Comparing power consumption of 12V compressor fridges with modern, efficient 240V fridges. Is 12V worth the price difference? (2 Viewers)

[CamperJack]

I planned on getting a 12V compressor (specifically a Dometic / Weaco crx50) but now it is time to buy one I am loathed to spend the extortionate amount of money they cost and for something so pathetically tiny compared to a 240V undercounter fridge. I don't understand why 12V should be so expensive, except for the fact that if a manufacture can get away with charging such a lot they will. I don't want to spend £600 on a fridge!

With that in mind I have been doing some research online. I am considering using a 240v fridge. Now, before everyone screams no at me, I'll show you my research and calculations. Then you can scream no at me.


POWER CONSUMPTION

Russell Hobbs RHUCLF2W 240V (£200)

Consumption = 110 kwh/year

110 X 1,000 = 110,000 w/year

110,000 w / ( hours in a year = 24 hours X 365 days) = 12.55 w/hour

12.55w / 12v = 1.04 amps/hour

1.04 X 24 = 24.96 amps per day.

Factoring in inefficiency of the invertor - 10% for the one I am looking at (Novopal 1000W pure sine wave) = 24.96 amps X 1.1 = 27.46 amps per day.

We also have to consider the invertor on standby, (not running the fridge compressor but still switched on and drawing power). For the Novopal that's 0.6 amps per hour so: 0.6a X 24 hours = 14.4 amps.

Total power: 14.4 + 27.46 = 41.86 amps per day.


Dometic crx50 (£600)

The amps rating given for the Dometic is 1.7 amps / hour.
1.7 X 24 = 40.8 amps per day.


So that's a difference of 1.06 amps a day in power consumption between the Russell Hobbs 240V and the Dometic 12V.


So, the difference isn't as colossal as I thought it would be!

However...

The figure of 1.7 amps an hour for the Dometic is at the higher end of the 1.2 - 1.7 amps rating. If we take it to be 1.2 amps the consumption figure is 28.8 amps with a difference of 12 amps in favour of the 12V. We can safely assume is is somewhere between the two depending on environmental temperature and how much it's open etc, perhaps 30-35 amps would be realistic, so a difference of 10.8-5.8 amps?

Also we have not accounted for the impact of extremes of temperature in a van on the running of a 240V fridge, and I would hope to assume those at Dometic have. But who knows the truth. Rather like my car is quoted at doing 61 MPG. In reality that is only in dream land! I

That being said I found a guy on YouTube from Sterling Power testing 12v compressor and 240V fridges via an invertor and his results were similar to my calculations. He measured the amps to run the 12V fridges and a 240V through an invertor was not using a huge amount more, and his 240V included a freezer, which my 240V didn't. In addition he showed that once at temperature the fridges used similar amps to maintain the set temperature.




With this in mind, and a difference in consumption likely to be somewhere between 1 amp and 12 amps, I am very tempted to at least try a 240V fridge. It would be worth saving £400! Even with the cost of the invertor (£150) I'd be saving £250 and I'd have an invertor for other 240V items like my stick blender etc.

To generate the 42 amps required I have 340W of solar and a 30 amp B2B. I also have 220ah of lead acid batteries.



As always though I hope you offer suggestions and opinions! Am I wrongly talking myself out of a 12V compressor?

 

[pappajohn]

Sounds do-able but where are you putting the fridge, they will be larger than a 12v fridge.
how are you getting the 24amps back in if you have a couple of sunless days and aren't planning on moving far/at all.

 

[Treeeev]

Hi CamperJack

I remembered reading a similar thread on the VWT4 Forum regarding using a normal domestic 240v fridge with an inverter compared to a 12v compressor fridge. Here’s the link to that thread which may help you with your decision

Cheers

Trevor

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[Raul]

I can confirm a crx50 will average 30ah per day. Some variables will influence its consumption. Placement of fridge, ventilation, internal thermal mass, voltage sag, and, freezer shelf choice.
On the other hand, a domestic under counter fridge, consumes about 300wh per day. Hence the 110kwh per year quote. That equates to 300wh per day. However, a inverter needs to be able to sustain the surge power on start up. A compressor can surge as much as 10x times the rated running power. If the inverter can sustain that, then happy days. Unless you got a super duper inverter fridge, that starts from 20-30w and gets going slowly till it reaches the speed necessary for the cooling needed at that time.
For the record, I have tested a victron 800va inverter and a photonic universe 1kw psw inverter, on a 230v small house fridge. One inverter did get returned back, it could not start the fridge motor.

