Inverter to power RV Refrigerator

sajack said:

Would it be possible to run a small RV refrigerator while towing the travel trailer that the refrigerator is in? My Ridgeline's alternator/7 pin connector wiring apparently can't handle it. The RV 12 volt battery drains completely on long trips. This refrigerator only pulls about 175 watts. The Ridgeline's invertor should be able to handle it. This is a Dometic refr. that can run on 12 volt, 120 volts, or propane.

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At 170 watts/12V DC, your fridge is putting a 14.5 AMP load on the electrical system in your trailer. That's frigging HUGE. Adding a 14 AMP load to your RL electrical system is completely unnecessary and taxes the alternator with a continuous load. Converting DC to AC only exacerbates the demand on your system(s) - inverters are notoriously inefficient. For the most part, IMO: the only thing an inverter is needed for is to temporarily power something that can't be connected to a 12-14 VDC source like a microwave or coffee maker. And when an inverter is used, it's only for very short durations - even an unloaded inverter is an current EATER on a DC system.

On the flip side, your Dometic fridge likely sips around 1/2 ounce of propane per hour.

In my coach, I precool the fridge and freezer for a day or two using shore power prior to a trip, then before departing, switch to propane for the duration of travel time. The choice of continuing to use propane upon arrival is purely a function of the camp site and your propane storage capacity.

I typically run the fridge on propane during an entire camping trip and still have plenty of fuel for BBQ, cook top burners and occasional heat when it gets cold. An 800 watt solar panel keeps 2 pair of Trojan deep cycle 105's charged when I'm rolling down the road. When camped, the DC system powers a substantial stereo system & TV during the day, while running lights and sound most of the night. I rarely camp in places with hook ups but have dry camped for 10 days at a time without hooking up to a generator. That simply wouldn't be possible powering the fridge via DC or an inverter.

Although I do carry a Honda EU 2000 generator for just in case.

I recommend staying as far away from DC to AC inverters as is practical for your situation. Use the RL electrical system strictly to keep the coach batteries peaked while being towed, run you fridge on propane always and get yourself a Honda EU 2000. That little generator is amazingly quiet, is super fuel efficient, is great for all around camping and can make all the difference during home emergencies.

I agree with OhSix that there is NO reason to be looking at 110V power for your RV fridge. My initial thought is:
- Your RV battery must be either very old/bad, or very small. No way should it drain that fast just running the fridge.

Beyond that, I will tell you that I towed travel trailer for years & did not have anything fancy in the way of battery on the trailer (brand-X, average sized deep cycle). I ALWAYS ran fridge on 12V when on the road (switched to propane when we arrived at camp, except for the rare occasions when we had hook-ups). First off, you should be able to do that just fine (run on battery) all day long! Secondly, you should NOT be running down the road towing your trailer with propane on (shut OFF the tanks before departing). You're asking for trouble otherwise. (that's not to say it isn't done a lot.... but it's just not proper practice, or safe)

You might consider stopping by an RV shop to get a quick electrical diagnosis, because I believe your rig is suffering some kind of voltage-drain (or connectivity) fault. Have it checked out, and I'll bet your problems will be solved either with a new battery or by locating/repairing your voltage leak (or bad connection).
It's also entirely possible that you have poor connections somewhere between your trailer hitch plug and your battery.... not uncommon at all on towed vehicles to have bad connections or grounds. You might not be getting any charge to the trailer battery at all..... although with a good battery, that shouldn't really matter.

In any case, I believe you're definitely barking up the wrong tree (for lots of reasons) by chasing an "inverter" solution.

Interested to know how this gets resolved. Good Luck!

Dnick said:

I agree with OhSix that there is NO reason to be looking at 110V power for your RV fridge. My initial thought is:
- Your RV battery must be either very old/bad, or very small. No way should it drain that fast just running the fridge.

