Run 3 way fridge on 12v permanently

Wooders

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I hate 3 way fridges, but the cost to replace to compressor in my Rollerteam is £1100! I never use 240v hook up and use my 3000w inverter to run the 240 sockets. This means I can run the fridge for free off the solar for about 6 hours a day here in Spain. However it would be way more efficient if I could run it off 12v all the time and not just when driving.
How do you do this? Any find info anywhere, but must be easy. Please belp

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A 3 way running 230v or 12v from habitation batteries will use a lot of power. It’s not like running a compressor fridge it’s much, much more. You will probably need that £1100 to boost electrical system (battery’s and solar) to do it.

Wait for other to say though as I don’t use 3 way since the 90’s in a caravan
 
Gas it usually okay in lower temps but a 3 way isn't fit for purpose if it get as warm as the UK did last summer, a compressor fridge is far better and you don't need to switch energy sources if you do a lot of stop start, much safer in a petrol station too.

Many fit a cheaper domestic version and run of an inverter.

Have a look on our sister site, they may help more, you are a member on there already.

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nabsim said:
A 3 way running 230v or 12v from habitation batteries will use a lot of power. It’s not like running a compressor fridge it’s much, much more. You will probably need that £1100 to boost electrical system (battery’s and solar) to do it.

Wait for other to say though as I don’t use 3 way since the 90’s in a caravan
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I already have the system to run it! So therefore why not?
 
Pudsey Bear said:
Gas it usually okay in lower temps but a 3 way isn't fit for purpose if it get as warm as the UK did last summer, a compressor fridge is far better and you don't need to switch energy sources if you do a lot of stop start, much safer in a petrol station too.

Many fit a cheaper domestic version and run of an inverter.

Have a look on our sister site, they may help more, you are a member on there already.

Home

Motorhome Builder Home Page
motorhomebuilder.com motorhomebuilder.com
Click to expand...
I’m not going to throw away €1000 on a new fridge till it breaks!
 
With a 3 way fridge
You could use an inverter and 240V but check the power usage.both for amperage used and how many amp-hours is the battery drain
12 Volts to 240 is 20x so a 5 amp load would draw 100 amps
If that works why fuss with 12V direct

Use 240V in the day (Solar) but maybe switch to gas overnight
A fridge not used much and very little when asleep
So Gas even though not as good it will be OK
 
Last edited:
jagmanx said:
With a 3 way fridge
You could use an inverter and 240V but check the power usage.both for amperage used and how many amp-hours is the battery drain
12 Volts to 240 is 20x so a 5 amp load would draw 100 amps
If that works why fuss with 12V direct

Use 240V in the day (Solar) but maybe switch to gas overnight
A fridge not used much and very little when asleep
So Gas even though not as good it will be OK
Click to expand...
I do use the 3000w inverter. But there is an energy loss from converting 12v to 240v. Way more deficient to move a few wires around and use 12v. I just need to know which wires and how!!
 
Wooders said:
Why would I pay for gas when the sun is for free?! The bottle only runs for 2 weeks of running the fridge, water and heating etc. crazy to pay when I have the electric system to run it. Why not just answer the question or not answer?
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why not pay to become a full member instead of being a freeloader :unsure:
 
Wooders said:
I’m not going to throw away €1000 on a new fridge till it breaks!
Click to expand...
You seem to be closed minded so difficult to help, or maybe you're not asking the right question in post#1, money is the issue with changing, I'd opt for a domestic fridge if I needed to replace it, much cheaper and more choice but repairs to the 3 ways are not usually expensive as there isn't much to them, most are DIY if you have a clue
 
Pudsey Bear said:
You seem to be closed minded so difficult to help, or maybe you're not asking the right question in post#1, money is the issue with changing, I'd opt for a domestic fridge if I needed to replace it, much cheaper and more choice but repairs to the 3 ways are not usually expensive as there isn't much to them, most are DIY if you have a clue
Click to expand...
I think the thing is to keep asking the question until you get an answer that suits what you want to hear, then say "told you so" :)

