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Old 01-13-2021, 08:01 AM   #1
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TAMING The power hog.

After posting for years about the advantages of a propane reefer,, I found some info on an RV site that might be useful to folks making a decision. Boondocking is same as anchoring out.

Sure one can kill oneself with stupidity , but a proper installation can be safe as so many folks with propane ranges have shown.

**********
Propane vs 12 volt power.

A gallon of propane contains 91,500 BTU.
A typical "full" tank of propane contains about 4.5 gallons (+/-)
4.5 gallons of propane contains 411,750 BTU.
A 2109S has two of these = 823,500 BTU.

That means you have 241,344 watts (or 241.3 kilowatt hours) of energy sitting on the tongue of your RV. https://www.rapidtables.com/convert/...U_to_Watt.html

So in electrical terms at 12 volts, 241,344 watts per hour = 20,112 amp hours. Let me repeat: Twenty THOUSAND amp hours!
https://www.rapidtables.com/calc/ele...alculator.html
The typical 12 volt group 24 battery that comes standard from the dealer puts out a measly 35 USABLE amp hours.

Until recently, the GOLD STANDARD for battery banks was 4 x 6 volt GC2 golf cart batteries in series/parallel that could deliver a whopping 230 USABLE amp hours. You don't have room on your tongue for that battery bank. You SHOULD install 2 x 6 volt GC2s that will reliably deliver 115 usable amp hours.

But think about it: Two "5-gallon" tanks of propane contain the equivalent of 87 of the gold standard battery banks!! These days, you can do better on batteries with LiFePo4 lithium batteries at roughly a kilobuck a pop. https://www.google.com/search?q=batt...hrome&ie=UTF-8 But they cannot compete with propane for usable energy storage.

If you have money to burn, get the 12 volt compressor fridge, a couple of LiFePo4s, and a good solar array to keep it running.

Solar? If you boondock, absolutely. This is a fantastic deal on great equipment: https://smile.amazon.com/Renogy-Sola...s%2C225&sr=8-5
Buy it while you can.

A pair of 6 volt GC2s? Absolutely...or spring for the LiFePo4s. A good long term investment. I have a pair of these: https://www.batteriesplus.com/productdetails/sligc115 I'm a profligate 12 volt power user...stereo, lights, even a 500 watt inverter powering an electric blanket for 20 minutes to take the chill off the bed. I have power to spare and in sunny Colorado, my batteries are topped off by about 1 PM.

But if you want hassle free refrigeration off the grid, propane is the way to go. And you can safely run it while towing. Another topic, but virtually everyone in the forum will confirm that this works well. Shut it down if you stop for gasoline, go thru a tunnel, or ride a ferry. Otherwise, no big deal.
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Old 01-13-2021, 08:44 AM   #2
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I grew up RVing with my family, and of course propane fridges are pretty much the standard there. There is the advantage that they easily designed to vent any propane leakage out the bottom of the RV, though.

Our fridge on our boat is the power hog, too. And, I have often thought about how "cool" it would be to have a system that worked like the propane systems on RVs.

I'm just not 100 per cent convinced it can be done safely. We don't even have a propane stove on our boat (and we have to crank the genie to run that, as well).

We recently took out our old full size freezer, and replaced it with one half as big, which did reduce our kilowatt usage by about a third. Theoretically, we can run it on our solar panels on long sunny days.
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Old 01-13-2021, 08:52 AM   #3
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My biggest issue with propane fridges is that many of them are terrible fridges, no matter how efficient and low maintenance. Many of them just remove a constant amount of heat, rather than being variable or cycling. So they don't regulate temperature well and take a long time to cool down any new food. That alone pushes me away from them in any application where it's possible to power an electric alternative.

Personally, I don't find powering a 12v fridge terribly hard. Mine isn't the most efficient or best insulated setup out there (look at some of the custom builds on sailboats to find that), but I'm still only looking at 50 - 80 ah / day at 12 volts, depending on usage and outside temperature. And my fridge is larger than a lot of people have on their boats. That's a decent bit of power, but if you're moving the boat frequently, or periodically running a generator for other purposes or can add 200-ish watts of solar, it's not a hard load to keep up with.

