inverter to run absorbsion fridge

[jimbamb]

Have heard it is a good idea to run 3 way caravan fridge on an inverter while traveling as the 12 volt system is virtually useless.(Ineffective)
The 240V element is 120W and they work really well on 240v.
The 12v element draws around 12/14 amps
Questions..
1 what size inverter would i need.
2 how much currant would that inverter use
3 should it be a sine wave inverter?
4What are your thoughts?
jim
While at it would the same inverter run the TV?(i think it draws about 6 amps)
Jim

[FNQCairns]

Each to their own with these things, I have a 1200watt inverter modified sine wave that will run the big plasma TV and the PVRs quite happily along with the desktop computer/phone/router etc during our fairly frequent blackouts.

If only ever owning one inverter size with the bigger one you have capacity and the extra power needed to push it is not that much of a drain.

Back to the 3 way, I found through much on the road testing that my chescold if the 12v power cable was completely replaced to a properly heavy standard it is very close if not identical in it's cooling ability to when running on 240v. I set the 4wd i had years ago with dedicated cables to run the chescold from the second battery when ignition was off and the main when ignition was on, they certainly suck the power.

[jimbamb]

fnq.
i have given up on trying to run the fridge on 12 v as there seems to be no effective gain.
i just put it on 240/gas when i stop and have never lost anything by being spoiled.just thought it May be worthwile.
jiom

[FNQCairns]

Jim whatever suit you I suppose, yeah certainly gas and 240 is best and easiest overall i probably wouldn't consider an inverter under 600w for your job, pure sine wave would be better for all of the jobs it might do in the future but the 3way will run on dirty power (cheap ones), inverter will draw a few % more overall than the total it is supplying....effectively it's not an issue.

Personally and i do not have the experience to back this up....I dislike the idea of 240V running anywhere commonly earthed for the want of the better technical term I suspect. I don't even like touching my largish inverter with my bare hands once they are battery connected and my daughter is banned from being anywhere near it....I am probably being a skirt.


Like the 3way more than the engle, only let me down once in 12 years or so but i learnt from it so shouldn't happen again.

[banksmister]

You will find most 3way fridges don’t even run the 12volt side of the system through the thermostat
Goes to show how confident the manufactures are of achieving very cold temps on the 12volt side

Darren

[FNQCairns]

You will find most 3way fridges don’t even run the 12volt side of the system through the thermostat
Goes to show how confident the manufactures are of achieving very cold temps on the 12volt side

Darren

So it runs flatout all the time Darren? if so I would agree with that, certainly the amp gauge in the car never wavered up and down once the chescold got plugged in, still had it set to flatout just incase.

[banksmister]

So it runs flatout all the time Darren? if so I would agree with that, certainly the amp gauge in the car never wavered up and down once the chescold got plugged in, still had it set to flatout just incase.

FNQ get your torch out tomorrow and look in the back the wires go strait from the plug to the element [not through the thermostat] where as 240volt does

[jimbamb]

Thanks banks,
Never knew why but it confirms my idea.
running on the inverter would probably use less power as the thermo Might cut in and out.
Would 600w be enough??
Jim

[banksmister]

Jim might pay you to go to jaycar or similar place with the fridge and ask them if you can try it
600w inverter should be well and truly enough you’d think as you only need 120w plus some energy loss
Just be careful but there is pure sine wave & modified square wave inverters this may [I am not sure] affect the inverter as all the fridge element is doing is a controlled short circuit
Seems to make good sense but what you’ve been told
Tell us how you go

Regards Darren

[oldboot]

bear in mind you are going to need heavy wiring to run the inverter.

One reason that sooo many 12 volt applinace do not work well is that people use wire that is far too light.

If you are only getting 8 volts to your fridge, of couse it wont work very well....... and neither will your inverter on the same wiring.

If your 240v eliment is 120 watt that will mean the invereter will have to draw about 10 amps pluss losses that puts you back to the 12-14 amps off the 12 volt supply.

so if you want to get 12 volts 15 amps to your fridge in your caravan, from the battery in the front of your car, probaly arround 10 or 12 meters, you will need a decent lump of cable...6mm automotive just wont cut it.....you'll need 6 or 10mm2 to be in the race.

As far as what inverter to do the job......its a heating eliment, it wont care what sort of inverter it is.

cheers

[finga]

Hey Jim....some quick maths.
If the 12V side draws about 12-14A then the element must be around the 140W or larger.
I wonder why the 12V is not as effective as the smaller 120W 240V element??
It's the watts that count.

With the inverter just have a gander at what the 100% duty cycle rating is. Most of them are rated at a silly duty cycle like 25% or less or even at peak output which means didly squat.

[jimbamb]

Thanks guys.
Seemed to be too good to be true
recon ill stick to my old plan.
Don't think there is much advantage in using 10/12 amps to run fridge and having to rewire the ute/van with huge cable.as it holds temp well while turned off without problems in the past.
Myth solved..
Jim

[blaze]

I fitted a 190w 24 volt solar panel to the roof of my van. I have 2 x 100amp batteries in the van + the second battery in my discovery all being charged by the panel when stationary. Off that I run the 12 volt comp fridge in the discovery and the 3 way fridge in the van on 12 volt. So when I park up for 3 or 4 hrs I am about nuetral on battery usage and on cooler but sunny days I have a slight gain. When travel again no problems. When camped up, depends on free camping or caravan park the 3 way goes to gas or 240. Have been on the road now for close to a month and the only time we were left wanting is on days of 40 degrees or better (had a week of about 45 + and that tested the resources but we did nt loose any food)
cheers
blaze

[jimbamb]

Thanks mate,
Geez i wish i was back over there, its a great life on the road..Keep reminding us how good it is!!!
Jim

[Rob29]

Thanks banks,
Never knew why but it confirms my idea.
running on the inverter would probably use less power as the thermo Might cut in and out.
Would 600w be enough??
Jim

i run the dark blue 55L dometic via 150watt inverter from jaycar and does the job fine as long as the revs are over 1500rpm.