Beyond that, I will tell you that I towed travel trailer for years & did not have anything fancy in the way of battery on the trailer (brand-X, average sized deep cycle). I ALWAYS ran fridge on 12V when on the road (switched to propane when we arrived at camp, except for the rare occasions when we had hook-ups). First off, you should be able to do that just fine (run on battery) all day long! Secondly, you should NOT be running down the road towing your trailer with propane on (shut OFF the tanks before departing). You're asking for trouble otherwise. (that's not to say it isn't done a lot.... but it's just not proper practice, or safe)

You might consider stopping by an RV shop to get a quick electrical diagnosis, because I believe your rig is suffering some kind of voltage-drain (or connectivity) fault. Have it checked out, and I'll bet your problems will be solved either with a new battery or by locating/repairing your voltage leak (or bad connection).
It's also entirely possible that you have poor connections somewhere between your trailer hitch plug and your battery.... not uncommon at all on towed vehicles to have bad connections or grounds. You might not be getting any charge to the trailer battery at all..... although with a good battery, that shouldn't really matter.

In any case, I believe you're definitely barking up the wrong tree (for lots of reasons) by chasing an "inverter" solution.

Interested to know how this gets resolved. Good Luck!

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To Dnick's point, the overall health of your DC power system is critical. IMO: placing a constant 14+ amp load on any DC system is huge, especially when that load causes the battery(ies) to go "dead" more than once or twice. It doesn't surprise me the OP author is having trouble with powering his fridge via DC only.

For the battery portion of the system, running it low or "dead" (10V or lower) causes sulfation - resulting in ever decreasing charge retention. In the simplest terms, sulfation is the separation of solids in the acid solution. When sulfur solids collect on lead plates inside the battery assembly, they become isolated to the point where lead can't interact with acid.

"Maintenance free" batteries are difficult to recover when sulfation occurs because the cure for sulfation is "boiling". Boiling is the (long-ish term) application of more than 14V (in a 12V system) and requires cell chambers to be open for venting escaping gases. As the lead plates are excited by the application of <14V, they "boil" sulfur solids off the plates, releasing them back into the acid solution thereby restoring the battery. Many battery chargers installed by trailer OEM's do not support this function - sometimes referred to as equalization, however most portable/external battery chargers have a "boost" function that will emulate equalization. And for the love of God, "topping off" battery juice should always be with distilled water! Calcium in tap water is hyper-bad. We haven't even touched on specific gravity gauges yet but that is important (& simple) test for non-closed cell battery systems.

Anyway, the point is... everything in the electrical system is important. Cables, connections, attachment points, on-board battery charger, ETC. Each link in the chain should be inspected and properly maintained. It isn't difficult - a little knowledge goes a long way improve camping enjoyment.

As for using propane during travel, that too is a matter of system health and OEM design. There are varying opinions and state laws about the topic. A google search will turn up all kinds of information and a wide array of opinions. I learned about this stuff during various restoration projects on my coach and have adopted the habit of using gas to power the system whenever shore power is not available - with no troubles. The current demands on a DC system to power the fridge have never been an option for me but every owner has their own concerns, real world experience and personal disciplines.

zroger73 said:

Actually, even the cheapest inverters are over 90% efficient. The rest is dissipated as heat. "Idle" power is typically only a few watts, if that. If you've got a 100-watt load, no more than about 10 watts is "wasted".

The Ridgeline's headlights alone consume 120 watts of power. Another concern is the type and size of inverter required to start a refrigerator's compressor and prevent it from overheating.

With a refrigerator that consumes 175 watts when running, it probably takes at least 500 watts to start it. The inverter will need to be able to supply this amount of power for a fraction of a second. A 200-watt inverter can't - it would simply turn off. To be safe, you really need about a 1,000-watt inverter. Then, there's the issues of true sine wave vs. approximated sine wave. The latter are cheaper and much more common, but cause motors and other inductive loads to run hot since the output is actually a series of square waves - very poor quality power.

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Oh hell, now you went and did it. The hatch covering the abyss of inverter efficiency and sine wave purity has been opened. That discussion has been beaten to death on RV and solar living forums all over the internets. Same goes with the "choppy" nature of inverter sine waves & their effect on resistive and inductive loads.

Still... 90% efficiency sounds great but only under ideal circumstances is 10% waste "OK". By ideal conditions, I mean the entire electrical system both DC and AC being in peak condition. Other than brand new, ideal conditions are somewhat unusual in the real world. After a few mechanics and/or do it yourselfers have stuck their hands in the mix, and time & weather take their toll on a new system, things degrade to less than ideal pretty quickly.

