Hey GregBrew, is this pretty much the kit you designed and built yourself?
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Further information on my setup.
I tied the negative cable of my inverter under-hood connector to the same location that the vehicle battery negative terminal is attached to. The vehicle battery negative cable goes through a toroidal current sensor, then to the grounding stud. The inverter under-hood connector negative cable does not go through the current sensor. The grounding stud is on the drivers side wheel well, and as such is a PITA to get to, but I struggled and was successful. I highly recommend being very careful about dropping anything (like tools) when you're elbow deep under the hood. I didn't drop anything, but I'm uncertain if it would be retrievable if I did. There are also several sharp metal surfaces in there. I have multiple superficial cuts on my hands to prove it.
I modified the procedure a bit. I've chosen to shift the Bolt into "L" before exiting from the passenger side, instead of "N". I'm doing this because the Bolt will hold its position when in "L", and it won't while in "N". I don't know if there's any power use difference between the two. (If any of you know, please speak up.) Of course, the Bolt has the parking brake set in either case.
I hooked up a 1500W pure sine-wave inverter, and plugged in a (heat shrink type) heat gun as a load. The heat gun has two settings: 900W and 1200W. Note that these are both on the load side of the inverter, so the vehicle draw is probably closer to approximately 1100W and 1500W, considering conversion efficiencies. Unfortunately, I don't own a DC clamp-on current meter.
Load current was provided by a Watt's Up meter.
At 1200W AC load, the vehicle DC-DC couldn't keep up, and the aux battery voltage dropped slowly.
At 900W AC load, the battery voltage cycled between 13.66V and 13.88V, measured with a reliable multimeter. I suspect that these values represent the hysteresis of the DC-DC to AGM battery system..."on" when the battery drops below 13.66, and "off" when it gets to 13.88. The cycling rate was probably every 5-10 seconds. That's a lot of cycles, but the cycle rate with a realistic load should be much slower.
I'm going to let it run with the 900W AC load for a couple of hours to verify that the system functions as expected. Using a gun-type IR temperature meter, I checked connection temperatures at the studs where the inverter cable is connected to the battery and grounding stud, as well as everywhere else, and am seeing no temperature rise beyond ambient. Surprising, when you consider I'm drawing around 100A through them all.
FYI. When I tried tying the ground lead elsewhere than the designated stud, I first-degree burned my fingers testing for temperature rise. Stupid!