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Old 08-10-2020, 02:23 PM   #1
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Another question RE: coping with "Residential Fridge" battery drain

Sorry for being so thick on this, guys, since there have been maybe thousands of posts on it, but what options do I have for keeping the all-electric fridge going on all-day pulls? We aren't going to boondock as far as we know, but with our current power configuration our batteries are nearly depleted when we arrive at our campsite after a 6-8 hour pull. I've pretty much ruled out running 4-6 gauge wire from my truck battery to a plug on the tailgate. I'm thinking now about putting one or two big deep-cycle batteries in the truck bed and running an 8-gauge wire out the tailgate to a plug and a pigtail from the trailer batteries to a corresponding plug. Then, when we set up for the night put a charger on the truck bed batteries. What does the group think of that idea? Thanks in advance!
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Old 08-10-2020, 02:47 PM   #2
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most people are able to pull all day long and keep a residential refrigerator going. what batteries do you have?

we have two group 27 90 amp-hr batteries and they work fine for pulling all day. the hardest load is the first day when you take off and the refrigerator has not been plugged in. it must run full time for 2 or 3 hours to get it down to operating temperature. once it
reaches operating temperature it will cycle on and off as required to keep the temperature. at that point the batteries only need to supply power intermittently.

here are some things we do:
the night before go put a couple of frozen milk jugs full of water in both the refrigerator and the freezer. it is amazing how much this will pre-cool the compartments.

make sure your batteries are full when you turn the inverter on. you should always store them fully charged.

turn off any extra cycles that you can on the refrigerator such as ice maker and quick freeze.

only load pre-cooled items into the refrigerator / freezer. do not put a warm case of water, beer, or soda into the refrigerator so it will be cold when you arrive. a can maybe. don't make the refrigerator work more by having it cool down things. you can do that once you arrive.

also, make sure your tow vehicle is actually supplying 12 volt power to the batteries. some people mention that their truck will not do this (ford especially) without installing a fuse and / or relay. while the truck may not fully charge the batteries while towing any current it can provide will help.

we have a generator in our trailer. we start it while we are loading on the morning of departure. even running it that 30 minutes gets the refrigerator cooling down so that the batteries will have less of a load.

once you arrive just hook up to electrical service as normal and let the batteries recharge overnight. by then the refrigerator will be a operating temperature. the next day of towing is much easier on the batteries as they do not have to provide power for an initial cool down.

we have never had a problem with the batteries running down while towing.
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Old 08-10-2020, 02:50 PM   #3
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Originally Posted by jrmartin67 View Post
Sorry for being so thick on this, guys, since there have been maybe thousands of posts on it, but what options do I have for keeping the all-electric fridge going on all-day pulls? We aren't going to boondock as far as we know, but with our current power configuration our batteries are nearly depleted when we arrive at our campsite after a 6-8 hour pull. I've pretty much ruled out running 4-6 gauge wire from my truck battery to a plug on the tailgate. I'm thinking now about putting one or two big deep-cycle batteries in the truck bed and running an 8-gauge wire out the tailgate to a plug and a pigtail from the trailer batteries to a corresponding plug. Then, when we set up for the night put a charger on the truck bed batteries. What does the group think of that idea? Thanks in advance!

I assume you've confirmed the truck is charging the batteries right? I know GM didn't used to ship their trucks with a fuse in place for this, had to add it, they label that fuse "post" and it's 50 amp big boy.
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Old 08-10-2020, 03:31 PM   #4
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Battery stuff

Hey thanks for the replies and help. I believe the batteries are Group 24, 500 CCA, 120 RC. We've a 2018 Surveyor, so I suspect the batteries are 3 years old or so. I assume I can replace them with a "higher" group (bigger battery), though I'd need to replace the boxes too. We do all the stuff you've suggested RE: fully charged, only putting cold stuff in, etc. And yes, I did install the relay and fuse for the trailer 7-pin connector, although I haven't put a meter to it to confirm it's putting 12 volts on the pin. Other posts on the Forum suggest the 7-pin doesn't supply enough amps (due to wire size) to effectively keep the batteries charged. Seems we need to replace the trailer batteries. Thanks again!
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Old 08-10-2020, 04:05 PM   #5
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Our batteries are 5 1/2 years old and still going. Itís not really a function of age as much as how they have been treated. Yours may or may not be good. For sure check the 7 pin cable to verify it is delivering some charge. It may not recharge the batteries but it can supply some charge which the batteries then donít have to supply. Sounds like you have a handle on things. Thereís so many variables in things like this. Youíll get it!
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Old 08-10-2020, 04:31 PM   #6
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If you need more power from your tow vehicle to both maintain the batteries on the trailer and run the residential refrigerator a sure fire way is to add a DC-DC Charger.

