Odd inverter question

[GallenH]

Ok. This may (probably?) be a stupid question but....I have a Dometic 3-way fridge which works ok but is wimpy in 12v mode. Only use it when driving but it still doesn't cool as efficiently as when it's on LP or 120v. Could you use an inverter and it on 120v. when driving? Would the inverter be sustained by the alternator/battery when driving so that driving would compensate for its use? Not making my question very clear, eh?

Of course, the next question is would running it off an inverter really equate to 120v shore power? Or would there be no gain? On my fridge there are separate 12v and 120v elements.

A humorous aside. Getting ready for trip. Had fridge on 120v and lowest thermostat setting. Got fridge down to 38 overnight. Sat in sun during day with windows closed (neighbors had gravel dumped raising huge dust cloud). Temp in RV got to 117 (we're talking PX,AZ). Fridge jumped to 58.

[markopolo]

Yes, you can run the fridge off the inverter while driving & yes it should perform a bit better than on 12V as it does equal shore power. I do that in both of my RV's.

[peteco]

Originally Posted by GallenH

A humorous aside. Getting ready for trip. Had fridge on 120v and lowest thermostat setting. Got fridge down to 38 overnight. Sat in sun during day with windows closed (neighbors had gravel dumped raising huge dust cloud). Temp in RV got to 117 (we're talking PX,AZ). Fridge jumped to 58.

A good fan ventilation system of the backside of the fridge should help somewhat. Park with the refrigerator on the shade side of the van. Solar heating of the fridge vent cavity can cause the fridge efficiency to drop significantly.

[rowiebowie]

Originally Posted by peteco

A good fan ventilation system of the backside of the fridge should help somewhat. Park with the refrigerator on the shade side of the van. Solar heating of the fridge vent cavity can cause the fridge efficiency to drop significantly.

I can confirm solar heating of the vent cavity is a real problem. When the sun is shining on the fridge side of my van, the cavity behind the compressor fridge reaches 20 degrees hotter than the van interior. The temp difference used to be closer to 30 degrees before I added additional insulation back there because apparently Airstream did not think it was that important.

[Bud]

Originally Posted by GallenH

Ok. This may (probably?) be a stupid question but....I have a Dometic 3-way fridge which works ok but is wimpy in 12v mode. Only use it when driving but it still doesn't cool as efficiently as when it's on LP or 120v. Could you use an inverter and it on 120v. when driving? Would the inverter be sustained by the alternator/battery when driving so that driving would compensate for its use? Not making my question very clear, eh?

Of course, the next question is would running it off an inverter really equate to 120v shore power? Or would there be no gain? On my fridge there are separate 12v and 120v elements.

A humorous aside. Getting ready for trip. Had fridge on 120v and lowest thermostat setting. Got fridge down to 38 overnight. Sat in sun during day with windows closed (neighbors had gravel dumped raising huge dust cloud). Temp in RV got to 117 (we're talking PX,AZ). Fridge jumped to 58.

It appears that your refer is working, working ok? I obviously don't know the answer, but if it is yes, it is all about making heat and cooling the heat.

Yes, you can drive down the road with ac from the inverter and the batteries will still be charging. I run on ac or propane, mostly ac, but both. Both make more heat than dc, never use it.

If I recall correctly, you have a PleasureWay. At times PleasureWay used fans to provide ventilation for cooling. Do you have a fan? Is it working? With Roadtreks, something has to be done while driving to improve, no FIX the lousy ventilation. I use fans, mostly while driving.

Bud

[GallenH]

Thanks for the replies. I actually don't have an inverter so would have to figure out if it's worth adding when that's really the primary purpose. How would I size the inverter? Where would it be placed with respect to the fridge or battery?

Yes, last year I added two computer fans to promote airflow in the fridge compartment. They're mounted pointing at an angle upward to draw air through the lower vent and direct it towards the upper vent. That seemed to improve cooling. Always hard to tell precisely since each trip involves different weather/temperature conditions.

