Dometic fridge: yay or nay?

[Bud]

Originally Posted by GallenH

I keep asking the inverter question because on 120v my 3-way runs much better, rivaling propane, than the 12v. So my thought was to add a small inverter solely dedicated to the fridge that would be active only when driving.
Just need to figure out how large since I assume that I have to be careful about not having it be unnecessarily large and taxing the alternator/battery components.

It is under 200 watts, the reason that it's lousy for making heat.

I use the same inverter for everything except microwave and a/c. A 400 watt inverter will do that, TV and sat receiver, fantastic fan or furnace, lights......

But not the refrigerator and other stuff together, but then you're driving.

[GallenH]

Originally Posted by Bud

It is under 200 watts, the reason that it's lousy for making heat.

I use the same inverter for everything except microwave and a/c. A 400 watt inverter will do that, TV and sat receiver, fantastic fan or furnace, lights......

But not the refrigerator and other stuff together, but then you're driving.

Thanks for the info.

[engnrsrule]

I am hoping Booster chimes in. I have heard it said that fridges run better on 120vac than 12v DC. One major thing to consider when upsizing an inverter is the feed cables from batteries to the inverter. As you up the inverter rating the guage of the cables must increase. Your batteries will drive the inverter and I expect your alternator would make up for the loss.

Do you have battery monitor (like the victron)? If so you can turn various things on and directly read the amp draw and determine whether the alternator provides for net gain.

I would add that with my new Dometic the 12v performance has been fine underway. If you get better performance on 110 then it follows that the draw of the inverter plus fridge load would necessarily be greater than the draw on 12v.

[GallenH]

I have a small Dometic (3.0cf) and the cooling on 120v rivals LP. 12v is nowhere close to either. That was the reason for my query into a small inverter dedicated to the fridge only when you're driving. It's pretty clear that either 12v or 120v via an inverter would drain my small battery when I'm not driving. There it's got to be propane.

I agree that the inverter being close to the battery would limit how much heavy gauge wire needed. I'd also have to have the capability for it to engage only when the ignition is on.

[booster]

Originally Posted by engnrsrule

I am hoping Booster chimes in. I have heard it said that fridges run better on 120vac than 12v DC. One major thing to consider when upsizing an inverter is the feed cables from batteries to the inverter. As you up the inverter rating the guage of the cables must increase. Your batteries will drive the inverter and I expect your alternator would make up for the loss.

Do you have battery monitor (like the victron)? If so you can turn various things on and directly read the amp draw and determine whether the alternator provides for net gain.

I would add that with my new Dometic the 12v performance has been fine underway. If you get better performance on 110 then it follows that the draw of the inverter plus fridge load would necessarily be greater than the draw on 12v.

We only had our 3 way frig a few years before we switched to compressor, but once I put a Snyder condenser fan kit on it there weren't major issues on any of the three settings unless it got too hot for it, like in the 90s. What drove us away was the parking level thing as many times we wound up by a ditch when parking at trialheads and such.


I would say it kind of followed the generality that I have heard the most often. Propane best cooling, AC next, and DC worst.

[hbn7hj]

Originally Posted by GallenH

I keep asking the inverter question because on 120v my 3-way runs much better, rivaling propane, than the 12v. So my thought was to add a small inverter solely dedicated to the fridge that would be active only when driving.
Just need to figure out how large since I assume that I have to be careful about not having it be unnecessarily large and taxing the alternator/battery components.

Just size the 12volt element in watts to be the same as the AC element. Put in a relay so it is on only when the alternator is on. Works fine.

[rogerstg]

Originally Posted by hbn7hj

Just size the 12volt element in watts to be the same as the AC element. Put in a relay so it is on only when the alternator is on. Works fine.

I planned on doing that until I found that the older dometic fridges (mine is 2353) do not use the thermostat on DC. It's all on, all the time. Things currently freeze on a long drive in 60F weather, but DC can't keep up in the 80s. Plus the cost was a few hundred for the upgrade.

For a few dollars more, I plan on wiring in an inverter (with remote) and auto transfer switch to the AC panel. Part of the upgrade is to also provide clean power for a computer and extra monitor for work while boondocking.

[GallenH]

My 2310 is at least 1997 vintage. The wiring diagram clearly shows power going through thermostat to 12v heating element. Re hbn7. The 12v element is 125w and the 120v is 160w.

[hbn7hj]

Originally Posted by GallenH

My 2310 is at least 1997 vintage. The wiring diagram clearly shows power going through thermostat to 12v heating element. Re hbn7. The 12v element is 125w and the 120v is 160w.

Wow! The 12 volt element on a RM2354 is 75 watts. You probably cannot get an 160 watt 12 volt element.

