Residential fridge draw on inverter.

[sunchaser]

The questions that often arise on the fridge issue tend to neglect one's individual on board battery, genset and ambient conditions. Then space, dock queen or at anchor. Then comes how much stuff do you plan on keeping cool.

Oh, don't forget that 20 ft3 fish freezer that also works for ice cream and left overs. My point? Define your wants, needs, cruising style, charging and inverter system, space and geographical location. Then do you mind defrosting or must you have a power hungry auto defrost unit?

To me, the energy star rating is an end of the line decision maker as opposed to a multitude of musts earlier in the thought process.

 

[koliver]

To add to Tom's post, All of those calculations will depend on whether your boat has other AC needs than the fridge, and if so is already running the inverter all the while that neither generator or shore power are supplying those AC needs. If the fridge is the only reason to have the inverter on, you need to add the wattage draw of the inverter. Mine draws close to 8 amps, which is over and above the AC things it is powering.

 

[O C Diver]

OC Diver, I have been following you for years. Looks like you have a different boat!

JimL

Same boat, unless you're think of my charter boat that was my avatar until 2015.

Ted

 

[O C Diver]

To add to Tom's post, All of those calculations will depend on whether your boat has other AC needs than the fridge, and if so is already running the inverter all the while that neither generator or shore power are supplying those AC needs. If the fridge is the only reason to have the inverter on, you need to add the wattage draw of the inverter. Mine draws close to 8 amps, which is over and above the AC things it is powering.

Wow! Either you need a new inverter or you have some loads you're not aware of.

As a point of reference, any of the Victron Phoenix inverters draw less than 1 amp in stand by mode. So having an inverter dedicated to the refrigerator becomes a reasonable choice.

Ted

 

[rslifkin]

My 2kva Multiplus is also under 1 amp in standby. It's about 10 watts / 0.8 amps, so we just leave it running 24/7. The 3kva version idles at twice as much, unless you get the newer Multiplus 2, in which case it's down to 13 watts / just over 1 amp.

 

[sunchaser]

RS and Ted
Where in your circuits is inverter load measured and with what device?

 

[rslifkin]

RS and Ted
Where in your circuits is inverter load measured and with what device?

I'm going based on the difference in battery monitor current display with the inverter on vs off. The numbers I'm measuring come up consistently within 1 - 2 watts of what's listed in the Victron spec sheet.

 

[luna]

The power consumption of modern inverters as stated above is quite low, likely 15 watts if on and idle, while about half of that while in search mode. In both of these modes, no power is produced.

But thats not the power consumed by the inverter when it is providing power only to the refer. Although inverters are said to have a peak efficiency of somewhere around 92%, that is not likely accurate when the inverter is just powering the refer. as there is a power production overhead within the inverter that is almost constant regardless of power output. I've yet to find an efficiency graph, based on power produced for any inverter.

You could get a better idea of the inverter overhead while powering only the refer by doing this:

-Run the refer. on the grid and measure the AC current, then convert to watts.

-Then, run the refer. on a cold inverter and measure the current leaving the batteries, then using the actual battery voltage, convert to watts.

-Do the same thing with a warm inverter, (no fan running) just like normal usage would dictate. The wattage will likely be higher.

I would not be surprised if the difference in power consumption due to the inverter overhead just running the refer. equates to 8 amps at 12V.

 

[rslifkin]

The power consumption of modern inverters as stated above is quite low, likely 15 watts if on and idle, while about half of that while in search mode. In both of these modes, no power is produced.

But thats not the power consumed by the inverter when it is providing power only to the refer. Although inverters are said to have a peak efficiency of somewhere around 92%, that is not likely accurate when the inverter is just powering the refer. as there is a power production overhead within the inverter that is almost constant regardless of power output. I've yet to find an efficiency graph, based on power produced for any inverter.

You could get a better idea of the inverter overhead while powering only the refer by doing this:

-Run the refer. on the grid and measure the AC current, then convert to watts.

-Then, run the refer. on a cold inverter and measure the current leaving the batteries, then using the actual battery voltage, convert to watts.

