Progressive EMS-HW50C unit

ktmrfs wrote:
However, I suspect the EMS design was more aimed at line power, which usually is "stiffer" than a generator, and when it falls below 104V it stays below for a fairly long time, long enough for the electroncs to detect it. But most generators aren't anything close to the "ideal voltage source" like the power line, and don't have the line regulation power lines have so voltage can swing rapidly.

Here are a couple of videos I shot several years ago that clearly support what you're saying. In the first video where I'm using my Honda EU2000i to power up a Coleman Mach 3+ 13.5K BTU A/C input source voltage supplied by the genset momentarily drops to just 58 vac ... compare that to the second test in which source power was a standard 15 amp drop in my workshop, with a momentary voltage drop to 105 vac. Yes, this genset's rated continuous output of 13.3 amp @ 120 vac is slightly less than the landline feed that's nominally rated for 15 amps @ 120 vac but that small a difference isn't enough to explain the vast difference in voltage drop when the A/C's compressor first ramps up to speed. These were the days before I even owned a surge protector of any kind ... later when I repeated these tests with my current EU2000i and Dometic Brisk II 13.5K BTU A/C, with my Progressive Industries EMS-HW30C in the circuit, it would chatter like crazy when the A/C's compressor attempted to start. Since I had hardwired my EMS into the trailer using 30 amp connectors I simply removed it entirely, repeated the test, and the A/C started right up, no issues at all. All this may point to why Progressive says their EMS units are designed to protect recreational vehicle electrical systems when plugged into a conventional campground power sources. Unfortunately the OP has yet confirm if the source they were using at the time was a conventional campground source OR a generator but if it was a generator I wouldn't be at all surprised their EMS chattered in protest.