Should I rewire instead of going from DC-AC-DC for RV 12V appliances? (Solved)

[Pappion]

I appreciate the graphs.

Can you tell me how many WH per day your new fridge versus the old fridge? Looking at your graph my estimate is 8 kwh per day with the old, and less than 1 kwh with the new.

I have a propane fridge running in electric mode right now ane the temp is comfortable 65 F outside. My fridge uses 350w to 400w when on, and when I run it on electric, it takes 5 kwh to power it. I think in the summer the fridge would use much, much more power.

His Frig has a problem. 17 years old and using to much power. Most likely gasses had crystalized.

Your 5kwh per day is about 208w per hour, about 50% duty cycle.

In the summer Air Conditioning makes a difference. 80F on 3 sides worked on my old A-frame camper.

Boon docking in the AZ mountains, with no AC, in 90-100F challenged the frig. I added ventilation fans in the vents for back of the frig. Also the freezer worked great, so I froze Blue Ice and would move it down to the frig part for midday. Also helps to have some liquid ballast (beer) in the frig.

IMHO: Absorption Frigs are not efficient, but they will run on propane

 

[chrisski]

IMHO: Absorption Frigs are not efficient, but they will run on propane

I feel on propane mode atan AZ winter of highs of 70 F, these propane fridges use an insignificant amount of propane, but am not coming up with a accurate way to measure propane usage. Always end up cooking on propane or turning the heat on so I can’t tell whenI fill it up. THe sticker says 1420 BTUs, but I don’t have a way to turn it into how much propane is actually used.

Appears to only burn a candles worth of propane, so next to none.

 

[Pappion]

You can upgrade or convert your RV Frig.
excerpts:
A. again unlike a residential fridge that draws between 6-8A 960W AC, my unit draws only .8 A 92W which is less then what most inverters draw by themselves
A. on paper the 12V is the most efficient @ 7.5A 90W, but it runs some slower than the 120V,
A in our testing @ 80F the AC compressor will run approx. 56% and the DC approx. 64%, that is not opening and closing the doors.
RV frig upgrade or conversion

There are other 12/24 volt refrigerators out there. Often one model is 12 or 24v by moving a jumper.
12v RV frig

keep Googleing

 

[Pappion]

I feel on propane mode atan AZ winter of highs of 70 F, these propane fridges use an insignificant amount of propane, but am not coming up with a accurate way to measure propane usage. Always end up cooking on propane or turning the heat on so I can’t tell whenI fill it up. THe sticker says 1420 BTUs, but I don’t have a way to turn it into how much propane is actually used.

Appears to only burn a candles worth of propane, so next to none.

There is no free lunch. Electric heaters are in the same column the propane heat rises into. So electric use is a good guide. The propane heat seems to be used well.

Your propane furnace is not efficient. Heat exchanger is just a pipe spiral wrapped around a few times. Burning propane is blown thru it, and out while still hot. Cabin air is blown over the pipe to get hot.
You water heater is not much better. It too has a hot pipe and blows out hot air.

I'm in my winter RV park in AZ. I am using electric heat mostly. I tamed the beast with a Wall Outlet Thermostat.
Outlet Thermostat
NOTE: Works with electric heaters that can tolerate the AC being turned on and off. So it's no good for Digital models that need setup or start button push.

 

[eXodus]

I feel on propane mode atan AZ winter of highs of 70 F, these propane fridges use an insignificant amount of propane,

the amount of energy stored in a propane tank is just mind boggling.
1 Gallon of Propane = 27kwh of energy
1 Gallon propane = 4.4lbs
Roughly 6 kwh per lbs. I refuel my propane tank in the RV with around 30lbs - that's almost 180kwh of energy storage.

My propane fridge needs about 4-5 kwh of electric a day (which is bad compared to a compressor with 1-2kwh) but that still gives me 30+ days of fridge service on the propane tank. And I got the feeling since propane burns hotter then the electric heating element gets - it might be even more efficient on the absorption fridge.

 

[12VoltInstalls]

that still gives me 30+ days of fridge service on the propane tank. And I got the feeling since propane burns hotter then the electric heating element gets - it might be even more efficient on the absorption fridge.

these propane fridges use an insignificant amount of propane

Older propane RV fridges without electronics use very little propane as well.
The AEG unit I took out and sold was 160W+ on 120V and took a day to cool from ambient. But on propane- between hot water, cooking, and fridge- it cooled in a few hours. I have gone well over a month on a 20# cylinder. Six weeks at least once. Not sure how efficient that was but it was inexpensive. Electricity takes a much longer time for the same cooling but on small solar 160W nearly continuously is “expensive.”

I’d agree. Propane absorption fridges don’t use an economically significant amount of propane.