-Do the same thing with a warm inverter, (no fan running) just like normal usage would dictate. The wattage will likely be higher.

I would not be surprised if the difference in power consumption due to the inverter overhead just running the refer. equates to 8 amps at 12V.

The on and idle mode does produce full output power. Search mode or other power saving modes either produce a modified output or no output. Adding a small load adds only slightly more than the load worth of additional draw on the DC side.

 

[Statistical]

Has anyone found a residential brand that they are particularly impressed with in the amperage draw area? I have worked the math on some of the main brands based on their KW/year, but I feel like gives a misleading result. Maybe I am not looking in the right places for the door stamp where the actual draw information lives.

The annual energy consumption is actually probably going to be better indication of energy usage.

As long as you have enough power (peak amps) the total energy consumption matters more.

Imagine two refrigerators
20A peak @ 12V 30% duty cycle = 24*30%*20 = 144 Ah per day (1.78 kWh)
15A peak @ 12V 50% duty cycle = 24*50%*15 = 180 Ah per day (2.16 kWh)

The first one actually uses less energy despite higher amp draw because it cycles off more often. That is why energy star tags are showing energy consumption not peak power.

 

[O C Diver]

So the information I posted was from Victron's website. The number wasn't the eco search mode, it was the stand by power consumption.

My Magnum Energy inverter consumes 2.9 amps in standby mode. With the refrigerator running, the consumption is 13.9 amps. This measured with my Victron battery monitor.

Ted

 

[luna]

The on (the inverter is enabled) and idle (but nothing is presenting a load) mode can indeed provide full power, but there is no load, so even though the inverter is poised to produce power, no usable power is actually produced. This mode consumes the 15 watts.
In Search mode it's common to find that all of the above is true except for about half the time (adjustable through the Sensitivity Setting via pulse length and spacing of the search) all of the inverter even the control circuits are off. That is what saves you half the power consumption, it's all off, half the time.

I know of no inverter that is capable of producing a modified output, (eg two different voltages or wave forms) it's either on or off. Once on, full output is available even if set to Search mode.

How did you quantify the "additional draw on the DC side."

 

[rslifkin]

The on (the inverter is enabled) and idle (but nothing is presenting a load) mode can indeed provide full power, but there is no load, so even though the inverter is poised to produce power, no usable power is actually produced. This mode consumes the 15 watts.
In Search mode it's common to find that all of the above is true except for about half the time (adjustable through the Sensitivity Setting via pulse length and spacing of the search) all of the inverter even the control circuits are off. That is what saves you half the power consumption, it's all off, half the time.

I know of no inverter that is capable of producing a modified output, (eg two different voltages or wave forms) it's either on or off. Once on, full output is available even if set to Search mode.

How did you quantify the "additional draw on the DC side."

The Victron inverters have a third mode called AES. It only saves a little bit of power compared to full idle mode, but instead of shutting off with periodic load checks like search mode, it modifies the sine wave to reduce power consumption slightly but stays on.

 

[Iggy]

Her is my 2 cents. Just buy the 12V fridge. Don't drive your self crazy in this. Life is too short and we have worked to hard to get to where we are.

Lithium prices are dropping. Maybe in 1 to 3 years you can upgrade to them giving you more amp hours and less wight or equal.

 

[luna]

Well, you see, you learn something new every day. Thanks rslifkin!

I suppose the smart guys at Victron could have deleted or clipped some of the voltage in the low voltage portion of the sine wave in order to "slightly narrow the sinusoidal voltage." This would result in somewhat of a stepped wave.
Fine for most electronics and the fact that it is said to be automatic and suitable for low loads, it likely turns itself off and reverts to a full sine wave should your refer's. compressor motor or some other large load turn on.
AES, if you have a small bank could make a meaningful difference.

Regardless, the power consumption of a 120 V. refer, powered by the grid will always be less that the power taken from your battery via your inverter, by exactly the amount of heat generated by the inverter and the 12 V. circuit.

Now back to that learning thing.

Iggy, or others. What is the native voltage of the compressor motor in a typical 12 V. DC refer?

