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

[kjswiley]

edit" Problem was the RV Fridge is a power hog that really should be run on Propane- I left my RV wired as DC-AC-DC. I bought a new fridge, problems solved. Added graphs to show the difference made in case anyone else is considering the switch from RV to residential fridge. I only bought a basic, 350$ unit from Home Depot as it was the same size as my RV fridge (Home Chef 10.1). I have gained a TON of interior space, and the fridge uses a fraction of energy. I am sure there are better residential units to buy, but this fit my needs and was easily obtainable.

Original question: long story short is the loss in efficiency noticeable with the following, or should I just ignore it and save my time and money leaving cables as they are?

I have a 48V system using the Growatt 5000ES Inverters off grid, these put out 240V (this will go into a house once built, otherwise 12V or 24V is probably a better choice). I have the auto-transformer to create the 120V Neutral. I have wired a circuit panel (powered by Growatt/Transformer) to my travel trailer (TT) circuit panel to power the TT. The TT panel connects to a small inverter (this is stock with the system) which converts from AC to DC to power the DC appliances and charge the TT AGM batteries (these were disconnected/ no longer part of the system).

Would it be worth my time to run a wire from the Victron 48V to12V DC-DC converter I already have to my 12V TT appliances instead, so only the 120V portion of the TT is powered by the main Growatt circuit panel....or is the loss not something that I would notice? Right hand side of pic would be fed by 120V, left side by 12V...disconnecting the two and separating them.

Current Setup:
Battery Bank -> Growatt/Transformer -> Main 240V Circuit Panel -> -> 120V Sub Panel -> TT 120V Circuit Panel -> 12V Appliances

While this is probably better, is it worth while?
Battery Bank -> Victron 48V-12V Converter - >12V Appliances





Edit: Here are the graphs that show the improvement from the fridge replacement. As you can see this plays much nicer with my system.


You can see when I finally turned off the electric from the water heater and switched to propane in the evening, RV fridge is still running.


New fridge:

 

[rmaddy]

It probably depends on how much DC load you have compared to AC load. If your daily DC loads are a tiny fraction of your daily AC loads then it probably isn't worth the effort. But if you use far more DC loads in the day than AC then you might save 10-15% of your battery each day. But keep in mind that the Orion 48V->12V converter has its own losses since it is not 100% efficient. Certainly more than your current DC->AC->DC conversions though.

In my trailer my daily use is 100% DC most of the year. Maybe once every few weeks I'll turn on my inverter for an hour or two for the rare times I need to plug some small AC device in. In the summer my inverter will be on a lot more during the day to run a small A/C to keep the trailer cooler.

 

[kjswiley]

Great I will leave it as is, the fridge/AC are the only real draws I have anyway.

 

[time2roll]

No 12v furnace? 12v lights? As a minimum I would measure the converter draw at idle to know what is the minimum wattage vs to DC-DC option.

Of course with tons of battery and solar maybe it does not matter.

I expected to see a 50 amp distribution panel with 240v split phase power.

 

[kjswiley]

No 12v furnace? 12v lights? As a minimum I would measure the converter draw at idle to know what is the minimum wattage vs to DC-DC option.

Of course with tons of battery and solar maybe it does not matter.

I expected to see a 50 amp distribution panel with 240v split phase power.

Will not need the furnace as I will be in tropical Mexico, but I have ran it since I am not there yet and it does not draw much power. Lights are LED so no real draw there......all things DC are drawing about 400W at their peak if I read things correctly (this number was definitely wrong haha), which is just the fridge and phantom/small electrical charges for furnace/oven when not in use. I may or may not run AC but my system can handle that as I did give it a quick test run.

The TT Panel is only connected to 120V, as I have separate panels for the 240V and 120V. I did not add it in to avoid confusion, but you are correct in that is how it would appear. I update the post for accuracy.

Thanks

 

[rmaddy]

400W! Do you actually mean that you have a constant 400W DC load? 24 hours per day? That's 9600Wh per day. That would use 90% of a 48V 200Ah battery bank every day.

 

[kjswiley]

400W! Do you actually mean that you have a constant 400W DC load? 24 hours per day? That's 9600Wh per day. That would use 90% of a 48V 200Ah battery bank every day.

No sorry I am reading it all wrong.

I just flipped the breaker and using my shunt for info there was only a 30 watt addition to the load when I turned it back on, which makes much more sense. I do not really have anything running so will see how high it climbs from the fridge etc.

 

[Pappion]

Your electronic controls loads are typically minuscule at idle for Absorption Frig, Hot Water Heater, Furnace, and AC.
When they are on: LPG solenoids ~ 1A, AC relay ~ 0.25A, 12v Furnace Blower varies by size: 3.5A, 7.5A and up

example: Atwood Water Heater model GC6AA-10E, LPG and Electric
OEM Board, HOT Idle: Both 0.01a, Heating: both 1.05a, elec only 0.24a, gas only 0.89a
Dinosaur Board, HOT Idle: Both 0.02a, Heating: both 0.75a, elec only 0.11a, gas only 0.66a

I power my Laptop from 12v adapter. Much more efficient than going thru 110v inverter.
The Travel Trailer Stereo is 12v. I have a small inverter for TV, DVD, Wiii and Hepa filter.

 

[kjswiley]

I assume you guys know RV loads, I do not....this TT is kind of new to me. I think my water heater comes on about 10 times a day, for about 15-20 minutes. I am guessing it is that based on the watts used and the fact that I have nothing going except laptops, fridge, heater (not running as temp is set low), especially late at night where you still see the spikes. I assume the medium humps are my absorption fridge, I can see where it ran for longer to get cold after having lost power.

