Refrigerator questions!

[Den]

Another newbe question:  We have a residential refrigerator that only runs on electric. On the road it is powered by batteries. Will that keep it cold and frozen.  2. Do the connections from the truck have power?

2016 Redwood 5th.  39 ft.  2019 Ram Laramie 3500 4x4 cummins diesel.

[lappir]

Welcome to the Forum, 

 

I too have a residential fridge. Yes it will stay cold for a while without electric, but each model may vary. I keep an Ice tray in my freezer with a penny on top of a frozen cube. If the freezer gets too warm the penny isn't on the top when I arrive at my next destination. (Or the power has gone off for other reasons.) There are many more high tech options I'm sure but it works for me. 

Your refrigerator is powered by an Inverter which is hooked to your battery bank aka House Battery. The length of time your inverter will power your fridge will depend on many things and how much other stuff is also powered by the inverter or the "House" battery. Many RV's have a power line from the vehicle connection to power some 12 volt items in the trailer, mine does not. 

I routinely get more than 12 hours of things staying fresh in the fridge and frozen in the freezer when I travel. That does depend on the ambient temperatures, and if you open the door at any time. Opening once while disconnected from power looses a lot of cooling with the inrush of warm air and the exit of cold. If it's not powered, do not open it is my rule. 

Rod

[Kirk W]

4 hours ago, Den said:

 2. Do the connections from the truck have power?

The first part has been answered so I'll address the second. Assuming that your truck is wired in the standard way and is using the standard electrical plugs, the answer is yes, there is a wire to connect the 12V power from the truck's system to the RV in order to keep the batteries charged up and to supply other 12V loads. Whether it will keep up with power demands would depend on the wire size used for that connection and the power demands of things in the RV such as the inverter that supplies your refrigerator. 

[jamtracy]

I get about 10 hours of power when traveling to keep my residential fridge going. We've only tested that a couple of times as we try to only travel about 5 or six hours a day.

 

[D&J]

5 hours ago, Den said:

Another newbe question:  We have a residential refrigerator that only runs on electric. On the road it is powered by batteries. Will that keep it cold and frozen.  2. Do the connections from the truck have power?

2016 Redwood 5th.  39 ft.  2019 Ram Laramie 3500 4x4 cummins diesel.

The frig is easy to figure out by disconnecting shore power and see if the light comes on when the frig door is opened, light comes on you have inverter power. I think all pickups coming from the factory with towing packages have 12V power to the 7 pin plug, to verify yours is working disconnect shore power and plug trailer into truck with it running and see if your battery voltage raises. Not sure on Ram but on Ford there has to be a supplied relay and fuse installed for the 12V power to work.

Denny

[trailertraveler]

The standard 7 pin trailer wiring harness does include a wire for connection of the tow vehicle battery to the trailer battery. Whether that wire in the wiring harness is connected by the tow vehicle manufacturer has varied by year and manufacture. Whether there is power to the trailer all the time or only when the engine is running or the key is in the accessary on position may also vary. For example, my 2004 Chevy Silverado came from the factory without the hot wire connected and no fuse in the slot for the connection. If I remember correctly, there was only power when the engine was running or accessories on. My 2018 Silverado came with the hot wire connected and hot all the time. This means that the truck batteries can provide power to the trailer all the time, but also means that leaving the trailer connected can draw down the truck batteries over time.

If you have a test light or volt meter, it is easy to test whether and when there is power to the trailer. Connect the light or meter to the hot terminal and the ground at the trailer plug in.  Which terminal is which may be shown on the cover of the 7 pin connector on the vehicle.

Edited September 19, 2021 by trailertraveler

[fpmtngal]

Would the amount of power going from the truck to the trailer through the 7 pin connection be enough to keep a big battery bank full of power?  My own experience with a small travel trailer is that the amount of power that the truck provides to the batteries is fairly small - the wire size that truck and trailer manufacturers use is small and there’s significant voltage loss.

To add to the comments and confusion about whether a truck will provide power to the trailer for house batteries - newer Ford F150s have a sort-of hand-shake procedure you have to do to activate that circuit.  I had to ask at a dealership to find out about that.  My current SuperDuty truck doesn’t need that - it provides power as soon as it’s turned on.

I know my Norcold absorption fridge is pretty efficient as a cooler - I often travel with it turned off and use blue ice bricks.  I used to use the penny on the ice cube but now have a fridge temperature sensors to keep track of what’s going on.

[D&J]

I run a chest freezer and at times a dorm refrigerator going down the road and my 2013 F350 has no problem keeping the batteries charged up I'm not sure how it would do if the batteries were down from the start but when starting out with fully charged it's fine with my Ford. 

Denny

[Star Dreamer]

We have a residential fridge also and it is powered by the batteries with an inverter while going down the road. Our truck has a 12 volt feed wire but doesn't recharge the batteries very well probably do to the wire size and distance from truck alternator to trailer batteries. We do have 400 watts of solar that keeps the batteries charged up while driving as long as the sun is out. 

