Fridge Power Options (1 Viewer)

[DDJC]

Hi, we have a Truma N3145 absorption fridge/freezer. I am hoping that my complicated question is easy for someone to answer!!

Earlier this year, we did the 8 hour Portsmouth to St Malo crossing. When we got back in, the fridge was still on auto and was stroppily telling us with error code 3 that the gas wasn't on. We had disconnected it, of course.

Which led me to wondering. How could I power the fridge, on low, to at least keep it burbling away. I uprated the battery from a 100ah lead acid, to a 300ah lithium. I already have an inverter fitted.

The markings on the fridge say:

Gas, 420 g/24
230 v, 220w
12 v 190w

Currently, the fridge will then work on mains electric through an EHU, 12v electric when the MH engine is on. And of course gas. My question therefore is:

Can it run off the 12v lithium battery?
or
Can it run off the 230v main, but via the inverter? I've tried, but the inverter doesn't seem to want to know.

Is there a way of putting in a switch on an independent circuit that connects the leisure battery directly to the fridge? Ideally, I want a simple solution so I can use the 300ah in the lithium battery, on a ferry or anywhere, where gas is not allowed to be used.

Cheers,

Dave

 

[WESTY66]

Yes it should easily maintain temp on 12v but for how long?? With 300ah but I’m guessing a good while, I’d guess it should easily do the 8hr crossing

 

[bigtwin]

Operating through the inverter will draw about 22A so will consume approximately 170Ah over 8 hours. However, in practice, it wont be drawing 22A for the full 8 hrs. Either way, your 300Ah LiFePO4 battery should be able to power it without any issues.

Ian

 

[ChrisL]

190w/12v = 15.83 ah, 300 ah battery/15.83 ah = 18.95 hours but you wouldn't want to run your battery that low I would guess, so it would be okay for a reasonably short crossing. The above calculation does not take into account any inefficiencies in the system.

 

[Sleeveless]

Seems a lot of faff for the odd ferry trip , just buy some bagged ice or freeze some water containers and keep the door shut , worked for us on Barcelona to Civitavecchia ( 10 hours) and other similar voyages.

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[bigtwin]

190w/12v = 15.83 ah, 300 ah battery/15.83 ah = 18.95 hours but you wouldn't want to run your battery that low I would guess, so it would be okay for a reasonably short crossing. The above calculation does not take into account any inefficiencies in the system.

But this would require some additional wiring (for a 3-way fridge) to enable it to run from 12V.

Ian

 

[DDJC]

Operating through the inverter will draw about 22A so will consume approximately 170Ah over 8 hours. However, in practice, it wont be drawing 22A for the full 8 hrs. Either way, your 300Ah LiFePO4 battery should be able to power it without any issues.

Ian

190w/12v = 15.83 ah, 300 ah battery/15.83 ah = 18.95 hours but you wouldn't want to run your battery that low I would guess, so it would be okay for a reasonably short crossing. The above calculation does not take into account any inefficiencies in the system.

So, the battery on inverter mode will run it for 8 hours and the battery on 12v mode will run it for 18 hours. Fantastic. That is the info I needed.
The guy who fitted my new life battery said it really didn't matter if I ran it down to nearly nil, as the battery (Fogstar) had clever safeguards and cut offs that meant that it wouldn't be damaged.

So, going back to my next question, what is the best way for me to convince the fridge to use 12v from the lithium battery, as well as the 12v from the MH engine?

 

[DDJC]

Seems a lot of faff for the odd ferry trip , just buy some bagged ice or freeze some water containers and keep the door shut , worked for us on Barcelona to Civitavecchia ( 10 hours) and other similar voyages.

I am glad that idea worked for you.

 

[ChrisL]

So, the battery on inverter mode will run it for 8 hours and the battery on 12v mode will run it for 18 hours. Fantastic. That is the info I needed.
The guy who fitted my new life battery said it really didn't matter if I ran it down to nearly nil, as the battery (Fogstar) had clever safeguards and cut offs that meant that it wouldn't be damaged.

