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Old 06-10-2020, 06:15 AM   #1
RMcNeal
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Residential Refrigerator and Inverter Questions

We have the 3791RD with the Samsung residential fridge. Our dealer DID NOT install a second battery and unfortunately, I didn't know any better when we purchased our unit to question it.
We normally do not travel far each day, so until recently, I would just secure the fridge and not worry about running on the inverter. Everything stayed cold for our 2-3 hour travel day without power. I recently started going a little further now and with summer time getting here in the south east, that really isn't going to work anymore. I have since turned on the inverter and run it while towing so the fridge will stay cold.
Question 1: Is it OK to leave the inverter turned on all the time or do I have to remember to turn it on when towing and off when on shore power?
Question 2: Will my TV (2014 F350) sustain the battery enough while towing with the fridge/inverter running?
Question 3: What is the best way, short of climbing inside the rig and opening the fridge, to make sure it is still running?
Question 4: A bit off topic, but, would replacing our single battery with 2 decent 12v deep cycle ~100 AH batteries be enough? We NEVER boondock. I have the solar prep only, no panels, etc. I do not carry a generator with me at this point, but I am considering a small inverter/generator like the Honda or Harbor Freight one that is pure sine wave.
Any advice appreciated.
 
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Old 06-10-2020, 08:20 AM   #2
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question 2 is no if you are traveling a long ways.
question 3 would be why would you want to know if it is running if everything is normal?
question 4: get 2 6 volt batteries and you'll do fine. about $100 each.
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Old 06-10-2020, 08:26 AM   #3
RMcNeal
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Originally Posted by mazboy View Post
question 2 is no if you are traveling a long ways.
question 3 would be why would you want to know if it is running if everything is normal?
question 4: get 2 6 volt batteries and you'll do fine. about $100 each.
Thanks, mazboy.
#2: that was my suspicion. Not enough juice to keep battery maintained.
#3: If you're asking, my reasoning is that I would want to know if the fridge is not running so that I can maybe take action to prevent losing everything.
#4: I had considered that, but weight and maintenance was making me think maybe they are overkill. We never boondock and only run 4-5 hours max without stopping where I'll have shore power to run/recharge. The original battery box is very small. I'm not even sure I could fit 2 batteries in it. Less than 12"x12" inside. I've never had lead acid batteries. How much maintenance can I expect realistically as far as refilling water levels, etc?
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Old 06-10-2020, 08:28 AM   #4
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For question 1 the answer is Depends on your Inverter. Some have a built-in transfer switch, that once shore power is detected it sends shore power to the fridge and the inverter goes into a standby mode. If it doesn't have either a built-in or external transfer switch you may have to turn it off to get shore power to the fridge.
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Old 06-10-2020, 08:32 AM   #5
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Originally Posted by mhs4771 View Post
For question 1 the answer is Depends on your Inverter. Some have a built-in transfer switch, that once shore power is detected it sends shore power to the fridge and the inverter goes into a standby mode. If it doesn't have either a built-in or external transfer switch you may have to turn it off to get shore power to the fridge.