We did a few tests at home with a battery state of charge (SOC) meter to see how long we could last. We have AGM batteries that you should not go below 50% SOC. With (2) 100 amp hour batteries, I could not last thru a night  without going below 50%. We increased our batteries to (4) 100 amp hour batteries and now can last through the night without being plugged in. Now our next issue was the next day, our 400 watts of solar, while enough to maintain what the fridge was using, would not recharge the batteries back up to 100% by the end of sunlight so I needed to plug in and run our generator to make thru another night without power. 

Try doing tests at home to see how long yours will last, just watch what type of batteries you have to make sure you do not discharge them too far to hurt their lifespan. Lithium batteries can go farther than the lead acid batteries 50% like deep cycle and AGM. 

[lappir]

5 hours ago, Star Dreamer said:

We have a residential fridge also and it is powered by the batteries with an inverter while going down the road. Our truck has a 12 volt feed wire but doesn't recharge the batteries very well probably do to the wire size and distance from truck alternator to trailer batteries. We do have 400 watts of solar that keeps the batteries charged up while driving as long as the sun is out. 

We did a few tests at home with a battery state of charge (SOC) meter to see how long we could last. We have AGM batteries that you should not go below 50% SOC. With (2) 100 amp hour batteries, I could not last thru a night  without going below 50%. We increased our batteries to (4) 100 amp hour batteries and now can last through the night without being plugged in. Now our next issue was the next day, our 400 watts of solar, while enough to maintain what the fridge was using, would not recharge the batteries back up to 100% by the end of sunlight so I needed to plug in and run our generator to make thru another night without power. 

Try doing tests at home to see how long yours will last, just watch what type of batteries you have to make sure you do not discharge them too far to hurt their lifespan. Lithium batteries can go farther than the lead acid batteries 50% like deep cycle and AGM. 

Thanks for the info. It will help me plan when I attempt Solar on my rolling home. 

 

Rod

[Kirk W]

On 9/19/2021 at 2:59 AM, Den said:

Another newbe question:

Let me ask first if this discussion has answered or at least helped with your reasons for starting the thread? I'd rather not hijack your thread into another direction until we at least know if we have helped?

After years of observing and participating in the RV community, I think that part of the problem has developed from the tremendous increase in electrical needs for modern RVs while the tow vehicle's electrical connections are still designed primarily towing cargo trailers and things of that type. There has been major improvement in towing packages for those since our first RV, but little if any improvement in the ability of the 12V supply from the tow vehicle to whatever is being towed.  Wire size used to be a minor issue because demand was very low and even today with most larger cargo trailers having a battery for brake-away application of brakes it is still not much of an issue, but RVs have increased 12V power demands have been very significant. The gage of wire used in the automotive s has been insignificant, if at all.

 

Edited September 21, 2021 by Kirk W

[noteven]

A nice bit of equipment to consider is a battery to battery charging unit also called a DC-DC charger. 

An explanation can be watched here:

Install of a battery to battery charger

[D&J]

51 minutes ago, Kirk W said:

Let me ask first if this discussion has answered or at least helped with your reasons for starting the thread? I'd rather not hijack your thread into another direction until we at least know if we have helped?

After years of observing and participating in the RV community, I think that part of the problem has developed from the tremendous increase in electrical needs for modern RVs while the tow vehicle's electrical connections are still designed primarily towing cargo trailers and things of that type. There has been major improvement in towing packages for those since our first RV, but little if any improvement in the ability of the 12V supply from the tow vehicle to whatever is being towed.  Wire size used to be a minor issue because demand was very low and even today with most larger cargo trailers having a battery for brake-away application of brakes it is still not much of an issue, but RVs have increased 12V power demands have been very significant. The gage of wire used in the automotive s has been insignificant, if at all.

 

I  don't know what GM or Ram are using but my last two Fords with trailer towing packages have a 30 amp charging circuit going to the plug and our present 2013 will keep the batteries charged going down the road with the freezer running and supplying power to the disk brakes or anything else running back there when needed. Will it pull power from the batteries when the compressor is running yes but the compressor doesn't run continuously so the batteries will charge back up during the off cycle. I've confirmed this by watching the digital inverter readout over the last few years. We also dry camp when traveling and the next day while going down the road the batteries still stay charged even with the freezer being off all night so it needed more run time. I'm running two of the biggest Optima Blue tops made.

Denny

Edited September 21, 2021 by D&J

[Kirk W]

6 hours ago, D&J said:

my last two Fords with trailer towing packages have a 30 amp charging circuit going to the plug

Our son just took delivery on a new F350 and his is also fused for 30a but we aren't sure at this point what the wire size is as wire sizes will be the primary limiting factor in what voltage will reach your battery and that voltage determines the maximum charging current. Of course the wire size limit is partly on the truck and partly the trailer.

[bruce t]

Ok I'm not an expert on the subject. Here in Australia we are far more self sufficient. The basis is that vehicles have "smart" alternators and rvs have DC to DC converters. 

