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swaggy

Fridge Fans (again) Help.

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I am in the process of fitting a couple of fans to help cool our caravan fridge in this hot weather. (Dometic 6270)    The fans  will be thermostatically controlled with a manual on/off over-ride.    Straightforward install but  I have a couple of questions for those who already use such a system.

 

1.     What do you sense with the temperature probe?  Is the probe just in the vicinity of the cooling fins so sensing the air temp behind the top vent or is it actually between 2 fins thus  taking the  temperature of the fins themselves.

 

2.    What temperature is the trigger point set at.    Obviously the air temp will be lower than the actual fin temp.   I know that the max  chill performance of these absorption fridges is about 30c below ambient.

 

Appreciate any guidance I can get.

Edited by swaggy
Typo

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The commercial offerings seem to use a spring clip thermal switch that clips onto the approx 3/4"-1" diameter pipe on the heat exchanger at the back. Close to where the condensate evaporation tray is fitted. There are also some proportional ones I hear that use an electronic sensor and vary the fan speed with temperature.

 

I think the temp trip point is usually set well above any ambient temperature likely to be experienced in ordinary conditions, so over 50C.

 

The Dometic has a permanent two pin low current 12v feed available on the terminal box at the back - otherwise unused. Their own offering uses that connector without a manual switch so it's important the trip is only going to be triggered when the fridge is working. Otherwise the fan may come on in storage draining the battery.

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Because of the high temperatures we're experiencing, I've tie-wrapped a couple of computer fans to the inside of the bottom grill and wired them up in series to give a gentle flow of air over the back of the fridge.   I switch them on in the morning and off again at night.   It's just a temporary set-up while we have these abnormal conditions, but it works, didn't cost me anything and can be easily removed when normal temperatures return.

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29 minutes ago, Crannoghome said:

Because of the high temperatures we're experiencing, I've tie-wrapped a couple of computer fans to the inside of the bottom grill and wired them up in series to give a gentle flow of air over the back of the fridge.   I switch them on in the morning and off again at night.   It's just a temporary set-up while we have these abnormal conditions, but it works, didn't cost me anything and can be easily removed when normal temperatures return.

 

I think it's suggested that fans fitted in place of the vent are placed in the upper vent, in case the fridge is run on gas and the direct fan draught interferes with the flame. The Dometic fan IS placed directly under the lower part of the heat exchanger but that point is far away from the burner assembly.

 

To the OP- I have a copy of the Dometic fitting instructions if you want any ideas where to place the sensor.

Edited by TinShack
Clearer wording

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TinShack

Thank you for your offer.   PM sent.

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47 minutes ago, swaggy said:

TinShack

Thank you for your offer.   PM sent.

 

Probably more useful to others to post here.   Hope that's OK with everyone. It's not exactly the most detailed document but it is all there.

 

Dometic fan. pdf

 

For the benefit of anyone else doing their own thing with the same positioning (Dometic) note that 100mm fans are the largest that will fit behind the fridge if it has been properly installed. e. g. the gap behind my fridge is 110mm. Bailey now seem to have quite a reasonable sealed fridge box on newer vans.

 

Probably easier to fit one or two 120mm or 140mm 12v fans behind the upper vent if going the DIY route. In my case I mounted a couple of 140mm computer fans from the spares box to a thin aluminium plate which is sandwiched behind the upper vent. They are PWM types so I used a tiny variable PWM speed controller to set a suitable speed. They are so quiet I can't hear them in the van. The official Dometic fan kit was bought for a friends van, but I haven't fitted it for him yet.

 

 

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We have twin fans fitted,they come on at 20c on low speed and 25c on high speed.

John.

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3 hours ago, TinShack said:

 

I think it's suggested that fans fitted in place of the vent are placed in the upper vent, in case the fridge is run on gas and the direct fan draught interferes with the flame. The Dometic fan IS placed directly under the lower part of the heat exchanger but that point is far away from the burner assembly.

 

To the OP- I have a copy of the Dometic fitting instructions if you want any ideas where to place the sensor.

 

My fans are on the left hand side of the vent, away from the burner and I'm running off the EHU, but thanks for pointing that out.  

 

I've had complaints from the management that the vegetables in the fridge are starting to freeze when it's set to four bars, so maybe the fans are not necessary after all!

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31 minutes ago, Crannoghome said:

I've had complaints from the management that the vegetables in the fridge are starting to freeze when it's set to four bars, so maybe the fans are not necessary after all!

 

Sounds like a result! Without the fans we kept ours on setting 5 in hot weather. With the fans on then 3 was OK apart from some scorching days when the sun was on the fridge side.

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4 hours ago, Crannoghome said:

Because of the high temperatures we're experiencing, I've tie-wrapped a couple of computer fans to the inside of the bottom grill and wired them up in series to give a gentle flow of air over the back of the fridge.   I switch them on in the morning and off again at night.   It's just a temporary set-up while we have these abnormal conditions, but it works, didn't cost me anything and can be easily removed when normal temperatures return.

 

Two 4" 12V comupter fans - draw about 50mA each - wired in series, but put one inside the bottom vent blowing in and one inside the top vent pushing out. The direction or rotation and air flow are shown by arrows embossed on the outside of the fan body. You don't need fan speed - hence why wiring in series - just enough to move the air.

