reflow (toaster) oven now earning its keep

I've been working on a reflow oven (and hijacking other people's threads to boot) so now decided to have my very own bragging thread

started with a 1 kW 9litre toaster oven 4 heating elements; 2 top 2 bottom

I added a K type thermocouple (actually took a couple of goes as the ifrst one melted!) I took it apart, cut off the smouldering ends, joined the new ends together used heat resistant (fibre glass?) insulation this time

disconnected all the oven control gear and wired it via a triac triac controlled by 'duino of course

software attempts to match the profile for reflow ovens

anyway - time for some pictures

here's the triac driver board it's inside the oven to keep mains voltage well away from small children and idiots (er and me :) )

2nd picture shows the much reduced internal wiring

3rd picture shows the first board "wot I made" it's a micro 'duino

once Nick Gammon helped me with the bootloader - it worked!

4th picture is part of a range of camera kit we're selling all the SMD parts sorted in < 10 minutes!

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finally last picture shows the sort of profile I'm aiming for, and achieving

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mmcp42: (actually took a couple of goes as the ifrst one melted!)

Poetic justice, eh?

Congrats. Triacs are something I haven't fooled with yet, sounds like fun.

[quote author=Nick Gammon link=topic=148358.msg1114666#msg1114666 date=1360618435]

mmcp42: (actually took a couple of goes as the ifrst one melted!)

Poetic justice, eh?

Congrats. Triacs are something I haven't fooled with yet, sounds like fun. [/quote]

indeed!

triacs seem to be dead easy I'm using a zero-crossing opto-isolator to drive it

all seems to work just fine :)

here's the final circuit (went through several iterations to get there - as you do!)

and here's the triac heater control

I've allowed for a fan to help the cooling down phase

if anyone is interested I'll post the sketch as well :)

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mmcp42: if anyone is interested I'll post the sketch as well :)

I'm interested. Does the opto isolator do everything (switching on the zero crossing) or does the sketch have to do that?

seems the zero-crossing bit does all that
you just send a logic high to the input side and magic does the rest :slight_smile:

sketch here…

if there’s any bit that needs explanation …

ReflowOven.zip (10.3 KB)

Looks pretty neat, thanks. :)

RE: profile.jpg

Are you using PID to control the temperature?

Have you considered adding a servo connected to the oven door to speed up the cool-down cycle? How about a fan?

Nice work mmcp42 - I'll get mine assembled one of these months :)

[quote author=Coding Badly link=topic=148358.msg1114872#msg1114872 date=1360626827]

RE: profile.jpg

Are you using PID to control the temperature?

Have you considered adding a servo connected to the oven door to speed up the cool-down cycle? How about a fan?

[/quote] not using a PID, yet need to get the temperature ramping fast enough at the moment there's nothing to control!

and yes, I have seriously considered a servo to open the door also a fan watch this space...

@CrossRoads cheers - and thanks for the initial inspiration :)

Thanks, but I am just following in the footsteps of many others here.

that's what I like about this forum so many generous people leaving footprints for lesser mortals to follow :)

shiny new temperature probe arrived today :) doesn't work :(

took it to pieces (what else! :) )

found the problem

the two wires are insulated with what looks like glass insulation then slipped inside a stainless steel "knitted" (thank you Mrs Noah) outer jacket

trouble is at the business end the trimming was awful with strands of wire touching the probe and shorting it out intermittently

so - trimmed it back - much easier said than done stainless steel is tough! wrapped the end of the metal in heat shrink - just to hold it while I re-assembled

temperature readings now rock steady :)

but :(

as the probe is inside a metal sleeve, there does seem to be some inertia in the measurement now the graph below shows the problem - (apparent) delay in getting started - overshoot at the intermediate temperature points

a naked thermocouple is much more responsive (see the original curve posted earlier)

I may well add PID processing - which should stop the overshoot next decision after that's all working

oh and for amusement here's a picture of the first probe not completely heat proof methinks!

added link to probe

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mmcp42: as the probe is inside a metal sleeve, there does seem to be some inertia in the measurement now

"Dead-time" in PID jargon.

I may well add PID processing - which should stop the overshoot

Not necessarily. There is a conflict between getting the response you want, the dead-time, and overshoot. If possible, you should first strive to reduce the dead-time as much as possible. That will make working with PID much much easier.

That stinks. Guess I'll stick with bare probe when I get around to assembling.

[quote author=Coding Badly link=topic=148358.msg1118019#msg1118019 date=1360790198]

mmcp42: as the probe is inside a metal sleeve, there does seem to be some inertia in the measurement now

"Dead-time" in PID jargon. [/quote] I knew that :coughs: !!

I may well add PID processing - which should stop the overshoot

Not necessarily. There is a conflict between getting the response you want, the dead-time, and overshoot. If possible, you should first strive to reduce the dead-time as much as possible. That will make working with PID much much easier.

indeed I'm looking at removing the end of the metal sleeve that way the thermocouple will be nicely inside the oven but still in free air (aka dangling!)

Probably breaks the budget but could you use a non contact sensor like this pointed at the PCB?

Riva: Probably breaks the budget but could you use a non contact sensor like this pointed at the PCB?

good thought a) cost exceeds £$€ spent so far! b) will it work through the glass door? c) actually measuring PCB temp would be really neat! still good thought though :)

Have been trawling eBay and found this that may hack to your needs.