Fridge fans fitted with unexpected results (1 Viewer)

[AlastairH]

Apologies for starting yet another thread on fridge fans.

Like many others travelling abroad I found that the fridge struggled to work effectively in high temperatures. Thanks to previous posts, which provided excellent advice, I fitted fridge fans recently in preparation for our sojourns to warmer climes next year. I was therefore surprised to find that on a recent trip to the NE Scotland where daytime temperatures were around 10C-13C the fridge fans came on on a continuos cycle of 40 seconds on and 30 seconds off. I had set the temperature controller to come on at 26C and wondered if it was working properly so I checked the temperature behind the top vent with a temperature probe and it did indeed reach 26C even when the outside temperature was well below 10C.

Considering the fridge manual recommends fitting Winter covers over the vents when temperatures drop below 12C, I was amazed to see the fans come on at low temperatures. It just goes to show how inefficient the venting system is and how hard the fridge has to work most of the time. I should mention that we were on an electrical hookup most of the time.

 

[Lenny HB]

Depends a lot on the installation, in hot temps external fans are essential. For general running fitting an internal fan makes a big difference to the overall performance.

 

[Reevsie]

A couple of years back I fitted my 2 fridge vents as per the handbook instructions. It was 6 deg outside. The next morning I was walking back to the motorhome after going for my morning walk, and I noticed the vents were a little warped. I took off the vents to find the top vent had warped out of shape as it got very hot. I dread to think how hot it must have got to melt the plastic. Had 2 fans fitted and will now only use the lower vent cover.

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[funflair]

@AlastairH what kit are you using, our CBE kit doesn't come on until above 30 deg and then stays on low for a good while (until the outside temperature changes I think), dont exactly know but it doesn't cycle as you describe.

Martin

 

[Gromett]

My fridge fan controller project is not forgotten. I have had larger projects this year such as getting the engine to start (thanks again @Wildbill) and a leaky diesel tank, welding the sills, fitting a towbar and fitting out the new trailer.

Next years first project will be redesigning and rebuilding the kitchen area which will include a new fridge. Once this is fitted the fridge fan controller will go back on the front burner.. It is a really interesting project and I am looking forward to getting it going.

 

[AlastairH]

Martin,
I bought two Arctic 120mm fans and a digital temperature controller per earlier threads on EBay that turns on the fans at the set temperature, which I set at 26C. I am wondering if a variable speed controller might be better. I also wonder about relocating the temperature sensor which might be too close to the outside.

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[bigtwin]

Sounds like your temperature sensor is measuring the temperature behind the vent rather than the external temperature?

Ian

 

[AlastairH]

Ian,
Well, yes because if it measured the outside temperature the temperature behind the vent would not be controlled.

 

[funflair]

Our temperature sensor is right in the middle of the two fans but they are two speed as well.

Martin

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[Lenny HB]

A couple of years back I fitted my 2 fridge vents as per the handbook instructions. It was 6 deg outside. The next morning I was walking back to the motorhome after going for my morning walk, and I noticed the vents were a little warped. I took off the vents to find the top vent had warped out of shape as it got very hot. I dread to think how hot it must have got to melt the plastic. Had 2 fans fitted and will now only use the lower vent cover.

Were you by any chance running on gas?
They always used to say do not use the covers if running on gas, they don't say it any more but I never fit the top vent when running on gas.

 

[Lenny HB]

My sensor is on a strip of alloy between the fans and controller set to 32, setting depends a bit on the installation last van I had it set to 35. Outside temperature is irelavent temp at the back of the fridge is what effects performance but equates to approx 25 outside temp when the fans turn on.

 

[Reevsie]

Yes, I was on Gas. According to the manufactures, both the vent covers should be fitted. But when it was repaired under warranty the fitter said he knew of several people this had happened to. I was told by the fitter never to fit the top vent cover unless it was below freezing and to drill a vent hole in the top cover close to where the heat is generated from the fridge.

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[MattR]

Martin,
I bought two Arctic 120mm fans and a digital temperature controller per earlier threads on EBay that turns on the fans at the set temperature, which I set at 26C. I am wondering if a variable speed controller might be better. I also wonder about relocating the temperature sensor which might be too close to the outside.

My next project is to fit the variable control to reduce the cycling of the fans. They are very efficient but they control panel makes a click each time they turn on and off. I'd rather they stay on for longer at a slower speed, especially at night when we're sleeping as the clicking keeps the current wife awake.

 

[Richard n Ann]

Our sensor is inside a plastic tube that fits snugly between the condenser fins the cut in temperature is 45c. I experimented and found it was best around half way across the condenser. I made the controller using a 555 timer chip and the switching is done with a power transistor so no clicking noise. Also the circuit uses zero power itself (I noticed on some other threads the controllers used more power than the fans )
At the end of the day it's the refrigerant temperature we're interested in, not the ambient temperature so having the sensor in the fins is best. Some AC outdoor units have them clipped onto the condensers too.
Circuit diagram available if you want to build your own controller

 

[AlastairH]

Thanks everyone for your contributions. Can anyone recommend a variable speed controller?

