Roman Black wrote:
> Wagner Lipnharski wrote:
>
>>>> Other than that, please take a look at the recent webpage I put
>>>> together about Home SMT Baking:
>>>> http://www.ustr.net/smt/index.htm
>
>> http://www.ustr.net/smt/oven.htm
>
>
> Wow! Another great page Wagner. :o) May I provide some
> comments;
> * instead of just twisting the thermistor wires, cut
> the "crimp tubes" off some small crimp lugs (just the
> metal tube bit) and crimp over the twisted wires.
> * NICE little 5 digit LCD display!
> * to mount the control box, use an alloy box, mount
> vertical in front of the knobs on some brass standoffs
> so there is a vert air gap. The control box will stay
> cool and be in a good place.
> * not trying to complain but the 2 element oven type
> you are using is about the worst for varying temp
> zones inside the oven. This is probably a compliment to
> your controller that it still works so well. A 4 bar
> element oven is much better and i've recently seen
> a couple of good *fan-forced* 4 bar ovens for about
> $120 USD, which is better still.
>> o)
> -Roman


Again, thank you for your comments.
Any suggestion is always, unconditionally welcome.

You are quite correct, I tried to make it works in a two elements toaster,
so moving to a 4 elements will be a piece of cake... pun intended?

To tell you the truth, the home made SMT OVEN is not that far to be
produced, and it seems quite easy to do.
I was thinking about the regular larger range coil heater.  It is a 7" in
diameter and probably 600W of consume, it covers and in whole a 5x6 board.
Probably using one on top and one at the bottom, half to one inch away from
the board, would give me faster and precise heat distribution.  The board
will be as a sandwich in middle of those heaters.  A small 7x7" inner
chamber could be built with thermal reflective material (non metalic), then
directly external metalic box.  By this way, the non metalic inner material
will not absorb the thermal IR radiation and will help to speed up the
heating ramp.

Considering the very small heat loss, propably the heating ramp will be
predicted, so, applying certain power for certain time would result in a
certain expected temperature.  I guess two same built ovens like that, will
have almost the same temp heat and cool profile.  So, once you find out the
numbers, probably it will not even need a temperature controller, just a
table of PWM power vs time.  A small door and openning, will also avoid
fast cooling, it means, once the soldering is done, opening the door will
cool it down slowly.  But a different thing can happens, as there will be
no metalic walls, probably it will cool down faster, so, perhaps still with
certain power applied to the heaters with the door open would be the way to
go, to avoid fast cooling and component damage.

I tried to find data for those coil heaters online, home-depot or
something, without success. Probably need to go there and try to find out
more.  I think the great advantage of the coils, are direct and close temp
distribution, better than the straight heat elements of the normal
toasters.

So, as an example, the procedure could be like this:

====================
press go key
Start process

100% power for 10 seconds; preheat to 100F
5% power
beep

open door
Insert board(s)
close door

press go key
100% power for 30 seconds ;
20% power for 210 seconds ; 160F for 4 minutes

100% power for 40 seconds ;
50% power for 80 seconds  ; 320F for 2 minutes

100% power for 40 seconds ;
80% power for 40 seconds  ; 450F for 90 seconds

beep

open door

20% power for 60 seconds
10% power for 30 seconds
0% power for 30 seconds

beep

remove boards.
==================


As a more high-tech solution, a simply DC motor could be used to open/close
the door, what will automate the cooling process, and make it nice.

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