Hi Guys, just wanna bounce this one off you guys...ive been testing my 3 way camec fridge on 12 v and its worse than pitiful really. I tried it on 240v running my 900w inverter with 150ah lithium battery. It works as well as 240v mains it seems. Draws some power but had it going for a good 8 hrs or so before voltage started to drop away..whats stopping me from doing that while driving.. or even overnight...im going to be putting a heap of lightweight solar on my roof too. Im thinking i might need one more battery to make it sustainable!
18' Series Fridge on 240 vs 12v
- Thread starter Linc
- Start date
Hi @Linc , you should clearly understand that 3 way fridges are not really designed to run as well on 12 volts as on gas or 240v. The primary sources of operation are 240 volt power when connected to grid, or gas when off grid. The 12 volt operation is just for maintaining the temperature that exists in the fridge itself whilst travelling.. It is not efficient enough to pull down the temperature inside or lower the temperature much if at all. Also, realise that the voltage from the alternator probably is not going to be constantly high enough to enable enough current to reach fridge , especially if you have a modern tug with variable voltage control. (unless using a DC to DC charger!!) Current needed to run an absorption fridge is probably more than 16A depending on heating element. The element in my 93L Thetford (a smaller one than you have) is rated at 175w at 12 volts , while the 240v element is rated at 0.71A. Extra solar won't solve your problem and its main priority is to charge battery/ies. If you want to run a fridge on electricity 240v or 12v, you will have to have a compressor fridge and that is a different story again. Suggest don't try running fridge on 240v via inverter. All that does is works the inverter very hard AND pulls too much juice from your lithium battery - estimated 90A from battery while connected to fridge and the rest supplied by inverter. Use the gas - much more efficient and cheaper too. You can get 15 to 20 days running a 3 way fridge on gas with one 9kg gas bottle. You will need two batteries if fitting a compressor fridge.
Hi,
your observation is quite common.
First step is you need to read your user manual and find out the wattages of the 240V element and the 12V element for your particular
fridge.
In some fridges the 12V element is the same wattage as the 240V element. For instance, the Dometic RM2350 95l three-way fridge
has a 175W 12V element and a 175W 240V element.
In this case, the fridge performance will be identical regardless of whether it is running on 12V or 240V. Watts is Watts is Watts and
it does not matter at all what the voltage is that is supplying it!
Now, the caveat. The most common cause of poor 12V performance (given that the 12V and 240V heating elements are the same
wattage) is simply that the voltage being supplied to the fridge is not sufficient. So, if your fridge is not performing well on 12V then
you must measure the voltage at the 12V terminals on the back of the fridge with the fridge switched over to 12V.
So, I will repeat it again: If the 12V element and the 240V element have the same wattage and there is sufficient voltage at the 12V
terminals of the fridge the performance of the fridge will be IDENTICAL regardless of whether it is running on 12V or 240V!
The voltage must be over 12V. The most common cause of low voltage at the fridge terminals is that the wiring going to the fridge
is too small.
A 175W fridge element will draw about 15A. The voltage drop from the battery to the fridge needs to be less than 1V.
In my setup, the voltage drop from the car battery to the fridge terminals is 0.7V. With the engine running, the car battery voltage is
around 14.5V and the voltage at the fridge terminals is 13.8V. I can assure you that my RM2350 will perform equally as well on 12V
as it does on gas or 240V.
I have a voltmeter permanently wired to the 12V fridge terminals and a digital thermometer mounted on the bench with the sensor
wired permanently inside the fridge. So the results are accurate and the performance has been monitored for over three years.
Another caveat. A fridge running directly from a battery that is not being charged at the same time is unlikely to have enough
voltage to deliver over 12V to the fridge terminals taking into account the voltage drop in the cables.
The second most common cause for poor performance is when the tug has a smart alternator. In that case, the battery voltage
will be lower and the voltage at the fridge terminals will also be lower. Increasing the wiring size even further will not fix the problem
and the most common fix is to install a DC-DC charger which will increase the voltage to the fridge. If you want to investigate, there
are also some hacks to increase the output voltage of a smart alternator.
Now, if your fridge has a 12V element with a smaller wattage than the 240V element there is very little that can be done.
