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Old 11-04-2018, 05:58 AM   #1
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Residential fridge and inverter.

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!
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Old 11-04-2018, 06:24 AM   #2
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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.
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Old 11-04-2018, 06:37 AM   #3
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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
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Old 11-04-2018, 06:46 AM   #4
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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?
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Old 11-04-2018, 06:54 AM   #5
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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
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Old 11-04-2018, 07:02 AM   #6
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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.
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Old 11-04-2018, 07:08 AM   #7
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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".
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Old 11-04-2018, 07:09 AM   #8
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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.
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Old 11-04-2018, 07:12 AM   #9
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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....
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Old 11-04-2018, 07:19 AM   #10
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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
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Old 11-04-2018, 09:30 AM   #11
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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.
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Old 11-04-2018, 10:11 AM   #12
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Thanks Jerry, that is what I thout but wanted to clerify.
Troy
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Old 11-04-2018, 11:59 AM   #13
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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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Old 11-04-2018, 01:16 PM   #14
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John, as far as I am aware, the fridge just gets juice from the rvs batts when I turn the inverter on. The inverter is a 1000w that is used soley for the fridge. The charging I thought was only when tv hooked up, or with 110v.
Are you suggesting to leave the inverter on at all times? Will that hurt anything either way?
I am sloooowly starting to understand this beast!
Thanks again.
Troy
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Old 11-04-2018, 02:17 PM   #15
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Some Keystone RV's with domestic (home style) refrigerators have a dedicated battery to operate the inverter. It is separate from the RV battery system and is not attached to the converter or to the power center. On that type system, the only way the refrigerator battery can be charged is with the inverter/charger that is also a part of that system. When plugged into shore power, the inverter functions as a charger for that battery (not for the RV battery/batteries). About 25% of RV's are wired this way.

The rest of the domestic refrigerators have inverters that are connected to the RV 12 volt battery system. Most of them have an inverter (not an inverter/charger) and draw their power from the same battery bank as the lights, water pump, slides and jacks. On that type system, the batteries are charged by the converter in the power center, just like most other RV 12 VDC systems.

On the first type, you need to leave the inverter turned on to charge the "dedicated battery". On the second type, you can turn the inverter off because the batteries draw their charge from the power center for the RV.

I don't know which type you have, so you'll need to determine whether your inverter is wired to a "dedicated battery" or if it is wired to the "RV battery system. Both wiring systems are found in Keystone RV's.
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Old 11-04-2018, 04:14 PM   #16
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Good info. Pretty sure mine only has the rv batts. I will just keep turning the inverter off when plugged into ac then.
Thanks!
Troy
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Old 11-04-2018, 04:17 PM   #17
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If you can put eyes on the inverter, just give us a make and model # and we can tell you.
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Old 11-04-2018, 08:42 PM   #18
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Always learning! If the inverter has a "BYPASSED" light that comes on when plugged into shore power is it safe to assume that it is not charging the batteries? (Yes I know what assume can mean but I couldn't think of another word to use) The service advisor had told me it was OK to turn the inverter off but now y'all have me doubting.
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Old 11-05-2018, 01:18 PM   #19
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Here are the inverter pics...

Troy
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Old 11-05-2018, 04:29 PM   #20
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I edited your posts to combine all the photos into one post. The top photo shows the name of your inverter, the second (black schematic) shows the connections/relay for the power transfer switch and the bottom shows the output plugs and power switch for the inverter.

The way your system is set up does not include a "dedicated battery for the refrigerator. The main 12 VDC battery system powers all of your requirements. There is no "refrigerator inverter/charger"... So, the way your system works is this:

The trailer battery charges from either the tow vehicle (when it's running) or from the trailer converter/charger when you're plugged into shore power. The refrigerator has a inverter that provides 120VAC when the trailer is unplugged which is powered by the trailer battery system.

When you unplug the shore power, the transfer switch automatically switches the power from the shore power side to the inverter side. This assures "seamless" power for the refrigerator. When you stop and plug in the shore power cord, the transfer switch automatically switches from the inverter to shore power, again assuring "seamless" power to the refrigerator.

In order to turn off the refrigerator, you can either turn off the inverter at the inverter power switch or turn off the refrigerator at the refrigerator control.

As long as you have batteries connected to your RV, you will have power to the inverter (unless there is a switch in the power cable from the battery to the inverter).

You can disable the inverter (and possibly prolong its life) by turning it off when you are on shore power. That is not "mandatory" but rather a personal preference.

Your inverter/transfer switch does not have any battery charging capability, so you must rely on the "WFCO converter/charger" in the power center to keep your trailer battery bank charged.

I hope this doesn't confuse you more than helps you understand your system.
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