It does have a transfer switch. I have the inverter on right now and shore power hooked up. No problems so far. Until this trip, the battery disconnect inside the front compartment for the fridge was bad from the factory and had to be replaced, so using the inverter wasn't an option. Now it's working, so I guess when not wanting to run the fridge I could either turn off the inverter or the battery disconnect now. Just wondering if it's OK to leave on.
It makes sense it would be, otherwise if power went out, there's no backup for the fridge like we had with propane before.
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Old 06-10-2020, 08:51 AM   #6
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We're Most Timers so ours normally stays on 24/7/365.
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Old 06-10-2020, 09:44 AM   #7
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As long as your reefer and all in it is cold before you leave you should be good for 6-8 hours even if it is not running. You can buy a remote thermometer to check your temp with getting in the rig.
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Old 06-10-2020, 09:50 AM   #8
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My ram has 2 alternators an option that came with the truck and it keeps the fridge running all day.
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Old 06-10-2020, 02:55 PM   #9
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When I had problems with my refg. inverter I called the Company WFCO. During the conversation I asked if I should turn off inverter when hooked up to shore power...he said not necessary. It goes into standby and then as soon as you disconnect from shore power it automatically turns itself back on. He said that way is best just in case you forget to manually turn it on when disconnecting from shore power. So that's what I do cause I know I would be the first one to forget to turn it on every time....been there, done that.
Also 2-6v batteries is best...AGM is even better but will cost more $.
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Old 06-10-2020, 03:11 PM   #10
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We have the same trailer and Fridge. It will stay running and keep a steady cold (-2F for freezer) for at least 5 hours when hooked to the inverter. We also only have one battery and since we always stay where there is shore power, that is all we have needed in over 12 months of travel on the road. Be aware that the fuse on the inverter tends to pop every time you hook up or disconnect shore power. I just push the button and make sure the voltage is showing right before shutting the bay and pulling out. I have never tried driving over 5 hours in the heat so not sure if the battery will go dead or not. I do have dual alternaters to generate added power though.
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Old 06-10-2020, 03:11 PM   #11
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Originally Posted by RMcNeal View Post
It does have a transfer switch. I have the inverter on right now and shore power hooked up. No problems so far. Until this trip, the battery disconnect inside the front compartment for the fridge was bad from the factory and had to be replaced, so using the inverter wasn't an option. Now it's working, so I guess when not wanting to run the fridge I could either turn off the inverter or the battery disconnect now. Just wondering if it's OK to leave on.
It makes sense it would be, otherwise if power went out, there's no backup for the fridge like we had with propane before.
We have the same RV, came with 2 12V batteries and found it just was not enough, even though there is enough juice for the Refer, in longer travel days there was barely enough for the jacks and slides. I upgraded to 4 6V batteries (total cost was $600) I also installed a automatic watering system for $80. So they are basically no maintenance batteries. Since AGM batteries have a shorter life and twice the cost this was the best solution short of spending $2k for lithium.