 

[Simi 60]

I reckon it's cheaper to buy more battery to run stuff than muck around trying for most efficient at much greater cost.

We run 4 household refrigeration units.
Hole size dictated what units we bought.

A large 4 door Akai fridge freezer
A Samsung bar fridge
A Kmart bar fridge
And a matching Kmart 4 draw freezer.

All running 24/7 for near 7 years off of a 5000/120 Victron multiplus, battery and solar.

 

[rslifkin]

I reckon it's cheaper to buy more battery to run stuff than muck around trying for most efficient at much greater cost.

Given adequate space, I absolutely agree. Squeezing out every last drop of efficiency starts to matter once you're space limited though. Depending on the boat, you hit a point where you have no more room for batteries or solar panels, so the only way to have more power available for one system is to make another more efficient.

 

[Mike H]

Although you can run the fridge off a good inverter, keep in mind that small 110 volt motors (less than 1 hp) are terribly inefficient. If you really want to lower the power consumption, get a dual voltage fridge. They typically have a 12 or 24-volt compressor (much more efficient) and a rectifier so you can use 110 volts.

To give you an idea on the power savings, just think of what size wire you would have to run for 55 amps DC for say a 20-foot run (remember, that's only 10 feet since the run is based on total circuit length). Then compare that to the size of DC wire required for a new fridge that is dual voltage. I forget what mine was, but I believe it was 10 awg for a decent length of run.

 

[koliver]

Wow! Either you need a new inverter or you have some loads you're not aware of.

As a point of reference, any of the Victron Phoenix inverters draw less than 1 amp in stand by mode. So having an inverter dedicated to the refrigerator becomes a reasonable choice.

Ted

Nobody with an existing inverter that will do the job for them will be running out to buy a new inverter in order to bring that basic load number down, until that existing inverter is at the end of its useful life.
So, yes, mine may be old and inefficient at idle. I know it. I turn it off until I need it.
I have a dc fridge, my cellphone and computer chargers are good enough that they will charge without turning on the inverter.
If I was to buy a residential fridge, that would happen only if my DC fridge failed. I have solar, so my batteries stay up with fridge draws. I don't think I need to change a thing.
Others may benefit from my point of view, though you may have another that is quite different, that others may also benefit from.

 

[rslifkin]

Although you can run the fridge off a good inverter, keep in mind that small 110 volt motors (less than 1 hp) are terribly inefficient. If you really want to lower the power consumption, get a dual voltage fridge. They typically have a 12 or 24-volt compressor (much more efficient) and a rectifier so you can use 110 volts.

The common Danfoss/Secop compressors used in the majority of 12v fridges are not 12v compressors. They're actually low voltage 3 phase AC, run off an inverter in the control module. Many of the more efficient modern AC fridges use similar inverter driven compressors.

 

[Capt Ray]

Something to be aware of:
One on-board challenge with the home refrigerator / freezers is the "no frost" feature.
Know that that usually includes a HEATER cycle in the mix.

Our OEM 23 year old, Nova Kool fridge/freezer on our 2000 Mainship 390 is still being made today, and one can be ordered to fit... direct replacement! That's the good news. When I asked the sales person, "Are the 2023 models more efficient than the 2000 model I have today?" Answer was "No" ... same technology as 2000. Amazing.

We have 800w of solar PVs and 540 AH of LiFePO4 storage. So our fridge is ALWAYS running on 12vdc... typically draws 4 amps.

A Powerworx DC power analyzer helps me track the consumption over time. (Amazon)

SEARCH for more info and pics at: Shellerina.com

 

[O C Diver]

Nobody with an existing inverter that will do the job for them will be running out to buy a new inverter in order to bring that basic load number down, until that existing inverter is at the end of its useful life.
So, yes, mine may be old and inefficient at idle. I know it. I turn it off until I need it.
I have a dc fridge, my cellphone and computer chargers are good enough that they will charge without turning on the inverter.
If I was to buy a residential fridge, that would happen only if my DC fridge failed. I have solar, so my batteries stay up with fridge draws. I don't think I need to change a thing.
Others may benefit from my point of view, though you may have another that is quite different, that others may also benefit from.

