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Old 08-19-2020, 06:23 PM   #1
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Powering a residential refrigerator

We're looking to purchase a Cedar Creek Cottage that will be parked on our undeveloped property. We will need to run off a generator as there is no power to the property. I believe the trailer has two 12-volt batteries. With that in mind will we have to run the generator 24/7 while we're camping in order to keep the refrigerator running or will it run off the batteries?

I don't mind running the generator during the day but not at night.
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Old 08-19-2020, 06:28 PM   #2
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Does it have an INVERTER?

If not, the ONLY source of 120v power will be your generator, but even then, no, a 120v residential fridge, if that's what you are referring to, doesn't 'run' 24/7, it only needs power 'when' the Thermostat calls for the compressor to come on, which is typically only several times per hour, and only then 10 minutes at a time, or similar timing.

Some of this is also dependent on YOUR usage - meaning, how often you open the fridge's door, how much 'stuff' is in the fridge, how 'cold' you want it to be, the outside temps, the inside temps, etc. There's no 'magic' answer, but the basic answer is if you are going to use the generator for air conditioning and to charge the House batteries, anyway, that's a fine time for the fridge to get much of the power it needs. Even without power for several hours, a fridge is not going to suddenly go 'warm', especially if you don't open the door much - after all, it's simply a big COOLER.
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Old 08-19-2020, 06:35 PM   #3
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I do believe the trailer does have an inverter. I might even be interested in seeing if I can upgrade the batteries or add a couple more after we get the trailer.
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Old 08-23-2020, 11:58 PM   #4
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Originally Posted by SacRV View Post
I do believe the trailer does have an inverter. I might even be interested in seeing if I can upgrade the batteries or add a couple more after we get the trailer.
Ideally, you would have the refrigerator and plug it into a Kill-a-watt with the kill-a-watt in the Watthour (WH) mode. Start the kill-a-watt about the time you would want to shut off the generator, and read it in the morning about the time you would start the generator. This will tell you how many Watthours the refrigerator will use overnight in current weather. Then add 15% for inverter losses. Then compare that number with your battery capacity (for AGM batteries, divide WH by 12.5 to get ampere hours).

The above won't help if you want to be prepared to not run the generator the first night but is the only accurate way to learn what you need to know to determine if a battery upgrade is needed.

If you know the model of the refrigerator, maybe we can find the power it draws. At night when it's cooler, the refrigerator will run less and this helps. Even energy star data would help.

This is the kill-a-watt device I have had for 15 years. This price seems high, but I don't know that I'd trust the cheaper copies. You will use this a lot as you add 120V devices or look for ways to economize on energy use.

https://smile.amazon.com/Power-Meter...244751&sr=8-45
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Old 08-24-2020, 07:08 AM   #5
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At $38.25, the price does not seem high to me at all.

Great advice in that post. It sounds like the best way to know, and not to be using educated guesses.

Also, to the OP: Why do you not want to run the generator at night? Are you concerned about the noise? Are you concerned about how the noise affects others? Something else?
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Old 08-24-2020, 07:15 AM   #6
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As a quick reference. Check the fridge current usage. For every 1 amp of 120VAC usage you will use 10A of 12VDC current.
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Old 08-24-2020, 07:31 AM   #7
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Not enough data. Likely not.

Typically the dealer puts in two marine batteries that only hold 80 usable amps of power. 80 each however you should never exceed 50% use in wet cell batteries.

The inverter on standby will use 1-2 amps of dc amps per hour. When the fridge turns on it will then use substantial power. Got to get that off the data on the fridge. Plus a cheap inverter is only 80% efficient.

A generator running during the days will not likely charge the batteries to 100% That takes more time. Lithium would help some. so you likely have less than 80 on the best day.

Will the fridge be properly installed. Must be free standing. Not in a box. The instructions normally say it must have 2-3" of air around it. Thus it will not operate at its most efficient point.

If the outdoor temps are somewhat high that does not help. The fridge runs more.

I would recommend 4 six volt batteries and 600 watts of solar.

I think otherwise you will be disappointed. 4 six volt batteries might work. 230 amps of power. Assume no other large user of power like a cpap or furnace. Two lithium batteries and a new converter might work.
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Old 08-24-2020, 02:17 PM   #8
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If the refrigerator turns out to be an electrical burden, look for ways to reduce heat transfer out of the refrigerator. I.e., add insulation if possible without reducing airflow to the coils. Even an old quilt draped over the top and sides will help. Again, ensure plenty of air flow over the coils.

Increasing air flow up the back (I'm assuming it has rear condenser coils) will also help efficiency. An inexpensive 12V computer fan (on a wall wart if only 120V is nearby) pushing air upward and into the rear coils can help measurably.

If the condenser and coils are at the top or bottom and use room air, clean the coils often.
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Old 10-19-2020, 01:24 PM   #9
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If the refrigerator turns out to be an electrical burden, look for ways to reduce heat transfer out of the refrigerator. . . .
Oops. Make that "ways to reduce heat transfer INTO the refrigerator" ...... add foam insulation to the sides and top (assuming rear coils). 2" R Max at Home Depot is R13.1.
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Old 10-19-2020, 02:11 PM   #10
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I am curious about adding insulation around a residential fridge.

