Fridge a/c or a/c-d/c

[cbouch]

Thanks, Beautiful boat.

 

[Mr. Blu]

What about solarpanels?

 

[sunchaser]

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.

Interesting, you leave your genset running all the time. That must be costly.

 

[dutch-barge]

AC household fridge
inverter...and automatic start of the generator when your SOC of your housebank is below 70.... great set up of Victron

 

[Albin]

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

 

[syjos]

I'm not sure about the newer Norcolds but the old ones had a swing compressor running at 110 VAC.

The compressors piston goes up and down as the AC reverses 180 degrees with each cycle.

An internal inverter converts the 12 volt DC to 110 AC.

 

[O C Diver]

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

Yours isn't quite a fair comparison as your fridge is an ammonia system as opposed to a compressor. The ammonia systems work extremely well but are actually much more efficient on propane as the energy input is to generate heat to make it thermal siphon.

Ted

 

[syjos]

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.

 

[Albin]

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.

 

[jeffnick]

We use a freezer as a refrigerator...it's a refreezarator...
https://72land-n-sea.blogspot.com/2012/10/freezerrefrigerator-findings.html?m=1

 

[Ski in NC]

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.

 

[syjos]

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.

Thanks Albin for correcting my sloppiness. I should not post tech and math at night after consuming adult beverages. Too late for editing.

I found my Seafreeze RF1000 DC 12 volt refrigerator specs and it consumes 6 amps. It runs about 50% to 60% of the time so about 72 to 90 amp-hrs per day and is 20 years old.
It is a two door frig, slightly bigger than a Norcold, has a remotely mounted Danfoss 12 v compressor and 3" insulation.

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.

 

[Mako]

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.

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.

 

[jeffnick]

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.

These thermostats are much more accurate than the built in ones -- plus, you can see the temp inside.

 

[Larry M]

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.

 

[Ken E.]

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.

 

[Larry M]

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.

I love it when you can bend a spoon in the ice cream.

We spent 6 years in the tropics on our last boat and learned a lot about refrigeration in the heat. When we bought Hobo, we had a SubZero refrigerator and freezer. I gave SeaFreeze the dimensions of the space and asked for 4” of insulation. They came back with: 4” of insulation on all the exterior walls, 2.5” between the refrigerator and freezer and 3.5” in the doors. They spec’d a Danfoss BD35 for the refrigerator and a BD50 for the freezer. Both units use the same model electronic module so we carry a spare. We’ve left the boat more than once, with no ac, for five days in the tropics in the summer and have come home to ice cream in the freezer and consumed less than 500 amps. After 12 years, I’d do it again.

 

[syjos]

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.

AC home refrigerators were not that efficient 20 years ago so Seafreeze and Nova Cool were the choice for efficient boat refrigerators when we were replacing the frig.

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.

As someone above mentioned, when ambient temperature climb into the 90's, the domestic frig will run more often. If the remote compressor is mounted in a cool location with adequate ventilation, the Seafreeze will run less.

 

[Ken E.]

Larry - We spend summers in Alaska and most of the time on the hook. Refrigeration and freezer performance is a big deal, although not as acute as your tropics scenario. I liked the freezer so much that I had Sea Freeze covert my 12 cu ft household Kenmore galley refer to 12 volts. Like the freezer, I don't have specifics on the energy I'm using now, but it's way less than before, just looking at my house battery bank voltage in the morning while on anchor.

 

[BruceK]

...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)...

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.

 

[Mako]

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.

Understood, if the space does not allow for a standard domestic fridge. Anything custom, especially in the marine world, is going to cost lots.

That reminds me of something George Buehler commented in his website about how large boats don't have to cost more than small ones, sometimes even less. He was commenting about how "big boat" or commercial items are available alot cheaper than little yachtie West-Marine equipment, especially from ship salvagers and commercial fisheries suppliers.

The only thing I ever bought from W.M. was a toilet set and a very expensive 12v bulb. Everything else came from Home Depot, commercial suppliers, etc., and nowadays from Amazon of course!

 

[FF]

"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."


Sorta like VW , tho VW efficient programming was in every car to allow all the owners to use less fuel, much to the dismay of the Air Police.

 

[bgillroy]

Check out vitrifrigo line of marine appliances

 

[Wings]

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?

 

[O C Diver]

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?

That would depend on your battery bank size, how often you recharge the batteries, and the idle power consumption difference between the 2 inverters.

Ted

 

[OldDan1943]

I have 2 small inverters. One 400 watts each devoted to the saloon TV and one outlet. The second 400 watt is devoted to the stateroom TV and one outlet. The big inverter, 1800 watt, devoted to either the microwave or 2 outlets in the galley area.
I do have 3X4D house batteries and 2X130watt solar panels. The big inverter, I shut off until needed. The other 2 inverters, I shut off when I leave the boat for an extended period of time. I opted for the 2X400 watt inverter because the life expectance of 200watt inverters just isn't as long as a larger inverter.

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.

 

[sunchaser]

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.

High hours on the genset vs the main is more common in areas where AC needed. For us, cruising on the west coast, AC needs drop way off. Our genset has about 1/3 the hours of the mains. In a 8 to 16 hour cruising day the genset sees little use as the alternators keep the batteries up. Shorter trips, more genset use.

 

[syjos]

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?

Compressors require some surge headroom during startup. Inverter needs to be able to handle the instantaneous peak demand of the compressor.

 

[Woodstock]

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.

 

[O C Diver]

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.

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.

Ted