So, going back to my next question, what is the best way for me to convince the fridge to use 12v from the lithium battery, as well as the 12v from the MH engine?

Personally I wouldn't run it until the battery turned itself off, there have been instances where the battery was not able to be recharged afterwards if i've remembered correctly. Raul is the best person to advise you on the reliability of BMS cut offs etc.

 

[DDJC]

Personally I wouldn't run it until the battery turned itself off, there have been instances where the battery was not able to be recharged afterwards if i've remembered correctly. Raul is the best person to advise you on the reliability of BMS cut offs etc.

Yes, I have heard similar. The Fogstar bluetooth phone app gives you a switch to stop it discharging, so I am working on the basis that it is effectively a 'battery off' switch that I can use if it gets lower than I feel is safe.

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[Bessy765]

We have 2 x 100 amp Transporter Lithiumm and a Victron 12/2000/80 inverter charger. On the Plymouth to Roscoff or Portsmouth to St Malo we leave the inverter on and the fridge (Dometic three way) on 2 lights and a Dometic CX 35 freezer set on -14 @ 12 volts with no problems. Have done this several times batteries are always 50% plus. Leave on lowest settings for both the day before we go.

 

[Richard n Ann]

Perhaps a compressor cool box would be an option, mine runs at just 2.5 amps if I remember correctly.
Then when on site you can run it as a freezer

 

[DDJC]

Perhaps a compressor cool box would be an option, mine runs at just 2.5 amps if I remember correctly.
Then when on site you can run it as a freezer

Yes we have one! A Dellonda 60l compressor fridge. Brilliant kit. Takes twelve bottles of wine.
Or water, I suppose.

 

[bigtwin]

So, the battery on inverter mode will run it for 8 hours and the battery on 12v mode will run it for 18 hours. Fantastic. That is the info I needed.

Basically, yes.

The reason that the consumption is higher on ac is because the heating element is more powerful and you have some inefficiencies associated with running the inverter.

So, going back to my next question, what is the best way for me to convince the fridge to use 12v from the lithium battery,

This would involve you providing a wire between the leisure battery supply and the 12V heating element at the back of your fridge. It really isn’t worth the bother.

Ian

 

[Vansflyer]

On our CBE control box you can bypass the D+ relay so 12V is feed to the fridge all the time, this will mean the fridge auto select won't work at a guess. The manual explains very badly translated this in case of a compressor being fridge fitted to the vehicle.
Not tried this myself but will work in theory without using a inverter and "wasting" power. Before checking this I would strongly suggest you confirm that feed is off the leisure battery... ours does btw in a 2019 Carthago.

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[rb62]

If you cool you fridge/freezer right down and put some frozen milk in the fridge a there is no reason to have the fridge on at all and it will still be cold even after the Santander/Bilbao crossing.

 

[Freo]

If you cool you fridge/freezer right down and put some frozen milk in the fridge a there is no reason to have the fridge on at all and it will still be cold even after the Santander/Bilbao crossing.

Totally agree. We found the exactly the same.
Travelled from Portsmouth to Santander (22 or 24 hour sailing at that time.)
Stuff in the freezer which had been frozen, was still frozen on arrival in Santander. Fridge/Freezer was unpowered for the duration of the sailing. Stuff in the fridge was fine, too, although it was no longer chilled after the journey. No loss of food, though. It was all perfectly edible.
Same on the return journey. Fridge/Freezer off for the duration - no issues.

 

[tonyidle]

.So, going back to my next question, what is the best way for me to convince the fridge to use 12v from the lithium battery, as well as the 12v from the MH engine?


Simple. Use a changeover switch to disconnect incoming D+ and then connect the fridge D+ to the fridge control 12v feed. All connections are on the fridge connection terminal block.

