Refrigerator Operation on Inverter

[MattSmith]

We're tempted to try installing an inverter to run the Norcold refrigerator on DC while driving in our 1994 Winnebago Adventurer. We have a couple of questions:

1. Does the engine alternator maintain the house batteries while driving?

2. I don't know the actual power consumption of the refrigerator on AC, but the Norcold schematic appears to show a 5 amp fuse in the AC heater circuit, so it can't be over 600 watts, and there are inverters available in this range. The same Norcold schematics show a 20 amp fused, separate heater for units with the 12 volt DC option (which we wish we had), obviously less effective than either AC or propane operation. The question: can the engine alternator handle the power requirements of the refrigerator in its normal AC mode, either via the engine battery or the house batteries?

3. Obviously I need to get a clamp-on ammeter and actually measure the AC current demand, but a meter costs more than an inverter would, and this is just in the thinking stage. Right now it's easier to see if the kid in the next seat knows the answer!

4. On paper, this would seem more efficient than just running the generator for the sake of the refrigerator. What am I missing, that the motorhome manufacturers know and I don't? - - Matt S.

[garykd]

Hi Matt,

Does your fridge have the choice to run on propane?

[tbutler]

Matt,

I assume you meant to say you wanted to run the refrigerator on AC, not DC while driving. You did mention later that you wish you had the DC option so I understand that. We had a '94 Dynasty with a refrigerator that ran on DC as well as AC and propane. You don't need an inverter to run the refrigerator on DC. We ran ours on DC all the time while driving. Having that option allowed us to shut off our propane when traveling. Now our refrigerator has only AC and propane choices. On AC it uses too much electric from the inverter so we either use the propane option or run the generator.

Your answer on the engine alternator is yes/no/maybe. Every motor home mfg. designs their own system and a single manufacturer will change systems over time. Without having the manual for your rig, I couldn't guess if it does or doesn't provide enough charge to the house batteries to keep them charged. Our '94 Dynasty did charge the house batteries. Our 2004 is rigged to charge the house batteries if the chassis demands aren't too large. As a matter of experience, it doesn't really keep up with demand in our circumstances. At the end of a long day of driving, the inverter will spend several hours recharging the house batteries after we hook up to shore power. It does keep the house batteries in the working range so that is all that is really needed. You might try calling Winnebago technical services to see if they can answer this one for you if you don't have the manual.

Personally we find an inverter to be indispensable and I'd recommend you get one anyway. Everyone has their own preferences. I've talked to people who have inverters and never have used them.

[MattSmith]

Thanks for the responses, Gary and Tom.

Our fridge runs well enough on propane, but all received wisdom dictates against traveling with the propane turned on, since it could be a pretty catastrophic fire hazard in any driving mishap.

Tom, since this fridge has no DC option as installed, my scheme would be to use a 600 watt (continuous-rated) inverter to provide AC from the (DC) house batteries. I find that the engine alternator does indeed charge the house batteries when the engine is running, and from a simple "watts out = watts in" thought process I was guessing that if the fridge demanded, say, 480 watts AC, the alternator would have to put a bit more than 480 watts DC, or 40+ amps at 12 volts, into the inverter when the fridge thermostat called for cooling. This seemed substantial but not too outrageous, and I was curious whether others had tried it. I guess the worst that could happen would be that the batteries would run at a deficit whenever the alternator couldn't keep up, then hopefully catch up when the fridge thermostat was satisfied.

The coach does have a 100 watt inverter intended for TV when dry camping, but we've never used it and it's way too small for this.

My premise in all this is that the 454 Chevy V8 is running anyway, and ought to use a lot less fuel incrementally than running the 4000 watt generator. Just have to remind myself to smile while fueling the coach! Cheers! - - Matt

[wolfe10]

Your refrigerator and RV were designed to safely run your refrigerator on propane while on the road.

And unless you turn of propane OFF AT THE TANK, the added risk of the tiny flame in the refrigerator is minimal.

You WILL put additional strain on the alternator. The more output demanded, the more heat they produce (like all mechanical devices, they are not 100% efficient).

Were this a DP with a 190 amp or larger alternator it would make a little more sense, but only a little.

