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Old 03-10-2020, 03:51 PM   #1
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Boondocking with a compressor fridge

I have years of experience camping with no hookups in a small travel trailer with an absorption fridge. FWIW, an absorption fridge is the classical LPG powered fridge used in all RVs until recently. I use about 10 amp hours each day with no furnace or fan use and maybe a few more Ahs for the fridge controls when on and quite a bit when I run the furnace which is rarely. I also have twenty years of experience (2 of them full time) boating with a compressor fridge.

I am considering an ERA RV which I believe comes with a compressor fridge and runs only on 12V DC.. My Ah budget ex fridge will probably be higher than my trailer- TV watching when decent cell data is available and just the base loads from all of those electronics in a new Interstate. So call it 30 Ahs.

Finding the amperage draw of a compressor fridge is difficult. Anyone know the specific make and model in the new Era? But my boating experience indicates that they will draw between 3 and 6 amps when on and run at a cycle time of 40% to 100%, the latter being when it is 95 inside. So lets call it 4.5 amps at a 60% cycle time or a total amp hour draw over 24 hours of 65 amp hours. That means that our use with no hookups in a mild climate will total about 100 Ah which is about what we used on our boat.

So how do you supply that 100 Ahs and replace it daily?

Not sure exactly what comes from the factory, but I have learned (I think) that there may be room for two 6V 220 Ah batteries which when wired in series gives 220 Ahs at 12V. Since you don't want to run lead acid batteries below 50% that means you will have to charge daily and replace 100 Ahs. I am going to ignore Li batteries for the moment.

Many newer Eras come with 200 watts of solar panels. These panels can be expected to produce 60-80 Ahs on a full sunny day. So between cloudy days and the difference between 60-80 and 100 you will need to do more charging. So for sake of further discussion lets assume you need to replace 60 Ahs daily on average beyond the solar contribution. And of course that depends on parking in sunny campsites which we rarely do.

So 60 Ahs in a sunny campsite and 100 Ahs in a shady one needs to come from the generator/converter.

The OEM converter is rather small, 45 amps typically and may be wired with minimum wire size which will produce quite a voltage drop. So lets assume that you upgrade the converter to 75 amps and with large wire to keep the voltage drop down to a few tenths of a volt.

You will be charging for about .8 hours with solar or 1.2 without using the generator. The generator uses about .4 gph at half load which is all you will pull running just the converter. So you will use 0.3 gallons or .5 gallons of LPG.

You can improve these values somewhat by having a larger Li bank and/or a larger bank of solar panels. 300 watts of solar and 200 Ah of Li (which doesn't have the depth of discharge restriction or the tail end restriction like lead acid) will probably cover your use entirely with minimal genset running time. Even with no solar or in a deep shade spot the ability of Li to charge up near 100% quickly only adds less than a half hour of genset running time and a few tenths of a gallon of LPG.

So what are my plans. I think I will start with the OEM 200 watts and upgrade the batteries to Battleborn LiFePO4 with the upgraded converter so I can discharge further but also recharge fully in a reasonable time.

I will have to watch my propane usage and refill the 15 gallon tank at least every two weeks, maybe more if we are using the stove significantly and are in shade.

OK, I realize that was a lot of data and math. I would welcome others experiences with managing a compressor fridge in an Interstatoe.

How does the propane usage running the genset to replace 100 Ahs stack up against an absorption fridge? Compressor fridges are pretty efficient but propane gensets are horrible. My guess is that it takes much more propane to run the genset to power the compressor fridge than to use it directly in an absorption fridge. This is balanced by the fact that the compressor fridge can use solar power efficiently where the absorption fridge cannot (well it can but it uses a huge amount of DC amps).

Finally, can anyone tell us how many amps the OEM chassis alternator will charge a well discharged coach battery bank at moderate, ie 1,500 rpms.

My TV will only charge my trailer at about 10-15 amps due to small wiring from the TV's alternator all the way back to the trailer's house battery. The charging circuit is rated at 30 amps. The small wiring is intentional to limit the current. I would expect that an integrated chassis/coach alternator/battery system would not have these limitations.

