I’m planning out a hardware refresh, moving to the new emonPI2 with emonVS for a US (split-phase) deployment. With the emonPI needing to be collocated with my panel (as opposed to my existing emonBASE being in my server area), I’m considering a small UPS to provide some battery backup and avoiding data corruption should there be a power loss. I’m presuming that putting the emonVS behind the power supply is not a good idea, as the UPS would be providing filtered power.
Am I correct that there’s not a simple way of giving battery backup to an emonPI2 in this scenario?
In essence, you want to split the emonVS so that the power to the emonPi comes from the UPS, but the monitor is on the main supply?
What you need is a 5 V supply from the UPS and a couple of diodes feeding power to the emonPi, so that it operates on the higher of the emonVS’s 5 V or the UPS’s 5 V, or probably better, a mains-powered changeover relay to avoid the diode forward drop.
It is probably worth emailing ‘The Shop’, I know there were suggestions of something along these lines - maybe it was a voltage monitor only - but I think it was never progressed.
I highlighted a potential issue with putting the combined (sensing and powering) unit on a calibrator. A lot of calibrators have very limited drive capabilities on their voltage outputs. At the time it was suggested they might do variants of the emonVS that does one or the other function and you’d use one of each when calibrating. Not sure if anything came of that.
I’ve got enough unfinished projects! 
