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Author Topic: Reflow oven (aka Toaster oven) modification  (Read 3020 times)
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I'd like to add an exhaust fan to my brand new toaster oven.
I can make it follow the preheat/soak and solder profile, but cooling down is taking a long time even with the door open.
Thinking of boring a hole at the back? and adding an exhaust fan.
Anybody done anything similar? Any tips?

2nd... I'd like to add a lamp inside. It's too dark to see anything.
Any recommendation? what lamp/socket can withstand the high temps inside the toaster oven? Probably a DC lamp will be safer than an AC lamp?


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Lurking.  Seems like lighting and cooling are going to be technical challenges given the temperature inside there.  I already scored an oven at Value Village Electronics Emporium for this purpose.
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Ok, I have this reflow soldering working very well... First I tried just (1) board, success.
Then on my 2nd attempt, I tried 4 boards at the same time. Everything worked.
This is better than I expected! 

I was planning on buying a real reflow oven and this toaster oven is just to tide me over, but I think I'm going to stay with the toaster oven.

My settings/workflow:

I set all my boards on a tray (that came with the oven). Then I hook up a temp probe from my Fluke meter.

1. Set oven to "PIZZA" setting and 450C.
2. Set Timer to 10 min. (no worries, it's not really going to stay in the oven for 10 min.)
3. Preheat toaster oven until 100C. (takes about 1:00 minute).
4. Open door, insert tray (containing all the populated PC boards).
5. Temp in oven will rise to 200C. (takes about 2:00 minutes)
6. Turn OFF power to oven.
7. Temp will continue to rise even with power OFF... around 210C or so, everything will start reflowing. This happens pretty quickly.
8. wait for it... Let it reflow some more, when temps reach around 240C, open oven door, and take the whole tray out. (be careful, hot and don't bump the tray into anything)
9. Set tray on top of oven gently. Temp will be now in the 245/250C range.
10. Get a piece of cardboard, and fan it manually.... or point an electric fan to it. Temps will rapidly go down proportionally to how much you're fanning it.

SIMPLE PLANNED MOD:
I'm thinking cutting out a square hole opening in the back of the oven.
Then using a .125" aluminum sheet, bolt it to the back of the oven.
On the aluminum sheet, there'll be a cutout for a 120VAC 4" fan (Radio Shack sells them, steel frame, not plastic like computer case fans)
I'll use this for EXHAUST, and just flip a switch to activate it.

If I can find a suitable lamp and socket for this, the lamp can also be mounted on the .125" aluminum sheet.

Next step... just write a simple Arduino program (just relying on timer() to time when to turn OFF oven and turn ON exhaust fan. No need for PID and all that complexity.  smiley
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If using a fan make sure its not too powerful - don't want to blow components off the board while the solder's
still molten(!).  I think I would use a blower pointing inwards to prevent the fan blades melting from the hot air, and
have the exhaust port just a metal grille.  To prevent leakage of hot air during operation I'd suggest mounting the fan
and the exhaust port on the underside (and add some legs!).    Or skip the exhaust port and just open the door.

Just my thoughts.

With my toaster oven I've moved the heating element that was underneath to the top so there are two at the
top now.   I open the door and _carefully_ slide the shelf forward to get more cool air on the board(s) - it seems
to work but I'd rather not risk disturbing the board of course.
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I just open the door once the temp drops below the reflow temp. Don't want cold solder joints from cooling too fast.
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If using a fan make sure its not too powerful - don't want to blow components off the board while the solder's
still molten(!).  I think I would use a blower pointing inwards to prevent the fan blades melting from the hot air, and
have the exhaust port just a metal grille.  To prevent leakage of hot air during operation I'd suggest mounting the fan
and the exhaust port on the underside (and add some legs!).    Or skip the exhaust port and just open the door.

Just my thoughts.

With my toaster oven I've moved the heating element that was underneath to the top so there are two at the
top now.   I open the door and _carefully_ slide the shelf forward to get more cool air on the board(s) - it seems
to work but I'd rather not risk disturbing the board of course.

Mark, thanks for the ideas.  Never occurred to me about moving the bottom heating element to the top. The oven I bought have (2) at bottom, and (2) at the top. I don't know if (4) on top may be overkill.

Re: fan blowing inwards, and just manually opening the door.. simple. I was just thinking down the road if I want to automate the exhaust fan turning on automatically, without the need to open the oven door. I saw a Youtube video of an elaborate setup with vents opening/closing/etc...

@Crossroads: I did try opening the oven door but I think the drop in temp is too slow/very slow.
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I found 120VAC fans with aluminum frame AND steel blades... so no danger of melting.
http://www.mcmaster.com/#standard-equipment-cooling-fans/=leleor



and stainless steel fan guards
http://www.mcmaster.com/#equipment-cooling-fan-accessories/=lelhb9
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Remember, there's stuff under the motor hub too, and it won't all be stainless steel.  I second the idea to use the fan to bring in cool air and let it exhaust somewhere else.  Even then the fan might get too hot, but who knows?
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I like the idea of moving the bottom heaters to the top - duly noted and added to list smiley

I was wondering about a fan as well
but concerned that blasting the fan with hot air at around 250 degrees might make it a very short-lived fan

so wondered about blowing air in rather than sucking it out
still need to make sure the fixing does get too hot else the fan will still melt and slide off the oven smiley

perhaps fit the fan in the bottom
with both heaters (now) in the top the fan will be a long way from the heat source

for lighting you might consider white LEDs
again mounted in the base to be as far from heat as possible

either that or cut a window in the back and shine the light through that
mounting the window will be fun
« Last Edit: February 10, 2013, 07:56:45 am by mmcp42 » Logged

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I use a bright torch to watch through the window - its a 12W LED in fact!  Intense point source lighting helps bring out
the shiny beads of solder as they melt.  Of course an LED isn't compatible with high temperature, but a small 12V halogen bulb
would be, there are holders for them with glass-fibre insulated wires too.

Some pictures of the conversion to top-side elements are in posting #44 here: http://forums.parallax.com/showthread.php/130196-How-I-do-SMT-soldering-in-toaster-oven/page3?highlight=toaster%20oven
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I have tried just putting a fan in front of the oven to help the entire structure cool down faster.

Becareful with when you open the door or any other rapid cool-down method.  Components, especially ceramic caps, are very sensitive to CTE mismatches.  You need to make sure you are not cooling down too quickly.

I've watched as people open an oven door right after reflow occurs.  That's a recipe for intermittent issues.
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Great ideas y'all. Keep em coming.

Quote
Of course an LED isn't compatible with high temperature, but a small 12V halogen bulb
would be, there are holders for them with glass-fibre insulated wires too.
I was just at the hardware store the other day looking at these MR16 lamps... I know they get real hot, so putting them inside the oven is probably no big deal for these bulbs.

I'm thinking mount these MR16 lamps behind the oven (beside the exhaust fan), and then have some L-shaped aluminum in front of the lamp so I'm not staring directly in to the bulb... it will be diffused lighting inside the oven. I can probably run these bulbs using a 5V adapter so the intensity isn't too much (or build an adjustable voltage regulator with a pot.)



* oven.jpg (39.91 KB, 527x333 - viewed 32 times.)
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Why not just use fan thats on the oven. With the right timing it should work fine just figure when to turn off the heat but leave the fan on
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I wish it were that easy. The built-in fan only turns on when heat is also on. There is no separate switch for it.
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It's much easier to modify an oven with a built in fan than to try and add one on.
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