The performance of the fridge on 12V will always be less than the performance on gas or 240V. One fix, as you have discovered,
is to run the fridge on 240V supplied from an inverter connected to the battery. Although there is some loss in using the inverter,
you will not have the loss in the 12V cable.
Cable loss on 12V (assuming a 1V drop) and inverter loss on 240V will both be somewhere around 10%. This makes sense if you
want to run the fridge from a van battery.
It is somewhat impractical to put an inverter close to you tug battery and run 240V cable all the way back to the fridge.
But I have read of it being done!
take care
Mike
your observation is quite common.
First step is you need to read your user manual and find out the wattages of the 240V element and the 12V element for your particular
fridge.
In some fridges the 12V element is the same wattage as the 240V element. For instance, the Dometic RM2350 95l three-way fridge
has a 175W 12V element and a 175W 240V element.
In this case, the fridge performance will be identical regardless of whether it is running on 12V or 240V. Watts is Watts is Watts and
it does not matter at all what the voltage is that is supplying it!
Now, the caveat. The most common cause of poor 12V performance (given that the 12V and 240V heating elements are the same
wattage) is simply that the voltage being supplied to the fridge is not sufficient. So, if your fridge is not performing well on 12V then
you must measure the voltage at the 12V terminals on the back of the fridge with the fridge switched over to 12V.
So, I will repeat it again: If the 12V element and the 240V element have the same wattage and there is sufficient voltage at the 12V
terminals of the fridge the performance of the fridge will be IDENTICAL regardless of whether it is running on 12V or 240V!
The voltage must be over 12V. The most common cause of low voltage at the fridge terminals is that the wiring going to the fridge
is too small.
A 175W fridge element will draw about 15A. The voltage drop from the battery to the fridge needs to be less than 1V.
In my setup, the voltage drop from the car battery to the fridge terminals is 0.7V. With the engine running, the car battery voltage is
around 14.5V and the voltage at the fridge terminals is 13.8V. I can assure you that my RM2350 will perform equally as well on 12V
as it does on gas or 240V.
I have a voltmeter permanently wired to the 12V fridge terminals and a digital thermometer mounted on the bench with the sensor
wired permanently inside the fridge. So the results are accurate and the performance has been monitored for over three years.
Another caveat. A fridge running directly from a battery that is not being charged at the same time is unlikely to have enough
voltage to deliver over 12V to the fridge terminals taking into account the voltage drop in the cables.
The second most common cause for poor performance is when the tug has a smart alternator. In that case, the battery voltage
will be lower and the voltage at the fridge terminals will also be lower. Increasing the wiring size even further will not fix the problem
and the most common fix is to install a DC-DC charger which will increase the voltage to the fridge. If you want to investigate, there
are also some hacks to increase the output voltage of a smart alternator.
Now, if your fridge has a 12V element with a smaller wattage than the 240V element there is very little that can be done.
The performance of the fridge on 12V will always be less than the performance on gas or 240V. One fix, as you have discovered,
is to run the fridge on 240V supplied from an inverter connected to the battery. Although there is some loss in using the inverter,
you will not have the loss in the 12V cable.
Cable loss on 12V (assuming a 1V drop) and inverter loss on 240V will both be somewhere around 10%. This makes sense if you
want to run the fridge from a van battery.
It is somewhat impractical to put an inverter close to you tug battery and run 240V cable all the way back to the fridge.
But I have read of it being done!
take care
Mike
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The short and sweet version is that 240v and gas will operate the fridge, pull it down to the temperature required, the 12v is just for maintaining temp when for example driving down the road it won't and is not capable of running the fridge for normal operation no matter how much battery storage you have, it just won't work.
To get the best out of your fridge run it for about 12hrs on 240v then pack some cold gear in it and let it run for as long as you can so it gets back to temp before you hook up and drive away, the 12v from the tug will keep it at temp, when in camp plug back into 240 or turn on the gas......... Theres no real solution to being able to run it on 12v and expect it to be more than a food warmer, soon as you open the door its stuffed.
There is nothing wrong with using gas in camp.