I am pretty sure they are designed to be free standing. Requiring an air space surrounding the box(installation instructions). Or, they get hot and require more energy.

It is pretty simple. If you want minimum generator time then solar and lithium batteries will work.

P=IV watts=amps * volts Look at the data on the fridge. Watts. I recommend looking at worst case. Like running 24 hours. 25% is probably more reasonable.

Remember an inverter on standby uses 1-2 amps per hour. When operating it is usually only 80% efficient. A rated 100 watt fridge would use about 10 amps of dc per hour of operation. About 35 to 240 amps depending on conditions per day. In this case 2-3 lithium batteries and 800 watts of solar and you would seldom need the generator.
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Old 10-19-2020, 03:59 PM   #11
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Originally Posted by tomkatb View Post
I am curious about adding insulation around a residential fridge.

I am pretty sure they are designed to be free standing. Requiring an air space surrounding the box(installation instructions). Or, they get hot and require more energy.
Yes, battery and solar!!! Though for a residential fridge, you might pay enough for the extra battery and solar to cover a 12V Danfoss/Secor compressor fridge. I don't know how large the 12V fridges come. Mine is 9.1 cu ft of which 2.5 is in the freezer. It takes less than 45 AH in 24 hours with powerful CA sun beating down on the back and top and temp 90-96 inside during day time. BUT, I have insulated it heavily with 2" Poly iso board (R13.1). The one I have does not have coils up the back, so I was able to insulate the back as well.

As for heat flow, considering heat to flow from hot to cold, the problem is keeping heat out of the fridge wherever possible. The sides of a fridge have maybe 2" of poly iso or similar insulation in them. If you could double that to 4", the heat gain would be greatly reduced and the running time reduced.

The residential fridge is no different. But, I think you are looking at a residential fridge with coils running up the back. This is very common. If you push this type of fridge into a cavity between cupboards in a kitchen, those coils will be starved of cooling air unless there is a gap under the fridge and/or along the sides of the fridge .... and on top of the fridge. In that case, YES, one must leave room for air to flow into the space behind the fridge and upward and escape someplace, probably forward over the top of the fridge. This is very inefficient since a natural chimney effect on the back is very limited and the coils will run hot. And, some warm air from the coils is flowing right over the top surface of the fridge where some of it flows through the insulation into the refrigerator. Air flowing along the sides similarly "convection warms" the side walls of the fridge albeit with ambient air. In summary, in this situation you have to live with inefficiency from 1) lack of cooling air on the condenser coils on the back, and 2) ambient air flowing along the sides of the fridge and hot air coming forward over the top.

The instructions you are thinking of surely are there to address this situation. I'd guess it's not common, but has to be covered.

If a residential fridge is truly free-standing, i.e., no air flow encumbrances around it, then adding insulation to the sides and top (and door if you can stand it) will reduce energy usage.

Earlier I specifically mentioned ensuring plenty of air flow over the coils. If I had the above situation I'd put muffin fans somewhere to force room air upward over the coils. This would worsen the "warming" of the fridge by convection on the walls, but at least the fridge would probably cycle off once in a while.

The ideal situation for any fridge, 12V RV or residential is to have unencumbered air flow over the coils and increased insulation anywhere that it will not limit the coil air flow. If the coils are on the back, and have their own air supply like RV propane and some RV 12V fridges do, then insulation on the top and sides will reduce heat flow into the fridge. Here I'm thinking of the typical outside air inlet near the bottom of the fridge and a chimney effect up the back leading to a roof vent. In this situation one can add insulation to the sides and top of the fridge to limit heat flow into the fridge without restricting air flow upward over the coils in the back.

If I had a rear-coil residential fridge in an RV and it did not have ample air flow from an inlet near the bottom rear and a vent at the top, I would install those.

My own 12V fridge has the condenser coils under the fridge and a fan circulates RV interior air over the coils. As such I was able to heavily insulate the sides, back, and top of the fridge. Image below. The result is just over 40 AH on a 90F day, with massive direct sun on the rear wall behind the fridge, and 60F lows at night. The RV interior runs 90-96F. The manufacturer suggested about 60 AH in a 70F ambient.

The downside of this design is that the fridge dumps warm air into the living space instead of outdoors (i.e., from coils up the back). It's also a bit noisier than one with the compressor in the lower rear. Though the fans on the coils of my propane fridge were quite audible.

The compressor on my 12V fridge came set at 3500 RPM. I'm running it at 2000 RPM even when it's in the 90's ...... though it rarely cycles off during the warm hours. That's fine though since the compressor is considerably more efficient running at 2000 RPM. I'm thinking of adding a time clock that will switch the compressor to 2500 RPM during the day and 2000 RPM at night.

I apologize for the sideways photos .......

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