Residential fridge and inverter.

Getn off · 11-04-2018, 05:58 AM

Have a new Sprinter Limited 3551fwmls with a residential fridge that comes with an inverter for it. When camping with electric, I keep the inverter on. I only turn the inverter on while it is not plugged in to electric. Am I doing this right? Question is do I need to leave the inverter on always, even with ac powering?
Next related question: how long will (roughly of course) the batts last while only powering the fridge? I have dual tv batts but nit sure size and dual hd batts with the truck - lets assumed plugged in. This was on my mind since I had to move my rig to the street without plugging in for the night due to demo of a garage on my property.
Thanks!
Troy
Btw, yes I realize that it is just a simple (to some) math question, but not for me!

jsmith948 · 11-04-2018, 06:24 AM

The TV batteries are not relevant. The inverter for your fridge gets the 12 volts it needs from the trailer battery/batteries. If your TV is running, it will add a small amount of charge from the TV's alternator, but not enough to be of much help. You will have to rely on the number of amp/hrs you have available from the trailer battery bank. Divide the available amp/hr of your battery bank by the amp draw of the inverter while it is powering the fridge to determine how long you can power the fridge.
Added on edit: On Ford trucks, the "hot" wire in the 7 way plug is cold unless the ignition switch is in the "on" or run position.

Getn off · 11-04-2018, 06:37 AM

Did not know the truck had to be on for the batts to charge, ty.
So, how long would an ave dual batt setup run an ave residential fridge? I dont have the math info to plug in. 2,4,24 hours?
Troy

jsmith948 · 11-04-2018, 06:46 AM

Can't even guess without more info. You have to know how many amp/hrs you have available when the battery/batteries are fully charged. Then you have to determine how much power is being drawn by the inverter while it is powering the fridge. Then you have to get an idea of how often the fridge cycles on/off. I would think this is a variable depending on how often the fridge is opened and the ambient temperature. The only other way (and probably the only really accurate way) to determine how long the inverter will power the fridge would be to simply time it.
Does the information supplied with the trailer offer any insight?

jsmith948 · 11-04-2018, 07:02 AM

Adding to my earlier post and to offer an example, our Laredo has a small, 120V fridge in the outside kitchen. I installed a 1000W inverter that is powered by two golf cart batteries rated at 200 amp/hr. I can run that little fridge all day while traveling without issue - even in our 105 degree plus valley. Of course, the batteries are receiving some charge from the TV while in transit. I don't know how much, but, I doubt that it is very much given the size of the wiring in the trailer cord. Also, while the fridge resides in a poorly insulated outside compartment and is subjected to the extreme heat we sometimes experience, the door isn't being opened while we are in transit.
None of this serves to answer your question regarding how long your fridge will run off of the batteries. I only offer the info to give you some idea.

notanlines · 11-04-2018, 07:12 AM

Troy, I don't have an answer to your entire question,, but I can tell you that our fridge (large, three door residential) will run from 6 PM when we stop until 6 AM when we leave without any problems, including us using our lights. Keep in mind that it is already cold from running during our travelling the day before.
I can't see why Walmart won't install 50 amp service in their parking lot for people like us....

**JRTJH** · 11-04-2018, 07:08 AM

To answer that question, someone would have to know the amp-hour rating for your specific battery system, whether there are one or two batteries connected to the inverter (some systems have a single dedicated battery, some systems use the trailer battery. They would also need to know the amp draw for the refrigerator and whether the ice maker is turned off or left on (yes the ice maker is a significant draw on refrigerator electric demand because of the heater element that causes the ice to release from the mold).

As an example, if you have a single GP 24 deep cycle battery, you might have an Amp/Hr rating of 75 and if you have a dual GP27 deep cycle batteries, you might have an Amp/Hr rating of 180, or more than double the capacity to run your refrigerator. If the ice maker is turned off, that may extend the run time possibly by double the hours, but depending on the state of charge of the batteries when you start and what other "hidden draws" are on the system (stereo memory, LPG detector, CO detector, Smoke detector(s), and remote control/electronic management system) which also affect the ability of the battery system to provide power to the refrigerator. Additionally, the ambient temperature around the refrigerator will affect the amount of time the compressor runs (more in hot weather, less in cool weather) as well as how often you open the refrigerator door and how long you leave it open.

It's not as simple as: "If you have one battery, it will run the refrigerator for 20 hours".

Getn off · 11-04-2018, 06:54 AM

I know that with the info ur asking for it would give an exact time. I am only asking if, from other peoples past experience with similar setups, my fridge would die before morning when i can move it again.
I do thank you for your help though.
And no, no info came with the rig.
Troy

**chuckster57** · 11-04-2018, 07:09 AM

If I can add, if your parked without being plugged into shore power, any lights, water pump, furnace usage will shorten the number of hours available for the fridge.

Really, there isn’t any accurate way of determining the length of time due to the variables involved. I would venture that a pair of gp27 batteries may make it through the night without the furnace being operated.

Getn off · 11-04-2018, 07:19 AM

Thanks guys.
It is not used while parked on the road. Just the fridge. Batts are fully charged. I keep them plugged in while parked next to my garage at all times.
Just got nervous while it was going to be parked without power and didnt want to unpack the fridge.
Troy

Old Mustanger · 11-04-2018, 09:30 AM

I don't think anyone addressed the other part of your OP, It is OK to turn the inverter off anytime you have shore power, it is bypassed when you're plugged in anyway. Just don't forget to turn it back on when you hitch up and go.

lindy46 · 11-13-2018, 09:19 AM

Quote:

Originally Posted by Old Mustanger

I don't think anyone addressed the other part of your OP, It is OK to turn the inverter off anytime you have shore power, it is bypassed when you're plugged in anyway. Just don't forget to turn it back on when you hitch up and go.