If I had a little more space around my fridge, I could add more insulation and cut the power use down more. A custom built box with some off the shelf refrigeration components would do even better. Figure a really well done fridge of the same size as mine (6.6 cu ft fridge, 2.5 cu ft freezer) could be down in the 30 - 50 ah / day range if you're not opening it too often or adding too much new food.
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Old 01-13-2021, 08:58 AM   #4
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The gray area involved with a propane fridge on a boat comes when it's time for an insurance survey. I doubt that there is a propane fridge that lists any approval for marine use. I could be wrong, but before entertaining installation of a propane fridge on a boat for which you plan to obtain insurance, you may want to investigate that whole approval aspect and have it in writing for your insurance underwriter. Venting can also be a problem since you're venting products of combustion in an environment for which the propane powered fridge is not designed, so getting the installation into compliance with the manufacturer's recommendations might not be possible, so you're on the hook for any claim that could be tied to the fridge. Don't ask, don't tell is a sure path to claim denial. In the litigious world of insurance, it's not a stretch that ANY claim could be denied on the basis of fraud.

If you peruse photos of RV fires, you may see a pattern where many of those fires originate in the vicinity of the refrigerator vent. An open flame is part of the function of a propane absorption system, so there must be a risk assessment made WRT the presence of an unattended open flame on board, particularly if you circumvent the installation protocols.

I'm not arguing that an LP fridge isn't a good way to tame the power hog, but the risk is high.
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Old 01-13-2021, 09:01 AM   #5
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Ammonia, hydrogen and a flame under the fridge? I don’t care if they gave propane away for free, I would never have one on my boat. Maybe statistically RVs don’t blow up all that often, I still don’t like the sound of it and there’s no point since electric is readily available and convenient.
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Old 01-13-2021, 09:04 AM   #6
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I'm with Group9 on the safety thing. Same reason I prefer diesel engines over gas.
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Old 01-13-2021, 09:05 AM   #7
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Quote:
Originally Posted by FF View Post
After posting for years about the advantages of a propane reefer,, I found some info on an RV site that might be useful to folks making a decision. Boondocking is same as anchoring out.

Sure one can kill oneself with stupidity , but a proper installation can be safe as so many folks with propane ranges have shown.

**********
Propane vs 12 volt power.

A gallon of propane contains 91,500 BTU.
A typical "full" tank of propane contains about 4.5 gallons (+/-)
4.5 gallons of propane contains 411,750 BTU.
A 2109S has two of these = 823,500 BTU.

That means you have 241,344 watts (or 241.3 kilowatt hours) of energy sitting on the tongue of your RV. https://www.rapidtables.com/convert/...U_to_Watt.html

So in electrical terms at 12 volts, 241,344 watts per hour = 20,112 amp hours. Let me repeat: Twenty THOUSAND amp hours!
https://www.rapidtables.com/calc/ele...alculator.html
The typical 12 volt group 24 battery that comes standard from the dealer puts out a measly 35 USABLE amp hours.

Until recently, the GOLD STANDARD for battery banks was 4 x 6 volt GC2 golf cart batteries in series/parallel that could deliver a whopping 230 USABLE amp hours. You don't have room on your tongue for that battery bank. You SHOULD install 2 x 6 volt GC2s that will reliably deliver 115 usable amp hours.

But think about it: Two "5-gallon" tanks of propane contain the equivalent of 87 of the gold standard battery banks!! These days, you can do better on batteries with LiFePo4 lithium batteries at roughly a kilobuck a pop. https://www.google.com/search?q=batt...hrome&ie=UTF-8 But they cannot compete with propane for usable energy storage.

If you have money to burn, get the 12 volt compressor fridge, a couple of LiFePo4s, and a good solar array to keep it running.

Solar? If you boondock, absolutely. This is a fantastic deal on great equipment: https://smile.amazon.com/Renogy-Sola...s%2C225&sr=8-5
Buy it while you can.