 

[Charlie9038]

The 12v fridge we had was quite noisy, the fans run constantly, something to bear in mind if your a light sleeper

 

[Lenny HB]

Not checked your figures but I know a few have fitted domestic fridges with success.
I doubt a cheap £150 inverter is going to be up to the job of running 24/7 you really need to spend around £400 on a Victron.

Has anyone taken into account the power consumption of the inverter when no current is being drawn. I know my cheapish 1000 watt pure sine inverter draws 2 amp, when it's on and no load. If the fridge was running a 50% duty cycle over 24 hours the inverter would be consuming 24ah when sitting idle.
I think better quality Inverters like the Victron are much better in a no load situation Raul may know.

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[Rob Turner]

Domestic fridge would probably fail after a while. Don’t think they’re designed to be bounced around.

 

[Raul]

The best for stand by consumption inverters, are the victron and studer. Victron has the old model 1200va series before the ve direct port being introduced. Those inverters have a outstanding 6w no load consumption and a 2w in search mode. In search mode, it does a sine wave every two seconds and if it detects a load greater than 30-40w, it will stay on. When load goes of, it goes back in search mode. The multiplus compact is a 9w on stand by up to 1600va model. As for surge capabilities, the victron is king, large toroidal transformer, quality caps, can sustain large surge, even with low power factor.

 

[Wissel]

I run a low power 240v fridge and have for 2-3 years.

Including the overhead of the inverter, it uses around 20-24a per 24 hours.

I first ran it from a Victron 500VA, which worked well (from LiFePO4, a bit higher voltage than some batteries under load), but switched to a Victron Smart 1600VA. I figured I had an inverter running 24/7, might as well have 240v on tap.

I've had quite a few 12v compressor fridges over the last 14 years. The big advantage (IMO) of a good 240v version is the silence.

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[Bolti]

Can't help with the power usage, but having had a 50l compressor fridge and now a 85l fridge. Believe me 50l is too small, even with all the shelves removed you can hardly fit anything in. The 85l gives lots more room.

 

[CamperJack]

Some interesting points, as I was sure there would be.

Sounds do-able but where are you putting the fridge, they will be larger than a 12v fridge.
how are you getting the 24amps back in if you have a couple of sunless days and aren't planning on moving far/at all.

That's the issue with any big draw I guess, be that a 12 or 240V fridge or anything else. But I think if I am going largely full time some form of refrigeration is a must. If there is no sun for a few days I will simply have to drive more. Hopefully the driving in the commute will help. Unless you have a better idea? I cannot think of anything else other than a horrible, noisy generator and I'm fairly sure that's a no go...

a inverter needs to be able to sustain the surge power on start up. A compressor can surge as much as 10x times the rated running power. If the inverter can sustain that, then happy days.

Do you not think a 1000W with 2000W surge is enough? How often will it need to surge that much if the fridge is left on?

I doubt a cheap £150 inverter is going to be up to the job of running 24/7 you really need to spend around £400 on a Victron.

Funny that is. £400 would be the entire saving on buying a 240V over a 12V.

Has anyone taken into account the power consumption of the inverter when no current is being drawn. I know my cheapish 1000 watt pure sine inverter draws 2 amp, when it's on and no load.

The power consumption when the invertor is on when no but current is being drawn is stated to be <0.6amps. I factored that into my calculations and it is responsible for 14.4 amps of the total 41.86 amps total consumption of the 240V fridge I used in my calculations above.

The best for stand by consumption inverters, are the victron and studer. Victron has the old model 1200va series before the ve direct port being introduced. Those inverters have a outstanding 6w no load consumption and a 2w in search mode. In search mode, it does a sine wave every two seconds and if it detects a load greater than 30-40w, it will stay on. When load goes of, it goes back in search mode. The multiplus compact is a 9w on stand by up to 1600va model. As for surge capabilities, the victron is king, large toroidal transformer, quality caps, can sustain large surge, even with low power factor.

6w no load equates to 0.5amps. The cheap invertor (£150) I'm looking at says it's No Load Current Draw is <0.6 amps.



A few of you have expressed concern that a cheaper invertor may not cope being on for extended periods. Would it not matter that the thing is only really doing something when the fridge detects more power is needed for cooling? What more expensive ones (not breaking the bank) would you recommend? The one I am looking at is linked below.

Amazon product ASIN B07JKNWDSQ

 

[GarryP]

Domestic fridge would probably fail after a while. Don’t think they’re designed to be bounced around.

I don't think so. Many American rv's use domestic fridges.

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[Lenny HB]

A few of you have expressed concern that a cheaper invertor may not cope being on for extended periods. Would it not matter that the thing is only really doing something when the fridge detects more power is needed for cooling? What more expensive ones (not breaking the bank) would you recommend? The one I am looking at is linked below.