To get the best out of your fridge run it for about 12hrs on 240v then pack some cold gear in it and let it run for as long as you can so it gets back to temp before you hook up and drive away, the 12v from the tug will keep it at temp, when in camp plug back into 240 or turn on the gas......... Theres no real solution to being able to run it on 12v and expect it to be more than a food warmer, soon as you open the door its stuffed.
There is nothing wrong with using gas in camp.
Yes @Drover , I have to fully agree with your thoughts regarding fridge operation on 12 volts, regardless of how much battery power or type, solar panels, inverters etc you have. Sorry @mikerezny. Most of us do not have tugs with a high enough constant alternator voltage output to maintain full operation whilst connected to tug. But that is not to say that it is not possible, because I have had limited success with my setup when I had to travel home 150kms when my gas system failed and no 240v available. There are too many variables with alternators, cabling and individual operations to be able to state that you can just hook up to a 12v line and expect the 3way fridge to work at its best...It just will not!!! (Disregarding DC to DC systems). And the moment you connect a "load" of 15A or higher onto a battery, whether being charged or not, there will be a considerable voltage drop even before considering any loss in cabling. Watts is watts is watts is correct, but without VOLTAGE at the LOAD, if voltage is low, it does not matter how many amps you have available to heat elements or other equipment. However, I do believe that Lithium batteries retain their voltage higher and longer as they discharge, until nearly flat, unlike the slow decline in voltage with Gel, AGM or Wet cell where voltage starts to drop immediately they have a load placed on them.
Indeed, most instruction books on 3way absorption fridges state that the 12 volt system should only be used when connected to tug and engine running. Failure to do so will result in battery being fully discharged to point of no return. The other obvious result not mentioned is that the fridge will not be able to operate as designed.
Indeed, most instruction books on 3way absorption fridges state that the 12 volt system should only be used when connected to tug and engine running. Failure to do so will result in battery being fully discharged to point of no return. The other obvious result not mentioned is that the fridge will not be able to operate as designed.
Hi,
I have never stated anywhere that the fridge should be run on 12V as an alternative to running on gas or 240V.
I am stating very clearly the requirements for the fridge to run in a most satisfactory manner on 12V and to dispel the
old wives tales, myths or whatever that have perpetuated over many many years mostly from people who did not wire
them up correctly, never measured the terminal voltage, had older fridges where the wattage of the 12V
element (125W) was less than the wattage on current model fridges (175W).
The current model Dometic RM 2350 on 12V is NOT a food warmer. When traveling my fridge will be colder on arrival
than when I started the journey. It is usual to depart with the fridge temperature at 4C and arrive with it at 0.4C.
Let me be VERY clear. In my experience, the fridge WILL work correctly on 12V if there is adequate voltage at the fridge input terminals.
If we are going to be fair and accurate then let's state that modern cars with smart alternators are not capable of
supplying enough voltage to enable the fridge to work correctly. It is not a problem with the fridge it is a problem
with having a smart alternator in the car.
A car with a smart alternator is also not capable of charging the van battery either. That is not the fault of the van battery.
Even the problem with smart alternators not supplying enough voltage to charge the van battery and run the fridge
can both be easily fixed with a DC-DC charger.
My initial post was absolutely accurate and is verified by a lot of analysis and testing. It also clearly covers the
conditions under which the fridge WILL work as well on 12V as it does on 240V and also those conditions
where it WILL NOT work adequately.
This is probably one of the most contentious subjects only surpassed by the belief that a three-way fridge is
absolute rubbish and must be replaced with a compressor fridge.
They are indeed old technology but as we all know, with some thought, analysis, and attention to detail, they can
perform adequately in temperatures up to 40C on gas, 240V AND, in my experience, equally well on 12V.
take care
Mike
I have never stated anywhere that the fridge should be run on 12V as an alternative to running on gas or 240V.
I am stating very clearly the requirements for the fridge to run in a most satisfactory manner on 12V and to dispel the
old wives tales, myths or whatever that have perpetuated over many many years mostly from people who did not wire
them up correctly, never measured the terminal voltage, had older fridges where the wattage of the 12V
element (125W) was less than the wattage on current model fridges (175W).
The current model Dometic RM 2350 on 12V is NOT a food warmer. When traveling my fridge will be colder on arrival
than when I started the journey. It is usual to depart with the fridge temperature at 4C and arrive with it at 0.4C.
