Cunning plan - three way fridge

[trevskoda]

If only it was that simple Trev.
No one will argue that a compressor fridge is the better fridge.
But they use a lot of power, particularly in summer months.
Lithium batteries are a game changer, making compressor fridges more viable for off grid use.
But the type of fridge which best suits your use, depends on what you do.
It would be great if battery technology improved significantly soon, to end the use of absorption fridges.

MIne goes 2 days on a 90 ah lead acid, this was a bench test, i have 2 lead acids in the van so no probs so far, i never stay in one spot more than a day so they get charged on the move, and 200w solar helps big time.

 

[Pudsey Bear]

I suppose that as the fridge gets its cooling from above it's co dependent so perhaps one would do.

 

[merl]

I suppose that as the fridge gets its cooling from above it's co dependent so perhaps one would do.

I think you're correct there kev, I wouldn't expect many/any? to have separate cooling devices for each compartment? I think what David experienced with the freezer side fluctuations (could be mistaken of course) was probably due to the whole unit sitting in a cold ambience temp and the temp probe being in the fridge, the cold ambient means the device hardly needs to work, consequently the freezer doesn't get a lot of input either. If you want to put a fridge/ freezer in a cold outhouse you need to choose one that's designed for it, most won't work properly.

 

[merl]

It is really remarkable (in a bad way) just how much impact it has both on opening the door and introducing food that is relatively warmer than the interior.

I noticed pretty much the same phenomenon WRT cooking.
Because we're now cooking with battery power and the Ah use can be monitored it's interesting to see that identical sized portions of chips can be cooked at various different temperatures and therefore times but overall battery consumption remains virtually identical. Also cook twice as many chips and you'll use nearly twice as much power. Sort of surprising but also obvious

 

[wildebus]

I noticed pretty much the same phenomenon WRT cooking.
Because we're now cooking with battery power and the Ah use can be monitored it's interesting to see that identical sized portions of chips can be cooked at various different temperatures and therefore times but overall battery consumption remains virtually identical.

well ..... The power consumption remains the same, but as you use higher power settings, you are hammering the battery more during that time.
If you go by Peukert, you lose capacity at higher C rates (for Lead), so by reducing the power and running for longer, you could actually finish the cooking with a higher battery SOC than using on full power

Also cook twice as many chips and you'll use nearly twice as much power. Sort of surprising but also obvious

 

[merl]

If you go by Peukert, you lose capacity at higher C rates

AHH but the C rate actually doesn't alter because the element is either full on or off. It's just the duty cycle that changes

 

[Canalsman]

If it needs cleaning many times could the jet need replacing as it may be making too much soot?

I have just replaced the entire burner assembly. The burner that I replaced has been in use for about 5 years I think, continuously, and I think the jet has become more prone to blocking with age especially recently.

I wonder if the jet is subject to some form of corrosion due to the contents of the LPG?

 

[Canalsman]

2nd part, fully agree with.
But fridge temp varies quite widely with ambient temperature? It really should not if working properly.
I think this could maybe be an operating characteristic of an absorption fridge, but a compressor fridge won't care what the ambient is (within reason. A major extreme can affect them)

Absorption fridge is often quoted as reducing temperature to 20 degrees below ambient.

I'd say that's about right though with the addition of forced cooling my fridge does better that.

However if the ambient temperature gets too high the fridge inevitably warms more than desirable. Conversely in colder conditions it is necessary to reduce the thermostat setting because it gets too cold.

 

[Pudsey Bear]

Are the 3 ways bad tech or just bad insulation?

 

[merl]

Are the 3 ways bad tech or just bad insulation?

The insulation aint particularly bad but the science behind the function is simply very inefficient compared to say running a compressor, I guess it's the price you pay for being able to get something to cool down by applying heat, ie work on gas.

 

[merl]

Absorption fridge is often quoted as reducing temperature to 20 degrees below ambient.

I'd say that's about right though with the addition of forced cooling my fridge does better that.

However if the ambient temperature gets too high the fridge inevitably warms more than desirable. Conversely in colder conditions it is necessary to reduce the thermostat setting because it gets too cold.

