New Gadget project started. Fridge fan controller. (1 Viewer)

[pyro]

Well, I think this is an excellent and very well thought out idea Gromett.

I especially like your use of the PID to do the thinking, and PWM proportionate fan control for quietness and efficiency. Cheaper than a thermostat or a solar panel, too

I look forward to hearing more

 

[2657]

PID......PWM.......diodes.....transistors.......ATTiny85 Microcontroller. £0.98 each.
Link Removed. £0.99 each
Broken Link Removed. £0.79 each (£1.58)

Whilst I have heard of at least two of those things I have no idea what they do, how to use them etc

I did buy a few of those connector thingies though and even managed to solder them..........and they worked

 

[Baycott]

Following with interest. Thanks @Gromett

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[Gromett]

@Gromett - do you know if fan efficiency is influenced by the cooling method, ie 230v versus gas? I've added a digital temperature display to my fridge and I'm beginning to suspect that fans make the biggest difference with gas.

I can only guess sorry. My guess would be the gas system generates more heat so the fans have a greater effect?????

 

[The Wino]

Are you sure the temp difference indicates the fan needs to be on just thinking on a cold day a big difference in temps top to bottom of the fridge flue indicates its working well on a hot day you would expect less convection?. I might be wrong!!. There might need to be a temp sensor in it as wwell to onlt switch on if its above a certain temp. The solar sounds simple and effective with no battery drain possible although a small battery to give an early evening run on might be even better. We are lucky ours worked well last year in 35c plus so it might be surpluss to requirements the germans next door had all their vents off to increase airflow but still seemed to manage an impressive alcohol consumption!!

David

 

[Gromett]

Are you sure the temp difference indicates the fan needs to be on just thinking on a cold day a big difference in temps top to bottom of the fridge flue indicates its working well on a hot day you would expect less convection?. I might be wrong!!. There might need to be a temp sensor in it as wwell to onlt switch on if its above a certain temp.
David

I did mention this on my first post. It goes to sleep if the lower sensor falls below a certain level.

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[Viennese]

Don't know what you mean sorry?

I will be fully documenting the project(s) and will publish all the software for free.

I meant, would you be willing to install one for someone else... I wouldn't be able to do that!!

 

[Gromett]

I meant, would you be willing to install one for someone else... I wouldn't be able to do that!!

Ahh, probably not sorry. This is just a hobby project for me. I'll have a think about the implications and if practical I may make some additional modules for a few people who want them. However no promises and I won't do it until it has been tested in my van for a decent period of time.

No promises. But if I get it to a stage where I am happy to make a few for other people I am sure you can find someone to install for you? It will just need a fused 12v supply and the fans mounting.

 

[Madcaravanner]

The problem with that for me as previously mentioned is
a) the fan is going full blast.
b) the fan is running all the time.

I am sensitive to fan noises and that would drive me up the wall.

I understand about noise but this one runs quietly and actually only make noise when there is a breeze that pushes air into it
The one I have is similar to this is a brushless motor too

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[magicsurfbus]

I can only guess sorry. My guess would be the gas system generates more heat so the fans have a greater effect?????

I certainly think heat from the burner's flue is conducted into the upper vent space and adds to the heat coming from the cooling fins. I suspect there may even be a sort of feedback effect on very hot days, ie turning up the thermostat creates more flue heat above the fridge, requiring more cooling and so on, but it's only a theory.

 

[TheBig1]

o you know if fan efficiency is influenced by the cooling method, ie 230v versus gas?

the fans are pulling air into the bottom vent, passing it over the heat exchanger and expelling from the top vents. in doing this, it increases the oxygen available to the flame

 

[bubble63]

Hi gromit

I' m totally with you on the concept,

My hi-fi amp fan only runs when it's plays loud/deep notes, when the music is quiet, it's quiet. It revs up in time with the output!

Will you be 'potting' the finished item

Neil

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[jansellsbond]

Just a thought! I fitted two of these behind my top vent blowing out. Almost no power drain and silent at low temp but ramps up to a healthy airflow when the going gets hot. Data on power consumption is included in the description.
http://www.ebay.co.uk/itm/Arctic-F1...9b374b2&pid=100008&rk=2&rkt=5&sd=182288768003
Ignore one of the 3 power connectors, drop the thermostat lead down in the gubbins somewhere and Robert is your father's brother. I pulled a 12v down from one of the fag lighter sockets and they are powered all the time the 12v is on but a simple switch would be easy to include.

 

[Birtha]

You could put some sort of heat exchanger on the condensing side of the fridge and cool it with water which would be silent, u could then use that hot water or dump it

 

[Gromett]

Will you be 'potting' the finished item

I haven't thought that far ahead to be honest. Probably not, A heatshrink sleeve would probably suffice if not then a small box. This is not a project intended for mass production.