Something like the Renogy DCC-1212-20 DC-DC charger.

When connected to the trailer batteries and the tow vehicle battery directly it will provide a full 20 amp supply to the trailer.

Depending on the year and make of tow vehicle, alternator output can be severely limited once the starting battery is fully charged.

The Renogy unit works best with a heavy gauge (I used #8 on mine) wire from starting battery to rear bumper (wire in plastic wire loom and zip tied to the regular wire going from under hood to rear bumper for trailer hookup). Using Andersen connectors I continued on to the DC-DC charger mounted in my TT. I run a residential type freezer (small) and charge my batteries while driving with a max of 20 amp available as needed.

$127 for the Renogy unit and wire, which I chose to use Marine Duplex (looks like romex) fine stranded wire, can run $60 or so depending on finished length.

This rates up there on my list of mods as one of the best.
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Old 08-10-2020, 04:49 PM   #7
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Kinda curious why you ruled out running large wire through a connector at the trailer.

I personally would do that and a DC to DC converter.
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Old 08-11-2020, 12:25 PM   #8
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The tow vehicle should put out enough amps to keep the fridge going. You might want to check the amperage output of your voltage regulator to see if its putting out enough to supply the trailer too. You might want to up grade it too.I don't think a residential fridge runs on the battery alone. Maybe your power converter should be on?
The voltage regulator regulates voltage. The only think it does is keep the voltage at a certain level when the amp draw becomes greater. The problem with the tow vehicle is that the wire has so much voltage drop since it is so small. The voltage drop limits how much current can be supplied.


The power convertor operates off of 120VAC.
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Old 08-11-2020, 12:55 PM   #9
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The voltage regulator regulates voltage. The only think it does is keep the voltage at a certain level when the amp draw becomes greater. The problem with the tow vehicle is that the wire has so much voltage drop since it is so small. The voltage drop limits how much current can be supplied.


The power convertor operates off of 120VAC.
If the tow vehicle is equipped with a battery management system the amount of current delivered to the trailer can be severely limited by the lowered voltage going into the beginning of the charge wire. Voltage drop of course will reduce charge current to very little.

If the Tow Vehicle has a small device like this on the ground cable there's a good chance it has a a BMS.



BTW, I believe this is why Renogy recommends running 12 volt source wires, both positive and negative, from their DC-DC charger directly to the starter battery instead of using a chassis ground for the negative. This makes sure that charging current doesn't bypass the Battery management system through an un-monitored ground.
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Old 08-11-2020, 04:08 PM   #10
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BTW, I believe this is why Renogy recommends running 12 volt source wires, both positive and negative, from their DC-DC charger directly to the starter battery instead of using a chassis ground for the negative. This makes sure that charging current doesn't bypass the Battery management system through an un-monitored ground.
My Ford truck has that exact BMS. That is likely a picture of a Ford. If you attach to the truck chassis, it still gets measured by that BMS.
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Old 08-11-2020, 06:21 PM   #11
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I tow 4 to 6 hours with our residential fridge running and have not had a problem with battery charge. We even open the slide a couple times at rest areas. One thing i have noticed is the batteries from factory/dealer are not always deep cycle but duel cycle that do handle a deep discharge as well as a true deep cycle. Duel cycle is a combo starting and deep cycle battery.
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Old 08-11-2020, 06:24 PM   #12
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Correction. Duel cycle does not handle a deep discharge. That wasn't spell check, that just my poor writing.
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I tow 4 to 6 hours with our residential fridge running and have not had a problem with battery charge. We even open the slide a couple times at rest areas. One thing i have noticed is the batteries from factory/dealer are not always deep cycle but duel cycle that do handle a deep discharge as well as a true deep cycle. Duel cycle is a combo starting and deep cycle battery.
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Old 08-11-2020, 06:36 PM   #13
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A gallon jug of ice placed in a cool fridge ought to last 8 hours until you get you to your destination without your fridge getting warm.
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Old 08-12-2020, 09:48 PM   #14
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The truck batteries should keep the RV batteries charged when driving?
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Old 08-12-2020, 10:42 PM   #15
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The truck batteries should keep the RV batteries charged when driving?
The truck batteries do not charge the trailer batteries.

