Fridge 12V Operation

[Lawrence W]

I had a new Norcold refrigerator installed in my 1980 Scamp by my dealership. They didn't hook up the 12v wiring, advising I shouldn't use it because it "drains the battery". The original Dometic fridge I replaced only ran on 110V setting, so I am not familiar with 12v fridge operation.

This is what the Owner's Manual says about 12v operation:

The refrigerator receives its DC power from the 12 volt system
of the vehicle; either the vehicle engine battery or an auxilliary
(house) battery. The 12 volt system of the vehicle supplies DC
power only to the refrigerator but also to any other DC appliances
of the vehicle. When operating on DC, the refrigerator has a high
current draw and can cause a rapid battery discharge.
DC operation precautions:
This refrigerator is made to operate on DC power while your
vehicle is "in transit" and AC power or propane gas sources are
not available. Operate the refrigerator on DC power only when
the vehicle engine is running.
For the refrigerator to operate correctly on DC power, the battery
must be maintained in a fully charged condition.
For the battery to be fully charged at all times during refrigerator
operation on DC, the vehicle engine must be running and the
battery charging system must be in good operating condition.
Keep in mind the following electrical precautions for DC operation
of the refrigerator:
- Good battery condition is necessary for correct DC operation.
- The capacity of the battery charging system must be more
than what is necessary for the refrigerator and other DC
appliances.
- While the vehicle engine is running, have a qualified service
technician make sure the voltage of the DC power supply
leads at the refrigerator is more than 11.5 VDC.

DC operation guidelines:
DC operation is intended only to maintain the temperature of the
refrigerator and its contents when they are already cool.
The DC operation is not intended for the initial start up and
cooling of the refrigerator. Always use either the AC operation
or propane gas operation to initially start up and cool the
refrigerator. The refrigerator must be cooled and the temperature
must be steady before you operate the refrigerator on DC.
Keep in mind the following guidelines for DC operation of the
refrigerator:
- Use DC operation of the refrigerator while the vehicle is in
transit.
- Do not use DC operation until the refrigerator and its
contents are completely cooled.
- Only use DC operation if the vehicle battery and battery
charging system are in good operating condition.


I wired the fridge into my 12v fuse panel, but before I test it I have some questions:

Doesn't the fridge run off my converter when I'm plugged into shore power (with it set on 12v)?

I plan to use the 12v setting while I am traveling to my destination, as the instructions indicate...the only "other trailer DC appliances" that would be involved are taillights and running lights....are there any caveats against that plan?

What does the instructions advise against using the DC operation to initially cool the fridge? Is it just because it takes longer to cool?

Should I also test the TV DC output at the hitch plug with the TV running?

Why does the battery have to be "maintained in a fully charged condition" if you only run the fridge on 12v mode when the TV is providing the 12v?

I removed the battery when I winterized the trailer. Any reason for me to have the battery installed to fully test the 12v operation of the fridge?

I appreciate any answers to my questions you could provide.

[Byron Kinnaman]

Originally Posted by Lawrence W

I had a new Norcold refrigerator installed in my 1980 Scamp by my dealership. They didn't hook up the 12v wiring, advising I shouldn't use it because it "drains the battery". The original Dometic fridge I replaced only ran on 110V setting, so I am not familiar with 12v fridge operation.

This is what the Owner's Manual says about 12v operation:

The refrigerator receives its DC power from the 12 volt system
of the vehicle; either the vehicle engine battery or an auxilliary
(house) battery. The 12 volt system of the vehicle supplies DC
power only to the refrigerator but also to any other DC appliances
of the vehicle. When operating on DC, the refrigerator has a high
current draw and can cause a rapid battery discharge.
DC operation precautions:
This refrigerator is made to operate on DC power while your
vehicle is "in transit" and AC power or propane gas sources are
not available. Operate the refrigerator on DC power only when
the vehicle engine is running.
For the refrigerator to operate correctly on DC power, the battery
must be maintained in a fully charged condition.
For the battery to be fully charged at all times during refrigerator
operation on DC, the vehicle engine must be running and the
battery charging system must be in good operating condition.
Keep in mind the following electrical precautions for DC operation
of the refrigerator:
- Good battery condition is necessary for correct DC operation.
- The capacity of the battery charging system must be more
than what is necessary for the refrigerator and other DC
appliances.
- While the vehicle engine is running, have a qualified service
technician make sure the voltage of the DC power supply
leads at the refrigerator is more than 11.5 VDC.