David
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Old 03-10-2020, 04:16 PM   #2
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200 Ah of LiFePO4 batteries and 300W of solar up top and you'll be good to go.
Lithium has so many advantages over lead acid, including faster recharge time, lower internal resistance, more consistent voltage discharge level under load, don't need to be fully recharged unless you run them to zero SoC, increased duty cycles, and more importantly, most of the pricier jars have built in BMS that will usually keep you from screwing them up, unless you try really hard. They are closer to idiot proof than lead acid, more like the set it and forget it "as seen on TV" stuff in the early infomercials.
300W solar will produce 15+Amps in good sun. If your use is around 60Ah/day, you can replenish that in 4 hours of decent sun.
If the ERA (or Interstate, as you mentioned?) comes with a Progressive Dynamics converter/charger that supports the Charge Wizard Pendant (available online for around $15 on Amazon), it's a worthwhile add on tool to let you control the rate of charge of the converter/charger, when you're plugged into shore power or running your generator.
So, if you can afford 200Ah of lithium and arrange 300W of solar up top, you'll be good to go with your usage estimate. In this case spend the money and relax.
In my opinion, of course.
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Old 03-10-2020, 05:45 PM   #3
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That 300 watts of solar won't do you much good in a well shaded site. That is why I plan to upgrade the converter to 75 amps so I don't have to run the genset as long. The propane generator uses almost as much fuel at half load as no load.

Managing propane for genset use in the shade is as important as managing solar amp hours.in the sun.

Did I forget and left an Interstate reference in the text abve. You caught me then, I first posted this to the Airforums site.


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Old 03-10-2020, 06:09 PM   #4
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If you're in a well shaded site, with electric hookup, you don't need the solar at all, you can charge your batteries, whatever they are, with shore power and a 45A charger. If you're planning on upgrading to a larger output charger, you'll need to add heavier wiring, too, to take advantage. Not worth the hassle in my opinion. If the ERA has a PD9245 or similar, just get the Charge Wizard Pendant, and bump the output up to 14V+ (Boost Mode) when on shore power. If you plan on doing some driving/touring, the alternator/solar combo will charge you up fairly quickly, while you go from place to place. If your sole concern is off grid camping, with solar and a propane generator, I would add lithium to the mix. Plan on getting some charging from the solar, and some from the generator, and some from the alternator (late model Sprinters have a 220A output alternator). Also, don't count on the propane being inexpensive to use for the generator. If you were to drop the DC compressor fridge for an absorption unit, you'll lessen your amp hour usage, but increase your propane use, assuming you also cook and heat the rig with it.
The Onan QG series propane generators aren't as economical on propane as you think. Be aware, just a friendly FYI, but some owners say they slurp, not sip, the propane at all load levels. The QD3200, by comparison, is a diesel sipper at full load, and doesn't deplete the propane for the other applications.
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Old 03-10-2020, 07:27 PM   #5
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If you truly like to boon dock a lot, I don't think the compressor refrigerator is right for you. This is especially true if, like me, you don't want to run a generator for extended periods of time. There are many threads on this subject on Winnieowners, IRV2 and other forums so I suggest you read as many as you can.

Spending one, maybe two nights away from shore power is a far cry from boon docking for a week or two.

I admit that I don't have any experience with the compressor refrigerator, mine have always been Norcold absorption refrigerators which have always worked fine for me. I don't see a need to change.
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Old 03-10-2020, 07:30 PM   #6
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See embeded comments in bold below:

Quote:
Originally Posted by Winterbagoal View Post
If you're in a well shaded site, with electric hookup Well, the thread title is boondocking, you don't need the solar at all, you can charge your batteries, whatever they are, with shore power and a 45A charger. If you're planning on upgrading to a larger output charger, you'll need to add heavier wiring, too Yep, to take advantage. Not worth the hassle in my opinion. It will cut the genet running time almost in half. If the ERA has a PD9245 or similar, just get the Charge Wizard Pendant, and bump the output up to 14V+ (Boost Mode) when on shore power. See first bold comment. If you plan on doing some driving/touring, the alternator/solar combo will charge you up fairly quickly, while you go from place to place.Not sure it will charge the last 15% very fast at a fixed 13.6 V output voltage. A Sterling regulator will help with this as it fools the alternator into thinking it is feeding a low voltage load.

If your sole concern is off grid camping It is, with solar and a propane generator, I would add lithium to the mix. Plan on getting some charging from the solar, and some from the generator, and some from the alternator (late model Sprinters have a 220A output alternator). I agree. Also, don't count on the propane being inexpensive to use for the generator. If you were to drop the DC compressor fridge for an absorption unit, you'll lessen your amp hour usage, but increase your propane use Don't think so. It takes a lot of propane to drive the genset to pwer the fridge, more than is needed to use directly in an absorption fridge, assuming you also cook and heat the rig with it.