Let me be VERY clear. In my experience, the fridge WILL work correctly on 12V if there is adequate voltage at the fridge input terminals.
If we are going to be fair and accurate then let's state that modern cars with smart alternators are not capable of
supplying enough voltage to enable the fridge to work correctly. It is not a problem with the fridge it is a problem
with having a smart alternator in the car.
A car with a smart alternator is also not capable of charging the van battery either. That is not the fault of the van battery.
Even the problem with smart alternators not supplying enough voltage to charge the van battery and run the fridge
can both be easily fixed with a DC-DC charger.
My initial post was absolutely accurate and is verified by a lot of analysis and testing. It also clearly covers the
conditions under which the fridge WILL work as well on 12V as it does on 240V and also those conditions
where it WILL NOT work adequately.
This is probably one of the most contentious subjects only surpassed by the belief that a three-way fridge is
absolute rubbish and must be replaced with a compressor fridge.
They are indeed old technology but as we all know, with some thought, analysis, and attention to detail, they can
perform adequately in temperatures up to 40C on gas, 240V AND, in my experience, equally well on 12V.
take care
Mike
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There is no sense in throwing heaps of $$$ at setting up to run your fridge on 12v whether hooked up to tug or when in camp, if you have a proper connection from tug to fridge it will perform and keep it cold as you travel, that means not using the original wiring, I have 8 B&S from tug battery to hitch and 6 B&S from hitch direct to fridge, no drama with power supply, loss in the point something...... If you must use 12v in camp then chuck the 3 way and buy a compressor fridge and make use of the extra $$$ spent on battery and solar, and save lots of money on gas.
Using an invertor to run something for long periods is wasted resources in anyones money other wise we would be using an invertor to generate power for us to charge our batteries on those cloudy days..........if I want 240 I get out TLRPS (The little Red Power Station) when not in use its used a signage..." Stay away generator user" can backfire as some feral pulls up thinking I won't mind, so I play some Beethoven.....
Using an invertor to run something for long periods is wasted resources in anyones money other wise we would be using an invertor to generate power for us to charge our batteries on those cloudy days..........if I want 240 I get out TLRPS (The little Red Power Station) when not in use its used a signage..." Stay away generator user" can backfire as some feral pulls up thinking I won't mind, so I play some Beethoven.....
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Hi Mike @mikerezny , that was a good "rant"!! Trouble is, it was wasted on me. All you quoted was correct IMO. I think the posts drifted away from the real issue with 3 way fridges namely, it is easier to connect up to 240v when ON GRID, and connect onto gas when OFF grid as these are the primary methods of maintaining refrigeration for most people with the minimum of knowledge or hassles. When you try to get the same efficiency on 12 volts, whether it be by tug battery/connection, or converting 12 volts DC to 240 volts AC via an inverter, there are lots of possible losses to be considered, and most people are not aware of these, hence the misconception that 12 volt operation does not work (as good as gas or 240v). But, personally I certainly would not consider using an inverter to produce 240v AC power from limited battery storage power just to run my 3 way fridge on 240v.. That is just a waste of resource, not to mention dollars.. @Linc has now tested the water without knowing the alternatives and hopefully he can now reconsider his options.
He is not alone on his thinking. A fellow caravanner friend on the Darling Downs has a television in his van which can be 240 volt AC with special transformer lead, or 12 volt DC operation with straight cigarette socket lead. No matter what we say or how many times we explain it, he still persists in connecting his inverter to watch television on 240v AC. Some Mothers do have "em!!!
Scanning the above, I can say jeez I’m glad I have a compressor fridge.
works wonderfully well on 12volts
the old 3 way is but a distant memory, although I am occasionally reminded of its presences when I see it sitt on the shed floor.
Must put it up on gumtree.
works wonderfully well on 12volts
the old 3 way is but a distant memory, although I am occasionally reminded of its presences when I see it sitt on the shed floor.
Must put it up on gumtree.
Hi,
@Boots in Action might be interested in your fridge for spare parts.
I was on the knife edge when I bought the Penguin in 2016 as to whether to take the standard three-way absorption
fridge or upgrade to a two-way compressor fridge. I decided to go with the flow and take the three-way.