My main peripheral reason for selling was so I could cold weather insulate. The primary up-front reasons I switched was to replace a 1977 fridge inexpensively before it failed and have 10-12CF options that cost less than a week’s take home pay. The 5CF I’m using was about $150 delivered- very inexpensive- though in hindsight I should have spent $350 for the 10CF

 

[eXodus]

it cooled in a few hours.

that would indicate higher efficiency.

Efficiency is defined "the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in."

Through the higher heat differential the fridge might more heat out of the fridge (good old thermodynamics) because the air rises faster on the back side compared with the electric element. So you might get more "cold" from one kwh of propane then compared with 1 kwh of electric.

To get back on topic:
Same for the 48V - 120V - 12V conversion - that might be more inefficient but it will be probably cheaper.

Electricity takes a much longer time for the same cooling but on small solar 160W nearly continuously is “expensive.”

it really all depends how much you use the RV in a year.

the 48V - 12V is better - but like the fridge- when you only use it 1-2-3 months in a year - it really doesn't matter. If you are full-time - different story

 

[12VoltInstalls]

you might get more "cold" from one kwh of propane then compared with 1 kwh of electric

Exactly what I think happens.

 

[kjswiley]

I appreciate the graphs.

Can you tell me how many WH per day your new fridge versus the old fridge? Looking at your graph my estimate is 8 kwh per day with the old, and less than 1 kwh with the new.

I have a propane fridge running in electric mode right now ane the temp is comfortable 65 F outside. My fridge uses 350w to 400w when on, and when I run it on electric, it takes 5 kwh to power it. I think in the summer the fridge would use much, much more power.

Sure. I grabbed this info for the new fridge just now, let me know exactly what you would like me to do and I am happy to pull more info, I don't really know how to get it. I ran the fridge for 1 hour (9:15 local time so not hottest of day, but it's not hot out anyway). Since the old fridge seems to be malfunctioning it is unhooked and will remain so. I shut off all loads except the inverter (70W draw, and the auto-transformer (10W draw). I plugged this into a dedicated receptacle I have connected to my panel (not RV panel), so all RV draws were off at this time.


9:15 - Inverter + Transformer. After screenshot I turned on Fridge




9:45


10:15

 

[kjswiley]

Also, I kept reading people say "they have so much more room", and rolled my eyes. Well, it is true, here are the same items pushed to the back of each fridge:

 

[KellyDood]

I'm doing more experimenting before posting my results with EcoDelta solar generator but, I noticed using the AC adaptor for CPAP used almost 3 times as much capacity as the 12-volt adaptor. I could be wrong, but that was my initial observation. It makes sense to me the inverter would eat up more juice.

 

[chrisski]

I'm doing more experimenting before posting my results with EcoDelta solar generator but, I noticed using the AC adaptor for CPAP used almost 3 times as much capacity as the 12-volt adaptor. I could be wrong, but that was my initial observation. It makes sense to me the inverter would eat up more juice.

Seems like some of this math is not linear.

 

[12VoltInstalls]

noticed using the AC adaptor for CPAP used almost 3 times as much capacity as the 12-volt adaptor.

The power needs of the cpap are probably handled by the adapter at the output listed. But an adapter is maybe 50% efficient at best - in your case 30-40% or something.

But that’s a big loss.

 

[Pappion]

Ran my Frig on a KiloWatt Hour meter. 4.35KW per Day. Average 181 watt per hour. Average duty cycle 45% for 400W heating elements.
Wintering in Benson AZ, 70-80f day, 30-35f night. 67f - 87f inside.

 

[Browneye]

You can upgrade or convert your RV Frig.
excerpts:
A. again unlike a residential fridge that draws between 6-8A 960W AC, my unit draws only .8 A 92W which is less then what most inverters draw by themselves
A. on paper the 12V is the most efficient @ 7.5A 90W, but it runs some slower than the 120V,
A in our testing @ 80F the AC compressor will run approx. 56% and the DC approx. 64%, that is not opening and closing the doors.
RV frig upgrade or conversion

There are other 12/24 volt refrigerators out there. Often one model is 12 or 24v by moving a jumper.
12v RV frig

keep Googleing

JC Refrigeration - the 'amish unit' - a unique category even for the ARP board folks.
This is a new source for me - their Hvac compressor conversion for a Norcold 841 at $735 is a game-changer!! ?

 

[chrisski]

Ran my Frig on a KiloWatt Hour meter. 4.35KW per Day. Average 181 watt per hour. Average duty cycle 45% for 400W heating elements.
Wintering in Benson AZ, 70-80f day, 30-35f night. 67f - 87f inside.

Pretty close to my results. I hit 5kwh per day for the propane fridge