Fridge 12v or 240v ? (1 Viewer)

[Yorick]

Currently wilding for a week and want to maximise the 8 hours sun per day as gas supply is limited.

Fridge is 12v or 240v.
When we're driving, I run the fridge off 24OV from the inverter - split charge relay.

But what's most efficient way when parked?

12v direct from 2x110ah leisure batteries?
Or again 240 through inverter?

I run off gas overnight.

It's a Dometic fridge and 150w solar panel. Batteries are slightly past their best.

Cheers.

 

[SteveB123]

I would run on gas day and night, the fridge doesn't use much gas

 

[Yorick]

I would run on gas day and night, the fridge doesn't use much gas

We can't refill here. So if it goes, can't make SWMBO a cuppa

And 28c here today, so fridge is working hard.

 

[Jaws]

Our fridge ( Thetford tower ) uses about a half a litre a week

 

[jnn]

Converting from one thing to another will never be 100% efficient (always an energy cost, you can feel some of this in that the inverter warms up a little) and so if the fridge itself is as efficient on 12v as 240v then direclty from the 12v likely most efficient.

(based on physics rather than motorhome experrience though)

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[Yorick]

and so if the fridge itself is as efficient on 12v as 240v then direclty from the 12v likely most efficient.

I always thought that 240 actually reduced temps whereas 12v just maintained it ?

 

[Dazzlin]

Our fridge uses about half a litre of gas a day!

Would have thought 12v more efficient, as less conversions.

12v reduces temp in our 2007 fridge. May not in more modern appliances.

 

[Yorick]

Thanks for gas info

But still curious about the leccy

 

[Boringfrog]

I always thought that 240 actually reduced temps whereas 12v just maintained it ?

That's what I thought.

 

[jnn]

What dometic model is it?

Bearing in mind I'm new to this lark and my fridge only runs on 12v: It woudl seem strange if yours says it can run on 12v but that that only maintains the temperature.

When you set off at the start of a trip away do you run it on 12v whilst driving? is it cold when you get there?

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[gus-lopez]

Mine, which is 3 way & that I have recently reinstalled after cleaning etc will drop the temperature even on 12v. It is most efficient on 220v & also excelent on gas Yesterday I left Baza with a temp of 11ºc & ,running on 12v, reached home 115kms away with fridge at -1ºc

Oh & it's 27 years old .

 

[Boringfrog]

What dometic model is it?

Bearing in mind I'm new to this lark and my fridge only runs on 12v: It woudl seem strange if yours says it can run on 12v but that that only maintains the temperature.

When you set off at the start of a trip away do you run it on 12v whilst driving? is it cold when you get there?

A 3 way fridge works differently from a 12v only.

 

[adonisito]

That's what I thought.

I thought that too. However, this year a blocked burner stopped it cooling properly when off EHU, however a 3 hour drive cooled it down again, although not as far as when on hook up. At least I could have a cold beer when we arrived.

 

[Lenny HB]

I always thought that 240 actually reduced temps whereas 12v just maintained it ?

Depends on the age of the fridge for about the last 10 years the 12v circuit is thermostatically controlled and the performance is should be similar to running off 230v.

 

[Reallyretired]

I believe the Fridge draws about 10A on 12v so a 150w panel will not be adequate to power it. Even 2x150w would only be adequate in the middle of the day.

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[Triple7]

swap to a compressor fridge? very little draw

 

[two]

The 12V element is marginally less powerful than the mains one, so will be less effective because of that. Voltage drop will affect 12V more than mains, reducing its effectiveness even more so run the fridge off inverted mains rather than direct 12V if you are unable to use gas. BUT it will flatten your battery very quickly.

A solar panel rated at 150W is only likely to produce that kind of power in summer around mid-day. Factor in inefficiencies and it’s going to be less still. In winter you’ll get very little but the fridge should not need to cool so much.

Automatic sensing fridges only use mains when EHU is available and only 12V when the engine is running to avoid flattening batteries.

 

[Yorick]

The 12V element is marginally less powerful than the mains one, so will be less effective because of that. Voltage drop will affect 12V more than mains, reducing its effectiveness even more so run the fridge off inverted mains rather than direct 12V if you are unable to use gas. BUT it will flatten your battery very quickly.

A solar panel rated at 150W is only likely to produce that kind of power in summer around mid-day. Factor in inefficiencies and it’s going to be less still. In winter you’ll get very little but the fridge should not need to cool so much.