Brett Wolfe

[garykd]

Hi Matt,

In addition to what Brett mentioned, consider seeking another recognized professional view of the safety features in your coach and the real risk of traveling with the fridge running on propane. The additional information may provide you the comfort needed to use the feature and sleep at night.

good luck,

[MattSmith]

Thanks again, Brett & Gary - -

We do in fact, perhaps superstitiously, drive with the propane turned off at the tank. I guess I'm more worried about a propane line getting ruptured in a collision than I would be about the small flame in the fridge.

Looks like I can buy a lot of fuel for the effort and cost of a suitable inverter plus possible shortened alternator life. It's still tempting, though, and I'll post any outcome if I give in to temptation! (With the inverter, I could at least use my electric drill while dry camping - - ! ? !)

Keep 'em flying! - - Matt Smith

[Barnero]

I would think the risk of the propane woould not just be the small flame. If you had an accident and ruptured a line, would that not represent a BIG hazard? Also, What are the considertions for using solar power to charge the batteries/run the frig?

[tbutler]

Regarding the use of solar panels to charge the batteries and run the refrigerator, this would be a really expensive alternative. Solar panels simply won't put out enough current to run the refrigerator unless you had several of them. Solar panels would provide a charge for the batteries which would slow the discharge rate but they couldn't keep up with the refrigerator. We have a single solar panel on our roof and it supplies only about 12% of the 660 watts needed to power our refrigerator. It would take eight panels to provide all the power for the refrigerator. Even if I had enough roof space for all those panels, I wouldn't spend the money to purchase seven more!

[PIPEWRENCHGRIP]

My take on running the frig on the road. If the frig is cold when you leave you home or campsite, it will stay cold for a long time before needing to run again, unless you open and close if frequently. We used to run the genset for an hour and then an hour off, that seemed to keep the frig cold enouigh for frig. Lately howver, we have been leaving the gas on or using our build in inverter.

Bill

[wolfe10]

Bill,

Weighing the risk of danger from traveling with propane on (with appliances designed to be used on the road like you have) VS the risk of food poisoning if you turn of the refrigerator when traveling, hands down, you are more at risk from food poisoning.

Run them on propane, or if that bothers you, on an inverter (assuming you will not over-tax the alternator).

Brett Wolfe

[MattSmith]

OK, Folks, here's my latest. This really does work! I treated myself to an Amprobe AC/DC clamp-on ammeter and found that our Norcold frig draws 2.7 amps AC on shore power, or about 324 watts at 120 vac. I then bought a 400 watt (rated continuous output) inverter ($59, half what the meter cost!) and wired it to our house batteries (two 12v deep-discharge type) and plugged the Norcold into it. It runs nicely - - doesn't know it isn't on shore power - - and the inverter draws a little over 30 amps dc from the batteries (360 watts or more at 12 vdc, since efficiency is never 100%). This particular inverter (a "Westward" from Grainger) shuts itself off if the input voltage falls below 10.5 volts, and is said to handle momentary surges to 600 watts. We're just back from our second one-week outings and are happy with it so far. I did forget to switch to propane one time and the inverter shut down some time during a 4-hour absence, but nothing warmed up much because we weren't there! No doubt a bigger, domestic-type frig would require more watts, but the principles apply.

As to driving with propane turned on, I guess we're responsible for our own phobias! Our first encounter with motorhomes was back in 1982 when we rented a 34' Southwind for a 5-week cross-country trip. The rental agent was adamant that we must never, never have that valve open when on the road, and we took that as received truth. And really, I wouldn't want to get broadsided and have that regulator get snapped off with the valve open - -

Happy holidays to all! - - Matt S.

[pkunk]

Leaving your propane tank turned on is the norm for motorhomes. A motorhome tank, like a home tank, has a built in 'excess flow valve' which shuts the flow of gas if a line becomes ruptured. The danger if you are in a wreck or blow a tire is minimal as a ruptured line will shut down almost immediately. The amount of gas (size of flame) on a MH fridge is so small that the flame from a wood kitchen match is greater.

I have run a fridge on an inverter, and believe me, if you forget to change over when you stop you will run your batteries down in short order.