If I had to make the same decision today, I would have a two-way fridge, roof-mounted solar, portable solar,
and 200Ah of batteries.
Having said that, since I already have a three-way fridge and I have invested the time and effort to install and
use it properly, it works adequately and it is just not worth the expense to swap it out and add the extra panels
and extra battery. That decision is mainly due to being both tight as a fish's ... and bone lazy.
If we intended to spend a lot of time camping up North over summer, then I would need to do something. Undecided
as to whether I would swap out the three-way or put a 50l portable compressor fridge-freezer in the car to supplement
the three-way in the Penguin.
But I don't need to worry for the moment since Dictator Dan won't let me go camping and use the toilets and showers
and Anna the Great as well as the other wise leaders from WA, SA, Tasmania, and the NT have wisely determined to keep us
infectious scum from NSW and Victoria where we deserve to be until we clean up our own back yards.
take care
Mike
Don't be too tough on yourself Mike @mikerezny . We only keep out the unclean, unwashed and the "contaminated". Once you have all that beaten, we Queenslanders will welcome you with open arms and be happy to take all your money that we are missing out on at the moment.
As far as the 3 way fridge is concerned, I too have not got the spare cash for such a conversion. However, having successfully and heavily modified both my fridges in all aspects for very little cost, except the costs of solar panels and MPPT controller to run extra fans etc, I am satisfied with what I have at the moment and feel I am well ahead. One must measure what one will gain by what one will lose!! Faster pull down of fridge temp verses the large loss of my cash!!
Wow! Opened up a can of worms there! Thanks for the input guys! I will do some more testing once i install the solar...hopefully will get to use the van again in the near future! The last time I did any free camping was in a Hiace I bought for 200 bucks. We went around oz in that with a 40l 3 way fridge, a second hand lead acid car battery, a $20 portable gas cooker and a bed. Was fn awesome.
Hi @rags , there is quite a demand for good 3 way absorption fridges for vans and RVs. As they rarely break down or fail - no moving parts - most of the problems of not working well is caused by poor installation and unreal expectations of performance. Within their limitations, they operate very well, albeit slowly in the pull down phase when first turned on, and recovery after door openings. But when it comes to freezing temps, my 3 way fridge freezer section has reached minus 24.2C when empty, and maintained minus 18.5C on gas during the hottest days (30.0C plus) even though full of frozen food, and when fridge was opened and closed during the day. Unfortunately, I cannot say the same about the fridge section (I only have a single door!) which fluctuated after breakfast between around 6.0C to 7.0C during the day and dropped to 2.0C overnight. So not as bad as some think. And no need to concern oneself about power generation and battery storage. You would have no trouble selling it on Gumtree I can assure you. Beer money??
A couple of years ago decided to check the insulation around my 3 way in our 5 year old Journey Outback.!So little it was non existant.Packed in heaps around sides and top.Made a big difference .
Same here @BJM , my 14.44 never had the fridge fitted properly, when I fired it up the bench top got warm so had a look and the top was open to the back cavity, so insulated the whole thing, fitted a duct panel to send the heat straight out the vent with the help of 2 computer fans and it worked very well after that, Big Mal got the same inspection, just a few squirts of foam and added some fans and it works very well can bring a beer down to drinking temp in freezer in about 20 mins...also lots of people have this fixation on fridge temp being near zero, it should be 3 to 4 degs, put a thermometer in your fridge at home and watch the temps move around when the kids are home, quite surprising, just that the house fridge will recover quicker than your van fridge.....2 door fridge is way better than single for travelling as you can keep frozen stuff better........ Anyway plenty of threads on this subject.........both fridge types have their downsides like most things...
Hey Boots, was that a typo. Wouldnt the inverter conversion of the 0.71A @ 240v be around the 17A from the batteries ?? If the fridge element draws 90A, when I run my microwave my van tyres would start melting
That was an interesting read. My last and current 3 way fridges have performed very well on 12v whilst in transit. With the widely repeated story 12v is pox, 12v only maintains cabin temps etc etc, I have always been perplexed as to why mine have worked very very well and, as you experience, consistently pull the cabinet temp down even in higher ambient temps. Having a fridge that works, and a lot of other stuff that doesn't, there's never been much motivation to research it ... (I have enough broken things that need attention, so I have better things to do than randomly reading up on why something is working fine). So thanks for the info, it explains a lot and again highlights how social media can grab hold of a mistruth and canonize it. For what is worth, according to my fridge specs the operating voltage is 10.5v - 15v. Maybe down the track I may tilt toward 2 way, but at this point I would stick to 3 way. I know the 3 ways many limitations but they are all easily managable for me, the 2 way on the other hand has only one limitation but its a doozy and that cant be managed easily for me without significant spending.