With cheap one the the specs are often optimistic particularly when it comes to the peak current, I doubt a 1000 watt one will handle the fridge startup.
As you are going to be full timing it's not worth skimping I would go for a Victron.

 

[CamperJack]

With cheap one the the specs are often optimistic particularly when it comes to the peak current, I doubt a 1000 watt one will handle the fridge startup.
As you are going to be full timing it's not worth skimping I would go for a Victron.

A 1000W Victron, or bigger?

 

[Lenny HB]

A 1000W Victron, or bigger?

A 1000w /1200va Victron should work but it really depends on the fridge.
If you buy a decent quality fridge it should have a better quality motor and compressor but not always true.
Make sure you buy the inverter from a reputable supplier in case you need to return it.

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[Raul]

Jack, with all due respect, the inverter you linked is junk. I doubt you understand how inverters are built, what components are needed for a sustained 1000w of a 12v supply. The 150 quid will not cover the components cost alone. Forget the design and build cost. For a inverter to have surge capabilities, will need quality fets, caps and transformer. All that costs. There is more to a inverter than just unproven specs. If you happy to spend the 150, go ahead. But you will buy twice. Or, buy proven reliable at the start.

 

[Raul]

A 1000W Victron, or bigger?

The 1200va is a 1000w and very capable in real world.

 

[TizzyOnTour]

Interesting thread.
This debate has been running for some time in the boating world. Most narrowboats spend the majority of their time off-grid, so inverters and solar have been widely adopted. With so many people having inverters, a lot have gone for the cheaper option of 240v fridges without experiencing any real problems. They have already footed the cost of a decent inverter anyway.
When our 12v fridge freezer on the boat broke down, I was chatting to the repair engineer, who told me that most marine 12v fridges are made by the same factories that manufacture the 240v, then modified with the addition of 12v Danfoss compressors by the marine suppliers. So when it comes to how robust they are, no difference. Just huge mark-up reflecting lower sales volumes. Not saying this is the case with Dometic but an interesting insight we thought.

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[CamperJack]

The 1200va is a 1000w and very capable in real world.

Is this the one we are talking about?

Amazon product ASIN B07JG23Z7D
Out of interest why is it called a 12 /1200?

I'm unsure now. It's so expensive you might as well just pay the extortionate 12V fridge prices and not have to worry about the extra power needed to run an invertor.

 

[CamperJack]

Interesting thread.
This debate has been running for some time in the boating world. Most narrowboats spend the majority of their time off-grid, so inverters and solar have been widely adopted. With so many people having inverters, a lot have gone for the cheaper option of 240v fridges without experiencing any real problems. They have already footed the cost of a decent inverter anyway.
When our 12v fridge freezer on the boat broke down, I was chatting to the repair engineer, who told me that most marine 12v fridges are made by the same factories that manufacture the 240v, then modified with the addition of 12v Danfoss compressors by the marine suppliers. So when it comes to how robust they are, no difference. Just huge mark-up reflecting lower sales volumes. Not saying this is the case with Dometic but an interesting insight we thought.

A lot of what I read online was from canal boats.

 

[Dazzlin]

We have been running a 230v domestic fridge for over a year now.

We bought the model with a freezer box in the top, which works for ice as intended, but is less efficient than a larder fridge as it just has a plastic flap over the ice box.

We started with a 600w £100 inverter, picked for high efficiency and low no load power. The first model was duff, and the replacement worked for several months before going into alarm mode on every start up of the fridge. At which point we bought the victron 1200 and use it on eco mode. Uses about 0.1amp compared to the other of 0.5amp on standby.

We do use an inverter, and are nearly full time, so a good inverter was on the shopping list anyway, therefore although I took the power into account, I didn't take the cost into consideration, just the saving of 230v v's 12v fridge.

We only have 200w of solar (I will be putting my other 2 x 80w panels up when we get back to Spain) and 235ah of Trojan batteries, but manage comfortably for a week in dull weather and indefinitely with bright days or when driving.
I have been looking into a 30A b2b but am still worried about what my 35 years old alternator will think about that!

Here in Scotland we have the sun in the morning on daughters drive and have not plugged in for 3 weeks.

Jan - march on sons drive we only had ehu when snow was blocking the solar panels!

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[stewartwebr]

I opted for the Siemens 230V fridge in my new Morelo. The main reason was to avoid the ugly grill on the side. The fridge freezer is powered from its own small inverter (Dometic) which is controlled from the compressor demand circuit. Therefore, no need for an inefficient inverter to be constantly running. The inverter switches on when the compressor is required to cool and switches back off when the fridge reaches temperature.

