Why do appliances give power draw in amps it’s so confusing.

[Datsolarboi]

This label confuses me, how many Wh does this fridge use? Why does it draw different amps from a car vs house battery?

Furthermore what if I had a 24 or 48v system- does this fridge not work on dc power in that case?

I’m trying to figure out my battery bank and panel requirement but I’m having a hard time with all these different variables. Please send help!

 

[Tulex]

Because circuit breakers/fuses are in amps.

If you are using 230/240v AC, you are drawing 1.4 amps, using 325 watts
If you are using 12v DC, you are drawing 23 amps from your vehicle, using 275 watts
If the fridge is on, it draws 2.0 amps, from the house battery, using 25 watts. Not sure it still draws those 2 amps if AC is connected.

The Manual
Installation

Manual says "Only select operation with DC power supply (battery mode) if the vehicle engine is running and providing sufficient voltage to the vehicle‘s light system, or if you are using a battery monitor."

The lower dc draw is operating mode. The installation manual clearly shows 2 separate sources of DC. The house DC is for power to run the fridge, the vehicle DC is to run the heating element in the fridge. So, I believe you have to have it connected to a house battery for any of it to work, (though it may work off of just AC) but it will work without a vehicle battery connected in AC or Gas mode.

As for DC voltage, it's a 12v system. You would have to step down from a 24 or 48v system.

 

[Gold Country Russ]

The label probably should be:
230-240V AC= 1.4 amp X230= 322W
120V AC= 2.7 amp X 120= 324W I'm pretty sure this line is a typo and should actually be 120VAC & 2.7A = 324W
12V DC= 23 amp X 12= 276W
The 46W difference between AC & DC is probably lost as heat converting the AC to low voltage DC.
Good Luck & Have a great & safe 4th of July,
Russ

 

[wattmatters]

Amps tells you the minimum wire gauge necessary for safe operation.

As to what type and voltage of supply it can use, that will be listed in the spec sheet.

 

[Tulex]

The label probably should be:
230-240V AC= 1.4 amp X230= 322W
120V AC= 2.7 amp X 120= 324W I'm pretty sure this line is a typo and should actually be 120VAC & 2.7A = 324W
12V DC= 23 amp X 12= 276W
The 46W difference between AC & DC is probably lost as heat converting the AC to low voltage DC.
Good Luck & Have a great & safe 4th of July,
Russ

I don't think so. The watt difference between AC and DC is because it has a heater for each source.
There is no 120v AC setting in the manual, this is only a 240v system.
The reason for 2 different DC ratings is because there are 2 separate draws from 2 different batteries. House battery to power the fridge, vehicle battery to power the heating element in the fridge.

 

[Gold Country Russ]

I don't think so. The watt difference between AC and DC is because it has a heater for each source.
There is no 120v AC setting in the manual, this is only a 240v system.
The reason for 2 different DC ratings is because there are 2 separate draws from 2 different batteries. House battery to power the fridge, vehicle battery to power the heating element in the fridge.

I was under the impression that this was an AC/DC RV refrigerator with optional propane operation.

 

[Tulex]

I was under the impression that this was an AC/DC RV refrigerator with optional propane operation.

It is.

 

[mikefitz]

The fridge you have have has two heating elements for electrical use, a 12 v DC rated element and a 230 volt AC rated element, each produces different amounts of heat.
The heating elements are resistive, thus the 12v element is designed for 12 volts. Connecting a higher DC voltage, 24 or 48 would cause a higher current to flow and the heating element would get too hot and fail.
Current =voltage / resistance
Power = volts x current

 

[Datsolarboi]

Thank you all for the replies! A few follow up questions:

Why does my fridge need a heating element?
Is the watts the watts/hour? And if so am I right I’m thinking the fridge requires 5000(!?) watts per day for the heating element, and 500 for the fridge?
Does this label specify how much power is required in LPG mode?
Why does an rv fridge run on 240 and not 120? Wouldn’t you need a split phase system to even produce that voltage?

 

[Tulex]

Heat is applied to circulate the refrigerant by changing the state of the refrigerant. That's why propane can be used to run a refrigerator.
How it works

Yes, watts is per hour, but only when being used. Like a 60 watt incandescent light bulb. If left on, it will use 60 watts in an hour. But, on half an hour at a time, it will use half that an hour. So, the ratings on the refrigerator are when drawing power. You can see this by looking at the yellow energy guide on appliances. Do the math, you will see that the total usage isn't just multiplying the numbers.

This Refrigerator for example. Draws 3 amps at 120v. That's 360 watts. If you multiply 360 X 24 hours X 365 days, you get 3154 kWh. Annual usage is actually only 410 kWh, because it isn't running at full watts all the time.

The 2 amps is what is used when using lpg. I'm not sure if it still draws 2 amps when plugged in though, but of course, you wouldn't be using lpg if plugged in.
Depends on what country you are in. Many countries households run on 240, not 120.

 

[CoolWill]

Watts is the rate at which energy is used. A 60 watt light bulb uses 60 watts the whole time it is on. If it is on for one hour, the total amount of energy used is 60 watt-hours. If it is on for half an hour it will use 30 watt-hours. But it always uses 60 watts. Watts is power. Watt-hours is energy.

The fridge only uses the rated watts when it is cooling. Once the temperature is reached, the thermostat will turn it off until it gets warm enough to come on again.