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[Gromett]

Just a thought! I fitted two of these behind my top vent blowing out. Almost no power drain and silent at low temp but ramps up to a healthy airflow when the going gets hot. Data on power consumption is included in the description.
http://www.ebay.co.uk/itm/Arctic-F12-TC-120mm-PC-Case-Cooling-Fan-Temperature-Controlled-Silent-Quiet/182257356550?_trksid=p2047675.c100008.m2219&_trkparms=aid=444000&algo=SOI.DEFAULT&ao=1&asc=39060&meid=4bb7b834cdd94a64806f87bf39b374b2&pid=100008&rk=2&rkt=5&sd=182288768003
Ignore one of the 3 power connectors, drop the thermostat lead down in the gubbins somewhere and Robert is your father's brother. I pulled a 12v down from one of the fag lighter sockets and they are powered all the time the 12v is on but a simple switch would be easy to include.

This is one of the ones I considered. There are 2 problems with this. It has a fixed temperature range. So if you visit a hot country it will be going all the time even if there is no temperature differential between the bottom and top vents. I don't want to include a switch as that involves manual work. I wanted mine to be fully automatic and work at all times at the minimum possible speed to achieve the result.

 

[Gromett]

You could put some sort of heat exchanger on the condensing side of the fridge and cool it with water which would be silent, u could then use that hot water or dump it

Too complicated

 

[Birtha]

Fair enough, why not monitor the temp coming out of the condenser, when ambient temp rises and the condensor overheats the sensing probe will bring your fan in or you can get discarge sensors for scroll compresor which make on temp rise, which would act as a controll for the fan.

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[Gromett]

Fair enough, why not monitor the temp coming out of the condenser, when ambient temp rises and the condensor overheats the sensing probe will bring your fan in or you can get discarge sensors for scroll compresor which make on temp rise, which would act as a controll for the fan.

Because the output of the compressor is always going to be hot irrespective of the ambient temp and airflow through the cavity behind the fridge. The only thing that matters in the space behind a fridge with respect to cooling is the temperature gradient between the top vent and the bottom vent. Measuring the differential between the top vent and the bottom vent is the only way and the simplest way to decide if a fan should be on or not, and if on how fast it needs to turn in my.

Also, I want this system to be extremely simple to fit, take account of ambient temp, not operate when ambient falls below a set level plus much more.

 

[Birtha]

On the output of the condenser not the compressor, when ambient temp rises and the gas does not condense in the condenser thats when the output temp of the condensor rises and the fridge struggles, if u use a bi metalic strip type sensor it acts as a switch and can control the fan, it cant get any simpler, i will find u a link to the sensors

 

[Gromett]

On the output of the condenser not the compressor, when ambient temp rises and the gas does not condense in the condenser thats when the output temp of the condensor rises and the fridge struggles, if u use a bi metalic strip type sensor it acts as a switch and can control the fan, it cant get any simpler, i will find u a link to the sensors

bi metalic strips are not sensors they are a temperature operated on/off switch. So basically the fan would be running at 100% or be off. That is one of the main things I wanted to avoid. Secondly it still doesn't take into account ambient temperature. A bi metallic switch operates at a fixed temperature. So if I buy one that switches on at 25C then go to a country that has 40C temperatures it would switch the fans on full speed ALL the time even if there was no differential between the top and bottom vents. If I buy one that works at 35C then I would lose out on the fans efficiency gains at home.

I have thought about this quite a bit, and the only way to ensure the fans run at the slowest speed to maximise effect is to measure top and bottom vent temperature differentials. The absolute temperature of any part of the fridge is irrelevant to how fast you need to spin the fans.

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[Birtha]

The only way we have been able to control the head pressure during high ambient temps on commercial refrigeration is to add an adiabatic cooling system to the condenser, it is the same for all refrigeration designed for uk spec. When the ambient rises above say 30degrees the gas wont condense back to a liquid in the condenser and you will loose the refrigeration effect, no matter how much air u pass over the condenser it will not condense the gas to liquid.

Your system will work to an extent but during normal temps watch out you dont over condense which can result in the refrigerant not flowing around the system.

Ok Gromet good luck with your project.

If you change you mind have a look into head pressure control for refrigeration systems.

 

[Gromett]

The only way we have been able to control the head pressure during high ambient temps on commercial refrigeration is to add an adiabatic cooling system to the condenser, it is the same for all refrigeration designed for uk spec. When the ambient rises above say 30degrees the gas wont condense back to a liquid in the condenser and you will loose the refrigeration effect, no matter how much air u pass over the condenser it will not condense the gas to liquid.