Your 'future' direction is what I did .....
3-way playing up on gas. Fixed it but left me unsure about how long would stay fixed (they are too temperamental for my liking).
3-way running on electricity is not feasible long-term. They use so much power it really is a non-starter.
I bought an LEC Fridge/Freezer with 240V Compressor. Run in on the inverter I already have.
I sold the old 3-way for a little more than the brand new Compressor Fridge/Freezer cost me, so cost to change was virtually nothing (bit of time and bits to make up a frame and fixing as the new Fridge was around an inch smaller than the old one)
 
Most 3 way fridges use about 120w on 12v and about 150w on 240v. BUT on 12v there is usually no thermostat, it uses 120w 24/7, it's just intended for use whilst driving only. On 240v there is a thermostat so its not 24/7 but at 150w its about 3 times as much power as a compressor fridge.
 
Mark135 said:
Most 3 way fridges use about 120w on 12v and about 150w on 240v. BUT on 12v there is usually no thermostat, it uses 120w 24/7, it's just intended for use whilst driving only. On 240v there is a thermostat so its not 24/7 but at 150w its about 3 times as much power as a compressor fridge.
Click to expand...

Need to factor both the power use when runnng and the duty cycle to get a good comparison

A 3-Way Fridge from being switched off takes a full day to get down to safe operating temperature. That is 24 hours of running constantly.
A Compressor Fridge takes around 1-2 hours to get down to the same temperature. that is a 10th of the time and at a lower power consumption per hour.
So that is the first factor.
This aspect is important when it comes to people who go off on intermittant and spontaneous trips - with a 3-Way, you might leave the fridge on all the time just in case. With a compressor fridge, if it is empty, no need to leave it on using power as you only have to switch it on a couple of hours before you need it.

Once running, both types of fridge do have on/off duty cycles, but a 3-Way fridge is on for longer than a Compressor fridge in any given time period.
Duty Cycle of a typical 3-Way Fridge running on AC
(just click on the red X if no image appears. Flickr playing up)

3-Way - AC Daytime by David, on Flickr

Duty cycle of Compressor Fridge for same time duration (10AM to 4PM)

Compressor Fridge - AC Daytime by David, on Flickr

So comparing the two fridges, you see when drawing power runnng on AC, the 3-Way is taking over 3 times the wattage of the Compressor Fridge
Maybe the newest 3-ways are 120W + 150W, but tend to be higher as per the photo below of mine.

Thetford 3-Way Electric Power by David, on Flickr
200W on AC vs around 55W for the Compressor Fridge.

Factor in the duty cycles and I calculated that the typical 3-Way Fridge used SEVEN times more power than a modern Compressor Fridge. And it doesn't matter if it is AC or DC for that difference. 240V Compressor Fridges actually tend to be slightly more efficient than 12C DC ones; include the inverter overhead and it switches around but either way very little to choose between 12V and 240V.

You see people complaining about not being able to run a Compressor Fridge off their battery bank (and you typically need 200Ah I reckon to avoid having to go into silly fridge power-saving routines)?
If that is the case, what kind of battery pack is needed to run a 3-Way on AC full-time when off-grid? It really is not worth it.

If you have enough spare electric to run a 3-way on AC for any extended duration, consider using that power to do your cooking with electricity, or use the electric element in your water heater. These are far better and efficient uses of spare electricity than an highly inefficient absorption fridge and by doing that you will likely save more gas than you would trying to use the Fridge on electric.

(FWIW, I have my Motorhome setup so if the battery gets to a certain SOC, off-grid AC Power is provided to the Truma Water Boiler, so any excess solar gets put to use that way. That adds up to around 850Wh of Power. That is not massively short of what a 3-Way Fridge would use on AC in a day. But if the boiler heated the water on the LPG, I think it would use more gas than the Fridge would in a day?)
 
as i understand it the 12v only maintains the temp so won’t refreeze if you open doors etc i have just had an episode with a suspected gas leak so ran the fridge on mains through the inverter maximum draw was -23 A couple of that being the inverter overnight about 11hrs it averaged 8A after allowing the aforementioned 2A inverter draw , it certainly cools better on electric than gas so will boost it like that when power is high currently getting 16.8 A going in on the algarve
 
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