On one level Im glad you've done the research and past that on, but on another level it's disappointing to learn that my fridge hasn't been touch by the hand of god, and isn't performing a yogurt cooling miracle. My Saintly fridge's value has sadly now plummetted, and wont be displayed in the museum with the Jesus toast and other miracles.
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You are getting very smart @Crusty181 at working out things. Yes, that figure was for full power of that inverter. Actual usage for @Linc using it to run 3 way fridge would be around 17.5A theoretically only slightly more than running direct from batteries at 12 volts. This fits in with his battery life of approx 8 hours before voltage started to drop with his Lithium 150ah battery. (8hours X 17.5A is 140ah.)
Rough formula for calculations for inverter use is as follows: Wattage X 1.2 divided by 12 equals amperes drawn from battery. (ignoring any losses)
So 900w X 1.2 equals 1080 divided by 12 equals 90A.
For @Linc's 3 way, it works like this (if fridge element rated at 0.72A at 240v AC - approx 175w): 175 X 1.2 equals 210 divided by 12 equals 17.5A. I think someone on this forum came up with an easier way too. Note wattage of 240v appliance and remove LAST digit to get rough draw in AMPS from battery. Easier than getting out calculator.
Tip from Australian Direct. "If you have a 700w microwave, that is rarely the upper limit of what they will actually draw. When the microwave starts, it will pull closer to 1500 to 1800 watts. So always go on the heavier side for inverters."
So there is where your batteries get a hammering on start up.
Thanks for the correction too.
Thank god I'm not getting smarts, I'm just a turn it on and it better work sort of bloke, figuring why makes my head spin............
I have worked out that the so called myth of fridge operation on 12v when travelling is because most fridges are fitted out by he builders, therefore even if lucky enough to have it installed correctly the wiring is usually rubbish, remember the infamous Jayco Birds Nest of wires, no explanation should be needed.. So not really a Myth as it does happen, (not to mention the lunch stop with kids and the fridge door kept open for 30mins)..... My old fridge in 36 or 38 degs between Winton and Julia Creek had a 12v fault (forgot to turn it on) it lost 3 degs over that time, this being after I fitted it out properly so its generally not the fridge but the fitting out, if I hadn't sorted it out things would have been different, while I have not fiddled with a lot with compressor jobs the few I have looked at have suffered from the same pith poor fit out.
I have worked out that the so called myth of fridge operation on 12v when travelling is because most fridges are fitted out by he builders, therefore even if lucky enough to have it installed correctly the wiring is usually rubbish, remember the infamous Jayco Birds Nest of wires, no explanation should be needed.. So not really a Myth as it does happen, (not to mention the lunch stop with kids and the fridge door kept open for 30mins)..... My old fridge in 36 or 38 degs between Winton and Julia Creek had a 12v fault (forgot to turn it on) it lost 3 degs over that time, this being after I fitted it out properly so its generally not the fridge but the fitting out, if I hadn't sorted it out things would have been different, while I have not fiddled with a lot with compressor jobs the few I have looked at have suffered from the same pith poor fit out.
Not so much of a correction. I have great faith in your (and Mikes) knowledge with this stuff, and get a bit panicky when I think my answer to the same question, that I was so confident in moments before, is now so way off. The challenge to ask without coming across as smart ar$e, sometimes that fails. My calculation method for Amps consumed in an inverter conversion is the wattage of the 240v appliance divided by 10. ie 1000w 240v microwave, 100amp from the battery. Much like your removing the last digit, but my cleverly designed formula takes into account actual Amps required, the energy consumed by the inverter in conversion, and then I apply a secret coefficient to make the answer 10, because I like 10 and its very easy to remember.