely lost power. > > On Wed, Jan 20, 2021 at 7:34 PM Rob Genovesi <[email protected]> > wrote: > >> 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 >> -- >> AF mailing list >> [email protected] >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> > > > -- > - Forrest > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >
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