We keep our RV on a permanent lot and it is always plugged in. I do leave the inverter on just in case there is a power failure at the campground. The batteries will keep the fridge running for 8-10 hours and we've never had a power outage that long.

Local150 · 11-13-2018, 03:04 PM

Quote:

Originally Posted by Old Mustanger

I don't think anyone addressed the other part of your OP, It is OK to turn the inverter off anytime you have shore power, it is bypassed when you're plugged in anyway. Just don't forget to turn it back on when you hitch up and go.

Good information,, thanks

Irv gates · 11-11-2018, 08:35 AM

I talked to a dealer last year about the use of the Inverter full time and his infro gave me the idea that the system was not engineered to work full time on the inverter. He was telling me that the frig couldnt get down to the cold temps that were needed when it was on the inverter. The Manuf recommended that you use the inverter system only when going down the road and limiting the travel time to 8 hours to maintain the frig at its best cooling level.
I can see where its possible for the inverter to maintain only a small amount of the energy neeeded if its limitations are such to only keep the frig in a limited cooling state. The specs on the inverter would indicate to me the capacity of the inverter for running full time on it. I dont believe your batteries would handle a very long time period on the inverter unless you have shore power to charge them or solar panels.

**chuckster57** · 11-11-2018, 09:53 AM

Quote:

Originally Posted by Irv gates

I talked to a dealer last year about the use of the Inverter full time and his infro gave me the idea that the system was not engineered to work full time on the inverter. He was telling me that the frig couldnt get down to the cold temps that were needed when it was on the inverter. The Manuf recommended that you use the inverter system only when going down the road and limiting the travel time to 8 hours to maintain the frig at its best cooling level.
I can see where its possible for the inverter to maintain only a small amount of the energy neeeded if its limitations are such to only keep the frig in a limited cooling state. The specs on the inverter would indicate to me the capacity of the inverter for running full time on it. I dont believe your batteries would handle a very long time period on the inverter unless you have shore power to charge them or solar panels.

Sorry but that makes no sense. Think about it, the inverter provides AC Voltage and a number of watts (amps) to operate the refer. the refer doesnt care where the power comes from, just that it gets a minumion amount and the inverter surely is rated for that. Maybe the ice maker will overload the sytem but I'm skepical of that too.

Local150 · 11-11-2018, 10:59 AM

Quote:

Originally Posted by Getn off

Thanks guys.
It is not used while parked on the road. Just the fridge. Batts are fully charged. I keep them plugged in while parked next to my garage at all times.
Just got nervous while it was going to be parked without power and didnt want to unpack the fridge.
Troy

If not opened it should easily last all night. Jmo

George1 · 11-11-2018, 08:01 PM

I'm glad you posted this because I was actually thinking about getting a residential fridge in my next 5th wheel upgrade. But I'm beginning to think that is a big pain in the butt as the inverter battery thing would not make it very much fun to do much boondocking. And in my world that's the whole point of having a camper not to be plugged into a Campground all the time. So thank you, in a roundabout way you just made up my mind for me that I will just stick with your generic old Dometic propane slash 50 amp plug in RV fridge

**JRTJH** · 11-11-2018, 08:41 PM

George1,

Take a look at the owner's manual for Keystone RV's, 2019 edition, page 44:
"Refrigerator-Residential Style
By design, these refrigerators will not operate properly when indoor air temperatures exceed approximately 110 degrees Fahrenheit. In addition, operating the refrigerator in these conditions could cause compressor failure which may not be considered warrantable. Leave the air conditioner set at a temperature below this if the refrigerator is left running in a vehicle that is not being used or shut it off."

Living around south Texas will put a significant limitation on towing with the refrigerator operating (interior RV temp will be well above 110F on a hot, sunny day and trying to boondock, not only will the battery limit your ability to operate the refrigerator, but even if you have a generator to provide power, unless your generator is big enough to also air condition the coach, you risk damaging your refrigerator cooling system if you're boondocking in "summer temps"....

That statement has been in the owner's manual for the past 5 or 6 years, so it's not new, just something many people either ignore or haven't seen. Towing a "residential refrigerator" through the desert in July, even with 4 batteries and all the extra power the tow vehicle can provide, unless you're also running the air conditioner, you risk damage to your refrigerator.....

There are some significant limitations to residential stuff in a travel trailer.

Getn off · 11-04-2018, 10:11 AM

Thanks Jerry, that is what I thout but wanted to clerify.
Troy

**JRTJH** · 11-04-2018, 11:59 AM

What Old Mustanger said applies to about 75% of all inverter systems. On some (unsure of the OP's system) the refrigerator inverter/battery are a separate system and not connected to the trailer 12 VDC charger/battery system. In those types of inverter/battery/refrigerator systems, the inverter is the only battery charger for the battery that supplies the power for the refrigerator. So, if you turn that inverter off, you won't recharge the battery and it will be "DOA" when you get ready to tow the next time.

So, check to see if your refrigerator battery is charged by the converter/power center or by the inverter. Depending on what you determine, you may need to leave the inverter turned on, at least until the refrigerator battery is charged.

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