I would like to be able to operate my 2004 Lennox G61MPV furnace using a 1200W, 12V DC to 110V AC power inverter. The blower works just fine, but as soon as it tries to ignite, the furnace shuts down. I suspect it may be a question of proper grounding--the furnace may be very sensitive to this. (The G61MPV uses a DC blower motor.) Any help?

You are likely right on the grounding. I have seen many posts on furnaces not running on generators, and I think the problem is the ground. Do you have a good 3 wire connection between the furnace and inverter, hot, neutral, and ground? Does where the power from the inverter goes into the furnace have the ground wire properly connected to the furnace frame? A 1200 watt inverter should able to keep the voltage high enough. I think my furnace only draws about 600 watts.

I was very gratified when my furnace fired right up when I tested it with my generator. When I installed the furnace, I was careful to connect the equipment ground from the house. The generator has a proper UL approved interlock and 4 wire connection to the main electrical panel.

labman:
Thanks for your encouraging response--ie, that your generator does successfully operate your furnace, that 1200 W should be enough, and that grounding is important. Unfortunately, my inverter is out on loan, so I can't check this out further right now. But as I have thought about it before, I'm not sure how the ground would work with just the two leads from the battery. Inside the inverter, what should be grounded and what would it mean?--like, what should be grounded to what or where. There is no "earth" ground when using a battery. I did try an alligator clip-lead from the inverter to the furnace frame, with no success. (I had disconnected the 110 volt power input so as not to feed voltage back into the house line.) So, if you have thoughts about how to make a proper ground using this (battery) approach, I would be most interested.

This gets into technical code areas. Apparently furnaces need the ground and neutral connected. In a properly installed furnace, the ground and neutral run back to the main panel where the neutral bar and equipment bar are bonded. Mine actually goes to a sub panel where the neutral and ground aren't bonded, but are connected to ones in the main panel that appear to be the same stamping. When I plug in my generator with its 4 wire plug, its ground and neutral aren't bonded, but both do connect to the ones main panel.

I think your furnace would run if you connected one inverter lead to the furnace neutral and ground, and the other to the hot. It might conform to code if instead you connected any metal housing or the heat sink to the ground bar of your panel and the neutral lead to the neutral bar. Make sure the furnace hot can't be connected to both the house and inverter. Avoiding back feeding is a critical issue with generators.

labman:

Good thought. I did not tie neutral to ground. When I retrieve my inverter, I'll give it a try. Thanks. Jp