DAVIS RAIN BUCKET HEATER

image of two 10 ohm resistors

All but the power supply was what I had in my junk box "A" is a bit of printed circuit board (PCB) that I heated up peeled off the copper sheet, the reson for doing that, is so the heat would not get transfered to the base plate of the rain gauge.The size is not important but my PCB size was 55mmx80mmx2mm. "B" is piece of aluminum sheet cut to 75mmx40mmx3mm, the screw size is m3. "C" are 50watt 10 ohm metel clad resistors (RS part number 158-339) but any metal 50watt 10ohm ones will do, they can be got from Ebay/RS/farnell/Maplin etc. "D" these heat sinks came from an old PC power supply, I found that I needed these to stop the ally plate "B" getting to hot. It was one long one to in haft, & it allows the heat to dissipate away from the ally plate "B" around the rain gauge funnel. Heat sinks can be got from old power supplys/TV's etc. or from RS/maplins/farnell/rapid electronics Ebay etc. also see Fig 1 at the bottom of page.

image of heat sink grease

"E" Between the resistor & the heat sink is some heat sink grease , (thats the white stuff) this helps to transfer the heat, agian this can got from Ebay/maplins etc.

image of nut spacers

image of two 10 ohm resistors

These fixing holes where already there in the base.

image of fixin‌g holes

image of resistors fitted

image of thermostat sensor

image of resistors fitted

image of resistors fitted

image of resistors fitted

image of insulation for funnel

image of insulation for funnel

In the last two pictures the insulation for the inside of the rain bucket, all this is, is the insulation that you can buy to fit on the wall behined a Central heating radators in the house.

image of control box

image of control box

In the control panel (I must really tidy this up a bit it looks a mess)there is a thermosat card that came with a sensor probe "F" that came from Ebay here, a 24vdc power supply, a relay, & a voltage dropper 24vdc to 12vdc. The PC power supply came from A friend for £5.00, the voltage dropper is needed because the thermostat works on 12vdc, the relay is needed because the relay that came with the thermostat could not handle ampage. Using this set up 24vdc & two 10ohm resistors in series (wired end to end or in line) gives you about 28watts of heat (the davis one is 24watts), your power supply it must be a 24vdc stabilized one & have a output of at least 1.5amps (1500mA) or more. You can use a 12vdc supply if you have one, & this must be a 12vdc stabilized one as well & have output of at least 3amps (3000mA) or more, the resistors will have to be changed to two 2.7ohm resistors in series, plesae see the wiring diagram below.

image of wiring diagram

image of heat sink

The link to the thermostat shows that the relay on the card can handle 10amps at 12 volt, so it should be ok 24vdc thats the relay not the thermostat card as for the 24v to 12v dropper it came from Ebay a long time ago, try searching for voltage step down buck converter, but it must have a out put of at least 1.5 amps(1500mA).I set my thermostat to turn on At 4c & turn off at 12c, Well I hope all this maks sense, if not please contact me & I try & help you out.

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