I vac the burner out on mine at the start of every season but I notice if the flame is playing up because the needle on the 'flame on' meter drops. I know that not all 3 ways have the same analogue meter but I wonder if it would be easier to monitor the output voltage from the thermocouple rather than set up an infra red detector?

 

[GWAYGWAY]

My Thetford three way fridge is in constant use and using gas for 99% of the time.

I have to clean the gas jet regularly to maintain performance. It's difficult to know when the cooling is less effective until the fridge thermometer, read remotely, shows it's getting too warm.

I've bought an infrared thermometer device and plan to check the temperature of the flame shield surrounding the burner on a regular basis.

The temperature should reduce when the jet starts to block since less gas is being burnt...

I'll report back in due course.

Many people do not realise there is a thermo gel between the finned part in the fridge and the pipework of the cooling unit. If it is unscrewed and taken off then the gel will have hardened or dried out, clean it and replace the gel, from a computer shop or online. Place the fined bit and make a good connection with the gel, also the little sensor should be on the third fin from the left. I was going through gas like mad but it wasn’t cool inside the fridge because of the dried out gel, I bought two tubes and it was plenty.

 

[merl]

Many people do not realise there is a thermo gel between the finned part in the fridge and the pipework of the cooling unit. If it is unscrewed and taken off then the gel will have hardened or dried out, clean it and replace the gel, from a computer shop or online. Place the fined bit and make a good connection with the gel, also the little sensor should be on the third fin from the left. I was going through gas like mad but it wasn’t cool inside the fridge because of the dried out gel, I bought two tubes and it was plenty.

Thanks for that.
It's called thermal paste or compound it's used between transistors or pc processor chips and their heatsinks, as you say it dries out and goes chalky after a few years and stops transferring heat and then the device get too hot and fail, I use it quite a lot but never knew the 3way in the van used it. Sounds like a winter project on a pleasant day! Was yours tricky to do? Did you have to remove the fridge or can it be done through the vents?

 

[Canalsman]

Thanks for that.
It's called thermal paste or compound it's used between transistors or pc processor chips and their heatsinks, as you say it dries out and goes chalky after a few years and stops transferring heat and then the device get too hot and fail, I use it quite a lot but never knew the 3way in the van used it. Sounds like a winter project on a pleasant day! Was yours tricky to do? Did you have to remove the fridge or can it be done through the vents?

The fins are within the fridge compartment. They act as the inverse of a heat sink, more of a cooling sink!

 

[Canalsman]

Many people do not realise there is a thermo gel between the finned part in the fridge and the pipework of the cooling unit. If it is unscrewed and taken off then the gel will have hardened or dried out, clean it and replace the gel, from a computer shop or online. Place the fined bit and make a good connection with the gel, also the little sensor should be on the third fin from the left. I was going through gas like mad but it wasn’t cool inside the fridge because of the dried out gel, I bought two tubes and it was plenty.

I didn't know that but it makes sense. I've never, evidently, done that but I'm not sure I need to. The fins are cold enough to form ice and small icicles at times that when they fall off can be heard quite clearly.

The other device is I think a thermistor. I moved mine one position along on the fins to get better control of the fridge temperature.

 

[Canalsman]

I vac the burner out on mine at the start of every season but I notice if the flame is playing up because the needle on the 'flame on' meter drops. I know that not all 3 ways have the same analogue meter but I wonder if it would be easier to monitor the output voltage from the thermocouple rather than set up an infra red detector?

My fridge doesn't have such a meter. The flame is lit whenever the fridge temperature rises and is controlled by a thermistor clipped to the cooling fins within the fridge compartment.

 

[GWAYGWAY]

Thanks for that.
It's called thermal paste or compound it's used between transistors or pc processor chips and their heatsinks, as you say it dries out and goes chalky after a few years and stops transferring heat and then the device get too hot and fail, I use it quite a lot but never knew the 3way in the van used it. Sounds like a winter project on a pleasant day! Was yours tricky to do? Did you have to remove the fridge or can it be done through the vents?

Takes half an hour deep socket to take the nuts off and pull the fins off, clean, retreat with the paste and stick it back well to squeeze the gel nicely.. the thermistor is meant to be third fin from the RIGHT end.