My insulation around the fridge (viewed from the back) consists of strips of fiberglass insulation; look to be 1" thick and 4" wide. Advantage perhaps to replacing with something wider? Thoughts?

best.

[Doneworking]

In BWorld, we always think of running down the road on 12 volts. Think about trailers and most Class Cs: they run down the road on propane for the refrig. Yes, you gotta remember to turn off the refrig briefly when fueling.

[Bud]

"Yes, last year I added two computer fans to promote airflow in the fridge compartment. They're mounted pointing at an angle upward to draw air through the lower vent and direct it towards the upper vent. That seemed to improve cooling. Always hard to tell precisely since each trip involves different weather/temperature conditions."

Fans are interesting and not understood sometimes. A fan will draw air from the path with least resistance which is from the sides! I can't see your fans, but it appears that they may be inside the refer compartment and not forcing air to enter from the outside. If not, there may be 'looping' of air in the compartment.

I added 2 fans to 2 of the exhaust vents of the refer compartment, pretty much worthless until I covered the other 2 vents. Then Bingo.

Bud

[Roadtrek Adventuous RS1]

Originally Posted by Bud

"Yes, last year I added two computer fans to promote airflow in the fridge compartment. They're mounted pointing at an angle upward to draw air through the lower vent and direct it towards the upper vent. That seemed to improve cooling. Always hard to tell precisely since each trip involves different weather/temperature conditions."

Fans are interesting and not understood sometimes. A fan will draw air from the path with least resistance which is from the sides! I can't see your fans, but it appears that they may be inside the refer compartment and not forcing air to enter from the outside. If not, there may be 'looping' of air in the compartment.

I added 2 fans to 2 of the exhaust vents of the refer compartment, pretty much worthless until I covered the other 2 vents. Then Bingo.

Bud

Our unit has a 3.6 cubic foot Dometic 3 way fridge..... unfortunately ... there's no room behind the cabinet to add a cooling fan.....

[Roadtrek Adventuous RS1]

Originally Posted by Doneworking

In BWorld, we always think of running down the road on 12 volts. Think about trailers and most Class Cs: they run down the road on propane for the refrig. Yes, you gotta remember to turn off the refrig briefly when fueling.

That's all you have to do...... once you are back on the road it's safe to go back to the propane......

[booster]

Originally Posted by Roadtrek Adventuous RS1

Our unit has a 3.6 cubic foot Dometic 3 way fridge..... unfortunately ... there's no room behind the cabinet to add a cooling fan.....

Pix show upper and lower outside frig vents on the van side, so there has to be some room there.



Have you had the frig out to confirm that, or removed the outside vents to look? There has to be some space or there would be no air going from the bottom to the top vent to cool the frig.

[Roadtrek Adventuous RS1]

Originally Posted by GallenH

Ok. This may (probably?) be a stupid question but....I have a Dometic 3-way fridge which works ok but is wimpy in 12v mode. Only use it when driving but it still doesn't cool as efficiently as when it's on LP or 120v. Could you use an inverter and it on 120v. when driving? Would the inverter be sustained by the alternator/battery when driving so that driving would compensate for its use? Not making my question very clear, eh?

Of course, the next question is would running it off an inverter really equate to 120v shore power? Or would there be no gain? On my fridge there are separate 12v and 120v elements.

A humorous aside. Getting ready for trip. Had fridge on 120v and lowest thermostat setting. Got fridge down to 38 overnight. Sat in sun during day with windows closed (neighbors had gravel dumped raising huge dust cloud). Temp in RV got to 117 (we're talking PX,AZ). Fridge jumped to 58.

My understanding is...12 volt battery power will just maintain the temperature.... won't provide any additional cooling..so, if the ambient temperature increases from 70 to 100 degrees outside....the fridge will not keep up.....

Normally, we leave it on propane when driving.... and have to go to batteries whenever we're getting fuel.... safety.....