 

[Hoovie]

So, the battery on inverter mode will run it for 8 hours and the battery on 12v mode will run it for 18 hours. Fantastic. That is the info I needed.

I think there may be a bit of "lost in translation" here
What you have concluded above suggests you are thinking if you run the fridge on 12V it will be over twice as efficient? That really is not the case.
What was said - at least the way I read it - was one chap said the battery would run the fridge for 8 hours and use 170Ah (so leaving 130Ah still in the battery) and the other guy told you how long the fridge would run for until the battery was totally depleted. Both bits of info are correct, but presented in a rather different way.

Now the Fridge element on 240V is 220W and on 12V it is 190W. Now again that doesn't mean the 240V is less efficient, it means the fridge will cool faster on 240V as it is using more power to do so.
All fridges have a duty cycle of ON vs OFF. A compressor fridge is only on maybe 25-33% of the time for example. An Absorption Fridge, such as the 3-Way Fridge you have, is ON much more than it is OFF (maybe 85% ON, 15% OFF say) once down to operating temp, but the duty cycle for 240V compared to 12V will be a little less ON, as the 240V is more powerful, so on average for that 8 hour crossing, the power it - the Fridge - uses on 12V will be the same as it is on 240V.
However what you do have to consider is the inverter overhead (wastage).... This means you will maybe use 10-15% MORE power - out the battery - on 240V than you do on 12V to run that fridge, and not the kind of saving that I get the impression you think you would get by using 12V?

The guy who fitted my new life battery said it really didn't matter if I ran it down to nearly nil, as the battery (Fogstar) had clever safeguards and cut offs that meant that it wouldn't be damaged.

So, going back to my next question, what is the best way for me to convince the fridge to use 12v from the lithium battery, as well as the 12v from the MH engine?

Given using the Inverter will use just 10-15% more than direct 12V power, is it worth making the kind of changes you might have to make for 12V (exactly what depends on the fridge and how it is wired in the Motorhome - there is not a simple one size fits all answer for this) compared to literally just supplying the fridge with [inverted] 240V and letting it get on with it?


Having said all that, given you have a 60L Compressor Coolbox, surely the simplest thing to do is move the perishables from the Fridge to the coolbox for the ferry duration and then once the 3-way is running again and down to temp, move them back?

 

[paddymcc]

My Hymer with an auto switch over fridge can be manually set to 12v. It then runs from the leisure battery. I know Lenny has said that this is normal for German vans, but don't know about Rumor(Italian?) .

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[DDJC]

I think there may be a bit of "lost in translation" here
What you have concluded above suggests you are thinking if you run the fridge on 12V it will be over twice as efficient? That really is not the case.
What was said - at least the way I read it - was one chap said the battery would run the fridge for 8 hours and use 170Ah (so leaving 130Ah still in the battery) and the other guy told you how long the fridge would run for until the battery was totally depleted. Both bits of info are correct, but presented in a rather different way.

Now the Fridge element on 240V is 220W and on 12V it is 190W. Now again that doesn't mean the 240V is less efficient, it means the fridge will cool faster on 240V as it is using more power to do so.
All fridges have a duty cycle of ON vs OFF. A compressor fridge is only on maybe 25-33% of the time for example. An Absorption Fridge, such as the 3-Way Fridge you have, is ON much more than it is OFF (maybe 85% ON, 15% OFF say) once down to operating temp, but the duty cycle for 240V compared to 12V will be a little less ON, as the 240V is more powerful, so on average for that 8 hour crossing, the power it - the Fridge - uses on 12V will be the same as it is on 240V.
However what you do have to consider is the inverter overhead (wastage).... This means you will maybe use 10-15% MORE power - out the battery - on 240V than you do on 12V to run that fridge, and not the kind of saving that I get the impression you think you would get by using 12V?