A pair of 6 volt GC2s? Absolutely...or spring for the LiFePo4s. A good long term investment. I have a pair of these: https://www.batteriesplus.com/productdetails/sligc115 I'm a profligate 12 volt power user...stereo, lights, even a 500 watt inverter powering an electric blanket for 20 minutes to take the chill off the bed. I have power to spare and in sunny Colorado, my batteries are topped off by about 1 PM.

But if you want hassle free refrigeration off the grid, propane is the way to go. And you can safely run it while towing. Another topic, but virtually everyone in the forum will confirm that this works well. Shut it down if you stop for gasoline, go thru a tunnel, or ride a ferry. Otherwise, no big deal.
So the part you seem to leave out of your equation is the conversion factor of turning propane into refrigeration. This is equivalent in concept to a propane generator. The energy in propane isn't equal to same amount of energy in electricity when you convert it through a generator.

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Old 01-13-2021, 09:19 AM   #8
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Originally Posted by O C Diver View Post
So the part you seem to leave out of your equation is the conversion factor of turning propane into refrigeration. This is equivalent in concept to a propane generator. The energy in propane isn't equal to same amount of energy in electricity when you convert it through a generator.

Ted



A 10 cubic foot propane refrigerator will typically consume 1.5 lbs, or .375 gallons, of propane per day. The energy content of 1.5 lbs of propane is 32,250 Btu or about 9485 watt hours. The Sun Frost RF12 consumes only 24 amps hours a day, which is equivalent to 288 watt hours a day. That is an astounding 32 times less.


Off Grid Refrigeration: Solar Electric Vs Propane | Sun Frost Blog.

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Old 01-13-2021, 09:29 AM   #9
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The part that you leave out is that batteries can be recharged and generators and engines run to recharge them so the available power is unlimited.
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Old 01-13-2021, 11:10 AM   #10
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I know some of you don't care but I've never seen a propane refrigerator installed on a boat that meets ABYC standards.
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Old 01-13-2021, 11:20 AM   #11
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there is also the fact that if you are in and out of a propane refrigerator it may not stay cold. also when I used my rv I would get the fridge cold 2 days before I wanted to use it .the boat 12v fridge takes a few hours . even with a few people getting a refreshment a few times an hour each it stays cold.
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Old 01-13-2021, 11:26 AM   #12
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My RV fridge was AC or propane. I ran it through a $100 inverter and a solar panel. Trouble free
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Old 01-13-2021, 11:44 AM   #13
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I have read that propane refrigerators need to be level when they are operating. Here, for example, is a website that talks about that:
https://www.godownsize.com/how-level-rv/

If this is true, then it would seem that operating underway would be a problem, unless your boat is extremely stable, and you are very careful about wave heights and such.

Even at anchor COULD be an issue, depending on how much your boat rolls.
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Old 01-13-2021, 11:48 AM   #14
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I have read that propane refrigerators need to be level when they are operating. Here, for example, is a website that talks about that:
https://www.godownsize.com/how-level-rv/

If this is true, then it would seem that operating underway would be a problem, unless your boat is extremely stable, and you are very careful about wave heights and such.

Even at anchor COULD be an issue, depending on how much your boat rolls.
It's true, such a warning is given in the instructions of all propane RV fridges.
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Old 01-13-2021, 12:09 PM   #15
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Fwiw...the fridges on my boats were all dual voltage. I relied on 12v away from the dock. I learned early on to turn OFF the fridge last thing before turning in for the night when I knew it wouldn't be opened again before morning. They were well enough insulated that even the ice cream in the freezer didn't thaw.

Another "trick" I learned when we had guests aboard was to keep beer, soft drinks and anything else that required opening the fridge door frequently in a cooler in the cockpit, reserving the fridge for the food needed at meal time.
Those two li'l "tricks" significantly reduced the fridge amp hour consumption on my boats and prob'ly will for any of you.

