{"id":345,"date":"2010-09-20T07:44:59","date_gmt":"2010-09-20T07:44:59","guid":{"rendered":"http:\/\/baulkolites.com\/wp\/?p=345"},"modified":"2010-09-20T07:44:59","modified_gmt":"2010-09-20T07:44:59","slug":"tot-reflow-oven","status":"publish","type":"post","link":"http:\/\/mynoellights.com\/blog\/?p=345","title":{"rendered":"TOT – Reflow Oven"},"content":{"rendered":"

I have a small 7litre oven that works a treat for Reflow of small boards.<\/p>\n

I recently upgraded to a 20 litre oven with two element top and bottom.\u00a0 Rated at 1500Watts, there is able power to heat the area.<\/p>\n

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Front Shot of 20litre Oven<\/p><\/div>\n

Having run the oven a couple of times manually I have concluded the following:<\/p>\n

    \n
  1. The Temperature setting is a waste of time.\u00a0 it appears to be a simple bi metal switch and not a thermostat.<\/li>\n
  2. The top needs some form of Insulation as the top lid gets really really hot.<\/em><\/li>\n
  3. The Rack inside the oven is not attached to the door – bonus as far\u00a0 as I am concerned.<\/li>\n
  4. I need to come up with some form of automated venting to cool the boards down.<\/li>\n
  5. I may<\/em> be able to fit another shelf and increase the throughput ( I am looking for some AL material with a 5mm grid of 5mm holes).<\/li>\n<\/ol>\n
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    Simple Layout<\/p><\/div>\n

    An interesting note: the top elements are connected in series, as are the bottom elements. This is quite nifty as there is no need for a neutral return.<\/p>\n

    For now I will leave the oven as is that start the Controller.<\/span><\/strong> <\/em><\/h3>\n

    I have been playing around with the Arduino IDE with the intention of teaching my girls Control theory.\u00a0 I have decided I would use this environment to develop the Oven Controller.<\/p>\n

    Maxim make a brilliant, if not slightly pricey Type K thermocouple digitises.\u00a0 it uses the SPI interface.\u00a0 ryanjmclaughlin has created an Arduino Library<\/a> for the MAX6675.\u00a0\u00a0 <\/a><\/p>\n

    Brett (aka br3ttb<\/strong><\/a>) had created a PID Library<\/a> – Some may say all the fun has gone.\u00a0 Well maybe, but I still get to pull their work together and make my oven how I want it.\u00a0 I will be adding an LCD to give feedback on where you are in the cycle. Graphic would be super – otherwise 2×16 will be OK.<\/p>\n

    Update 1<\/em><\/span><\/strong><\/h3>\n
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    Thermocouple Nut<\/p><\/div>\n

    Found an old thermocouple from a previous Jaycar project.\u00a0\u00a0 The Type-K thermocouple is constructed with a 3.2mm Diameter Stainless Steel barrel and is an exact match for the MAX6675 for testing.\u00a0 I am not sure if this will be the final one I will use but for now it will suffice.When I was in the workshop, I realised how easy it would be to make a mounting nut for the thermocouple.\u00a0 Starting with a 3\/8W bolt, I drilled a 3.2mm hole through the middle.\u00a0 I then drill a pilot hole in one the bolt head flats and tapped it with ISO M3.<\/p>\n

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    Thermocouple with Nut installed<\/p><\/div>\n

    The MAX6675 performs cold-junction compensation\u00a0 and digitizes the signal from a type-K thermocouple.\u00a0Direct
    \nThe data is output in a 12-bit resolution, SPI\u2122-compatible, read-only format.
    \nThis converter resolves temperatures to 0.25\u00b0C, allows readings as high as +1024\u00b0C, and exhibits thermocouple accuracy of 8LSBs for temperatures ranging from 0\u00b0C to +700\u00b0C.<\/p>\n