DC operation guidelines:
DC operation is intended only to maintain the temperature of the
refrigerator and its contents when they are already cool.
The DC operation is not intended for the initial start up and
cooling of the refrigerator. Always use either the AC operation
or propane gas operation to initially start up and cool the
refrigerator. The refrigerator must be cooled and the temperature
must be steady before you operate the refrigerator on DC.
Keep in mind the following guidelines for DC operation of the
refrigerator:
- Use DC operation of the refrigerator while the vehicle is in
transit.
- Do not use DC operation until the refrigerator and its
contents are completely cooled.
- Only use DC operation if the vehicle battery and battery
charging system are in good operating condition.


I wired the fridge into my 12v fuse panel, but before I test it I have some questions:

Doesn't the fridge run off my converter when I'm plugged into shore power (with it set on 12v)?

Yes it would, but why stress the converter when 120 V is available. Also in 120 and Propane modes there's some control over the box temperature.

I plan to use the 12v setting while I am traveling to my destination, as the instructions indicate...the only "other trailer DC appliances" that would be involved are taillights and running lights....are there any caveats against that plan?

Using two different tow vehicles at different times, one will keep the battery charged and run the fridge one won't. So it depends on the tow. I doubt most would handle it. On that note, the insulation is good enough to keep things cold for a few hours while traveling.

All running lights are run from a different circuit from the tow vehicle, they isolated from the house 12 volt system.

What does the instructions advise against using the DC operation to initially cool the fridge? Is it just because it takes longer to cool?

Yes it takes longer, and no control.

Should I also test the TV DC output at the hitch plug with the TV running?

What I did was run the battery down a bit, hook up the TV and measure the charging current. Then turned on the fridge and rechecked the battery charging current. In one case the charging current went negative, (meaning I was drawing some current from the battery) in the other it stayed where it belonged. Towing in case where the charging current was near zero results in a dead battery at destination.

Why does the battery have to be "maintained in a fully charged condition" if you only run the fridge on 12v mode when the TV is providing the 12v?

The answer above pretty well explains it, I think.

I removed the battery when I winterized the trailer. Any reason for me to have the battery installed to fully test the 12v operation of the fridge?

I'm a believer that when testing systems they need to tested in the manner in which they'll be used.

I appreciate any answers to my questions you could provide.

All that said, I very rarely use the 12 V setting my fridge. Even in a two day trip (driving for two days) I leave the fridge off. If I'm really concerned about keeping things cool I put a bit ice in zip lock bags. I use the zip lock bag/ice method for over a week in Death Valley. Worked good.

Another thing to consider is the foods you keep in fridge. Less sensitive to warm temperatures foods means less worry about one system.

[Thomas G.]

Originally Posted by Lawrence W

I wired the fridge into my 12v fuse panel, but before I test it I have some questions:

Doesn't the fridge run off my converter when I'm plugged into shore power (with it set on 12v)?

Yes, but at a cooling rate. Better to run off 110 v when you have it.

I plan to use the 12v setting while I am traveling to my destination, as the instructions indicate...the only "other trailer DC appliances" that would be involved are taillights and running lights....are there any caveats against that plan?

Make sure that you have a large gauge wire (10 gauge or thicker) running from TV battery to trailer. You probably won't be able to charge your battery in the trailer at the same time as running the fridge while driving unless you use a really large wire (like 6 or 8 gauge).

Why do the instructions advise against using the DC operation to initially cool the fridge? Is it just because it takes longer to cool?

Yes the DC heater has less (heating) cooling capacity

Should I also test the TV DC output at the hitch plug with the TV running?

Yes, the voltage will be higher when it is running as the alternator puts out 13.8 to 14.5 volts.

Why does the battery have to be "maintained in a fully charged condition" if you only run the fridge on 12v mode when the TV is providing the 12v?

Because the TV probably can't both run the fridge and charge the battery at the same time - usually due to wire size.

I removed the battery when I winterized the trailer. Any reason for me to have the battery installed to fully test the 12v operation of the fridge?

I appreciate any answers to my questions you could provide.

It would be insightful to see if the fridge draws down the battery with the engine running. Others with light wiring have reported this. An unpleasant surprise to get to your destination and find the battery down.

[Lawrence W]

Byron/Tom:
Thanks for your quick and thorough responses. They really helped.

Byron: I note we are both from Oregon (me from Albany), and we both have Dakota TV. I may have met you at Waterloo a couple of years ago.

[Byron Kinnaman]

Originally Posted by Lawrence W

Byron/Tom:
Thanks for your quick and thorough responses. They really helped.

Byron: I note we are both from Oregon (me from Albany), and we both have Dakota TV. I may have met you at Waterloo a couple of years ago.

I think I've been at all the NOGs that were at Waterloo so we probably have met. I was in Albany this morning, a short drive from south Salem. If I can help anymore let me know.

[Donna D.]

Yep, you guys have met! I made arrangements with Larry to return a table to him (and wife) in Salem in 2011.

NOGs are fun!!