Many, many 4x4's have large fridges. Kirk has seen them all lined up in our stores. Many RV's only have compressor fridges. Few Rvs have inverters to run refrigerators.

The key to having a cold fridge while travelling is both the smart alternator and the dc to dc chargers. We have a 12volt compressor fridge in our rv. It works off the battery. While travelling the smart alternator charges not only the chassis battery but also the house battery.

Someone with more knowledge than me can explain it better than me. But the key is the smart alternator and the dc to dc converter.

[D&J]

4 hours ago, bruce t said:

Ok I'm not an expert on the subject. Here in Australia we are far more self sufficient. The basis is that vehicles have "smart" alternators and rvs have DC to DC converters. 

Many, many 4x4's have large fridges. Kirk has seen them all lined up in our stores. Many RV's only have compressor fridges. Few Rvs have inverters to run refrigerators.

The key to having a cold fridge while travelling is both the smart alternator and the dc to dc chargers. We have a 12volt compressor fridge in our rv. It works off the battery. While travelling the smart alternator charges not only the chassis battery but also the house battery.

Someone with more knowledge than me can explain it better than me. But the key is the smart alternator and the dc to dc converter.

When you are taking about DC to DC converters it's using a power source that puts out a higher voltage and then converters to drop it down at the point of usage to a lower voltage. As with both AC and DC current the higher the voltage the less amps so smaller wire size can be used or use the same size wire with less voltage drop.

Your DC compressor on your refrigerator is a AC compressor with a dedicated inverter built into it so it will run on DC unless something else has come out sence the last time I looked.

Denny

[D&J]

17 hours ago, Kirk W said:

Our son just took delivery on a new F350 and his is also fused for 30a but we aren't sure at this point what the wire size is as wire sizes will be the primary limiting factor in what voltage will reach your battery and that voltage determines the maximum charging current. Of course the wire size limit is partly on the truck and partly the trailer.

What size wire Ford is using I haven't looked and I'm not going to open up a sealed wiring harness to find out because it works and doesn't need fixing. The smallest gauge wire our trailer has is the umbilical cord that feeds the trailer and it's #12 the rest is #10 into the trailer. Do I get voltage drop from the truck charging system to the trailer batteries sure but that's the nature of DC current but it's not great enough to cause any major problems, running the freezer off the inverter I will see 12.6 to 12.8 volts with a small grain with the compressor and truck running but it will go up to 13+ when the compressor cycles off with the truck running, I've run the thing all day long going down the road and it's always the same so it's not going to worry about it. 

One thing I found when running a compressor style frig going down the road is if the unit is in the back of the trailer like my dorm frig is located the bouncing way in the back came cause the compressor to hydrolock from oil getting into the compressor section, you can't compressor a liquid. It didn't happen often but it did happen a few times until I stopped running it when in motion. What I'm sure is happening when the trailer going over dips and bumps causing the oil in the crankcase fly up and get pulled into the compressor locking it up. I got it to restart by waiting for the thermal overload in the motor windings to reset and then bumping the compressor by plugging and unplugging it a few times to get it to run, when it did start I could tell by the chatter that it had oil in the cylinders. The 15 year old freezer that is more to the front of the trailer where the ride is better has never had a problem in the 10 years of running it off a inverter in motion. I've never looked at a cutaway of the newer rotory compressors being used and they may fair better than the piston type. 

Denny 

[bruce t]

We had a bus conversion with a domestic fridge. The compressor was replaced with a 12v danfoss compressor. Never missed a beat. Our current camper has a modest size fridge. 12 volt only. Never missed a beat. Camper has a smart alternator and dc to dc. One 210 amp battery and 200watts of solar. Never without power or frozen ice cream. If the sun doesn't charge the battery while camping we can start the camper up and idle for about 30 minutes. Battery full again.

They key is your expectations. But here in Australia a huge percentage of new campers are almost all electric with diesel heating. A/C it the weak link.

 

[sandsys]

10 hours ago, bruce t said:

But here in Australia a huge percentage of new campers are almost all electric with diesel heating

My custom conversion van was like that. I didn't want to deal with propane and the engine was diesel so it was an easy decision to make to have it be all electric except the heater that was diesel. I had lots of solar but no generator. I miss that van and wish I'd kept it if only for short trips.

Linda

[johnpeters]

A residential refrigerator has its own needs when it comes to power. This type of fridge operates solely on electricity, so make sure that you have a 120 Volt AC power source in your RV.

[Kirk W]

3 hours ago, johnpeters said:

A residential refrigerator has its own needs when it comes to power.

That is true but there are a number of 12V, electric only refrigerators now that operate by compressor and are very power efficient. More and more are now going into RVs.

[sandsys]

6 hours ago, Kirk W said:

That is true but there are a number of 12V, electric only refrigerators now that operate by compressor and are very power efficient. More and more are now going into RVs.

True. I had a 7 cf 12v compressor fridge in my last van and I could boondock for a week without problems just using the four 100 watt solar panels on my van's roof to keep my batteries charged. Even with nearly everything in my van being electric including my cooking and water heating appliances.

Linda