Go with an AC fridge. More choices, more sizes, and yes cost. We dock in a marina and live aboard but when we are out, our gen is running all the time (mostly for our AC's, we live in Florida so always freaking hot) but the fridge too. Prior owner had a crappy, but functional fridge that we ended up swapping out for a stainless panel GE fridge that fit in nicely and better power consumption.
I guess this is part of my confusion. The inverter is using the same set of batteries from which I would be sourcing the 12 volt power. Is using 12 volt directly more efficient than converting those same 12 volts to 120 ac via the inverter??
Hi Cliff,
I have an ancient (25+ yrs) Norcold fridge on my boat which still works beautifully. It can run on DC, AC or propane although I never used that last option. As far as DC vs AC, I did a test to measure the power usage in each situation which is calculated as P=V x I. (power(watts) = voltage x current). Interestingly the fridge ran about 30% more efficiently when I ran in AC mode through my inverter. It didn't seem to matter if the inverter was a true sine wave or modified sine wave (I have both). I was told the reason is that these old fridges actually have AC motors with a built in old style and relatively inefficient inverter that allows them to run in DC mode. However the built in inverter is nowhere near as good as an external modern inverter so it works more efficiently in AC mode powered by an external inverter connected to the house batteries. If I had to replace my fridge I would definitely buy an AC only fridge and run it from batteries through my inverter. I would recommend installing a backup inverter since it is such a critical piece of equipment.
Cheers, Jeff
Downside to running an ac compressor via inverter.
120 AC frig running 4 amps running 5 hours per day is 20 amps.
20 amps ac X 120 volts ac = 2400 watts.
2400 watts ÷ 12 volts DC = 200 amps.
12 volt DC frig running 8 amps, 18 hours a day, which would be a poor frig would consume 144 amps.
Not counting inverter efficiency, thermal loss or actual voltages.
And guessing on the ac frig electrical consumption.
Syjos, I'm sorry but your math makes no sense. Unless they have changed the science since I got my engineering degree, here's where you went wrong. First of all your units are all wrong. Anything drawing 4 amps for 5 hrs results in 20 amp-hours, not 20 amps. Amp-hours is a measure of electric charge but is more commonly used to describe battery capacity. You multiplied amps-hours x voltage which does not make any sense. It's amps x volts = watts. Also, I doubt an AC fridge would draw 4 amps at 120 V. Mine is closer to 1.5 which is 180 watts of power. 180/12= 15 amps which is what my inverter draws to power the fridge in AC mode. If I run the fridge for a total of 8 hrs per day (seems to be the cumulative average) then I use 120 amp-hrs of battery capacity which is about 30% of my house bank and well within acceptable limits. I hope this helps. Let me know if you have any questions.
Seafreeze is claiming 48 amp- hours per day for their new RF1000 12 volt model. Dave at Seafreeze is usually conservative with his advertised consumption claims.
These thermostats are much more accurate than the built in ones -- plus, you can see the temp inside.Those top loading chest freezers make a lot of sense. I helped my neighbors set up one to chill home brew beer in pepsi kegs. Got that external thermostat and taped the probe to the side of the keg. Worked like a champ. Freezer plugs into tstat, tstat plugs into wall.
I was looking at that rig and thought it would be perfect in a boat. Too big for my small ride, but if you have room for one, they can work as a really great fridge.
Has anyone re-insulated or added additional insulation to a unit? This where the SeaFreeze and SunFreeze units shine. If you raise the ambient temperature around the unit from 70 to 90 degrees F, it can cost you 50% more in energy.
I had Sea Freeze make me a 6 cu ft 12 volt freezer with 4" insulation. I don't know how much juice it consumes, but it isn't much. Ice cream and everything else is rock hard.
That Seafreeze unit is 8 cubic feet, burns 580 watts daily and costs $3500. Similar to a Sunfrost but those are super-affordable at only $2500
Meanwhile a Samsung or LG digital inverter domestic unit, A+++ rated, about 12 cubic feet, burns about 500 watts daily and costs about $800. Most people have an inverter already, but you can spend a few hundred bucks for a cheap PSW inverter and you're good to go for $1k.
25%-50% larger, 1/3 the price, 5% less power required (assume 10% loss in the inverter).
You guys live in a different plane of existence than me because I just don't understand the desire to blow money just because someone owns a boat.
I`m a huge fan of our home front load LG washer,still good after 9years. But be careful with LG fridge performance tests, they were caught here special programming the fridges they supplied for testing, such that the testing organization began buying test fridges retail....a Samsung or LG digital inverter domestic unit, A+++ rated, about 12 cubic feet, burns about 500 watts daily and costs about $800. Most people have an inverter already, but you can spend a few hundred bucks for a cheap PSW inverter and you're good to go for $1k.
25%-50% larger, 1/3 the price, 5% less power required (assume 10% loss in the inverter)...
Dave at Seafreeze can manufacturer any size refrigerator to fit the existing space with no modification. Trying to fit a domestic frig into existing space require fillers to fill gap or enlarging the opening.
We have an AC fridge run off a Freedom 3000 inverter. Does it make sense to install a smaller inverter dedicated only to the fridge and turn the larger unit off when not needed?
One thing we should remember is, if you have a generator, USE IT. That's an expensive piece of equipment to leave sitting there shut down, gathering dust. It would not be unusual (in my history) to have twice the hours on the generator as the main engine.
We have an AC fridge run off a Freedom 3000 inverter. Does it make sense to install a smaller inverter dedicated only to the fridge and turn the larger unit off when not needed?
While I prefer AC units as they are more economical and many are more energy efficient, the choice to have an AC/DC unit could be as simple as a dead battery charger at the dock. IMO, it's about having opinions when you have a problem. For most of us, having a DC problem could be overcome by simply starting the generator.Would like to tag onto this thread with a related question. If 12V operation is usually more efficient, why would anyone need an AC/DC unit as opposed to a less expensive DC only? I have an AC/DC unit but the AC side doesn't work so I run it on DC only even though we are almost always on shore power so inverter/charger keeps the DC side charged. I could replace the fridge control unit to allow for AC operation but why should I? It us just an AC to DC converter.