RV Fridge propane vs 110v on inverter

[Asross72]

Thoughts that tickle my brain at 2am....

I’m installing an inverter and deciding which circuits to put on it.   So, is it better/ more efficient, to have the fridge running on propane or let it use the inverter 110 power? 

[Ray,IN]

It is much better to operate it on LP unless you have solar to keep the larger battery bank recharged. The efficiency is the same, only the heat source is different. Read the owners manual to find  current draw on 120VAC, the inverter will draw approx. 10X that amount  of 12VDC from the batteries, which is the normal conversion factor.

[GlennWest]

Yes they pull a lot of electricy. Basically a heating element boiling fluid. Haven't ran the numbers but it may rival a residential fridge. But if you not paying for electricty, why not. If on battery power, propane.

[jcussen]

As mentioned, if you have enough solar to keep batteries up, will work. Other scenario is driving with alternator charging house batteries. Bear in mind, many heating elements in propane refrigerators can use up to 500 or more watts, far more than a electric only compressor refrigerator.

Edited July 1, 2020 by jcussen

[oldjohnt]

ross 72 Great question here's my experience and understanding of the situation.

Based on your question I'm assuming you have a typical RV Combination Electric Gas fridge correct ????

Heres the deal on that:

 1) As far as electric consumption is concerned, those fridges are NOT as energy efficient when operating off 120 VAC via Battery and Inverter power as the modern 12 VDC Compressor units are. 

2) If you had PLENTY of Solar and PLENTY of battery energy storage capacity plus an adequate sized Inverter, and even if the operation isn't extremely efficient, SURE you COULD use battery solar and Inverter and save on LP Gas use when dry camped..........

3) Although I (typically usually mostly lol) have adequate battery and solar and Inverter capacity to run my Gas Elec fridge on electric when dry camping (Im sized to run ALL EXCEPT AC)  THERE MAY BE TIMES WHERE IT RAINS DAYS ON ENDS OR IM PARKED UNDER TOTAL SHADE CANOPY

  THEREFORE, since LP Gas consumption is sooooooooooooo small and I want to conserve all the solar energy I harvest in case of low sun days (it happens) I RUN MY FRIDGE ON LP GAS WHEN DRY CAMPING. PS  I have no idea of the watts your unit requires to run on 120 but depending on size it may be 300 to 500 ??? That is quite a draw on your batteries when dry camping !!!!! 

4) The thing is if you choose to use it on LP Gas versus having an adequate sized battery and solar system YOU CAN GET BY WITH A MUCH SMALLER  LESS EXPENSIVE SOLAR/BATTERY SYSTEM 

5) As far as what circuits to power up using Battery and Inverter Power (Unless you have one HUGE system), DO NOT connect to any high energy loads such as Hair Dryers or Microwaves or Crock Pots or Coffee Makers etc AND DO NOT power up your Converter/Charger  with the Inverter that's a loosing proposition. ALSO as I explained above I would NOT run the fridge off battery and Inverter but use LP Gas for extended dry camping. If you have a small to mid sized system you could run 120 VAC  TV and computers and small electronics and charging etc etc using your battery and inverter, BUT that fridge on 120 or any heating devices will suck your batteries............

6) You have to figure out how to utilize the Inverter be it a separate sub panel or transfer switching etc etc but thats a whole other thread, I'm not going there now lol  

 

 John T  Retired n rusty engineer and 49 year RV owner

[Blues]

56 minutes ago, oldjohnt said:

THEREFORE, since LP Gas consumption is sooooooooooooo small

What kind of refrigerator do you have?  Mine is a 4-door Norcold 1200, and it uses 1/2 gallon of propane per day.  I consider that kind of a lot.

On electric, it uses about 8 kwh/day.  A residential refrigerator usually uses about 1.5 kwh/day.  People have to get pretty big solar arrays to handle residential refrigerators; there's no way solar could keep up with an absorption refrigerator on electric.

I do have friends who, when their batteries were topped up by solar, would plug their absorption refrigerator into the inverter in order to use the excess electricity and save propane.  I don't think it's worth the hassle just to save a few hours of propane use, plus you run the risk of forgetting to change it back over once the excess solar can't keep up, and the refrigerator starts draining the batteries.  But I can see the appeal.