Given using the Inverter will use just 10-15% more than direct 12V power, is it worth making the kind of changes you might have to make for 12V (exactly what depends on the fridge and how it is wired in the Motorhome - there is not a simple one size fits all answer for this) compared to literally just supplying the fridge with [inverted] 240V and letting it get on with it?


Having said all that, given you have a 60L Compressor Coolbox, surely the simplest thing to do is move the perishables from the Fridge to the coolbox for the ferry duration and then once the 3-way is running again and down to temp, move them back?

Cheers, I nearly understood some of that
I am a DIY arse and so clearly this is something that I can't and don't want to do myself.
I am going to go to the go-to motorhome guy nearby, and ask for what Vansflyer and Tonyidle suggest. It's going in for habcheck, service and a mifi antenna anyway.

 

[CAB96]

Even simpler.

You have a 3-pin plug on the inverter?

Get a 3-pin to EHU cable adapter (like many people use at home to plug in their van.

Plug EHU cable into inverter.

Run cable out of window.

Plug in van.

TURN OFF THE BATTERY CHARGER!!!

Switch fridge to 240v.

Viola! No new wiring, easy peasy!

(try it on your driveway first though! Anything else powered off the 240v? Heater? Make sure they are off.)

 

[Jonno1103]

We use a portable compressor fridge connected to an Ecoflow Delta powerstation. it will easily do Harrogate to Santander. We don't carry much in the way of perishables preferring to buy fresh produce in France, Spain etc.

 

[stevewagner]

I would fit an automatic changeover switch and connect the inverter to your consumer unit. Turn off the battery charger and then you can run the fridge from the inverter. Alternatively by a Renogy inverter which has a built in automatic changeover switch.

 

[DDJC]

We use a portable compressor fridge connected to an Ecoflow Delta powerstation. it will easily do Harrogate to Santander. We don't carry much in the way of perishables preferring to buy fresh produce in France, Spain etc.

Seems a lot of faff for the odd ferry trip , just buy some bagged ice or freeze some water containers and keep the door shut , worked for us on Barcelona to Civitavecchia ( 10 hours) and other similar voyages.

This would involve you providing a wire between the leisure battery supply and the 12V heating element at the back of your fridge. It really isn’t worth the bother.

If you cool you fridge/freezer right down and put some frozen milk in the fridge a there is no reason to have the fridge on at all and it will still be cold even after the Santander/Bilbao crossing.

Totally agree. We found the exactly the same.
Travelled from Portsmouth to Santander (22 or 24 hour sailing at that time.)
Stuff in the freezer which had been frozen, was still frozen on arrival in Santander. Fridge/Freezer was unpowered for the duration of the sailing. Stuff in the fridge was fine, too, although it was no longer chilled after the journey. No loss of food, though. It was all perfectly edible.
Same on the return journey. Fridge/Freezer off for the duration - no issues.

I wanted to try to keep this a purely technical electric question, but you guys deserve an explanation because it might help to understand how a non-electrical solution/tips and tricks answer doesn't work for us.

Mrs DDJC and I have two boys. Well, I say boys, the eldest is 19 and the younger is 16 (DDJC - initials geddit?!) Anyway, the 19 year old is non-verbal autistic (and a whole load more syndromes with three letter acronyms) and the 16 year old has semi verbal autism. And so here is the relevant thing. They eat the same thing - exactly the same thing, every single day of the year. The elder is a tad more adventurous with food, but not much. He is 6'4" and eats like a horse, but the younger will simply not eat, rather than try something new.

We have to carry (smuggle) the foods they will eat whenever we travel. Mostly frozen, but most can't be found in Europe. We have a 138l fridge freezer in the bus and a 60l Dellonda, set up as a freezer in the garage. Both are full of the only things they will eat. I adore food shopping in Europe and me and Mrs DDJC eat local stuff all the time, but for a three week tour, we leave home with full freezers and fridge for our boys.


So, it has to be an electric solution, which I now think I have a couple of options, so thanks all.