As a single guy I think I should just turn the water heater off for most of the day. I have a water heater switch on the wall which I turned off today but I still have these loads which is why I am confused (perhaps the switch is bad and it is always on, I will check that tomorrow). Any other item you can think of RV wise.....I did not run the microwave or AC though a spike was from a shop vac briefly running. The Growatt inverter shows me using about 27% of the 5000W when it spikes, so I figure it must be the water heater. I shut off the power a few times as I was working on an unrelated water leak, but there is something cycling that is taking more power than I think I would like. I can tell it is a DC load from the TT as kicking the breaker for the TT AC-DC converter (which kills all 12V) drops it from 27% down to 1.3%-6%.

Is this also a case of I should just ignore the brief loads?

 

[time2roll]

My inside switch controls the propane burner. The electric shut off is outside behind the service cover. Simple rocker switch.

 

[Pappion]

If your running the FRIG and Water Heater on AC it will cost you many hundreds of Watts.
Turning off the 12VDC will shut down the control board and AC relays.

My FRIG has an AC 440W heater element. Which makes the Absorption gasses move.
My Water Heater has an AC 1400W heating element.

 

[kjswiley]

If your running the FRIG and Water Heater on AC it will cost you many hundreds of Watts.
Turning off the 12VDC will shut down the control board and AC relays.

My FRIG has an AC 440W heater element. Which makes the Absorption gasses move.
My Water Heater has an AC 1400W heating element.

Thank you, after I wrote that I was thinking about how that was too many watts for a dc appliance, but couldn't figure out why throwing the breaker would otherwise cut the load. Those wattages match up with what I am seeing as well.

I assume no one shuts down their heater via the rocker switch outside, so will probably ignore everything for now, but shutting it down would save me some power so we will see how it pans out as I learn how to use the system.

 

[time2roll]

I have a 30 amp RV and generally run the fridge and water on propane only to manage electric power better. My switch is mostly off.
Yes an absorption fridge is about 300+ watts and about 60% duty cycle in normal conditions. Mine runs mostly on propane.

 

[HRTKD]

I have a 30 amp RV and generally run the fridge and water on propane only to manage electric power better. My switch is mostly off.
Yes an absorption fridge is about 300+ watts and about 60% duty cycle in normal conditions. Mine runs mostly on propane.

Same here. I run my absorption refrigerator and the water heater on propane. I do turn the water heater on/off as needed when the weather is reasonable. When the temperatures are below freezing the water heater stays on all the time.

 

[kjswiley]

Same here. I run my absorption refrigerator and the water heater on propane. I do turn the water heater on/off as needed when the weather is reasonable. When the temperatures are below freezing the water heater stays on all the time.

Appreciate it, still figuring the RV thing out...going to increase my battery bank anyway but will probably use propane for the fridge and water heater now that I see everyone's responses.

 

[HRTKD]

If you want to reduce propane use, consider a DC compressor refrigerator. There are units available that fit within the same space as the existing absorption refrigerator. If my absorption refrigerator dies, I'm switching to the 12 volt DC compressor unit.

 

[kjswiley]

If you want to reduce propane use, consider a DC compressor refrigerator. There are units available that fit within the same space as the existing absorption refrigerator. If my absorption refrigerator dies, I'm switching to the 12 volt DC compressor unit.

edit: Jesus, according to my growatt my fridge runs for 50 minutes each hour more or less....I will try turning it down but maybe the fridge is bad as it is only at 6. If it is original it's 17 years old, maybe I should throw in the DC compression fridge after all.

I was thinking about that as well, the ARB in my truck is great when it comes to power consumption. I too must wait until my fridge goes, unfortunately nothing wrong with the one I have so I will see how I feel about propane. Good news is I will not need heat, and if propane is a pain I can forgo the water heater as it is the tropics.

 

[Pappion]

edit: Jesus, according to my growatt my fridge runs for 50 minutes each hour more or less....I will try turning it down but maybe the fridge is bad as it is only at 6. If it is original it's 17 years old, maybe I should throw in the DC compression fridge after all.

I was thinking about that as well, the ARB in my truck is great when it comes to power consumption. I too must wait until my fridge goes, unfortunately nothing wrong with the one I have so I will see how I feel about propane. Good news is I will not need heat, and if propane is a pain I can forgo the water heater as it is the tropics.

The fridge should not run that often, especially in winter. Here are some tips:
1. Level your RV. Frig side to side tilt should be less than 3 degree. Frig front to back less than 6 degrees.
This allows the gases/liquids to roll down the serpentine tube to the reservoir.
2. Check for outside vent obstructions. Such as mud, nests, and spider web. Check the heat exchanger fins too.
3. Check the Fins inside the Frig. Are your contents obstructing air flow?

So, failing to do #1 will eventually cause crystallization and hurt efficiency.
Also overheated pipes might crack and cause fires. Yellow-Green residue is toxic.

 

[HRTKD]

edit: Jesus, according to my growatt my fridge runs for 50 minutes each hour more or less....I will try turning it down but maybe the fridge is bad as it is only at 6. If it is original it's 17 years old, maybe I should throw in the DC compression fridge after all.

I was thinking about that as well, the ARB in my truck is great when it comes to power consumption. I too must wait until my fridge goes, unfortunately nothing wrong with the one I have so I will see how I feel about propane. Good news is I will not need heat, and if propane is a pain I can forgo the water heater as it is the tropics.

Makes me think your fridge is on AC only. It will still use some DC power for the circuit board.

 

[Bobert]

I have a 48v all in one inverter on my travel trailer and I opted just to leave the original 12v system in place. I did upgrade my converter/charger just before installation of the all in one. I do loose some efficiency but I think it is worth it for redundancy and convenience. If my solar setup goes down I still have water/frig ect. If I wish at night I can shut off the inverter and loose all my AC loads till morning. If I need to sell the trailer the original system is still in tact