So far we have been very impressed. The cooling efficiency is great, getting down to temperature in around 30 minutes and to our relief we have heard absolutely no noise coming from it. We are not light sleepers, but I was conscious of the potential noise and was listening out for it, but heard nothing yet.

Not had the pleasure of using the van much yet due to COVID, but hoping that will all change soon.

 

[Ivory55]

Vw alan does exactly what you’re thinking of doing, he might be able to answer your questions.

 

[CamperJack]

I opted for the Siemens 230V fridge in my new Morelo. The main reason was to avoid the ugly grill on the side. The fridge freezer is powered from its own small inverter (Dometic) which is controlled from the compressor demand circuit. Therefore, no need for an inefficient inverter to be constantly running. The inverter switches on when the compressor is required to cool and switches back off when the fridge reaches temperature.

So far we have been very impressed. The cooling efficiency is great, getting down to temperature in around 30 minutes and to our relief we have heard absolutely no noise coming from it. We are not light sleepers, but I was conscious of the potential noise and was listening out for it, but heard nothing yet.

Not had the pleasure of using the van much yet due to COVID, but hoping that will all change soon.

That's the idea. Only having an inverter run when it detects a demand from the fridge to run the compressor.

Which dometic inverter are you using?

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[Raul]

Is this the one we are talking about?

Amazon product ASIN B07JG23Z7D
Out of interest why is it called a 12 /1200?

I'm unsure now. It's so expensive you might as well just pay the extortionate 12V fridge prices and not have to worry about the extra power needed to run an invertor.

That’s with the ve direct port added to it. It’s the newer version. I had the older version before the ve direct was added, but are the same inside. This inverter has put up with my 1100w deep well pump, one fridge and a ladder freezer. When the pump was on, it could still start the fridge. It’s amazing capabilities are above the spec. Of course we have upgraded the system and this one is a back up item just in case. You can run 230v fridge quite well of a inverter, but as you pointed; by the time you splash on inverter, you might as well go for the 12v version. When we planed our van, I made sure most loads can go direct of 12v, and only opportunistic Loads run of inverter. Fridge and pump is essential, the rest can be worked around if power is scarce until normality resumes. One think we learned from living off grid for fe years is, have redundancy as much as possible on everything, and more than one option. For example heating: diesel, gas and electric. Cooking gas and electric. If the sun is out you save precious fuel for rainy days. But for fridge to be of inverter 24/7, first think I would make sure that inverter does not go south. If it does, needs a temporary back up to get you out.

 

[Raul]

That's the idea. Only having an inverter run when it detects a demand from the fridge to run the compressor.

Which dometic inverter are you using?

Just run the victron in search mode. That’s 2w power consumption. A 48wh per day, or 4ah.

 

[CamperJack]

Just run the victron in search mode. That’s 2w power consumption. A 48wh per day, or 4ah.

Are you able to activate search mode without buying the additional dongle thing?

I didn't realise it was that low. I thought it was "No-load power consumption: 7W". Is search mode a different setting?

Thanks for your help. If it's as low as 4ah I think I'll get the invertor so I can run other 240v stuff too. I'd like to have a stick blender because I make lots of soup.

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[Raul]

My bad, the newer version is only 1w. The older was 2w. Look up at the 12/1200 model on the attached for the spec.

https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-VE.Direct-250VA-1200VA-EN.pdf

For normal operation, just flick the switch on eco, for set up, you will need a Bluetooth ve direct dongle, or a ve direct to usb cable.

 

[CamperJack]

My bad, the newer version is only 1w. The older was 2w. Look up at the 12/1200 model on the attached for the spec.

https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-VE.Direct-250VA-1200VA-EN.pdf

For normal operation, just flick the switch on eco, for set up, you will need a Bluetooth ve direct dongle, or a ve direct to usb cable.

You likely think I'm simple by now, so thanks for your patience with me and my lack of understanding. It's great that people are so willing to help on here!

Would it be true to say that if I put the switch into eco mode and the fridge isn't running the compressor and there is nothing else plugged in to the invertor the power consumption would be only 1 or 2 watts, depending on the model?

 

[BDM]

10 year old Dometic f/f packed up again last year so I replaced with 240v domestic f/f, it's narrow so fitted where the Dometic came out.
To run it I am using a Victron Multiplus 800 inverter/charger.
Works fine and actually does get down to correct temps and is quiet.
Only managed 2 weeks, 3500 miles and only 5 of those night not on EHU, but so far it works very well.
Control Victron from the phone app.

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