Also note I added a switch to my negative cable to the battery that way I can shut the batteries down 100% otherwise there is always a small battery drain when unplugged.

Here is what I did in my 3791RD

I installed my 4 Trojans removing the two 12v. As you can see the battery box barely fits but is doable. Even if you only buy two 12V you should still buy the 4 battery box so you can easily upgrade. You can just build a filler to take up the extra space. This is also enough for an over night boondock if needed...

As mentioned above I purchased 4 Trojan T105 Plus 225 AH $125 Ea no tax and no core required ($500 total )https://www.onlinebatterysale.com/store/

the Battery Box was purchased from All Battery Sales and Service $80 https://allbatterysalesandservice.co...atteries-gcq-g

I bought the 2" vent for the lid from Amazon $5
https://www.amazon.com/gp/product/B0...0?ie=UTF8&th=1

I Just ordered the Watering system for $79 so they will for the most part be Maintenance free as I will gravity feed the system.
https://www.rvupgradestore.com/Flow-...bg-u24v-4g.htm

Total Cost of new 4 new batteries and box $665

Watering system and added negative switch not shown in picture I added those a week after pics taken



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Old 06-10-2020, 04:37 PM   #12
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with one battery were were able to go as long as 13 hours and still have enough battery to set up
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Old 06-11-2020, 06:25 AM   #13
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In past trips during cooler weather, we were able to go 5-6 hours without running the fridge on inverter (mostly because the inverter and disconnect were bad and had to wait on replacement). Everything stayed cold as long as we had it cold before leaving. Now with warmer weather, I've noticed that even on a 4 hour trip the fridge would be up to 47-48 degrees when we did get hooked up again. Freezer in the 20's. They were 36 and -2 degrees when hooked up.
I barely have room for 2 batteries without completely redoing the battery compartment like lightsout suggests. I would consider the 6v, but if 1 goes, I'm dead in the water. At least with 2-12v, I can still limp home and get a replacement. I have never owned a deep cycle lead acid battery. How often must you check/add water? Is it a weekly thing or maybe every month or so? I have only had maintenance free, I assume AGM gel mat batteries. So never had to add water or anything.
Any advice regarding 2-12v other than making sure they are matched and same age/size, etc?
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Old 06-14-2020, 03:15 PM   #14
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I’m plugged in all but when traveling. Travel days are usually 7-9 hours. I have 2 12volt batters. Never a problem but will lose a little on ling travel days when outside temp is 95 or better.
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Old 06-14-2020, 06:26 PM   #15
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Question 1: I never touch my inverter.
Question 2: I don't know if the TV provides enough power, but if you start the towing day with full batteries, you should be good all day.
Question 3: a fridge that remains closed all day should keep food cold; I never check mine.
Question 4: two 12v deep cycle batteries are enough, but two or four 6v batteries are better.
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Old 06-14-2020, 07:21 PM   #16
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hello eagleback. my 2019 Ram 2500 w/ Cummings TD may or may not have two alternators. if it has 1 are you thinking my truck won't keep my residential fridge running interrupted on an 8-9 hour drive?
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Old 06-14-2020, 07:26 PM   #17
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Under most conditions, a typical lead/acid battery should last five years, or longer. I’ve run diesel boats with lead acid, and AGM battery banks, and found that experience to be the case. Rarely do you have to top off your batteries, but you should check them regularly, first weekly, then monthly, to be sure. If they start “loosing “ water, at that point you start questioning why. Battery maintenance is really pretty straight forward and simple. And it’s all about amp hours. Two 6 volt units will deliver more amp hours than two 12 volt units.
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Old 06-15-2020, 05:44 AM   #18
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hello eagleback. my 2019 Ram 2500 w/ Cummings TD may or may not have two alternators. if it has 1 are you thinking my truck won't keep my residential fridge running interrupted on an 8-9 hour drive?



Not sure, just saying that thats an option on the rams. and it keeps the fridge running.
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Old 06-15-2020, 09:28 AM   #19
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Electricity is like water going through a hose, small hose small volume. 1, 2, or 6 alternators can only put so much charge through the tiny wire from truck to batteries.
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Old 06-15-2020, 01:33 PM   #20
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hello eagleback. my 2019 Ram 2500 w/ Cummings TD may or may not have two alternators. if it has 1 are you thinking my truck won't keep my residential fridge running interrupted on an 8-9 hour drive?

regarding the powering of the 5th wheel with power from the tow vehicle

the limiting factor isn't how much electricity the tow vehicle can make; the limiting factor is the wiring which gets the power to the 5th wheel

for example
The 7pin connector is fused with a 40amp fuse (meaning that the 5th wheel is going to be getting a fair amount less then 40amps at 12 volts). So at the limit of popping the fuse your tow vehicle can give 40 x 12 = 480 watts of power.

Your fridge is 110volt; lets guess that it uses 5 amps when running. So that fridge is using 110 x 5 = 550 watts of power.

The above numbers have the 5th using 70 watts more power then the tow vehicle can provide at the limit of the fuse.

In reality, that 7 pin is outputting a lot less then 40amps; tow vehicles aren't providing a pile of power to the trailer and a 110volt load quickly consumes more watts then a 12volt system can generate.



To the 8-9 hour towing question
If the fridge uses 5amps@110volt(550watts) running 70% of the time and the tow vehicle outputs 30amps@12volts(360wattts) 100% of the time.

Over 9 hrs you will consume (550x(9x.7))=3463amp/hrs and produce (360x9)=3240amp/hrs. Meaning your battery only has to provide 223amp/hrs.

A fully charged deep cycle should handle that without issue; but you'll be down say 30%.
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