Also, the sun and ambient temperature had a huge effect on the absorption refrigerator......I'm not a big fan of this, but, without a larger battery bank and power, gas absorption refrigerators do have a place.

We have a 160 watt solar panels system.... and two 6 volt AGM batteries..... not enough to go to a conventional refrigerator.... I

[booster]

Originally Posted by Roadtrek Adventuous RS1

My understanding is...12 volt battery power will just maintain the temperature.... won't provide any additional cooling..so, if the ambient temperature increases from 70 to 100 degrees outside....the fridge will not keep up.....

Normally, we leave it on propane when driving.... and have to go to batteries whenever we're getting fuel.... safety.....

Also, the sun and ambient temperature had a huge effect on the absorption refrigerator......I'm not a big fan of this, but, without a larger battery bank and power, gas absorption refrigerators do have a place.

We have a 160 watt solar panels system.... and two 6 volt AGM batteries..... not enough to go to a conventional refrigerator.... I

Lots of folks get by with two 6v GV batteries, some solar, and a compressor frig as long as they don't want to stay a long time in one place without driving and/or always in the shade. We did it for years while testing.

[Roadtrek Adventuous RS1]

Originally Posted by booster

Pix show upper and lower outside frig vents on the van side, so there has to be some room there.



Have you had the frig out to confirm that, or removed the outside vents to look? There has to be some space or there would be no air going from the bottom to the top vent to cool the frig.

Yes, they were going to install a couple of 12 volt fans similar to what you find in computers.... couldn't do it due to space......

I called Roadtrek back before the closure and they said "yeah, we don't do cooling"... never even thought about doing it?? Not good. It's a space problem. It's such a small unit... they didn't think it was necessary.

[Roadtrek Adventuous RS1]

Originally Posted by booster

Lots of folks get by with two 6v GV batteries, some solar, and a compressor frig as long as they don't want to stay a long time in one place without driving and/or always in the shade. We did it for years while testing.

OK, please give me an example. I don't like the fact that our fridge is sensitive to elevation..... anything over 3200 feet and it doesn't work.... yes, in the owners manual...WTF😠.

And, it might not be the most efficient on batteries... seems to start flashing lights if it has been on batteries and not plugged in.....

I'd like to think about changing this to a conventional refrigerator.... my RV mechanic says I'd be crazy to do that....he says that the propane refrigerator is one of the most efficient models out there and it's a 3 way fridge....

It is temperature sensitive... when it's 100 degrees.. cooling even on shore power is around 55 degrees inside....

I'm not impressed with it..... although I really don't want to spend a lot of money on this right now..... other issues..

The 160 watt solar panel does keep the two 220 Amp batteries pretty charged up, but, there's only so much power in the two batteries..... can't get too many hours on those. It would run down my power to quickly.

Any ideas...or suggestions? I'm open to hear about options. thanks.

[booster]

Originally Posted by Roadtrek Adventuous RS1

Yes, they were going to install a couple of 12 volt fans similar to what you find in computers.... couldn't do it due to space......

I called Roadtrek back before the closure and they said "yeah, we don't do cooling"... never even thought about doing it?? Not good. It's a space problem. It's such a small unit... they didn't think it was necessary.

If there isn't enough room for fans, then it likely also violates all the install rules. There is normally a gap between the absorber and condenser that has plenty of room for small fans most of the way across the frig. Some pics of a current 3.7cf Dometic show that configuration. Fans in the middle are fine as long as they are properly baffled to keep the flow from bottom to top without looping.



I don't think "they" looked very hard for a location and fans.


Roadtrek thought lots of stuff "wasn't necessary" as we have seen over time, but they certainly weren't always correct, and would never admit they were in error.

[Bud]

"I'd like to think about changing this to a conventional refrigerator.... my RV mechanic says I'd be crazy to do that....he says that the propane refrigerator is one of the most efficient models out there and it's a 3 way fridge...."

Then there is the onan mechanic and sprinter mechanic.

