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Thermostatically Controlled Cool Box


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This was one of the jobs on my to do list that i thought i would share with you.

Price of thermostatically controlling the Cool Box so that it doesn't run 24-7 = £5.58

Price of having Cold Beer on the Boat = Priceless

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Hi Jonathan,

You can buy the The Velleman Thermostat Kit from Rapid Electronics Pt. No. 70-4048

Wire up the Relay so that it is Normally Closed when not energised.

The relay is rated at 10A, but the Kit says 3A, which i believe is down to the pcb terminals. So i soldered the leads directly to the pcb.

The Thermistor only needed short leads attached in my case due to where i was able to locate the pcb, which was where the mains & 12vdc leads were stored.

This was really handy, as i am easily able to get to the Pot to set up the temperature i require.

I have been testing it out with a thermometer inside and have it set to 6 degrees at the moment, but the temperature i am measuring is at the bottom of the box & the thermistor is located in the lid at the top. Also, as current passes through the thermistor it will create its own heat, all be it very small.

I wouldn't expect the difference from the bottom to the top to be massive, but i will check it just to see.

Anyway, seems to switch itself on and off ok & when i check the temperature at intervals it seems to always be at 6 degrees.

So that will do for me.

If you need any more info, just ask.

Hi Trevor, I might just blob some silicone on the tiny bit of bare wire exposed on the thermistor if i get around to it..............

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That's brill, Grant! :clap:clap:clap

We have a Halfords cool box lying around but stopped using it for probably the same reasons you modified yours:

1. It will freeze the contents if the ambient temp is low!

2. It uses about 5amps which can soon flatten a battery!

Many Thanks from me for the cool beers and Mary-Jane for some fridge space! cheersbar

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Reminds me of a project a colleage of mine built. He was given an old chest freezer. He modified it for brewing and or storage, the project involved installing a heater in the form of a light buld and a thermostat arangement. By means of which he could control the temperature over a huge range from freezing cold to about 20 degrees. cheersbar

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I took the whole lot down to the Hockham Eagle tonight, more in hope than expectation!!!

One of our regulars owns a firm who make test gear for Martin Baker (Ejection Seats).

"How do I do this, Chris?"

"You can tell the polarity by the length of the wires" he said........ you can, it's fixed! :clap:clap:clap

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Sorry about the delay answering your question Mr Hockem.

The Cathode sometimes has a flat side on the Led and where as the Anode does not. Also the Anode always has the longer leg and the Cathode has the shorter leg. If you look at the Pcb, you will see that it shows the the orientation drawn on it, clearly showing the flat side. This is where you insert the short leg (Cathode)

If you have a 2nd hand Led, where the legs have been cut and have no flat side either, then the Anode & Cathode can be identified using a Multimeter on Ohms or Diode range if it has it.

The Led that is supplied with this Kit has no flat side on it, but does have different length legs of the diode.

Regarding making sure that the polarity is correct, Most definately, because if you don't it will get hot & if nothing goes open circuit before it goes bang, then it will produce an Arsenic Gas. (so don't go sniffing it when it pops)

Anyway, hope you are up and running now.

Don't forget to put some cold bottles of water etc in the cool box when testing it to stablise the temperature. otherwise it will switch on & off more often that you would like.

One more thing, I may modify this further by separating the peltier & the fan, but this is something i will do later.

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Inside your Cool Box is the Peltier Cooler, a Fan & a Switch Mode Power Supply.

The Peltier Cooler is a thermoelectric device which basically can heat or cool depending on the polarity of the supply & can also generate a voltage with a temperature change as well. This is how some (not this one) can heat or cool just by reversing the polarity.

The Fan is basically to create the air flow and the Switch Mode Power Supply is to provide the 12vdc via Mains 240vac input.

The Peltier is the part that draws the most current, where as the fan does not, so i may experiment by separating the two & only thermostatically controlling the Peltier alone purely to see if there is anything to be gained. Bearing in mind that the Cool Box is located at the back of my boat, so i don't hear the fan from where we sleep.

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Thanks for that, Grant. I was unaware of exactly how it worked.

Unfortunately, when I connected it all up, the led flashed repeatedly for a few seconds when I reset the potentiometer and then went out... sounds terminal and it doesn't work... where did I go wrong? I discount soldering errors as my hobby is Amateur Radio and I've been wielding an iron for 50 years or more.

What I did do was to turn the potentiometer with a small electrical screwdriver, as I don't have room for the plastic control. Might I have shorted something? Any suggestions welcome, preferably not rude, before I get another kit... :naughty::naughty::naughty:

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If the Led was flahing on & off, then i can only assume that the Relay was doing the same. The Transistor is switching the ground for the relay coil and is controlled via pin 14 of the IC through R3 (10k ohms). It may be worth checking the pins of the IC to make sure that it is locates the correct way around and that all the pins are located in the socket correctly. The pot should be ok, i can't see you causing a problem using a small screwdriver, unless you have physically damaged it, but i would have thought that could be seen. At the end of the day though, it only costs just over 5 quid, so if all is lost, just by another one.

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