Furnace on inverter.

[BradHend]

Hi folks. 
I’ve been experimenting with the MoHo in the driveway this weekend just to see what I can get out my batteries should I ever find myself needing to camp without power.  
Seems everything works fine with the exception of the furnace.  
Plugged into shore power or on generator -  furnace works fine.  Once on inverter power, furnace acts fine except the flame goes out a second or two after igniting, tries again after a set time and repeats the process over and over.  Again, only on inverter power.  
Would you say this is an inverter issue, a battery issue, or something else?

Thanks,

[Dr4Film]

Your furnace should be 12VDC whereas your Inverter provides 120 VAC power. Barking up the wrong tree.

[BradHend]

Correct, but I suppose i was more pointing out that if the inverter is on which is using the battery…could my batteries be too weak to use the furnace.  If plugged in, batteries are charging and then the furnace is fine. 

[Ivan K]

Any kind of valve at the propane tank that is not powered in that situation? Still weird as it would effect the stove burners also.

[BradHend]

Ivan, It has the solenoid switch, works fine, looks like a newer regulator and the stove works just fine all the time.  I don’t believe it’s a propane supply issue.
Been trying to chase this one down for some time now, just not sure which route to take in determining the problem. 
Thanks!

[Dwight Lindsey]

Brad:

I'd bet flame sensor.  When that happened to me I opened the access panel and removed and replaced all the spade connectors, cleaning the connections.  For me it was the spade connector to the flame sensor that was dirty

[BradHend]

Thanks Dwight, I’ll have a look into that this week!

[Ivan K]

Does it fire at least for a second to give the flame detector a chance to feel it? I don't have a propane heater anymore but think that's how it worked with our old one?

[cbr046]

If no shore, generator or inverter power does the flame still go out?  Should run all night on 12V power. 

- bob

[Harvey Babb]

I concur that the flame sensor is what's failing, but that still leaves a lot of ground to cover. My first suspect would be reduced blower flow due to low 12 volt DC causing an already marginal flame to fail to cover the flame sensor rod.  A easy check is to remove and inspect the burner. I have seen the burner diffuser screen block with rust and have also seen screens rust through leaving holes that make the flame miss the sensor. 

Checking connectors in the blower motor circuit would also be a good idea.

 

[BradHend]

Seems in only happens specifically while not hooked up to shore power and not running on generator power.  This is only happening when the inverter is on.  I realize the furnace runs on 12VDC, but there just seems to be a relation there and I’m not sure which way to go.  Appreciate the feedback!

[Dwight Lindsey]

Besides checking the flame sensor and blower motor circuit as Harvey suggested, you might check the battery voltage when you're having this issue.  If the 12v DC voltage is lower when not on shore power and if you're losing some voltage due to dirty connections, that might explain it.

If you've not personally replaced the batteries, it would be good to know how old they are and how well they've been treated.  Multiple cycles of complete discharge can damage batteries.

Dwight

[Tom Wallis]

2 hours ago, Dwight Lindsey said:

Besides checking the flame sensor and blower motor circuit as Harvey suggested, you might check the battery voltage when you're having this issue.  If the 12v DC voltage is lower when not on shore power and if you're losing some voltage due to dirty connections, that might explain it.

If you've not personally replaced the batteries, it would be good to know how old they are and how well they've been treated.  Multiple cycles of complete discharge can damage batteries.

Dwight

I agree with Dwight. I'm thinking it's a low voltage issue. Turning on the inverter might drop the voltage just enough to cause the problem.

[Dr4Film]

Dwight & Tom are spot on.

What's happening is when you switch to Inverter power the voltage draw-down on the house batteries is putting a strain on them reducing the voltage such that your furnace driven by 12 VDC cannot operate correctly.

When hooked to shore power or generator power the charger is putting out enough 12 VDC to keep everything "happy".

Install a fresh set of house batteries and your problem will most likely disappear.

[cbr046]

2 hours ago, Dr4Film said:

What's happening is when you switch to Inverter power the voltage draw-down on the house batteries is putting a strain on them reducing the voltage such that your furnace driven by 12 VDC cannot operate correctly.

My old gasser furnace (Suburban) would run down to 8-9 volts by morning.  Made for some nice quiet running, too.  I got every coulomb out of those batts before replacing them.  The HR furnace is an Atwood, but doubt that makes any difference. 

But still . . . . it would be prudent to put a meter on the board while the furnace is running.  Pick a place off the board (power and ground), so that connectors to the board are also tested.

- bob

[pulsarjab]

I have had several incidents of furnace not working properly. Each time, cleaning all of the spade connectors cured the issue, including the one you are describing.

Greg

2000 Diplomat

[Chuck B 2004 Windsor]

Is your inverter a pure sine wave or a modified sine wave inverter?  

[BradHend]

57 minutes ago, Chuck B 2004 Windsor said:

Is your inverter a pure sine wave or a modified sine wave inverter?  

Modified. Xantrex Freedom 458 Series

[Chuck B 2004 Windsor]

You will find that some devices will run OK on a modified sine wave inverter and others will struggle or not run at all.

[JohnC3]

Just a suggested diagnostic. While on batteries, turn off the inverter and see if the furnace will run normally. Since this is easy and free, you can verify the issue is voltage related if it runs w/o inverter pulling on the batteries. You should be able to turn off your inverter either at the inverter or the main fuse box (or sub panel if you have it).

Poor connections (i.e. dirty spade connectors) can cause voltage drop that seems reasonable. 

My suspicions are (in no order)

1) Inverter is drawing battery voltage down to a level where your flame sensor (or your control board) are not working well.

2) Dirty contacts on flame sensor circuit as mentions a few posts above. Could also be the blower that moves the heat, if the fan is not running normally, it might cause a flame detect failure.  Wondering if this fan has a start capacitor like AC fans... just a thought.

3) Batteries are getting too weak. (check that they are charging well and are fully charged (don't want to replace batteries if its the chargers fault)

 

FYI, I am not a pro, just skilled at going from symptoms to possible causes.

Good luck,

John 

[BradHend]

Appreciate the input, everyone!  I will look further into it this week and report back with any findings.  
Thanks again!