 

[Datsolarboi]

Heat is applied to circulate the refrigerant by changing the state of the refrigerant. That's why propane can be used to run a refrigerator.
How it works

Yes, watts is per hour, but only when being used. Like a 60 watt incandescent light bulb. If left on, it will use 60 watts in an hour. But, on half an hour at a time, it will use half that an hour. So, the ratings on the refrigerator are when drawing power. You can see this by looking at the yellow energy guide on appliances. Do the math, you will see that the total usage isn't just multiplying the numbers.

This Refrigerator for example. Draws 3 amps at 120v. That's 360 watts. If you multiply 360 X 24 hours X 365 days, you get 3154 kWh. Annual usage is actually only 410 kWh, because it isn't running at full watts all the time.

The 2 amps is what is used when using lpg. I'm not sure if it still draws 2 amps when plugged in though, but of course, you wouldn't be using lpg if plugged in.
Depends on what country you are in. Many countries households run on 240, not 120.

Thank you! I’m in canada so it’s confusing why this would be 240VAC not 120

 

[Tulex]

Thank you! I’m in canada so it’s confusing why this would be 240VAC not 120

Most likely you found a series sold to the 240v market. When I search for that product, the site that comes up is in New Zealand, which is 240v
This looks to be a comparable 120v version from the same people.

 

[RCinFLA]

Small refrigerators are normally less efficient. 320 watts run power for a 188 liter (6.6 cu ft) is a piggy.

Typical 400-450 liter (16-18 cu ft ) full sized refrigerators have typical run power of about 200-250 watts with an average of 20-25% run time duty cycle (plus some defrosting power every 16-20 hours) for an average daily energy of 900-1200 wH per day.

Duty cycle depends on individual use case. Lot of children opening door often, high room humidity and/or high room temperature raises run duty cycle. When you load up refrig from grocery store it runs longer to cool down all the stuff added to cool down. Lots of room temp can drinks make it run for a long time to cool them down.

Refrig's and air conditioner energy consumption highly depend on particular user use case.

Double French doors are worse for dumping in room temp air every time doors are opened. Conversely, a freezer slide out drawer with topside access is best to reduce outside air exchange when freezer opened.

 

[wattmatters]

Small refrigerators are normally less efficient. 320 watts run power for a 188 liter (6.6 cu ft) is a piggy.

It sure is. Our kitchen fridge power draw from yesterday. It's a medium large fridge with bottom freezer draw.



The larger block of power draw would be an auto defrost cycle.

In total yesterday it consumed 1.09 kWh

 

[ULR]

Small refrigerators are normally less efficient. 320 watts run power for a 188 liter (6.6 cu ft) is a piggy.

This isn't just about small units being less efficient than large (which they aren't to such a great extent.)

This is an absorption refrigerator. That means it effectively acts as both a heat engine to convert heat flowing across a temperature difference into mechanical energy in the form of pumping gas, then uses the pumped gas to perform the refrigeration. Comparing it running on just electricity to a compressor-type fridge is like comparing a system consisting of:

• A gas powered backup generator using a burner to heat a Stirling engine to turn the genny,
• With a resistance heater to heat it when running on electricity only,
• Powering a compressor fridge.

to just a compressor fridge powered by the electric grid or a battery. Apples to oranges. You're skipping the losses in the engine or the carnot cycle penalty in the power plant (which you "threw away" when you burned post-heat-engine electric energy into pre-heat-engine heat in the resistive heater.

When running on gas an absorption cycle fridge is not all that much worse than a compression fridge powered by a gas-fired grid plant or generator. The heat-engine side is a little worse, but the cooling side is about as good as a compressor system using ammonia for the refrigerant.

When running on electric only it takes abou t5ish times as much power as a compressor fridge - mainly because of the throw-away-the-carnot-cycle-tax-then-pay-it-again bit with the resistive heater. But the use case makes sense: A horsepower is 1/3 kilowatt. You have electricity to burn when a gas or diesel tow vehicle engine is runing, at only a slight reduction in mileage. Much cheaper than having a second compressor fridge mechanism just for that. Similarly, when parked and on shore power at a campground, the mains power is often flat rate rather than metered.

Re: the feeds and ratings:

• In gas mode the "house battery" line powers the brain, gas valve, igniter, and maybe a small heater around the door seal to avoid condensation and mold.
• When the engine is running (indicated by the "vehicle battery" voltage being up over 13V), the brain switches off the gas and powers a heater (through a relay or transistor switch) for the fridge cycle from that line - though the brain, etc. is still likely powered by the "house battery" line (and thus from the engine by the house battery charging circuit).
• Similarly, when line power is available the brain will use another (line voltage) heating resistor through another relay / semiconductor switch. (I'm not sure whether Dometic then powers the brain, etc. from the house battery line or also has an internal line-powered supply so it can run just on line voltage if the house 12V system is turned off.)

 

[wattmatters]

A horsepower is 1/3 kilowatt.

More like 3/4 of a kW

1 hp = 745.7 W

 

[ULR]

More like 3/4 of a kW

1 hp = 745.7 W

Sorry, I typoed that. 3/4 kW is what I meant to type. (745.7 is within 0.58% of 750, so it's convenient for thinking about kW vs HP.)

Thanks very much for catching it

 

[Whats_per_question]

Great write-up @ULR