Absorption fridge - 12V vs 120V

[Bert06840]

What I don't see being mentioned here, is the impact of external factors on power consumption.

This is what makes all the difference.

- when it is hot (say, 100F) around the fridge, you need about three to four times as much electrical energy to keep the inside of the fridge at the same temperature than if the the fridge is at, say, 70 degrees F. This assumes that you don't open the door even once.
- when you use a chest fridge, you have one MAJOR advantage: the cold air stays inside when you open up the top, and one opening cycle has a much lower energy cost than if you had a vertical household model. Depending on the number of opening cycles, this difference can be easily a factor two, other things being equal.
- particularly when you have a regular vertical household fridge and the temperature differential is large (on a hot day, when you need a cold drink often!), the number of opening cycles has a radical impact on energy consumption. You open the fridge, cold, dense air "falls out" from the bottom and hot, humid, air takes its place. The fridge will be busy the next 30 minutes cooling the hot air down that you just let in.
- the more fully loaded your fridge, the more energy efficient it becomes - once it has reached thermal equilibrium. A fridge stocked chock a block with chilled beer cans, loses much less cold air mass when you open the door to take out a can, than if there were just a few cans inside. The cold air literally can't fall out.
- the more hot fluids you ask the fridge to cool, the more energy it consumes. Say you put two fridge packs of coke (12x12oz each) at 100 degrees F in your fridge, and you want them chilled to 35 degrees. There's about 400 Watt-hours of thermal energy in there, so it will take perhaps 1kWh of electrical energy from your batteries.

So, having a fridge, sitting there, at 70 degrees, not being opened, drawing 350Wh a day is one thing. Using it normally, for its intended purpose, opening it dozens of times a day, taking chilled things out, and putting hot things in, in weather like we are having here today (almost 90!) is another thing altogether.

In my experience, I can see a factor of about 7 or 8 to 1. My big fridge/freezer draws about 2kWh on a hot day when used unrestricted by family members, and about 250Wh just running idle when it's 65 degrees or so.

[Rucker]

Great points all Bert! If I might add, these other factors apply to consumption (battery needs), and not 'will the darned thing actually fire up'.

My comments were more focused on minimum viable setup, and assume (although I did not state it explicitly) that you may need more solar direct, if your system allows, and/or more battery capacity due to those usage factors.

[musigenesis]

Originally Posted by WIbluebird

To piggyback on this thread, people who are using residential style 110v fridges: did you put the fridge on a dedicated circuit breaker or was it on a shared circuit with other outlets?

Pros/cons to either approach is greatly appreciated since I have to make a decision on this soon.

I have two small 110V chest freezers, one of which will be used as a fridge with a gadget that keeps it around 37°F. I'm trying to find (or build) a switch to ensure that only one or the other will be drawing current at any point in time, and then the two together will share a dedicated circuit breaker.

I was hoping a switch like this would be a common off-the-shelf thing but apparently it is not.

[rffffffff]

I agree, really good stuff, Bert. It’s really a great illustrator of why you need *more* solar panels. Cloudy day with people inside using the fridge your solar needs to cover typical usage and charging the batteries too. Some days there’s little you can do but if it’s kinda grey you should still be net positive if you want to have an easy life.

[Bert06840]

Originally Posted by musigenesis

I have two small 110V chest freezers, one of which will be used as a fridge with a gadget that keeps it around 37°F. I'm trying to find (or build) a switch to ensure that only one or the other will be drawing current at any point in time, and then the two together will share a dedicated circuit breaker.

I was hoping a switch like this would be a common off-the-shelf thing but apparently it is not.

You could take an old school mechanical timer for four or five bucks and a single pole double throw relay. 30m on, 30 off. Freezer a, freezer b, freezer a, etc.

Simpler Still.. you could take two timers. One on for 15m, both off for 15, the other on for 15, both off for 15, and so on. Those things have synchronous ac motors inside so they’ll stay in sync.

[Bert06840]

Originally Posted by rffffffff

I agree, really good stuff, Bert. It’s really a great illustrator of why you need *more* solar panels. Cloudy day with people inside using the fridge your solar needs to cover typical usage and charging the batteries too. Some days there’s little you can do but if it’s kinda grey you should still be net positive if you want to have an easy life.

I agree. Panels are so cheap (relative to batteries, and other parts), you should max out your roof.

[rffffffff]

Originally Posted by Bert06840

You could take an old school mechanical timer for four or five bucks and a single pole double throw relay. 30m on, 30 off. Freezer a, freezer b, freezer a, etc.

Simpler Still.. you could take two timers. One on for 15m, both off for 15, the other on for 15, both off for 15, and so on. Those things have synchronous ac motors inside so they’ll stay in sync.

Simplest is just to run two wires and two breakers (unless it’s too late!) or if you want to experiment put them on a 20a circuit together and don’t worry about it, but test that before you commit!