Your system will work to an extent but during normal temps watch out you dont over condense which can result in the refrigerant not flowing around the system.

Ok Gromet good luck with your project.

If you change you mind have a look into head pressure control for refrigeration systems.

I am not trying to improve a fridge system or fix a specific problem with the fridge itself.

It has been proven many times that in the motorhome settings the vents don't allow the optimum airflow over the cooling fins at the back of a fridge. A simple set of PC fans improves things dramatically. This has been tested by many people on here and it is a valid and workable solution to the issue. The problem I am trying to fix is when to switch the fans on, and how fast to spin them. For me personally the sound of a fan going irritates the hell out of me. So I want the fans to be spun up at the lowest speed necessary to have the desired effect and for them to be off when they are not needed. I want this to be totally automatic. For the cost of less than £4 I am able to do this using my basic electronics and programming knowledge.

I am not disputing that in a commercial setting fitting an adiabatic cooling system is a worth while investment in time, effort and money. For a motorhome it is just isn't practical nor is it necessary or cost effective in my opinion.

 

[Gromett]

Just got back from collecting my deliveries. Quite a lot of parts. I am just going to get my head down now for a bit of sleep. When I get up I will be unboxing/unbagging stuff and starting to inspect.

Looks like not all of the parts have arrived yet. I think mainly it is the BangGood stuff that hasn't arrived but it is a long way from China. I will be driving back over on wed/thu to see if the rest has arrived. I was really hoping to started tomorrow

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[Gromett]

Quite a bit arrived. I ordered for 3 development models. Unfortunately there is at least 1 part from each model missing.. Typical. I can't get on until some more parts arrive.

 

[wizzer59]

Some of us can't read or understand anything without Pics Gromitt

 

[Gromett]

Some of us can't read or understand anything without Pics Gromitt

ok. I will post pics in a bit

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[Gromett]

The bags at the top are full of resistors.
The white bit on the left is a prototyping board. It has spring clips in each hole and connections between them in each column. I can push components into this board to hold and connect them to each other to form a circuit. If I make a mistake or want to change out a component I just pull it out and refit. I will be using this to create a programmer for the ATTiny85 microcontrollers.

To the right of the prototyping board is a full computer/microcontroller on a chip. I will be using this during the testing of the code for the ATTiny85. Using this I can upload the program I write to the little chip on the left of the board and run it.

To the right of this is 5 TIP-120 power transistors. I ordered these to run the PWM speed controller for the fan. However I decided against these as they are nasty current hogs and will get hot. I have ordered some power mosfets instead but these haven't arrived yet.

On the bottom left is a 20 x 4 LCD display. It can display 20 characters across by 4 rows high. I will be using this to display the input temperatures, fan speed and various debugging information during development. It won't be part of the final package.

On the right is a Microcontroller development board. I will be using this during the initial development of the code. The ATTiny doesn't have enough Interface ports on it to allow for diagnostic display to be added.

The process I will be following is.
1) Create the circuit using the Prototyping board and test using the Uno.
2) Write the control software with outputs going to the display.
3) Once it is all working, test it using the USB ATTiny85 USB microcontroller.
4) Once I have confirmed this is working. Create a final circuit board and program a standalone ATTiny85.

I am missing a USB cable for step one. I am missing the temp sensors and mosfet for testing on the ATTiny85, and I am missing the standalone ATTiny85 for the final circuit.

Also just noticed I am missing the Diodes and the Capacitors as well.

 

[Gromett]

For those who understand electronics. I chose the TIP-120 because I was familiar with them from 25 years ago when I last did electronics. Back then I used Mosfets but they were very expensive and not readily available for use in power circuits. I used them mainly in high frequency low power circuits. However things have moved on since then so when I saw that power mostfets were only a few pennies more than power transistors and the specs were that good I had to swap over.

For those not into electronics.
Transistors are current operated. They are like a switch whereby the more current you put into the base of it the more current flows through the main part. The ratio between input and output varies depending on what transistor you use.

Mosfets are voltage operated. I have found some that work fully on 5V and dissipate next to no power themselves when full switched on. Much better.

 

[tonyidle]

For those who understand electronics. I chose the TIP-120 because I was familiar with them from 25 years ago when I last did electronics. Back then I used Mosfets but they were very expensive and not readily available for use in power circuits. I used them mainly in high frequency low power circuits. However things have moved on since then so when I saw that power mostfets were only a few pennies more than power transistors and the specs were that good I had to swap over.

I think the makers of inverters and small PSUs have noticed too .

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