I recently bought a house with really nice hardwood floors, but the builder didn't put any thought into installing a humidifier system. I'm now looking into my options and steam humidifiers seem to be the highest output solution, albeit overkill. Unfortunately, the only power source I have available in the furnace room is on a 15A breaker shared with two bathrooms, but my tinkering instincts won't accept defeat so quickly.
I'm thinking that I could use a UPS with sufficient output power to support the 7A steam humidifier. The trick is that I would use a current switch to sense when the humidifier is on and subsequently turn off the power source to the UPS (with a relay) and when the humidifier is off the UPS will reconnect and start charging. My theory is that the no load charging current of a UPS is always lower than the maximum load current. Someone correct me if I'm wrong.
The question is:
How do I determine a UPS's charging current spec? If this is low enough to put on the 15A circuit then I'm good to go. If it's still too high then I have to accept defeat… unless someone has another clever solution. Given the construction of the building I cannot run a new 20A drop to this room.
Assumptions:
Yes, I know, this isn't what a UPS is meant for.. but that isn't a part of the question.
Also, I'll probably go through a set of batteries in a year and I'm OK with that.
Best Answer
No.
You definitely want to put the humidifier on its own circuit, or a circuit that is not shared with two powder/bath rooms. You could look for a convenience receptacle in the basement and determine if it's on the same circuit. If not, you can probably come out of that for the humidifier. If the humidifier pulls it's full 7A rating when it starts, you probably want to avoid having it share a lighting circuit, as the lights could dim when it turns on. That can cause premature wear on ballasts and greatly reduce the life of any incandescent lamps you might have in use. Take care to know exactly what else is on any circuit you find in the neighborhood.
NEC requires wiring devices, such as the relays you're talking about to be listed and approved. Assembling something to cut the power to the UPS when the humidifier kicks in using all listed and approved parts does not constitute a listed and approved device. Your approach, while very creative gets a little too far into the "Rube Goldberg" brand of tinkering.
My advice is, have an electrician install a single use receptacle for the humidifier on its own 15A circuit, even if that's slightly overkill. If your panel will not accommodate this, and tandem breakers aren't a possibility, then consider increasing the size of your panel and / or service.
Two bathrooms on a single 15A circuit is problematic enough, it sounds like you need to bite the bullet and get a few additional circuits where they're needed.