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750 watt grill to SMD reflow "grill"

my take on trying to convert a cheap €15 grill to an smd reflowing apparatus.

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As the description implies, ill be trying to convert an 750 watt grill to an smd reflow "grill"

I've been getting deeper into electronics lately, but i dont have the capability to reflow components/pcb's. So i'm going to try and solve that problem with some engineering and programming. At least i'll be learning something, and i hope my readers will to!

enjoy!

NOTE:

  • This is my first Project that i'll be documenting. So if there are any improvements i can make, please tell me!
  • if there are any grammatical errors, please let me know. i'll be happy to squish them.

  • 1 × 750 watt grill an 750 watt grill (the cheapest i could get)
  • 1 × Arduino mega

  • getting started..

    Ian S02/01/2018 at 15:34 0 comments

    Where do i start?

    So, i decided i needed to start somewhere. I didn't want to buy a reflow oven, because there to expensive for my liking (like €440 here). And i didnt trust the ebay or amazon import type of oven's. So i was willing to try and make this work.

    First i plugged the grill in and verified that it worked.

    I've taken some measurements and this where the things I found worth noting:

    • initially the temperature of the plates rose to around 200C
    • it then fell to around 160-170 C and stayed there
    • there was a temperature difference between the top and bottom plate (around 10 - 20C)

     Then after i've let it cool down i took it apart (of course!).


                                                                                               the case, or what's left of it..
                                                                         The top heating element(with temperature controlled switch)

    After tearing the grill apart I've learned a few things:

    • The grill has his heating elements in series (2x 110-120V 375 watts = 220-240V 750 watts)

    This explains the uneven heating in between the top and bottom grill,

    because the resistance of the heaters is never exactly equal to the other heater (and therefore giving more or less heat).

    In combination with the temperature sensitive switching element that is mounted on one of the two plates. 

    It all results in that 10-20C temperature drift in between the two plates.

    •  If you don't understand ohms law, please i highly discourage you to even think of this, or work with mains voltage.           Mains (230V ac) is more than enough to kill you or someone around you (It won't make you prettier either).
                                                                                    close up of one of two heating elements

    Now what?

    well, i've got  2 options I think I can consider now:

    1.  I can "leave" the heaters in series, hoping that reflowing with the lid closed will limit the amount of temperature difference that can develop in between the heater surfaces.
    2. I can put the heaters in parallel, but because the heaters are rated voor 110-120 V AC i'll need to transform mains (230V) down to 120V. this will require an decent transformer that is capable of handling roughly 6.25 Amps > 6.5A (constant load). on the secondary winding. this will cost some money (like €80-€90). or i'll have to wind/find my own transformer, from an microwave oven transformer or something...

    I think i'll stick with my first option, just because it's easier to do, and is sounds a lot cheaper. And if i find out that series heaters are worthless for something as delicate as SMD reflowing than i'm forced to rethink my options.

    I'll have to get the following things:

    • Temperature sensors (thermocouples).
      •  apparently i'll need three I/O's per thermocouple (if i use a MAX type thermocouple amplifier (it uses SPI)) i was thinking about adding 4-6 thermocouples but that would mean i'll have to use an arduino mega, (Because an arduino uno has only 13 digital io's and i would...
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