[rffffffff]

Originally Posted by musigenesis

I have two small 110V chest freezers, one of which will be used as a fridge with a gadget that keeps it around 37°F. I'm trying to find (or build) a switch to ensure that only one or the other will be drawing current at any point in time, and then the two together will share a dedicated circuit breaker.

I was hoping a switch like this would be a common off-the-shelf thing but apparently it is not.

I’d run two wires and two breakers and not worry about it, but there’s this:

https://www.usabluebook.com/p-346183...2ar100s0x.aspx

Pretty sure it’ll do what you need but I didn’t dive in.

[Rucker]

Originally Posted by musigenesis

I have two small 110V chest freezers, one of which will be used as a fridge with a gadget that keeps it around 37°F. I'm trying to find (or build) a switch to ensure that only one or the other will be drawing current at any point in time, and then the two together will share a dedicated circuit breaker.

I was hoping a switch like this would be a common off-the-shelf thing but apparently it is not.

I'm solving another similar problem with current-sensing switches. Maybe if you put the sensor on the power line to each device so it shuts off power to the other line when drawing current, the devices could take turns.

[Bert06840]

I just thought of one thing. My dorm fridge starts a defrosting cycle every time you plug it in. You can see it on the killawatt and hear the PTC clicking.

So putting that one on a timer would be a terrible idea.

Also, fridges aren't that bad in the current they draw, I would not even bother for two circuits. A single circuit for both fridges should be fine. If your inverter cannot handle that, then there is DEFINITELY no point in having two circuits.

[BeNimble]

Absortion fridges are made to run on 12v to run from the alternator while driving,
when you can't run it on propane, and 120v to run from the campground power,
and propane when none of the above applies. Great for that. Otherwise they are really poor efficiency. As Bert says, the key is to not make the fridge do anything more than keep something already cold, cold.

So remember to always drink beer because you can buy it already cold at the store.

[incubus]

Propane,absorption way to go. Flame is size of pilot light, run mine year round. Electric cycle is just a coil producing heat instead of flame,not efficient at all. Amish sell conversion units that can be fitted to most any kind of fridge. Also my unit,Dometic,has to be turned down to keep it from freezing everything. Not bad for 25 years old.

[Rucker]

Originally Posted by incubus

Propane,absorption way to go. Flame is size of pilot light, run mine year round. Electric cycle is just a coil producing heat instead of flame,not efficient at all. Amish sell conversion units that can be fitted to most any kind of fridge. Also my unit,Dometic,has to be turned down to keep it from freezing everything. Not bad for 25 years old.

Good info.

[BFlinn181]

An absorption refrigerator needs heat to operate. That heat can be supplied by an LP flame, 120v AC heating element, or a 12v DC heating element. The 12v DC element is so power-hungry that most fridges are wired to only operate when the engine/alternator is running. For the last couple of decades, small, DC compressor-operated fridges are actually more efficient and do a better job than the older RV absorption models. I'd seriously look for a DC compressor model if you plan on solar power and lithium batteries.

[john61ct]

Yes +1000, again.

If you are already using propane, of course they can be made to work, but a couple of identical Engel portables and some solar are IMO a better way to go.

[incubus]

You know it's kinda like wine ,everyone e has their preference. I had hard time justifying the cost of panels,batterys and controlers to power even the new DC refrigerators. Some one said DC is colder, yet I set temp control back because everything in the lower compartments froze. Its icecream cold. I buy propane about once every 18 months,not bad since I cook with it too. Like I said it's like wine, so drink what you like.

[Booyah45828]

I assume yours is mainly ran off propane then?

If so, absorption is the only way to go. There's no doubt that there is a place for them, and thousands of campers use them to this day. Truthfully, one could argue that a propane fridge is more efficient if the metric is based off of Wh/kg. But propane isn't a renewable resource, whereas solar/battery is.

For those that don't have propane on board, or want to be solely solar/electric, an absorption fridge is not electrically efficient.

[incubus]

I under stand the non renewable propane and respect your views. I often in the fall threw November in Lubec Maine. We get about 4 to 5 hrs of usable sun. The rest the time seems I'm in the woods Pokomoke Md. and in the woods in Smokie mountains. I have solar for my old school 4 golf cart batterys,lighting ,music ,some TV. I get about 10 days with out having to recharge before panels. That's using propane for cooking and refrigeration. Allows me to go and park anywhere I want.Oh, and by the way, how much energy does it take to make those solar cells ? There is no such thing as free energy.

[Doktari]

I recently installed a new JC Refrigeration 12/24 volt compressor unit on my old Dometic absorption fridge. It was $750 plus shipping. It’s installed but I haven’t tried it yet. Should be very efficient and a nice 8 cubic feet fridge and freezer. Removing the old absorption guts and installing the new guts was a bit tricky the first time but the videos helped a lot.

[Booyah45828]

Originally Posted by incubus

Oh, and by the way, how much energy does it take to make those solar cells ? There is no such thing as free energy.

I've got no argument on that. Especially if you use lithium batteries and factor in their cost to mine as well. But, battery tech is advancing rapidly though, so I'm confident we'll have a more eco-friendly solution soon.