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Old 01-16-2021, 12:09 PM   #1
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AC or DC fridge?

Hello all,

Im trying to plan my refrigerator out for my short bus build. We will have 400 watts of solar on the roof with 200ah of lithium batteries. Besides led lighting we also want to be able to run a small 700w microwave for maybe 10 minutes total a day, a fan for the toilet, a rooftop fan and a diesel heater, water pump and charge a laptop.

Im trying to figure out if we can get away with a 3.3 cu dorm style fridge vs spending a ton on a 12v upright option. We really dont want a chest style fridge.

I realize energy consumption carries many variables but just looking to hear from some experienced people with this sort of situation. Thanks
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Old 01-16-2021, 01:03 PM   #2
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The fridges sold in 240V jurisdictions with ever more stringent energy efficiency regulations

are **much** less thirsty than normal units in the US market.

But obviously cost more.

Finding out the Ah per 24-hr consumption at a high temp delta

compared to your current Ah/day surplus will remove the uncertainty and guesswork.

Adding other energy sources

or just getting to overnight shore power more frequently

also can make up the difference.

But personally, my choice s investing in ultra efficient gear two identical portable DC compressor units

each capable if running as a freezer

combined with good quality 4-day coolers and some freezer packs

gives a lot of flexibility.
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Old 01-16-2021, 02:10 PM   #3
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You will need an inverter to run a microwave, so you can use that to run a small fridge. They draw a lot of startup power but running not so much. The 'dorm fridge' have pretty minimal insulation, but you could just add more as long as you don't get one that has the condensor coils embedded in the fridge walls. Get one that has a coil on the bottom next to the compressor.
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Old 01-16-2021, 02:22 PM   #4
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You need to do an energy budget. I don’t think your 400W/200Ah setup is big enough to run all of that. Maybe without the microwave. But crunch numbers to find out.

I’d avoid the inverter to run the fridge. Get a DC fridge/freezer. I have a chest style fridge/freezer. Get one that is programmable so you can run both as fridge or turn off one compartment if you’re low on juice.

When figuring the energy usage for the fridge use a 50% duty cycle, so wattage x 12 hours. This of course is extremely variable.
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Old 01-17-2021, 07:29 AM   #5
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I’ll disagree with the comments above a bit.

I do think you need more solar and an additional battery or two, but the dorm style fridges are doable, and a lot of people use them.

My diesel heater, 5.1 cubic foot “dorm style”fridge plus lights, a laptop chargers and a little bit of heat tape on a pipe, water pump and hot water heater will eat about 60-90ah at 24v overnight depending on the temp. The 5kw diesel heater eats most of it, surprisingly, and it’s way worse when it’s colder out. The 12 degree nights recently were 90ah nights, 25 degree nights are typically 60ah.

It’s important to translate to watts, though, so roughly 1500-2200 watt hours overnight. I think the fridge is about 700 watt hours over the course of 14 hours, and the diesel heater makes up 75% of the rest, more when it’s colder and the fan is on high all night. We’re pretty liberal with lights and Netflix on the laptop, usually doing dishes and running the pump a bit after dinner, and my whole setup is inefficient as I run a 24v inverter to power my house panel then an extension cord to the bus that powers my 12v charger that runs the lights, etc. so the 12v is all being converted twice and really dumb for the moment.
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