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Old 01-13-2021, 12:59 PM   #16
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Hi Boatpoker,

Code:
I know some of you don't care but I've never seen a propane refrigerator installed on a boat that meets ABYC standards.
You're right on the money. For very good reason. I believe this is because ABYC requires any propane refrigerator to be directly vented to the exterior of the boat. Not just the source of the propane (bottles on the topdeck, for instance), but the unit itself. So, unless your boat allows the refrigerator to be placed against an exterior bulkhead, or outside the living spaces (in the cockpit, for instance) that simply isn't possible.

I believe this requirement exists as propane refrigeration requires both an ignition and a propane source to be active 24/7. An unattended propane-powered refrigerator, supposedly with a foolproof (yeah, right.....) electronically-controlled piezoelectric igniter and/or solenoid valve, may fail to ignite on demand from the thermostat. This can and will dump propane fumes into the interior of your boat. Boom....

I'm not even going to say much about the lunacy of an open-flame pilot on typical RV refrigeration. Sheesh. Not in MY boat, anyway!

There's a fundamental difference between a propane refrigerator and a stove that does NOT need direct overboard venting. And that's the lack of a human in the loop to turn on and off the propane when needed. While propane refrigeration has viability in off-grid homes and RVs, and perhaps in a very few unique boat designs, it's a non-starter for me.

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Old 01-14-2021, 07:44 AM   #17
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Interesting 100% negative responses, from mostly folks that have never used the system on a vessel.

The install can be easy , just stick in a self draining cockpit or if above the WL build a well that can drain overboard and vent it.

Our unit was in the cockpit as so old that it was labeled a Motorola not Dometic and a BBQ bottle would run 3 weeks , including the Hiller range and oven.

"So the part you seem to leave out of your equation is the conversion factor of turning propane into refrigeration. This is equivalent in concept to a propane generator. The energy in propane isn't equal to same amount of energy in electricity when you convert it through a generator. "

True but running a noisemaker, 30% efficient to spin an alt 50% efficient to charge a batt set ??% efficient to operate the DC comes with the price that the machinery is wearing out and must eventually be replaced

At a buck a day for propane it seemed a good trade off for not listening to a noise maker , servicing it and replacing it. Especially with a 40 or 50 year unit that only requires a chimney brush every 6 months or so.

Sure if you live in the South and need air cond. 24/7 the fridge operation addition is small.

The older units did need to be mostly level , but these days if you can stay in bed with out a belt or bunk boards its level enough.

Motion at anchor actually helps the refrigeration process.

I started this discussion to hope some folks would investigate alternate concepts , as with modern equipment, LED lights , etc the need for a noisemaker could be eliminated saving many thousands .

Should I continue with other alternate concepts , in the hope others can add ideas ,
or will the board censors find it too disturbing as they find other topics?
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Old 01-14-2021, 07:59 AM   #18
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Propane fridges need to be level when stationary for periods of time.


Bouncing and swaying and leaning while driving are not an issue and neither is rocking and rolling in a powerboat (permanent severe list would be as is a long tack with more than acceptable heel on a sailboat).


This is from decades of reports I have read from propane reefer users on boats or RVs.


I am not supporting their use... unless very specific use with a strong eye on safety precautions. Wouldn't work for me as I see it.
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Old 01-14-2021, 08:34 AM   #19
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there is also the fact that if you are in and out of a propane refrigerator it may not stay cold. also when I used my rv I would get the fridge cold 2 days before I wanted to use it .the boat 12v fridge takes a few hours . even with a few people getting a refreshment a few times an hour each it stays cold.
The one (Dometic) in our new travel trailer gets cold very quickly and stays cold. As a matter of fact we have to turn it down cause the fridge part gets too cold.
I guess things have changed.
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Old 01-14-2021, 08:37 AM   #20
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True but running a noisemaker, 30% efficient to spin an alt 50% efficient to charge a batt set ??% efficient to operate the DC comes with the price that the machinery is wearing out and must eventually be replaced

Or just find a spot for a couple of quiet, no-maintenance solar panels and let those charge the batteries. Then you're only bound to the generator when you need it for something else or you get a few very cloudy days in a row, but normal fridge use will be taken care of.
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