On the topic of AC inversion for running a 3 way fridge, IF the fridge in question is an absorption design (which is by far the most common) the principle behind the system is heat causing ammonia to convert to a gaseous state. That heat can originate from a small flame fueled by propane, or heating coils powered by either AC or DC. When the fridge is running on either electric source, there is no "start up" current spike caused by a compressor motor - therefore 175 Watts (DC) is pretty much a flat current demand whether starting up or running steady state. Setting aside start up energy, the most efficient heat source for the common 3 way fridge is propane. With little more than a pilot light flame, it generates sufficient heat for ammonia conversion to gas, at an average rate of about 1/2oz/hr. Since DC power is a precious commodity when camping, my preference is propane first, AC second (when connected to shore power) and DC as a last resort but only when batteries can be replenished by solar or generator.

In my rig, a Trace Legend II manages both battery and inversion tasks. As a battery manager, it's nearly perfect. As an occasional AC inverter, it's been super handy - but based on experience, I stay away from AC inversion tasks unless they are momentary or early in the day - which gives the solar system time to replenish batteries. If I need AC power for anything more than a few minutes, I'll run the little Honda generator, but that's just me being anal about keeping the house batteries about 11.5 V at all times.

OhSix said:

Oh hell, now you went and did it. The hatch covering the abyss of inverter efficiency and sine wave purity has been opened. That discussion has been beaten to death on RV and solar living forums all over the internets. Same goes with the "choppy" nature of inverter sine waves & their effect on resistive and inductive loads.

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SIX, I started busting up in the first 2 sentences of this write up by you. I always feel like I learn something by the time I'm finished reading your posts..

Dnick said:

...... another thing not mentioned here is that while traveling, the propane flame 'can' blow out, depending on trailer / fridge design & winds encountered (cross-winds, etc.), which of course ends the propane cooling. No wind-worries on 12V, and I don't know of any reason to to use 12V on the road if your systems are functioning properly.

And I'm not sure I am remembering correctly, but it seems to me like there might have been auto-switching that moved from one source to another (e.g. when propane runs out or flame goes out) on one or more of the RVs I used???? Does that sound right to anyone?

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Dnick, yes no wind no worries, and I would go as far as to say that if the 3-way refrigerator MFG, has instructions for operating while in motion, vs campground (shore power) vs off the grid camping, that's where I'd start.

When I was a kid, the first travel trailer my grandparents had a 3 way refrigerator and we ran it as OhSix suggests, problem was the pilot always blew out and was pretty worthless from Michigan to Florida (winter trips) or Michigan to Tennessee (summer trips) so what we needed was in coolers til camping in nice campgrounds for a week to 10 days with shore power, or overnight with propane cooling things while in rest areas or cheap $10 no connection spaces along the route. The 2nd trailer a much nicer 5th wheel, had I believe either a much more insulated/wind blocked setup or some kind of auto pilot/switching mechanics which we stocked it, once and left the coolers behind.

Carsmak said:

SIX, I started busting up in the first 2 sentences of this write up by you. I always feel like I learn something by the time I'm finished reading your posts..

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By the time you finish reading? Are you suggesting bloviation on my part? Like I'm verbose? Long winded? A blow hard? HAHAHA. Glad someone gets something out of these posts. I tell you what, this forum taught me enough about the RL to be confident with a buying decision and to be a well informed RL owner. If it wasn't for the forum members here, I might have missed the opportunity to be a happy RL driver, and that would be a tragedy. THIS is what social media should be. :act010: The 06 is the first used daily driver purchased since the early 90's. And it has been the best damned buying decision ever. This vehicle is an absolute joy to drive and work on. I actually get excited when there is time available to tinker with her. She just turned over 103K so it's time to bust out the checkbook for the timing belt and related preventative maintenance. In a younger day I'd tackle that work myself but I learned to leave major stuff like this to the guys who do it for a living. Besides, waste fluids are a hassle to deal with.

Regarding wind, flames and absorption fridges, guess I've been lucky that way. And it never occurred to me keeping a flame lit might be an issue in other rigs. The little click of desert rats, race fans and camping buddies in my world haven't mentioned it being an issue - but maybe they have solved the issue in other ways. After all, after camp gets set up, who's gonna sit around the fire with a cold beer talking about the issues with keeping a flame lit when the solution is to flip over to DC power? LOL.