[Carol H]

Larry I dont use the 12V on my fridge either due to the draw. I have 3 small freezer packs that stay in the trailers freezer when the fridge is running. When its off and I am traveling I stick the packs in the main fridge compartment right up against the items that really need to stay cold. I just dont open the fridge at all when its turned off. Works well.

[ericw]

I installed a similar fridge and it works very well for us.

As you indicated, we start the fridge on 110V on 24+ hours before we leave the house. We have had no problems running the fridge while traveling. I checked the voltage at the battery and our TV wiring can run the fridge and charge the battery at the same time. Obviously when it is doing both it is charging the battery more slowly when some of the power is going to the fridge. If you don't know how to run that test, feel free to ask.

We used it all the way from MI to CA and back and never turned it off. We stopped many times for ~8-10 hours where it just ran off the battery. Even in the desert we left it for about 20 hours and it was still fine.

Note these fridges use less 12V power than the 3 way fridges. Most of our camping is with 110 power and we only need the battery to get us through our various stops. I hope it works well for you also.

[Ron in BC]

Originally Posted by ericw

I installed a similar fridge and it works very well for us.
Note these fridges use less 12V power than the 3 way fridges. Most of our camping is with 110 power and we only need the battery to get us through our various stops. I hope it works well for you also.

I've had the same experience with these fridges. It seemed to me that the instructions were a little too much CYA and didn't take into account that the user had any common sense and more commonly these days solar panels. Using them on 12V for a while without the battery being actively charged is no big deal. The only thing I'd recommend is having a digital display to monitor battery voltage. There're a good idea, 12V fridge or not.

Ron

[Francesca Knowles]

This is why I always advise folks to save their money when buying fridges and go for the two-way 110v/propane option. The only real utility of 12v is running the fridge while traveling so that the tug provides a continuous power flow.

There's a significant price differential between 3 way and 2 way....

If the folks that installed the O.P.'s fridge also sold it to him, it seems to me that their assessment of the 12v option would have served his interests better had they advised him before he paid for the option that they so blithely after-the-fact opined was useless.

Francesca

[Bill Robison]

Francesca -

It all depends ...what type of new Norcold fridge you had installed - was it ammonia process or small compressor? All 12v fridges are not equal in terms of amps of draw. If yours is a 120v/12v compressor type - similar to what we had in our EggCamper - then it should be able run easily on either 120v or 12v depending on what is available. We had one group 24 Deep Cycle battery with no solar and the Norcold (compressor) would run very effeciently off the battery for three to four days with amps to spare. I would monitor the battery voltage levels and when we were ready for showers in the boondocks I would start the Honda EU2000i for electric water heater - then let it idle to re-charge the battery for an hour or so.

When the majority of campers hear '12v' and 'fridge' in the same sentence they assume it means 'ammonia type' cooling, which is efficient on propane but certainly not on 12v. If yours happens to be 'ammonia type' then disregard using 12v and stick with 120v and/or propane - it will cooler nearly *forever* on LP ;-)

Hope this helps a bit rather than cause confusion on this topic.

BTW - 'Hi' to all our friends on Fiberglass RV - I haven't been 'stopping by' as often since we bought our View...

Bill

[Francesca Knowles]

Originally Posted by Bill Robison

Francesca -

It all depends ...what type of new Norcold fridge you had installed - was it ammonia process or small compressor? All 12v fridges are not equal in terms of amps of draw. If yours is a 120v/12v compressor type - similar to what we had in our EggCamper - then it should be able run easily on either 120v or 12v depending on what is available. We had one group 24 Deep Cycle battery with no solar and the Norcold (compressor) would run very effeciently off the battery for three to four days with amps to spare. I would monitor the battery voltage levels and when we were ready for showers in the boondocks I would start the Honda EU2000i for electric water heater - then let it idle to re-charge the battery for an hour or so.

When the majority of campers hear '12v' and 'fridge' in the same sentence they assume it means 'ammonia type' cooling, which is efficient on propane but certainly not on 12v. If yours happens to be 'ammonia type' then disregard using 12v and stick with 120v and/or propane - it will cooler nearly *forever* on LP ;-)

Hope this helps a bit rather than cause confusion on this topic.

BTW - 'Hi' to all our friends on Fiberglass RV - I haven't been 'stopping by' as often since we bought our View...

Bill

I have the original true 3-way fridge in my trailer...each power source is independent of the other two.

So-called "two-way" fridges that are 12v/110 should in my opinion be instead referred to as "all-electric" so as to differentiate them from a true 2-way, which is electric/propane.

That's the setup I recommend to folks, and as far as I know, there's no such fridge available with a compressor. In my experience, all propane-fired refrigerators are absorption units...but I don't pretend to be up on the latest technology and hope someone will correct me if I'm wrong.

