Converting our 3 way fridge to compressor. (1 Viewer)

[wfdTamar]

Interesting way to do it. I'm just in the process of installing a Beko 240 volt fridge run off inverter and 300 watts of solar.

 

[Richard n Ann]

Interesting way to do it. I'm just in the process of installing a Beko 240 volt fridge run off inverter and 300 watts of solar.

That's not too bad if you can switch the inverter off with the thermostat via relay/contactor. That's what I did with a small freezer I set up in my shed

 

[Raul]

Or use a inverter that can detect the load in eco mode and turns on/ off when load present.

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[BOWHOUSE52]

I wish I was clever like some of you lot got to g

 

[BOWHOUSE52]

Sorry prest post reply to soon I was going to say got to go for a lay down

 

[DP+JAY]

Couple if questions,
Are you testing the fridge empty or loaded?
Is there a kit available for a domestic fridge with freezer above?
Thanks.
DP

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[Richard n Ann]

Couple if questions,
Are you testing the fridge empty or loaded?
Is there a kit available for a domestic fridge with freezer above?
Thanks.
DP

Empty.
Yes dometic make various different kits but they're more money, I'll look for a link...


Edit; Here is what could be the freezer version, don't know how successful it would be without a door on the front

<Broken link removed>

 

[DP+JAY]

I was wondering how being full will affect the the run & off times, large mass of cold stuff taking longer to warm up & cool down.
DP

 

[Richard n Ann]

I was wondering how being full will affect the the run & off times, large mass of cold stuff taking longer to warm up & cool down.
DP

It will a bit, more so if you put something warm in, but not too much because the thermostat is fastened to the back of evaporator which will get cold quickly regardless of food temperature.

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[Richard n Ann]

Posted link above

 

[DP+JAY]

I'll look forward to real life figures to compare with the 12 hours you did empty.
DP

 

[PaulOH]

That is seriously impressive! And done at home!!!

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[Richard n Ann]

Half filled it and ran it overnight, about the same 6 start ups per hour.

Nice steady temperature :

I'll measure the amp hours used again tonight

 

[Steve and Denise]

Can any one explain how our home fridge/freezer you can set say the freezer to -18 and the fridge to +3 I assumed it must have 2 thermostats but only 1 compressor, where the fridge/freezer in our van std Dometic absorption shares the same cooling plate in the rear with the freezer getting the lions share.

 

[Richard n Ann]

Can any one explain how our home fridge/freezer you can set say the freezer to -18 and the fridge to +3 I assumed it must have 2 thermostats but only 1 compressor, where the fridge/freezer in our van std Dometic absorption shares the same cooling plate in the rear with the freezer getting the lions share.

There are different arrangements, sometimes the fridge stat operates a solenoid valve and the other stat brings the compressor on.

Sometimes there's 2 compressors (less common)

Mostly though the system is calibrated so the refrigerant goes into the fridge after the freezer and it all works out OK. Thermostat is in the fridge on this type so if you keep it in your garage over winter everything defrosts

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[Richard n Ann]

Another little job. Dometic should have done this one, but I suppose if they can save a couple of quid it makes sense

I wired it up through the other pole of the off switch so the battery isn't draining all year.

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[Richard n Ann]

Exactly the same, 7ah used, 6 start-ups per hour..

 

[wfdTamar]

I tried mine running the inverter in eco mode (polls for demand every few seconds and only turns on if required), but then the Fridge light doesn't work if the fridge isn't running. If it makes a significant difference and I need to conserve power, I'll do it, but I don't think that's likely.

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[Richard n Ann]

Right that standard thermostat is ridiculous, it was switching the compressor on every 5 minutes. Fitted a little digital module this morning for full temperature control
It has differential settings, compressor protection, probe offset and even alarm

Positioned the thermistor to sense cabinet temperature 3°c with diff of 2.
No defrost setting but I can sort that manually.

 

[Richard n Ann]

Much better now, switching on about 3 times an hour rather than about 10 times according to the battery voltage graph.
Earlier I timed it to run 14 minutes, then off for 10 minutes so just starting up every 24 minutes.