The running truck alternator provides the charging current to the trailer.

Unfortunately, the truck alternator is designed to provide power to everything needed to run the truck and charge the truck's starting battery.

The charging current provided by the alternator is determined by the net voltage of the truck battery and the connected trailer battery.

The alternator will cut back on charging well before the trailer battery is charged up because the truck's starting battery will accept current (and become fully charged) much faster than the deep cycle battery in the trailer.

See the attached article for a full explanation of why a running truck alternator will keep a charged trailer battery charged, but will not do a very good job of recharging a low one.
Attached Files
File Type: pdf Automobile Alternators as Chargers.pdf (805.9 KB, 11 views)
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Old 08-13-2020, 07:18 AM   #16
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BTW, I believe this is why Renogy recommends running 12 volt source wires, both positive and negative, from their DC-DC charger directly to the starter battery instead of using a chassis ground for the negative. This makes sure that charging current doesn't bypass the Battery management system through an un-monitored ground.
I ran positive/negative from our truck starting battery back to the charger, but on the output side of the charger used the trailer chassis instead of pulling a new negative wire all the way back to the batteries.

My Victron DC-DC charger is the isolated version but it seems to be working fine like this. Their wiring diagram shows wiring the negative on the output directly to the trailer batteries. They also make non-isolated chargers that allow for using chassis.

This is an answer that I could not find anywhere online, so I rolled the dice and it worked out.
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Old 08-13-2020, 08:17 AM   #17
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Clean the connectors between the truck and trailer. Just spray some electrical contact cleaner in there and fill with dielectric grease to keep them clean.

If your trailer batteries are not fully charged when you start out the truck's alternator will have difficulty trying to charge them while powering the refrigerator inverter at the same time.

Same principle for the refrigerator. If it's not full of cold items before starting the trip it will have difficulty cooling everything on the road.

Start with fully charged trailer batteries.
Start with fully cold food in the refrigerator.

I don't know the GM specs but my Fords have a 30amp fuse in the trailer battery charge circuit which should be more than enough to run the refrigerator and charge the trainer battery.

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Old 08-13-2020, 09:52 PM   #18
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"residential refrigerator" vs. Batteries

Wow, thanks for all the counsel, folks. One thing I did do was buy a 7-pin connector tester from Amazon and found that the idiot who installed the relay and fuse for the trailer charge circuit (that would be me) put the fuse in the wrong place, so no, the truck has not been charging the batteries on the trailer at all. As for installing a DC-DC charger and running that 8 gauge wire, well, that's a project for another time, like when we get back from our 2-3 month road trip. I'm also installing new batteries on the trailer. The originals were Group 24's and I'm going back with Group 29's. More capacity, etc. We shall see. Thanks again for sharing all your hard-earned wisdom.
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Old 08-14-2020, 06:16 AM   #19
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glad you have a plan! i think you will be fine. getting the charge (whatever level it is) from the tow vehicle will help! it won't surprise me that even you existing batteries will work now that you have the charge from the two vehicle. but new larger batteries will also help. the key is to have the batteries fully charged when you leave in the morning.

now go enjoy!
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Old 08-14-2020, 07:38 AM   #20
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Not to start yet another battery discussion but a pair of 6v GC ("golf cart") batteries in series make 12v, will vastly out perform typical deep cycle flooded batteries, and they have the same foot print as the Group 24s currently on the trailer. Just an inch or two taller.

Double check your truck wiring diagram. I know the Ford trailer charge line is relay controlled and is only connected with the ignition is On to prevent anything in the trailer like a fridge from sucking the truck battery dry when parked. This would include a pop-up 3-way fridge running on 12vDC as well as a "residential" fridge running thru an inverter.

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