 

There was an article in a caravan mag a year or two ago about how to do it. They mounted the fans on some ally strip (Meccano-like) and attached the strips above and below the grilles inside the aperture.  

 

A friend did the same and made the fridge so efficient it froze everything even at the lowest temp setting - so an on/off switch or electronic thermostat is probably a good idea.

 

If you have a Bailey caravan that is out of warranty it is also a good idea to do something similar with the power box, blowing air in through the grilles at the top on the left side of the power box front assembly and pulling it out through the grille on the top right edge. The power supply is prone to internal fan failure or sensing system failure so the unit overheats due to the poor natural air circulation where the box is fitted (usually under a bed.) A 2" fan will do, and it needs to be wired such that it only runs when mains EHU is present.

 

 

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I posted extensively about the retrofit I did. Both fans sucked air out and the sensor was set to respond to ambient temperature under the van as that is what is of interest, not the fin temperature.

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BFM, do you have a link to your write up?

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I'm just in the process of building my set up, I've ordered two 120mm fans from Novatech for less than £7 delivered.

I have also ordered a digital thermostat and was going to set it to come on at about 25 degrees. That was from eBay and a couple of quid have a look for w1209.

I will probably power mine through a plug socket near the sink using and adapter and some 12v plugs I have left from my strip light build. 

I intend to site them on the top vent either fitted inside or in replacement for the vent depending on how much room I have when it's all together.

 

My only question to those who are ahead of me on this is that is it better to wire the fans in series or parallel and why, just to quieten down if series?

Thanks

Edited by Jiffy176

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This what I have used. Very quiet, fan speed varies from off to high speed automatically. Can be set on auto or manual also has a timer capability. Plus a on/off setting. Temp sensor located just above the heat exchanger fins. Low consumption if off grid. Pleased with it .

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C14DAB57-67EC-4195-92EF-CEC2E706108A.jpeg

D71F3345-A4F1-46EB-B17F-B47C5234CBA2.jpeg

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On 12/01/2020 at 22:11, Jiffy176 said:

My only question to those who are ahead of me on this is that is it better to wire the fans in series or parallel and why, just to quieten down if series?

Thanks

 

Wire them in parallel, otherwise you will split the voltage between them and they will only be about 6volts each and if they do run they wont be fast enough.

 

 

To answer an earlier question, what temperature to set as switch-on and where to mount the sensor?  I mount the sensor at the bottom vent so it's sampling incomming ambient temperature as it's high ambient temp that is causing the issue.  Non-compressor fridges, (absorbsion types) can cool to about 20 degrees from ambient, therefore I've set it swich the cooling fans on at 20C, this gives me a little wriggle room on minimum setting. 

 

I've used mine in France and one fan just wasn't good enough, with 2 on last year during that hot spell, we were ok, but not brill, and the fans were running almost 24 hours a day so we opted for a compressor type in addition. In my opinion, that is the only real answer if you are going to be living for any length of time in a very hot environment, warm beer is one thing but food poisoning is no fun at all.

 

Dave.

 

 

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We travel in hotter climes most years and quite a while ago I investigated the fan assistance solution, but upon removing the external vents found that there was no room for installation, so we struggled on with what we had.

Last year I bought a compressor cool box for the beer and the perishables like meat and dairy, and it was an incredible improvement.

 

Edited by onewheelonmywagon

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1 hour ago, Pickled Onion said:

 

Wire them in parallel, otherwise you will split the voltage between them and they will only be about 6volts each and if they do run they wont be fast enough.

 

 

To answer an earlier question, what temperature to set as switch-on and where to mount the sensor?  I mount the sensor at the bottom vent so it's sampling incomming ambient temperature as it's high ambient temp that is causing the issue.  Non-compressor fridges, (absorbsion types) can cool to about 20 degrees from ambient, therefore I've set it swich the cooling fans on at 20C, this gives me a little wriggle room on minimum setting. 

 

I've used mine in France and one fan just wasn't good enough, with 2 on last year during that hot spell, we were ok, but not brill, and the fans were running almost 24 hours a day so we opted for a compressor type in addition. In my opinion, that is the only real answer if you are going to be living for any length of time in a very hot environment, warm beer is one thing but food poisoning is no fun at all.

 

Dave.

 

 

Thank you.

It's only for the annual two week haul so changing the fridge is not worth it until it gives up. 

I was thinking somewhere between 20 and 25 so I will try at 20. The thing is digital so should be easy enough to change if it is to low.

Thanks.

Jiff

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I have my own designed set-up with twin fans and a temperature sensor in the bottom vent sampling incoming air. The temperature controller is set to initiate the fans at 28C. This system has worked well in temperatures up to 35C and with the fridge thermostat set at medium. Even at the highest temperatures we have encountered, the fans only run for a few minutes before cycling on and off, however I am a firm believer in good fridge performance being very closely related to correct caravan manufacturer installation. My fridge is installed with the cooling fins 18mm from the caravan wall, so within the 15 - 20mm recommended by Dometic.

 

John. 

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