• PicŪ Basic


  • Easy Hot Plate

    This is how you can make an easy Hot Plate. Put the soldering iron away, it is way too big for those little pins and besides, you shake like an old women :-))

    You are going to need a TC temperature control, here is an easy to build one.

    http://wiki.picbasic.org/index.php?n...eratureControl

    To make a hot plate you will need a piece of aluminium, an offcut from retailers will do and you should get it at a bit of a discount price too. The size is up to you, A1 paper size is a bit much, but I suggest you source the element first.



    Spiral stove elements can be bought loose. Their top surfaces are flat where the pot sits on it, and this is desirable. This flatness will give good thermal conductivity between the plate and the element. I also suggest you get a low wattage element, 500W will be perfect, although a 1000W will do. The difference is the power consumption and the rate at which the plate will heat up. Don't go to 2000W, it's ridiculous, even if your plate is going to be bigger than your buddy's. 500W is good.

    The element won't work very hard at 180 to 200 degrees, expect it to live to close to forever.




    Once you have the element, you can get the size plate that will cover it. The plate should be no thinner than 8mm, 10mm would be even better.



    I couldn't find a spiral element, instead I used one of our solder pot elements for illustration. A spiral element would only be round. I went to a shop to take the two pictures you see above.

    Place the element in the centre of the plate and mark evenly spaced holes that would clamp the element to the plate. The holes should be so that if the element swells out it should be contained in place. In the picture above, it would work if I bend the washer's lips down both sides to contain the element. The idea is to maintain good thermal connection between the element and the plate.

    Drill the holes to almost through the plate. This is a blind hole and you have to tap thread in it. You can drill right through, the PCB's won't mind, but it looks much neater if the top surface is without holes. 4, 5 or 6mm should be good for this, but check out the size penny washers that is available, they should protrude beyond the element.

    The ends of an element is 'dead' and there is only a conductor in it, so the ends doesn't get as hot as the center would.

    Some elements cannot be bent, the spiral ones cannot, it will break if you try. If you are going to use an element like the one in the picture then the manufacturer should indicate the minimum bend radius for that element's diameter. The heater wire is in the centre of the outer housing, the gap in between is powder filled. This can get damaged if the bend is made too sharp and it could then make a short that will trip the earth leakage.

    Easiest is going to get the spiral element, washers large enough to extend over the element and you can bend those ends down, screw the element in place and it will be fine.



    The thermocouple should be screwed in place in the plate, but tight against the element. This will heat the thermocouple up quickly and the element won't get red hot while the plate is still cold. The plate may heat up a bit slower but nothing extreme would happen.

    You are going to have to mount the hot plate. This is done easiest by drilling another four blind holes in the plate's corners, this time to get long screws of threaded rod in there. The threaded rod space the plate up, so leave this untill the box is done.



    Wood would be the easiest to use as an enclosure, and no, it won't catch fire. Just leave a gap between the plate and the wood. The hardboard on the right is to have a rest for your hand if you need to rework a component. The box should have a bottom, four sides and the hardboard on top.

    You can now measure the length the long screws or threaded rod pieces should space the plate up.

    There are five (5) wires that should go from the hot plate to the control PCB. They are protection earth, the two thermocouple signal wires (and RED is NEGATIVE), and the two mains wires that gets switched by the triac.

    You should use silicone wire from the element to the control box, just precaution in case you get more heat on the wires you anticipated. The 5 wires can be sleeved in silicone sleeving. The control box can be desk mount or wall mount. Cabtire feeds 230V supply (US 110V) to the control box.

    Make sure you have a good earth from the supply plug to the plate surface.

    If you place a populated PCB on the plate, allow about 15 seconds to lapse before the solder begins to melt. A thin 0.2mm PCB should not burn brown if it lies on the plate for a few minutes.

    You can get more info on this here -

    http://www.faze.co.za/Hot%20Plate.html

    Don't burn yourself when you solder. It hurts ;-)

    Compliments Fanie
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