Inverters and AC motors

It should.

furnace blowers are just plain capacitor run induction motors, with no crazy starting coils, so there's not a need for a hugely oversized inverter.

You will need to dream up some switchover scheme that still meets code. And those AGM batteries are not to compact. But they are good exercise to move around.

From a project for a battery based APU, the Odyssey batteries turned out to be best. They were jammed with 100Amps and charged just fine, but don't try that at home. I really wish I could put one in my car but AGM is finicky about charging voltage and my regulator runs kind of high.

standard

You might not even need a pure sine wave. I was able to run a 1/2 to 3/4 HP pump motor on a 2000W Harbor Freight "modified sine wave" inverter that cost only about $100. I was also able to run a 2 HP three phase motor using a

You might even consider a bank of 20-30 smaller 12V batteries in series to get the DC link voltage directly. I bought some 12V 12Ah SLAs on eBay for a little over $22 each, so for about $500 you can have 3.6 kWh capacity which should run a 1/4 HP (200W) furnace fan for about 12-15 hours total. Of course, you can also get 12V 100Ah flooded lead batteries for less than $100 each.

Paul

I don't know how much power mine takes, but it must have 16 wires going to the variable speed motor. Also makes a lot of RFI. I don't see me using an inverter but who knows.

Just got to hooking up my solar panels.

Greg

furnaces have overly complex micro controlled nonsense in them these days, so not blowing out the electronics might be a consideration, over the older furnaces with a relay, gas valve and thermocouple wired to a thermostat.

OP has a complex sounding motor too- are they no longer using one or two speed fan motors?

My thoughts on switch over is very very simple, manual switch over.

Re-wire the furnace romex with a three prong plug/outlet.

Plug the furnace into the three prong outlet.

When the power goes out, un-plug the furnace for Public Service and plug into the inverter.

I will look at Odyssey.

Thanks

hamilton

I once tried running a simple house fan on a modified sine way. Apart from a buzzing noise, it seemed OK, until the smell indicated that it was overheating. Presumably it didn't like the higher harmonic currents that were flowing.

The message here being that the first indication you get that running with a modified sine way isn't a good idea may be that the motor stops - permanently.

Sylvia.

Thank You Sylvia,

This is the kind of information I am looking for.

hamilton

house.

Just the same it has to be motor rated. It has to be robust enough to handle a couple of seconds of 10X rated current. Cap run does not fix that.

?-)

to

an

Sounds like a poorly implemented variable frequency drive.

?-)

I just checked the current on my furnace with variable speed motor. The motor uses a whole bunch of wires with switching control. Not much current for exhaust and ignitors. Ramps slowly up to just under 3 amps 120 vac. Im not sure if it increases a bit if it goes into full btu mode. It's also a dual 50k 70k btu burner. Yes, I'm hooking my solar system, 6 panel harbor freight and just got a 1kw sine inverter. I have not hooked everything up, but I was impressed on 3 panels delivering current on a cloudy day. I'll be taking more measurements. I didn't intend on using the inverter on furnace, but looks promising. Still got 3 gas generators. 1kw, 3.5 kw, 5kw .

Greg

house.

flowing.

no

current

Im

Maybe you have a high grade furnace with a VFD. How old is it? If it is more than 10 years old VFD is very unlikely. Two or three speed can be done with multiple windings with different pole counts (ceiling fans).

looks

they're just boring fan motors, no starting coils and they're not even all that powerful, so the inrush current won't be all that exciting. If I get bored this weekend I'll take some current readings off one (entire blower assembly from a furnace.)

I've been musing over the problem of lack of heat for so many homes in the aftermath of Hurricane Sandy.

It seems almost a trivial problem to make a natural-gas-powered blower, then furnaces work even when electricity is lost. ...Jim Thompson

But not thermostats or water pumps or lights. I've been considering a natural gas powered standby generator for some time, but our lights usually go back on within a day, which makes such a beast a very expensive luxury. Cool though.

Cheers

Phil Hobbs

Once upon a time, ~1970, it was actually cheaper, in Arizona, to run a gasoline powered VW engine driving a generator, than to buy electricity from Arizona Public Service. One of my technicians did just that for a cabin too far from distribution.

And we ran all the costs including maintenance. ...Jim Thompson

house.

It's 6 years old. Goodman.

Greg

I've known a couple of people who did this:

One was basically enough to run the 'fridge, freezer, and a few lights. It was an otherwise stock gasoline generator. In both cases, an inspection was done by a licensed plumber ( always a great idea when messing with natural gas ).

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Iff you can recover the waste heat from a natural gas powered generator and use that for space heating, the efficiency gets crazy good. Trick would be to level out the electrical demand with some form of battery storage and conversion.