Automatic sensing fridges only use mains when EHU is available and only 12V when the engine is running to avoid flattening batteries.

Thanks. We're in Lanzarote with 8 good hours of sunshine and driving an hour a day with split charge relay putting extra power in.

 

[Yorick]

swap to a compressor fridge? very little draw

Selling it soon

 

[Jaws]

Our Thetford tower def. only maintains temperature on 12v.. Even says that in the handbook ...

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[two]

Yes, the reason for that has puzzled me, too. I have come to the conclusion that the primary cause is voltage drop. Watts = Volts*Volts/Resistance, so a small drop in voltage will cause a much bigger drop in its ability to cool. Add to that, the fridge will turn off for up to 20min every time you stop. It won’t switch directly to gas in case you have stopped for fuel. In a caravan the voltage drop can be considerable due to the cable run and connections. That shouldn’t be so bad in a m/h. A more scientific approach would be to use a thermometer in the fridge and measure temperature over time under controlled conditions and I’ve never been inclined to bother with that.

 

[Lenny HB]

Our fridge ( Thetford tower ) uses about a half a litre a week

That sounds a bit on the low side, a Dometic 160Lt fridge freezer uses 380g/24 hours that is 2.66kg/5.2Lt a week. Ties up with the amount of gas we use.

 

[gerry mcg]

our PVC will have a 65l compressor fridge that is 12v only rather than 3 way -
a look at the dometic website Link Removed indicates a current consumption of 1.6 Ah/h at +25 °C ambient temperature, 1.9 Ah/h at +32 °C ambient temperature, both at +5 °C interior temperature. How long would our 190Ah battery bank work on this (assuming 50% capacity (95Ah) I guess this is around 60hrs without recharging or other current draw.
We are thinking of adding a solar array so that should probably keep on top of this tho.

 

[gerry mcg]

A check on a domestic 3 way absorber fridge indicates a 12v energy consumption of 2.2kWh.
An online conversion indicates 2.2kWh load on a 12v system = 183Ah, compared to the 1.6 Ah load of the compressor fridge

 

[Vanman]

our PVC will have a 65l compressor fridge that is 12v only rather than 3 way -
a look at the dometic website Link Removed indicates a current consumption of 1.6 Ah/h at +25 °C ambient temperature, 1.9 Ah/h at +32 °C ambient temperature, both at +5 °C interior temperature. How long would our 190Ah battery bank work on this (assuming 50% capacity (95Ah) I guess this is around 60hrs without recharging or other current draw.
We are thinking of adding a solar array so that should probably keep on top of this tho.

Hi Gerry, I'm buying a similar set up so have been over this in my head several times and come to the conclusion that until I've lived with it for a few weeks I won't really be certain what I need and don't want to install the wrong thing. One thing that you may need to factor into your equation is that if you drain your battery past 60%, maybe 50% it will kill it, it won't recover fully, so a 95Ah battery is only good for half that time - max, or at least that's the way my head sees it today!!

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[gerry mcg]

@Vanman , I understand that discharging battery deeply will ruin it. So that is why I only allowed for 50% capacity (95Ah) of our twin 95Ah battery setup (190Ah) total.
We have solar prep in our van order and like you will monitor use to see if we need to augment out power with solar.
It seems the compressor fridges are much more efficient on 12v than 3 way absorber tho

 

[two]

I think a compressor fridge and solar panel would make a good combination because the fridge will consume more power at times when the sun is out. You may need to supplement this by running the engine or hooking up to mains, though.

 

[Lenny HB]

A check on a domestic 3 way absorber fridge indicates a 12v energy consumption of 2.2kWh.
An online conversion indicates 2.2kWh load on a 12v system = 183Ah, compared to the 1.6 Ah load of the compressor fridge

No, a 160Lt Dometic fridge consumes 2.4kw over 24 hour which is an average of 0.86 amps per hour @230v or 8.33 amps @12v.

 

[Yorick]

No, a 160Lt Dometic fridge consumes 2.4kw over 24 hour which is an average of 0.86 amps per hour @230v or 8.33 amps @12v.

So does that answer my original question? Is it better 12v or 240v through inverter?

 

[Vanman]

I think a compressor fridge and solar panel would make a good combination because the fridge will consume more power at times when the sun is out. You may need to supplement this by running the engine or hooking up to mains, though.

I thought I read somewhere that running the engine whilst stationary was a bad idea because it wrecked the exhaust system (cat?).

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