reflow (toaster) oven now earning its keep

[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 :)

schematic.jpg|991x759

heater.jpg|900x404

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

profile2.jpg|750x564

DeadProbe.JPG|985x599

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.

I decided to "adjust" the temperature sensor...

stripped it down again the plan was to "simply" saw 1/3" or so off the sealed end, so the thermocouple would hang in the middle of the oven took a hacksaw to it - no effect looks like it's stainless steel

tried a Dremel with one of the little "parting" discs knife through butter!

cleaned the end with the same disc so now have a slightly shorter tube with thermostat out in the open

tried a profile run last night MUCH closer to the first graph (several posts ago) close enough that the dead time seems to have gone away

so next step is to look at stirring PID control into the equation(s)

modified probe and resultant profile shown below

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IMG_0114b.jpg|373x293

profile4.jpg|723x555

ok PID now implemented much nicer looking profile you can see target and actual temp and also the PID control turning the heater on and off :)

I'm also wondering about using some loft insulation to pack the sides of the oven might make the up-ramps faster?

need to get cooldown quicker

time to get out the metal cutting tools and install a fan shaped hole :)

profile5.jpg|588x579

ok took an axe to the oven to day well almost

decided to move the bottom heaters up to the top of itself it didn't make much difference

big bonus is I can now put what they call the crumb tray on the top shelf effectively cutting the heated volume to around a third

by fiddling with the PID parameters I now get this curve (thanks to retrolefty for a steer there!)

so I'll probably stop playing now and get on with the day job (apart from adding a fan in the bottom, which now stays at room temperature :) )

profile8.jpg|595x581