I understand that it doesn't make sense in your situation to replace a working inverter. The point to be made was that if your refrigerator died, the cost to replace it with a significantly better insulated (efficient) apartment refrigerator and a small inverter to run it efficiently is less expensive than than an RV / boat refrigerator (atleast in the USA).

Ted

 

[Hippocampus]

Read this thread with interest but think your choice some what depends upon boat use profile.
If while cruising you usually have no access to a car and are on the boat for stretches of weeks to months that’s very different than days to a week at a time. Our style is months and also includes side trips where we leave the boat rent an air B&B and a car. I don’t like running a genset when not on the boat. I’m even nervous about having shore power fail (lightening strike on the marinas supply or getting disconnected).

So for long interval users would only have AC/DC units made for boat use. For short interval users where you’re always on the boat don’t think it matters much. Run times are short and you’re on the boat(days). Food is removed when you leave the boat. Additional expense not worth it. Second thing for long interval users is I’d have at least two freezer units. We have this. Freezers use less energy when full. Cooling air is hard. Frozen high water content food once frozen takes less energy to stay frozen. Also once you’ve eaten enough food you can consolidate to one freezer and turn one off entirely. We have the second freezer in the salon. Don’t think that’s ideal. Rather have it in below the sole someplace as below the waterline surrounding air tends to be cooler. Obviously not in the ER. Even in the tropics think water cooled may make sense over air cooled units.

Our units aren’t frost free so that’s another chore. So for new construction would go with freezer draws and refrigerator draws. Each being able to serve either function and each able to turned on or off independently. Think opening drawers has less air exchange than doors. Cold air is heavier so pores out of open doors. Separate pure top loading freezer unit placed in the coolest place in the boat. SOC sensors automatically turning on genset(s). Enough alt energy to carry all hotel loads. At present have a new to us boat. Not worth the expense as if it’s not broke don’t fix it.

 

[rslifkin]

So for long interval users would only have AC/DC units made for boat use.

Or plan to have the inverter always on so it takes over if shore power fails. And ideally, if leaving the boat with things powered up, some kind of remote monitoring is good so you know if there's a power issue. In either situation, the concern is that without adequate solar, etc. the fridge is only going to run so long before the batteries are drained (regardless of DC vs inverter as the source).

 

[HeadedToTexas]

For those that have a residential refer. that consumes multiple times the normal amount of running current when first energized, it's likely the resistive defrost element that is right next to the evaporator that is powered. Its automated.

This heater usually turns on when first powered up and then again at some timed interval (about every 5 hours) while the refer. remains powered. Its job is to keep the evaporator free of ice, so it can cool the refer.

My Norcold DE0061 has a defrost element. The key identifies item 85 as the Divider Heater and it must serve that defrost function. Interestingly, the manual indicates that only DEC0061 models have the Divider Heater, though this model number is cited nowhere else in the manual (copy here).

My digital thermostat upgrade will get a real world test in the coming week, but it passed the power up on the hard. Finger are crossed. Anyway, my plan is to leave the Divider Heater out of the circuit and live with manual defrost.

 

[Bmarler]

My Norcold DE0061 has a defrost element. The key identifies item 85 as the Divider Heater and it must serve that defrost function. Interestingly, the manual indicates that only DEC0061 models have the Divider Heater, though this model number is cited nowhere else in the manual (copy here).

My digital thermostat upgrade will get a real world test in the coming week, but it passed the power up on the hard. Finger are crossed. Anyway, my plan is to leave the Divider Heater out of the circuit and live with manual defrost.

I thought a divider heater was in the section between the fridge and freezer. To keep it from icing up. Am I totally wrong on that?

 

[O C Diver]

Read this thread with interest but think your choice some what depends upon boat use profile.
If while cruising you usually have no access to a car and are on the boat for stretches of weeks to months that’s very different than days to a week at a time. Our style is months and also includes side trips where we leave the boat rent an air B&B and a car. I don’t like running a genset when not on the boat. I’m even nervous about having shore power fail (lightening strike on the marinas supply or getting disconnected).

