Power Consumption Furnace Question

[DD716TED]

I have a 27 ft Travel Trailer. It has a Progressive Industries 30 Amp EMS system installed (hard wired). This past weekend we were camping at a campground that had pedestal 30 Amp power. We noticed that when the Suburban furnace came on, the lights might dim a little.. I watched the EMS display and with no furnace on, the display showed 2 amps which I attributed to the refrigerator. BUT when the furnace came on, the display showed 8 amps.. Isn't the furnace a 12 VDC item? why would the EMS show 8 amps which is measured on the AC input? Should the converter draw that much? My first thought is poor park pedestal 30 Amp power or 12 v Batteries are failing.. Never noticed this before.. Ideas??

[MEXICOWANDERER]

One of the weaknesses of garbage engineering and manufacturing.

An 8 amp rated German brushless dual ball bearing squirrel cage fans would bulge the walls.

But another weakness is central distribution with a single fan is hopeless. I have four 5" fans that are positioned high.

My suggestion is this. Buy an inexpensive pistol type thermocouple laser pointer. Start doing audits of temperatures on floor, ceiling, around doors and windows. Pay attention to true exhaust fans and vents. Chances are great you'll be in for some surprises. Check underbay air corridors when they exist.

Each weak area may not be entreme but totalled up be a whopper of BTU loss

[DrewE]

A normal RV furnace is a 12V (and propane) powered device. You should not see a 6A increase in the 120V power supply from using the furnace.

There are a few possibilities for what's going on. It may well be, as others have noted, simply that the EMS current display is not accurate. My PI EMS seems to have a roughly accurate current display, at least most of the time, but it's far from a precision instrument for current measurement.

Some RVs use heating systems other than a standard furnace, or in addition to the furnace. A heat pump could perhaps use 6A running. Some thermostats will also turn on the air conditioner fan to circulate air when the furnace is on, and 6A for that would be believable. There could also be an electric heater somewhere that's used in conjunction with the furnace.

[pianotuna]

Hi,

Did you happen to notice the 120 voltage?

My furnace draws about 8 amps @~ 12 volts =~ 96 watts.

Do the amps go up on the EMS if the fridge is turned off, when the furnace starts?

Thanks for the 6th power information on incandescent lights.

[time2roll]

Measure and post the battery voltage change as the furnace cycles on and off. Should be fairly steady at 13.6 volts.

Yes my PI EMS seems to read the amps a bit high. Good information but I would not use it as a diagnostic tool.

[ktmrfs]

well the PI current display is NOT very accurate, I called them to talk about what I saw was verifiable errors when checked with a NIST calibrated current meter. They agreed, it's not very accurate or repeatable. A qualitative readout at best.

But, the furnace should draw around 6-12A from the 12V source, that's an additional 1A or so from 120V.


the lights dimming some isn't unusual. A fraction of a volt drop can cause a noticeable drop in incandesent light brigtness. brightness is related to the 6th power of applied voltage!

[BFL13]

It is reasonable for the ammeter to show an increase of 6 amps DC when the furnace fan comes on. also the lights would dim a bit from lower "loaded voltage" with the furnace fan on too.

So it appears that your converter is not supplying any 12v--you are on battery for that.

Lots of possible reasons why no 120v to the converter or if there is why no output.

I see that DD 716 was "Wiltsie" Those were the days!