The Onan QG series propane generators aren't as economical on propane as you think. Be aware, just a friendly FYI, but some owners say they slurp, not sip, the propane at all load levels. The QD3200, by comparison, is a diesel sipper at full load, and doesn't deplete the propane for the other applications. Yes the Cummins specs say that the diesel genset uses a few tenths of a gphless at half load than the propane genset..
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Old 03-10-2020, 09:09 PM   #7
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David
So, you've already made up your mind, and you weren't looking for opinions or constructive advice, you were just looking for a blessing on your decision, and/or an argument?
Good luck with it, then.
Adios.

p.s. Another friendly FYI. Keep the original post shorter and less meandering and you'll get more responses. Some might even be to your liking.
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Old 03-11-2020, 05:03 AM   #8
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Well yes my mind is made up about things like charging from a fixed voltage alternator and more importantly that all I care about is boondocking with no hookups available.

The article was more of a statement of how DC refrigeration affects boondocking than a question. I definitely appreciate what others have to say about their DC refrigeration boondocking experiences, particularly with data.

Hey I am a retired engineer. What do you expect

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Old 03-18-2020, 06:22 PM   #9
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I have been using two Danfoss 30 compressors in a 65 quart freezer and a 45 watt refrigerator running off two LiFePO4 Battle Born batteries in my boat for about 2 years. I average about 80 amp hours a day.

At lake Powell 200 watts is enough to keep them charged. But for the average camper I would go with 300 watts of solar panels
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Old 03-19-2020, 09:00 AM   #10
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You are thinking correctly by asking all those lengthy questions. Here's the short answer. Lead acid batteries work really well when they aren't REALLY needed. A compressor refrigerator will draw more power than all other typical RV loads combined, therefore, you REALLY have serious power needs. So unless you only drive from one shore power to the next, lithium power is the best, and IMO, the only way to go.

Forget the weight difference, your RV won't notice it. You'll get about 50% more useable power from the same space limitation. You will recharge about 5 times faster with lithium. And if planning on boondocking, adequate solar (likely 400+ Watts) will be a necessity as nobody wants to hear generators running in a great boondocking area. And "No.", I don't sell lithium batteries.
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Old 03-19-2020, 09:16 AM   #11
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I don't boondock, so not something I'm familiar with. But wouldn't it be better to just get a fridge that works off propane?
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Old 03-19-2020, 09:25 AM   #12
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OK, I buy all of the advantages of Li batteries. If I were to buy a Class B Sprinter based RV with a compressor fridge, this is what I would need to do:

1. Install at least 200 Ahs of Li batteries, two LION or Battle Borns probably.
2.Change out the OEM converter to a PD 9180 an 80 amp single stage 14.6V capable charger. Use big maybe #1 wire
3. Install a Redarc or Sterling battery to battery charger to boost my chassis alternator charging to 40A.
4. Solar- None, I like to camp in shady spots, but maybe 200 watts.

So with the above and with a compressor fridge I suspect I will use 100 Ahs each day of power. That means running the generator for about an hour each day which will power the PD converter and replace approximately 80 Ahs. Then after 3 days of camping when the batteries are down by 100 Ahs use that day plus 60 Ahs of accumulated under charging, I drive four hours to my next site. That four hours of driving should recharge the Li batteries by 160 Ahs which should fully recharge them for the next go around.

So does this all make sense? Will pulling 40A for several hours from the Sprinter's chassis alternator damage it?

David
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Old 03-19-2020, 10:11 AM   #13
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Quote:
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I don't boondock, so not something I'm familiar with. But wouldn't it be better to just get a fridge that works off propane?
Difficult to retrofit such a thing if your RV did not leave the factory with one.

Do compressor fridges use more electricity? You bet. Do they work better than absorption fridges at being a fridge? Yep. So you have to figure out what works for you.
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Old 03-19-2020, 10:18 AM   #14
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Difficult to retrofit such a thing if your RV did not leave the factory with one.
I know some RVs are moving entirely away from propane, but are there any units that would likely be used for boondocking that would not have a propane stove? Unless the stove is on the other side of the RV from the refrigerator (something I have seen), I don't see it would be all that difficult (assuming no size difference). But I guess there would be a difference on the exterior too. I hadn't thought about that.

What's ironic is I don't boondock and I would be very reluctant to get an RV that doesn't have the option to use propane for the fridge.
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Old 03-19-2020, 03:13 PM   #15
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I know some RVs are moving entirely away from propane, .....chop..