[booster]

Originally Posted by Roadtrek Adventuous RS1

OK, please give me an example. I don't like the fact that our fridge is sensitive to elevation..... anything over 3200 feet and it doesn't work.... yes, in the owners manual...WTF😠.

And, it might not be the most efficient on batteries... seems to start flashing lights if it has been on batteries and not plugged in.....

I'd like to think about changing this to a conventional refrigerator.... my RV mechanic says I'd be crazy to do that....he says that the propane refrigerator is one of the most efficient models out there and it's a 3 way fridge....

It is temperature sensitive... when it's 100 degrees.. cooling even on shore power is around 55 degrees inside....

I'm not impressed with it..... although I really don't want to spend a lot of money on this right now..... other issues..

The 160 watt solar panel does keep the two 220 Amp batteries pretty charged up, but, there's only so much power in the two batteries..... can't get too many hours on those. It would run down my power to quickly.

Any ideas...or suggestions? I'm open to hear about options. thanks.

We have done it, as mentioned, as have many others here. I am not going to start chasing all your "prove it so it would satisfy me or NASA but I still won't believe it", as all the information you need is on this forum.


If you have an RV mechanic that thinks the 3way is the most efficient frig, it is no wonder he couldn't find a place for fans (with both hands).



If your 160 watts on two 200+ah of AGM can't run a compressor frig reliably, you either are sitting a long time in the poor sun and not driving either, or your batteries, solar, and charging systems aren't working well. Or you are wasting lots of battery capacity somehow.

[Davydd]

These are the fans behind the refrigerator Advanced RV installed. Our 2-door refrigerator/freezer is about a big as you can get in a Class B at 6800 cubic Inches and the cabinet is a standard 24" deep and the overall refrigerator/freezer is 20-1/2" deep and I have researched very few any deeper. Air is drawn in at the baseboard and exhausted inside with cabinet slots surrounding the microwave installed above the refrigerator. There are no outside vents so if air conditioning is on it is circulating conditioned air instead of outside air and the wall is fully insulated. Refrigerator is a compressor refrigerator always in 12V mode which is about 1/3 the energy draw of a comparable absorption refrigerator operating on 12V.

I don't know how you can find a refrigerator much more efficient in cooling if it is 90-100 deg. F. outside and drawing that air fans or not. Most people in this day and age keep their home refrigerator in conditioned air between 70 and 80 deg. F. Despite what we have the temperature does climb higher than 41 deg. F. in the heat of the day since I tend to not run air conditioning and can live easily up to and around 90 deg. F. with air circulation on creating an inside breeze on a calm day.

[GallenH]

If you go back to my first post and the last paragraph: So with the windows open and the ceiling fan on, the van dropped down to 87 by evening. By morning the fridge was once again at 35. And we loaded for the trip.

About a 3 hour drive to the rim on 12v. The rim in AZ is where the land dramatically rises in elevation. We camped on the rim for several nights and the fridge, on LP, held a constant 38-40. Temps are milder than phx. That's why we go there in the summer. Highs 80s/lows50s. We then went to the White Mountains for 2 days. Highs 80s/lows 60s. Again, fridge on LP held temps 38/40. We then drove home to Phx. About a 5 hr drive but delayed by 2 hrs given a wildfire near road (Entire road shut down leaving us in a very long line of traffic...standing still..on the highway). We were running 12v and by phx the fridge had risen to 58. Fans in fridge compartment running during trip home..

The fridge is a Dometic 3-way 2531. That's a small fridge of the vintage where there is no circuit board. You're either tapping 12v from the battery, 120v from shore, or using LP which ignites manually with a piezo spark.

Several points. Obviously the 12v is a weak link here. I'm hesitant driving with LP on and simply don't do it. Ok, I did it once and, as some have noted, turned it off when fueling. Over cautious?

Also, I know what the Dometic manual states, but the rim is at 8000 feet elevation and the White Mountains 9100. I'm not making numbers up. The fridge cooled to the above temps at those elevations. Now bear in mind that's with the thermostat at max setting.