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Community => Exhibition / Gallery => Topic started by: mmcp42 on Feb 11, 2013, 10:25 pm

Title: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 11, 2013, 10:25 pm
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!


Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 11, 2013, 10:26 pm
finally last picture shows the sort of profile I'm aiming for, and achieving
Title: Re: reflow (toaster) oven now earning its keep
Post by: nickgammon on Feb 11, 2013, 10:33 pm

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


Poetic justice, eh? <grin>

Congrats. Triacs are something I haven't fooled with yet, sounds like fun.
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 11, 2013, 10:35 pm


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


Poetic justice, eh? <grin>

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


indeed!

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

all seems to work just fine :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 11, 2013, 10:40 pm
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 :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: nickgammon on Feb 11, 2013, 10:52 pm

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?
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 11, 2013, 11:01 pm
seems the zero-crossing bit does all that
you just send a logic high to the input side and magic does the rest :)

sketch here...

if there's any bit that needs explanation ...
Title: Re: reflow (toaster) oven now earning its keep
Post by: nickgammon on Feb 11, 2013, 11:09 pm
Looks pretty neat, thanks. :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: Coding Badly on Feb 12, 2013, 12:53 am

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?
Title: Re: reflow (toaster) oven now earning its keep
Post by: CrossRoads on Feb 12, 2013, 01:00 am
Nice work mmcp42 - I'll get mine assembled one of these months :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 12, 2013, 09:48 am


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?


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 :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: CrossRoads on Feb 13, 2013, 04:54 am
Thanks, but I am just following in the footsteps of many others here.
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 13, 2013, 10:04 am
that's what I like about this forum
so many generous people leaving footprints for lesser mortals to follow :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 13, 2013, 09:41 pm
shiny new temperature probe (http://www.ebay.co.uk/itm/160947386705?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2648) 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
Title: Re: reflow (toaster) oven now earning its keep
Post by: Coding Badly on Feb 13, 2013, 10:16 pm
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 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.
Title: Re: reflow (toaster) oven now earning its keep
Post by: CrossRoads on Feb 13, 2013, 10:19 pm
That stinks. Guess I'll stick with bare probe when I get around to assembling.
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 13, 2013, 10:21 pm

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 knew that :coughs: !!

Quote
Quote
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!)
Title: Re: reflow (toaster) oven now earning its keep
Post by: Riva on Feb 14, 2013, 10:00 am
Probably breaks the budget but could you use a non contact sensor like this (http://www.robotshop.com/phidget-usb-ir-temperature-sensor.html) pointed at the PCB?
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 14, 2013, 10:52 am

Probably breaks the budget but could you use a non contact sensor like this (http://www.robotshop.com/phidget-usb-ir-temperature-sensor.html) 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 :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: Riva on Feb 14, 2013, 12:56 pm
Have been trawling eBay and found this (http://www.ebay.co.uk/itm/Quality-LCD-Infrared-Digital-IR-Laser-Thermometer-Temperature-Sensor-C-F-/121063822562?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item1c2ff754e2) that may hack to your needs.
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 15, 2013, 02:10 pm
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

Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 15, 2013, 07:45 pm
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 :)
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 17, 2013, 10:30 pm
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 :) )
Title: Re: reflow (toaster) oven now earning its keep
Post by: CrossRoads on Feb 17, 2013, 10:35 pm
I thought your other curve followed your desired profile better.
Am guessing its not all that critical if it can be controlled by hand just rotating a temperature control knob and a thermocouple stuck it the tines of a fork to hold in place near the card being reflowed ...
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Feb 19, 2013, 03:26 pm
further update on the probe that I had to fix
before leaving eBay feedback I emailed the vendor
very responsive - bottom line got £1.00 refund
I'm happy - the probe works and it (now) only cost me £1.52
the fix was dead easy
here's a picture of the problem/fix

the red circle shows the stainless steel outer after I cut it back
the blue circle is where the outer stopped originally
with the frayed wires shorting out the probe

cheers
Mike
Title: Re: reflow (toaster) oven now earning its keep
Post by: mmcp42 on Apr 04, 2013, 09:17 pm
been a while
tinkered a bit (as I tend to)

here's the latest EAGLE files and sketch if anyone is considering going down the same path :)
enjoy

if anyone does find it useful or makes any changes - do let me know :)

cheers
Mike
Title: Re: reflow (toaster) oven now earning its keep
Post by: samwell on Apr 05, 2013, 11:31 pm
Awesome work~!
Title: Re: reflow (toaster) oven now earning its keep
Post by: ScottG on Apr 05, 2014, 10:44 pm

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


In your circuit, what's the purpose of R5?  Also, I see you have the mains hot connected to MT2 on the triac.  Does it matter which way the triac is wired?  Would it make a difference if MT1 went to mains hot and MT2 went to the oven?