Francesca

[Carol H]

I suspect that the confusion comes in a little as most people such as myself assumed when running a 3 way fridge (even my oldie ammonia one) on propane it wasnt using any battery power at all - as I discovered while looking for a new fridge option & looking at the full specs of what I already have that wasn't/isnt actually true. Most fridges do even when running on propane use a *little* bit of battery power.

[Francesca Knowles]

Originally Posted by Carol H

I suspect that the confusion comes in a little as most people such as myself assumed when running a 3 way fridge (even my oldie ammonia one) on propane it wasnt using any battery power at all - as I discovered while looking for a new fridge option & looking at the full specs of what I already have that wasn't/isnt actually true. Most fridges do even when running on propane use a *little* bit of battery power.

I remember the discussion we had about that...but I emphasize again that it's only more recent three-way fridges that use any electricity at all when on propane. I don't know when that became true...but it certainly wasn't true in the '70's, when many of our older trailers were built and equipped.

Francesca

[Bill Robison]

Originally Posted by Francesca Knowles

I have the original true 3-way fridge in my trailer...each power source is independent of the other two.

I guess I missed that your fridge also had LP capability, while reading the above posts...

So-called "two-way" fridges that are 12v/110 should in my opinion be instead referred to as "all-electric" so as to differentiate them from a true 2-way, which is electric/propane.

You are correct - that they should perhaps be referred to as 'all electric'; however, the MAJOR difference is the TYPE of cooling process used. For example, my Norcold was 'all electric' (120v/12v), but since it had a compressor rather than ammonia - it was able to efficiently run on either 120v or 12v. '

That's the setup I recommend to folks, and as far as I know, there's no such fridge available with a compressor. In my experience, all propane-fired refrigerators are absorption units...but I don't pretend to be up on the latest technology and hope someone will correct me if I'm wrong.

Again, I agree that 'all propane refrigerators are absorption units', however, this thread got a bit clouded with repeated references to 'this type' of fridge without clearly describing *what* that type was. Further, there are compressor fridges widely used in marine environments - and some campers, which are *compressor* type rather than absorption type and run with low draw via 120v or 12v.

Francesca

Not attempting to be argumentative - simply trying to be clear for those on the forum who are running their compressor type fridge on 12v in the boondocks - it's OK to do so. Just don't try it with an absorption type...

Peace

Bill

[Bob Miller]

Just to add a bit more to the confusion:

A Typical absorbtion type refrigerator running on the 12 VDC heating element will pull about 8-10 amps. The bad news is that it can be difficult to get that much current flow from the TV's alternator, through the trailer connector and 25+ feet of wire, to the refrigerator. As a result, it's not uncommon for the refrigerator to hog necessary current from the coach battery as well. As a result you can arrive at your destination with a low or dead coach battery. The lesson is to measure current flow through the charging line and be sure there is enough to charge the coach battery as well as run the refrigerator.

[Raz]

I think the original post was referring to a 3 way absorption fridge and someone along the way confused it with a Danfoss compressor type. Raz

[Carol H]

[QUOTE=Francesca Knowles;347974..but I emphasize again that it's only more recent three-way fridges that use any electricity at all when on propane. I don't know when that became true..[/QUOTE]

Recent is a relative term My 20 year old Dometic 3 way absorption fridge a model that is no longer make does use of a *tiny* bit of power when on propane.

[Thomas G.]

Originally Posted by Francesca Knowles

I remember the discussion we had about that...but I emphasize again that it's only more recent three-way fridges that use any electricity at all when on propane. I don't know when that became true...but it certainly wasn't true in the '70's, when many of our older trailers were built and equipped.

Francesca

Right. The only electricity that mine uses running on LP is what the thermocouple generates.

[Byron Kinnaman]

Originally Posted by Bob Miller

Just to add a bit more to the confusion:

A Typical absorbtion type refrigerator running on the 12 VDC heating element will pull about 8-10 amps. The bad news is that it can be difficult to get that much current flow from the TV's alternator, through the trailer connector and 25+ feet of wire, to the refrigerator. As a result, it's not uncommon for the refrigerator to hog necessary current from the coach battery as well. As a result you can arrive at your destination with a low or dead coach battery. The lesson is to measure current flow through the charging line and be sure there is enough to charge the coach battery as well as run the refrigerator.

Part of that is the alternator in the tow vehicle. Wiring to get enough current is fairly easy, even if you had to add another charge wire. The biggest problem is the alternator and the current drawn by the tow vehicle. I have one that doesn't put out enough to charge the battery and run the fridge, one that does. (1998 Blazer with towing wiring add, 2005 Dakota with heavy duty tow package)

Even with the Dakota I usually don't run the fridge on 12V, I've found that the fridge stays cool enough without running while moving from one place to another.