What's ironic is I don't boondock and I would be very reluctant to get an RV that doesn't have the option to use propane for the fridge.
Answer: Don't buy a new RV, they mostly have compressor refrigerators now. Buyers whined about LP refrigerators for many long years, exaggerated reports of fires and demanded residential/compressor refrigerators. Guess what, the manufacturers listened. So...aside from the total amount of body work and fabrication required to retrofit a LP unit into a rig that came stock with a compressor fridge it is just not money/time wise thing to do. Easier by far to just accept the new reality and install LiFeP04 and charging system and enjoy frozen foods that stay hard frozen.
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Old 03-22-2020, 03:38 PM   #16
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So, you've already made up your mind, and you weren't looking for opinions or constructive advice, you were just looking for a blessing on your decision, and/or an argument?
Good luck with it, then.
Adios.

p.s. Another friendly FYI. Keep the original post shorter and less meandering and you'll get more responses. Some might even be to your liking.
I didn't think that David M's replies to your suggestions were out of line or disrespecting your thoughts.

David stated he agreed with some of your suggestions.

It really looked like David was adding his thoughts and perhaps experience to your suggestions.
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Old 04-20-2020, 02:43 AM   #17
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I replaced my Norcold double door elec/propane cooling unit last November, with a JC Refrigeration 120v compressor cooling unit. After 9 years, the Norcold unit developed a leak, ammonia smell, yellow gunk, yuck. It was cheaper to get the new compressor unit that a replacement Norcold unit.

As far as performance goes, it cools much more consistently, faster, and colder. When boondocking, when running, it draws 66watts of power from my 1000w inverter, hooked to my bank of 4 Costco GC2 batteries.

The draw is practically negligible, I usually run my generator in the morning to recharge, and during the day if a/c is needed. While driving, it keeps all cold, produces ice cubes, just as if we were parked. And no pilot light blowing out when semi's go past. Very happy with the choice.
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Old 04-20-2020, 08:50 AM   #18
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I would be surprised that the power draw is "practically negligible. Absorption fridges aren't very well insulated which is what you started with for the conversion to an AC compressor and AC compressors aren't very efficient compared to Danfoss inverter compressors. You say it draws 66 watts even though JC's web site says "less than an amp" AC ,I presume which means less than 120 watts.

Do you know how many watt hours you use in a day? Or do you know the cycle on percent over a day. Absorption fridges often run continuously in warmer weather.

If it uses 66 watts that is probably about 6 amps DC given inverter losses and about 72 amp hours daily at a 50% duty cycle and double if it is running continuously.

72 to 144 amp hours daily to me is not "practically negligible".

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Old 04-21-2020, 02:40 AM   #19
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Everyone needs to figure out their own camping style, shore hookups, and boondocking. We probably boondock four weeks out of the year, spread out in Casino lots and BLM lands. The rest of the time, we are hooked up when not travelling. So our priority was for keeping the food cold during travel, and occasional boondocking.

For us, the compressor duty cycle is more like 20% - 30% except for a few hours when the sun is directly on the refer side of the coach, then it might be 40%. I spent a month with digital remote thermometers fine-tuning the various locations of the thermistor, internal fan, and coldness settings. Observing and learning more than I ever wanted to know about refrigeration.

With the lowest freezer temps of -10 degrees, I worked upward to get a balance of 9 to 12 degrees in the freezer, and 35-38 degrees in the refer box with the coldness setting at #3. With my power meter, I monitored power use at the 120v plug, 90w at startup, 66w when running steady.

Yes, I know that my 440ah of battery power only really gives me 50% of that. But for me, and my coach, we go to bed with 12.5v showing on the inverter, and in the morning, it shows 12.3-12.4v. To me that is negligible power use. And of course when traveling, the engine alternator keeps those batteries charged, so no worries at all for that.

Others may get different numbers, but that is what I am getting with my particular Norcold box.

And JC Refrigeration does make a 12v model as well, which would be more efficient, power wise, by not going through the inverter, but not quite as efficient cooling action, as was told to me.

I lived with the Norcold for nearly 10 years, and these last 6 months with the compressor have been immensely better.
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Old 04-21-2020, 06:42 AM   #20
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Interesting as well as appropriate: One person's negligible is another person's significant.

Personally I lean to the side of the "significant", but totally agree with the perspective that when you run your generator enough to keep the battery bank charged to 12.5V when you go to bed and have 12.2V to 12.3V in the morning, that could be negligible power usage. IF you can keep the battery bank charged to 12.5V when going to bed. Many people find that difficult to do.

More usage things to keep in mind:
-- 66watts, about 6 amps of 12V DC and a duty cycle of 50% for the fridge is the 72AH a day that DavidM wrote.
-- However if you are using a whole RV inverter (usually 2000watts or greater), that inverter will pull from 1.5amps to approaching 3amp even if there is no 120V AC load. That means you must add 36AH to 72AH to your total power consumption for each day.
-- Now you have 108AH to 144AH each day to account for.
-- Don't forget to add in the other usage for TV, laptops, phones, lights, etc.

These numbers really put me on the side of "significant" usage.
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