So here’s the scenario. A client calls, and says he purchased a Samlex 1500 Watt SW Inverter ($314) for his propane water heater (electronic ignition, powered exhaust).
The water heater will not fire up, but neither does it trip any overload indications. Battery voltage at the inverter terminals is 12.6v during “ignition” attempt. The unit does work on grid.
With some research, it’s found that some of these water heaters require a bonded neutral / ground on the AC. This is a no-no with cheap MSW inverters (lets the magic smoke out), but usually ok with a quality unit like the Samlex. However (don’t you hate that word?), this Samlex came with a GFCI outlet. Other versions of this inverter are designed for hard wiring. GFCI is designed to prevent a leakage of current to ground by tripping of the circuit.
There are two solutions. The first is a warranty voider. Replace the outlet with a non-GFCI, or hardwire to the GFCI input (some GFCI outlets you can just move the line wires to the load pins, bypassing the GFCI functionality).
The second, more reasonable approach (though more costly), is to add a 1:1 isolation transformer to the output of the inverter (plug it into the GFCI), and feed the secondary to the water heater, bonding the ground and neutral wires. This trick will work with the cheap inverters as well.
There you go, a simple solution to a perplexing problem.