Generator/Furnace question - House HVAC

[vartz04]

So I got this generator brand new in box in some horse trading. its a champion 2000 Watt peak 1600 Watt continuous inverter generator (like the honda's)

http://www.cabelas.com/product/Watt...=GoogleProductAds&WT.z_mc_id1=03137796&rid=20

Anywho I figured it be good to keep around instead of selling off. One of the things I would like it to do is power my gas furnace (lennox G40UH series) so i wired a single outlet and a pigtail with a cord coming out of the furnace so I can just unplug the furnace and plug an extension cord from the generator to the furnace

So I tried it out so I wasn't messing with it during a power outage. Won't work. Furnace comes on, vent blower starts up, glow ignighter starts, gas valve opens and flame starts to go across all burners, about 1 second later the flame cuts out and i get a flashing code meaning one of 2 things - improper ground or line voltage below 90 volts.

I tried doing it with a bonded neutral/ground and without it being bonded (generator is not bonded) It does the same thing either way. The generator lugs a bit when the blower motor kicks on. Is that quick lugging what is the problem? I have a UPS and I might try plugging the generator into that and then the furnace into the UPS to see if that can pick up the slack when the generator lugs. Its an inverter generator so the dirty power thing shouldn't be an issue.

Any ideas?

 

[domain]

Have you measured the voltage?

 

[vartz04]

yep coming out of the generator is a nearly rock solid 123V it drops slightly when the furnace kicks but i tried it a bunch of times and it was never less than 90 V on my meter.

 

[dfiler2]

It sounds to me like the furnace is sensing the generator is not grounded. Also did you make sure the polarity is correct on the cord you made. You said you unplugged the furnace, is the furnace really just plugged into an outlet? If not be sure you are not back feeding power into the rest of your electrical system.

 

[vartz04]

Yes it's plugged into an outlet. It's hooked up that way so I could use a generator to power it. It works fine when plugged into the outlet on the furnaces dedicated circuit. I didn't make a special cord I just made a plug end that jumpers the ground and neutral so they are bonded at the generator. It's plugged into the empty outlet on the generator and I verified with a meter that the neutral and ground are bonded.

 

[dfiler2]

I'm pretty sure the furnace won't like the ground and neutral being connected at the generator. What I would try if possible is to place the generator near the ground rod for the home then use some jumper cables to connect the frame of the generator to the ground rod.

 

[kd3pc]

You need to the read the manual...I don't think it is correct to jumper the neutral and the ground in the cord.

The new inverter generators are a special beast and do play well with "grounds"...the manual usually gives you info on how to fake the ground, or where to remove a jumper internal to the generator, so that it does not see or sense a "ground fault"

 

[Rookie2]

Try it on a larger generator. spec sheet said G40UH uses less than 12amps. (1440 watts)

 

[vartz04]

so you guys are thinking its a not enough juice issue and not the ground issue?

 

[theoldwizard1]

I tried doing it with a bonded neutral/ground and without it being bonded (generator is not bonded) It does the same thing either way.

A lot of furnaces will not start at all with unbonded portable generators.

The generator lugs a bit when the blower motor kicks on. Is that quick lugging what is the problem?

My guess is, yes.

I have a UPS and I might try plugging the generator into that and then the furnace into the UPS to see if that can pick up the slack when the generator lugs.

It had better a "good" sine-wave UPS, but yes, that is worth a shot. Be careful as most UPS are rated in "VA" not watts and yes they are different.

 

[vartz04]

is there any way to bypass that shut down or delay it on a furnace? would a newer blower motor use less startup current? I don't want to drop a ton of money making this work as our power rarely goes out but with a new baby on the way here in the next month or so it be nice to know I have the option.

I like the idea of using this generator as my wife can start it. its super light, and super quiet (53dB) and runs 6-8 hours on a gallon of gas. Ill likely keep it either way as it runs our fridge no problem. I could always buy another ($500 ish) down the road and they sell a kit to parallel them so you get double the power.

 

[theoldwizard1]

I'm pretty sure the furnace won't like the ground and neutral being connected at the generator.

You need to the read the manual...I don't think it is correct to jumper the neutral and the ground in the cord.

This IS correct for an unbonded generator assuming that the furnace is NOT picking up "ground" from somewhere else (not likely). Of course this does mean, that the generator ground should be connected to a proper "earth ground".