So for long interval users would only have AC/DC units made for boat use. For short interval users where you’re always on the boat don’t think it matters much. Run times are short and you’re on the boat(days). Food is removed when you leave the boat. Additional expense not worth it. Second thing for long interval users is I’d have at least two freezer units. We have this. Freezers use less energy when full. Cooling air is hard. Frozen high water content food once frozen takes less energy to stay frozen. Also once you’ve eaten enough food you can consolidate to one freezer and turn one off entirely. We have the second freezer in the salon. Don’t think that’s ideal. Rather have it in below the sole someplace as below the waterline surrounding air tends to be cooler. Obviously not in the ER. Even in the tropics think water cooled may make sense over air cooled units.

Our units aren’t frost free so that’s another chore. So for new construction would go with freezer draws and refrigerator draws. Each being able to serve either function and each able to turned on or off independently. Think opening drawers has less air exchange than doors. Cold air is heavier so pores out of open doors. Separate pure top loading freezer unit placed in the coolest place in the boat. SOC sensors automatically turning on genset(s). Enough alt energy to carry all hotel loads. At present have a new to us boat. Not worth the expense as if it’s not broke don’t fix it.

I consider myself a long interval user, cruising 7 months a year. In addition to my 120 VAC apartment refrigerator I also have an Engel freezer.

I'm not sure how you see a difference as both will work on Shore power and seamlessly switch to battery power. Unless you have enough solar to power your refrigerator, both are dependent on dock power when away from the boat.

Ted

 

[luna]

As I don't have a Norcold Refer, I'm not familiar with their design but understanding that this "Divider Heater" is in the control circuit, I don't think it's a timed evaporator defrost system that would render the unit "frost free." These frost free heaters consume too much power for a typical control circuit to provide.

From your thermostat block diagram this heater is on whenever the compressor is running and the door is closed. The door's position is likely not important to the function of this heater (it should be closed 99% of the time) but use of the door switch to source the heater's power means that only the heater or the interior light can be on at any given time. Not both.

My guess is that as all of the cold air is likely delivered to the freezer compartment of this refer. and then some is feed through the divider between the freezer and the fridge compartment by way of an air channel, this "Divider Heater" keeps this short air channel free of frost. To do this small job it would only take about as much power as the interior light consumes (say 5 watts) which the control circuit can handle because the door is closed and the light is, or should be off.

If so, disabling the heater may in time, result in a warm fridge compartment and a continuing running compressor.

Perhaps I'm wrong and other Norcold owners will enlighten us further.

 

[HeadedToTexas]

I am clearly less than clear about the function of the Divider Heater. Among the data I have yet to collect is current draw with and without the Divider Heater in the circuit. It seems counterproductive to have a heater between the freezer and refrigerator sections, though something is certainly needed to maintain separate temperatures. Given the very wide temperature swings, like more than 8º F, in the refrigerator with the original thermostat, it was not hard for me to believe that Norcold is a very low tech unit.

 

[Hippocampus]

My experience to date is marinas lose power for a few days not indefinitely. Even with a small house bank supplemented by solar power should come back on before you get below 50%soc and destroy your bank. Given you take DC and make it to AC to run a AC refrig you add inefficiencies. DC to a DC device avoids that.
You can have the genset flip on automatically. If you leave the boat with full fuel tanks it’s very. Unlikely you will burn through that just running your frig(freezer) and the usual stuff ( bilge pumps, monitoring systems etc.).
Given our lifestyle and to check on other stuff in the past had yacht management stop by. Depending upon setting every week or two. With the current boat have just given food away and shut down the frig/freezer if we’re going to be away for more than a week. You have stuff go bad once and you realize what a mess it makes.
Although the food is great in the windwards the beef throughout the Caribbean is dismal. Hamburger is ok but not steak. Every once in awhile you can find a store that sells to the magayacht crowd and are willing to sell to you. You freeze those steaks and don’t want to lose them.