Effeciency must have changed over the years.

[engnrsrule]

Combining a few responses: On upsizing the fridge 12v element I would be concerned about the ability of the existing 12v circuit to carry the additional load.

Auxiliary cooling fans are a big help. Many times the void behind the fridge is ill-designed and churns the hot air. I added 4 computer fans exhausting at the top vent plus a baffle to funnel the air flow. They are controlled by a 3 way switch in the cabin - Off - On - Auto, with the latter run thru a thermostat switch on the to cooling fins. Also have an internal 12v fan that is just on/off.

Check out the thread on my electrical upgrade from original 750w modified sine wave inverter-charger to a 1500w (3000w peak) pure sine wave inverter and separate charger. https://www.classbforum.com/forums/f...ade-10087.html

[ChicagoTom]

That's comical. Propane for a fridge is about 30 cents a day. Ran mine, while working on it, for a good 3 months. Had to hav e the propane valve replace and there was still about 3 of the 6 gallons left. So, about a gallon a month at $6 and I may be generous at that. What states are you talking about? LOL Use your battery, and please post when you forget to turn it back to auto and your new battery cost a couple hundred bucks...>>>My problem is needing to comply in states where they require propane off. Propane may be cheap but when rolling 12v is practically free.

[engnrsrule]

<<<<That's comical. ... What states are you talking about? LOL Use your battery, and please post when you forget to turn it back to auto and your new battery cost a couple hundred bucks>>>>

New Jersey and New York require propane turned off at the tank when driving, and they are in between me and my regular destinations. I have encountered bridges and tunnels in Virginia (where I live) as well as other states where you must pull off and they check to see that your valve is closed. Some tunnels and bridges (Baltimore, NYC) prohibit vehicles equipped with propane tanks, even if closed.

These rules are easy to check on the internet, and even if you do want to ride with it on it is prudent to check requirements in the trip planning phase to avoid surprise route changes or hefty fines.

I am not debating the value of these laws or the relative risk of propane being on when driving, and know that it is legal in most places.

As for forgetting and killing my coach batteries, I have a label maker and a few labels to remind me of various things (including propane), and battery monitor that alerts my cell phone if my state of charge goes too low. So I would say don't hold your breath waiting for me to post about killing my battery. Likewise you can post when you get fined or unexpectedly rerouted because you didn't know (or care) about the requirements. But I will try and have the good taste not to mock you or laugh about it.

[@Michael]

I went down a rabbit hole looking for references to the specific laws and/or regulations related to transporting propane on highways (not tunnels) in a few of these states. They are hard to find. Best I can come up with is:

New Jersey "§ 19:2-4.4. Transportation of dangerous articles"

(c) No person shall transport in or upon any Expressway project, any dynamite, propane, nitroglycerin, black powder, fireworks, blasting caps or other explosives, gasoline, alcohol, ether, liquid shellac, kerosene, turpentine, formaldehyde or other inflammable or combustible liquids, ammonium nitrate, sodium chlorate, wet hemp, powered metallic magnesium, nitrocellulose film, peroxides or other readily inflammable solids or oxidizing materials, hydrochloric acid, sulfuric acid, or other corrosive liquids, prussic acid, phosgene, arsenic, carbolic acid, potassium cyanide, tear gas, lewisite or any other poisonous substances, liquids or gases or any compressed gas, or any radioactive article, substance or material, at a time or place or in a manner or condition as to unreasonably endanger or as to be likely to unreasonably endanger persons or property.

(d) If a violation of (c) above shall result in injury or death to a person or persons or damage to property in excess of the value of $5,000, it shall constitute a crime of the third degree.

I drew a blank on New York State.

As far as tunnels, the NJ/NY Port Authority 'Green Book' is specific as applies to the tunnels that they regulate:

6.2 Tunnels and the Lower Level of the George Washington Bridge.

(a) Vehicles using compressed flammable gases, other than compressed natural gas, such as, but not limited to, propane, butane, liquefied petroleum gas, acetylene, as fuel for heaters or refrigeration elements are prohibited from traveling through the Tunnels and the lower level of the George Washington Bridge

[hbn7hj]

Originally Posted by @Michael

I went down a rabbit hole looking for references to the specific laws and/or regulations related to transporting propane on highways (not tunnels) in a few of these states. They are hard to find. Best I can come up with is:

New Jersey "§ 19:2-4.4. Transportation of dangerous articles"



I drew a blank on New York State.

As far as tunnels, the NJ/NY Port Authority 'Green Book' is specific as applies to the tunnels that they regulate:

Guess I lucked out. Ive been through the Holland Tunnel and on the Long Island Expressway. Valve closed but that probably doesn’t matter.