With the furnace plugged into the generator and the generator turned OFF, but properly bonded, check the resistance inside the furnace between neutral and ground. It should be close to zero ohms.

 

[vartz04]

not even sure where the ground wire goes in this furnace. It doesn't have a ground wire connected (older house with just 2 leads ran to each outlet/the furnace. There are no ground wires running to anything except what I have added when working on the house/the garage. Every time I work in a room I add one.

should there be a separate wire or a terminal the ground would connect to within the furnace? I guess I need to get the exact model number and find a wiring diagram now.

 

[theoldwizard1]

is there any way to bypass that shut down or delay it on a furnace? would a newer blower motor use less startup current?

The low voltage sense is effectively "instantaneous". I know of no simple (inexpensive) way of making a motor draw less startup current.


In THEORY, you could increase the generators surge capacity. The generator creates a 3 phase AC, variable frequency, high voltage that is immediately turned into high voltage DC. This DC is then turned into 60 Hz 120V AC ("inverted"). There are some coils and capacitors between the DC and final AC stage to help deal with surges. In THEORY, increasing these would give you better surge "ride through".

 

[theoldwizard1]

not even sure where the ground wire goes in this furnace. It doesn't have a ground wire connected (older house with just 2 leads ran to each outlet/the furnace.

Hmmm ... Very odd !
Unless this is a VERY old furnace, it will have an electronic control board that usually will REQUIRE a ground that IS bonded to the neutral !

 

[danski0224]

Something is wrong with the grounding in your configuration.

The furnace will have a ground wire in the electrical connection box. Your generator probably has a grounding lug on it. I'd try connecting the two points. Check with a meter before actually using wire to make sure there is no line voltage present.

Hot and neutral could also be reversed.

The furnace needs to sense ground in order to work properly. If it is still connected to the house panel ground, that may be throwing it for a loop.

This is worth what you paid for it, a service call to fix a fried board could be in your future

 

[vartz04]

Its a furnace with a control board.

about 6 months ago i swapped the hardwired configuration to a plug/outlet configuration (this is how the furnace was installed in my parents house down the road when the house was built about 10 years ago.) this would allow me to plug in the furnace to a generator (same reason my dad had his installed that way) when I took the hardwiring out from the furnace there were only two wires running to it. (neutral and Hot) there are some wires running along the gas line going to the furnace so maybe one of those is connected to the ground. All of this makes sense then because that would mean the ground is there and still connected and its confusing the furnace because the power and ground are not coming from the same place.

 

[dogdog]

just wondering what kind of wave form these inverter generators produce.... I had the 1200 Watt cheap inverter that ran off the battery won't even start up my smaller fridge... and looks like it's a horrible square / saw tooth wave when I put it under the oscilloscope. even thought it says 60Hz and 120 ish volt under the volt meter.

 

[vartz04]

the literature that comes with it says it has a true sine wave
http://www.championpowerequipment.com/media/2350/sine_wave_white_paper.pdf

which explains why this generator sells for between $500-$600 and a non inverter 2000 watt generator is $150-$200.

 

[theoldwizard1]

all of this makes sense then because that would mean the ground is there and still connected and its confusing the furnace because the power and ground are not coming from the same place.

ding ding ding !

 

[brewchief]

There will be a ground connection in the small box on the side where the wires enter the furnace. The furnace is probably picking up a ground through the ductwork, gasline or even just from sitting on concrete.

Some newer furnaces will even have issues with some of the cheaper whole house generators.

 

[vartz04]

So whenever the ancient furnace that was replaced before I bought it someone ran a ground along the natural gas line to meet code instead of running a new set of wiring from the box to the furnace with the ground wire in it? Makes sense but seems like a half assed way to do it.

So likely if I ran a 10-12 gauge wire from the ground lug on the generator and connected it to the ground wire going into the furnace it would work fine.

My dads furnace is newer than mine (probably by 15 years) and runs fine on his non inverter generator. oh well. my house is only 1000 SF + Basement. If the power is out for too long a small space heater + fireplace will be enough

 

[dogdog]

easy to test right ? borrow your dad's generator and hook up to yours the same way to see if it is grounding issue or generator under power issue?

 

[vartz04]

yep Ill have to give that a shot this weekend.

 

[John3603]

Did you ever get your generator to work? I have a new lennox that was doing same. I have not tried grounding gen set yet. But wondering how you made out? Thanks