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[bigtwin]

Ian,
Well, yes because if it measured the outside temperature the temperature behind the vent would not be controlled.

I’d understood, perhaps incorrectly, that the objective of fitting the fans was to overcome a drop in efficiency in conditions of high ambient temperatures (hence the requirement to monitor the external (ambient) temperature).

A high ambient temperature will reduce the temperature differential between the bottom of the column and the top and hence reduce the rate of circulation of the refrigerant. Hence the need to reduce the temperature at the top of the column.

Whether or not you measure the temperature external to the vent or internally perhaps doesn’t matter too much (other than the level at which you trigger the fan (lower if outside and higher if inside)). Sounds as though you are triggering it at too low a temperature.

Ian

 

[Minxy]

Our sensor is inside a plastic tube that fits snugly between the condenser fins the cut in temperature is 45c. I experimented and found it was best around half way across the condenser. I made the controller using a 555 timer chip and the switching is done with a power transistor so no clicking noise. Also the circuit uses zero power itself (I noticed on some other threads the controllers used more power than the fans )
At the end of the day it's the refrigerant temperature we're interested in, not the ambient temperature so having the sensor in the fins is best. Some AC outdoor units have them clipped onto the condensers too.
Circuit diagram available if you want to build your own controller

I'm wanting to install a couple of fans in our camper so any info you can supply on what you used and how to do it would be gratefully received.

 

[Richard n Ann]

R2 & R3 set the temperature and must be the same value. I think I ended up with a pair of 31k in the end to get the temperature up to 45c.

R4 is the differential. With this resistor at 3.3k, and with only one fan fitted, for some reason, near the set point the circuit kept switching on an off really fast, which made the fan start slowly (and quietly) and then if the sensor got even warmer it would slowly speed up as the on time increased. How cool is that! PWM without even trying

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[Richard n Ann]

Veroboard layout. All the components are very common and are all on ebay. I can probably send you most of them when we get back home next month

I wouldn't bother with the screw terminals again, it's easier just to solder the wires in.

 

[Richard n Ann]

Most of the work is done. This is what's inside the 555 integrated circuit...

Good job everything's on an IC these days isn't it. I suppose they are a bit like apps, but physical... There's an ic for that lol

 

[busby]

I don't have a temp sensor fitted on mine,,i just switch the fan on manualy when its hot and turn it off when it cools down,,BUSBY.

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[funflair]

I'm wanting to install a couple of fans in our camper so any info you can supply on what you used and how to do it would be gratefully received.

Hi Minxy

I dont know if you want to build your system or just fit an existing kit, if its a kit mt experience is here,

Martin

 

[jockaneezer]

I don't have a temp sensor fitted on mine,,i just switch the fan on manualy when its hot and turn it off when it cools down,,BUSBY.

I'm the same. There was a hella socket in the cupboard next to the fridge, so I just drilled a 4 mm hole into the cupboard from the space behind the fridge and plug the fans on as and when.

 

[AlastairH]

Minxy Girl (Mel)

I bought everything I needed on Ebay. Here is a list of what I bought:

2 X Arctic Cooling F12 PWM 120mm Fan Cases (£11.75). Make sure the fans you buy fit inside your vent.
1 X 12v Digital heat cool Temp Thermostat - Temperature Control Switch (£3.59). This is just a circuit board but you can buy a case for it, see below or buy a more expensive unit that is all enclosed.
1 x PWM Fan Splitter Cable 4 pin plug to twin male 4 pin Sockets (2.21). This joins the fan cables together and allows you to unplug and remove fans easily if need be.
1 X 30cm PWM Fan extension cable 4 pin male plug to female Socket lead. (£1.86). I used this to connect the fan wiring to the temperature controller.
1 X For XH W1209 Digital Temperature Control Module Clear Acrylic Case Shell Kit (£1.25). This is a neat box to house the temperature controller.

Type those descriptions in to Ebay and the items should come up. The biggest problem I had was finding a 12v supply for the setup, which was not hard. If you need to know how to wire up the controller, then just let me know. I tested it all worked before installation by connecting the whole lot to a 12v battery and using a hairdryer on the temperature probe.

Good luck!

Alastair

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[MitchandJenny]

I am also about to start the "Fridge fan install".
I have found a 12v feed and an earth, behind the lower removable grille on the Base of the fridge recess.
I bought a thermal operated controller off Ebay or Amazon (can't remember) that cost less than £3 incl postage (from China) and includes the thermal probe, which I plan to fit in the upper grille recess on top of the finned piping. Got a couple of old PC vent fans which I plan to mount on the outer lip of the upper grille recess.
Just got to bite the bullet now and get started.
Mel, I think John (published author) Laidlaw had the details of the thermal controller.
Good luck.
Mitch.