 

[Richard n Ann]

I've turned the controller down to 0°c (cut out 0° back in at 2°) because the thermistor is at the back near the evap, that gives a middle fridge temp of 3 to 4°
Last night the fridge used about 9 amp hours. It's cloudy today but the battery is now just about recharged with 1ah to go.

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[Raul]

That’s super efficient fridge, I don’t think factory dometic CRX range are that efficient as yours. It’s worth the effort you put in. Also hysteresis of two deg is pretty good for keeping a constant temperature.

 

[Richard n Ann]

Just at York THS having a 'compressor' beer teeth shattering
Battery was recharged by 10am

 

[Richard n Ann]

Oh by the way I've upped the diff to 3°c and the compressor only comes on once an hour for about 20 minutes now so even more efficient

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[Ditcha]

Just at York THS having a 'compressor' beer teeth shattering
Battery was recharged by 10am

View attachment 642017

On another note Richard what's the THS like is it the rugby/ cricket club looking at going in a couple of weeks

 

[Richard n Ann]

On another note Richard what's the THS like is it the rugby/ cricket club looking at going in a couple of weeks

Yes it's very good. Quite full at the minute. Nice level grass pitches No booking allowed but you'll be ok if you avoid weekends. The club house does great burgers made by the local butcher and there's a discount on drinks if you take your club card.

 

[wfdTamar]

Mine is working very well. Been in temperatures up to 39 (in France). I just wish it had an electronic temperature control like some bigger fancy fridges have. I had it turned down a bit too cold the other day. Top is fridge, middle freezer, bottom room temperature. Haven't gone below 80% battery capacity yet. It's great being able to rely on your fridge regardless of weather.

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[Lenny HB]

Battery was recharged by 10am

Something I forgot to mention, you have a gel battery so yomay think it was fully charge it was probably 80% charged and will need at least another 4 hours of the absorbtion phase to reach 100%.

Anyway its worked out really well a great option for ageing fridges.

 

[Richard n Ann]

Right that standard thermostat is ridiculous, it was switching the compressor on every 5 minutes. Fitted a little digital module this morning for full temperature control
It has differential settings, compressor protection, probe offset and even alarm

View attachment 633527

Positioned the thermistor to sense cabinet temperature 3°c with diff of 2.
No defrost setting but I can sort that manually.

Well that Chinese module thermostat thing didn't last long. It started switching on and off randomly yesterday, couldn't do anything with it so I've reconnected the mechanical stat. I'm going to look into fitting a standard 29x71mm controller.

 

[Hoovie]

Very Interesting thread. I replaced my Thetford 3-way fridge with a standard 240V Domestic unit. I did contemplate fitting a compressor conversion kit but decided to go with the simple option (I did also sell the old Thetford for just a little less than the new 240V Compressor one, so that was handy).

..... Mostly though the system is calibrated so the refrigerant goes into the fridge after the freezer and it all works out OK. Thermostat is in the fridge on this type so if you keep it in your garage over winter everything defrosts

Well that Chinese module thermostat thing didn't last long. It started switching on and off randomly yesterday, couldn't do anything with it so I've reconnected the mechanical stat. I'm going to look into fitting a standard 29x71mm controller.

Ref the two comments above I quoted, I found that the thermostat being in the Fridge compartment does stop optimum Freezer performance, so I fitted a temp sensor in the freezer and I am using that information as the basis to control when the unit gets power. I have a Victron Cerbo based system and I use the value of the Temp Sensor added to the Freezer to control a relay that switches the Freezer on when one temp is reached, and then off again when another temp is reached. Interestingly, the difference between the two temps (which you could refer to as the hysteresis) is only 1C.
It may seem not enough, but it seems to work well and you can see from the graph below the fridge comes on every hour or so for around 15 minutes.

I guess the right value would be determined by a combination of how fast the compressor brings the temp down and how good the insulation is at stopping it rising again, so could vary from fridge to fridge.
I haven't disabled or rewired the original thermostat in the fridge, but just set it to MAX which makes the compressor run whenever the fridge has power - so it becomes a matter of controlling when it has power (as can be seen above in the blue line)

Be interesting how you finish your project. Hopefully the above may have been of some interest?

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