As for putting an absorption refrigerator on an inverter circuit permanently, be aware that you'll be using up some of the inverter's capacity.  For example, we have a 50-amp coach, but the inverter circuit has a 30-amp breaker.  We moved the water heater to the inverter circuit in order to use it on solar/inverter when boondocking and it works fine, but having the water heater on the inverter circuit does mess with the "balance" of loads in the coach when on 50-amp shore power.  A water heater is a much bigger draw than the absorption refrigerator, but the refrigerator doesn't draw "zero" so it's something to be aware of.

 

[jcussen]

Just bought a sprinter class c. Small [5 cf] absorption fridge has 120 volt electric heating elements wired to inverter. Draw is about 240 watts. Believe there is a device that senses when alternator is charging batteries and allows it to run on electric when battery voltage is above a certain point, but when batteries are not being charged, it will switch to gas.  Handy in some tunnels or ferries where you are required to turn off any propane. Plan on adding enough solar so fridge can stay on electric, at least during the day when sun is out.. 

Edited July 1, 2020 by jcussen

[oldjohnt]

2 hours ago, Blues said:

What kind of refrigerator do you have?

Its ONLY a small two door Dometic LP Gas/Electric (not as big as your nice unit). A 30 Lb tank can run it like nearly all summer/winter season  of frequent dry camping UNLIKE if I use the water heater and cooking and grilling that really sucks the propane lol. Even though I have 1080 Solar Watts and can run ALL EXCEPT AC  since my fridge uses so little LP I prefer to save all the solar energy I harvest for all except AC. Sure I have the capacity and have ran it on electric but I choose to use LP when dry camped long term subject to the suns time and intensity and angle 

 DITTO I agree I don't think its worth the hassle to switch it to Battery and Inverter Power just to save a small amount of propane 

STILL ITS A MATTER OF PERSONAL CHOICE AND PREFERENCE provided one has the capacity to run it on Battery/Inverter or LP

 

 Fun sparky chatting with you, take care and God Bless

 

 John T 

[sundancer268]

Try it both ways, then you can make an informed decision that is actually based on your habits and equipment.  Remember the 12 volt electricity is uses to keep the control boards working in most Propane equipment and your lighting, computer & phone charging needs also draw on the batteries.  Only you can run the tests, in my case, Propane is the best choice for me and my family, I really pay the electric bill when I forget to force the reefer to switch to propane when I disconnect the shore-power cord.

[hemsteadc]

22 hours ago, Asross72 said:

I’m installing an inverter and deciding which circuits to put on it.   

Put them all on it.  Wiring directly the the AC panel is so much easier, then run things as you want.

[Asross72]

Thanks everyone. Some good info. 

[GlennWest]

On 7/2/2020 at 11:21 AM, hemsteadc said:

Put them all on it.  Wiring directly the the AC panel is so much easier, then run things as you want.

Depends on the rv. Mine not that easy. Basically have to use a fish tape

[mptjelgin]

On 7/2/2020 at 11:21 AM, hemsteadc said:

Put them all on it.  Wiring directly the the AC panel is so much easier, then run things as you want.

We not only use our inverter for boondocking, but also as an uninterruptible power supply to keep things running when the power drops unexpectedly.  For this reason we prefer the sub-panel, as we don't want our electric water heater element or air conditioner on the inverter circuits. 

[Second Chance]

2 minutes ago, mptjelgin said:

We not only use our inverter for boondocking, but also as an uninterruptible power supply to keep things running when the power drops unexpectedly.  For this reason we prefer the sub-panel, as we don't want our electric water heater element or air conditioner on the inverter circuits. 

Same here.

Rob

[oldjohnt]

26 minutes ago, mptjelgin said:

For this reason we prefer the sub-panel, as we don't want our electric water heater element or air conditioner on the inverter circuits

Valid point, and to add to that, in addition one doesn't want a Converter/Charger operating off the Inverter as that's a loosing proposition lol.   If I'm dry camping I prefer to power my LP Gas/Electric Fridge using LP Gas instead of Inverter powered 120 VAC but that's what started all this............People get by fine with and without inverter fed sub panels, there's more then one way to skin a cat,  be it using sub panels or other switching and manual or automatic selection methods............

Best wishes yall

John T

[hemsteadc]

I run air for my cat on the road when it's real hot outside.  Also just  bit of cooldown at bedtime when the gens are off.  Breaker for HW is always off.  I also use mine as uninterruptible to keep the DTV receiver on 24/7.

Yes, you must pay more attention with a whole house inverter. Just depends on your needs.

Edited July 8, 2020 by hemsteadc