Last time I approved soldering baby resistors was an experience, I’ll acquaint you what. They were about as acceptable to stick to my soldering adamant as they were to stick to the board, and I austere affluence of them in half.
Admittedly, I don’t accept the world’s best soldering station. In fact, what I accept is a abominable old pencil iron, not abundant bigger than what you’d buy at RadioShack—no adjustable temperature ascendancy and no dispensable tips. I additionally don’t accept US $500 to advance in advance my station, but alike if I did, it wouldn’t advice much. I’m accepting older—and so are my eyes.
The band-aid was obvious: Build a reflow oven!
First off, let’s get all the disclaimers out of the way: This activity involves alarmingly aerial voltage at aerial currents! Be careful!
The plan was a simple one: Design a controller. Put it in a toaster oven. I searched the Internet and begin some agnate projects. This was comforting, as it meant that the toaster oven would get balmy abundant to do the job.
I absitively to use a PIC microcontroller (from Microchip Technology) and a blazon K thermocouple as the temperature-sensing device. I did some analysis on thermocouples. It turns out that I’d charge an “ice reference” of some sort. I chose an Analog Devices AD595.
This affair was activity to be absolutely boiler 3.0 compliant, with three preset ascendancy curves (lead/tin, RoHS, and one manual-entry curve), an LCD on the front, and RS-232 advice to adviser the temperature contour from a PC. In added words, I would be able to breeze accepted lead-tin adhesive and the “green” solders, and do some custom curves for apparatus that crave it (like big, honkin’ FPGAs). I spent some time putting calm block diagrams. I alike got so far as selecting best of the parts. The absolute amount would be about $400.
I was aloof starting to put calm schematics aback a acquaintance at assignment broke the accomplished activity (thanks a lot, Ryan). He acicular me to a company, Annex Depot, that sells PID ramp/soak controllers for about $75. Last time I looked at such things was a brace years back, and they didn’t go for beneath than about $500. Ain’t Moore’s Law great? Unfortunately, the affidavit larboard article to be desired—it was ailing translated into English from Chinese. Also, the assemblage that would best fit central the oven apartment was out of stock.
I looked about some added and begin addition company, Auber Instruments, that awash a agnate artefact (SYL-2352P) that was American-made and had abundant bigger documentation, for the aforementioned price. Auber additionally sells the thermocouples (with a 4-inch delving tip), 40-ampere solid accompaniment relays (SSRs) for affluence of margin, and SSR calefaction sinks, all cheaper than I begin elsewhere.
Wow! Absolute amount (including a additional thermocouple and the toaster oven) would be appropriate about $200. I spent $153.85 (including shipping) with Auber and a bit beneath than $50 at Walmart for a Atramentous & Decker toaster oven with an centralized alteration fan (to abbreviate hot spots). It took me beneath than a day to accommodate the system. It took me best of addition day to get a reasonable ascendancy heating contour (lead-tin) out of it.
Removing the oven’s screws is one of the added absorbing genitalia of this project. The beneath spiral on the aback isn’t a Phillips, it’s a “star”—presumably to accumulate morons like me from arise the case accessible and accepting electrocuted.
The aing ambush is the LRF (little elastic feet). These little plugs cull out to admission the screws underneath. My oven had a allotment of angled metal that aching my kitchen table. Fortunately, it’s not a new table, and I accept kids, so my wife didn’t notice.
Photos: Tom Burke
BEFORE AND AFTER: There’s not abundant to the oven’s innards, so there’s affluence of allowance for rewiring. Click on angel to enlarge.
With the awning off, you can see the innards. There’s not abundant in there. To the far left, you can see the backs of the controls; in the average is the fan motor with a cooling fan and accurate shroud. See the thermal absorber about the atramentous wire? There’s a aqueous articulation in there. I took it out. On the far ancillary of the oven, you can see the metal confined anchored to affix the boiler elements in pairs (top and bottom). The continued white affair is the door-hinge mechanism—it’s absorbed to a bounce in the back.
It’s accessible to cull off the knobs by inserting two accepted screwdrivers adverse anniversary added and prying them up. See those metal tabs? Align them out as best you can and the metal awning will pop appropriate off the front. You can again aish the controls.
Use the access ambassador as a arrangement to circumscribe the breadth to be cut out—the aboriginal aperture for the neon lamp was about altogether sized for the controller. I acclimated a Dremel apparatus with acid disks. (Be abiding to abrasion assurance glasses!) Deburr the aperture with a animate file.
I acclimated the old ascendancy awning as a arrangement for a new ascendancy cover, which I fabricated with some 25-millimeter aluminum bedding from Home Depot. Don’t balloon to accomplish tabs to authority it on. (Note: You can angle and align those tabs alone about three or four times afore they break.)
Source: Tom Burke
Click on angel to enlarge.
We’re about there. Assignment a aperture into the thermal alcove and use two wrenches to install the thermocouple. Angle it into the airflow, aloof beneath the shelf.
Connect the base to the SSR according to the schematic (above). You charge to do this above-mentioned to ascent the broadcast in the anatomy because of approval issues. Note that the fan is active to run the absolute time the arrangement is acquainted in. You may additionally appetite to add a ability switch—it should arrest ability to aloof the ambassador and the fan.
The two rear elements are already active together—just cut their affiliation to the AC ability bond and rewire it to the SSR. Affix the added ancillary of that cut affiliation to the added ancillary of the SSR; add addition wire in that side’s affiliation to accumulation the controller. Aback the SSR is energized, it will accumulation a aisle to neutral, acceptance the elements to be powered. Affix the two ascendancy affairs to the SSR, application altered colors so you don’t get them abashed later.
Mount the SSR on the calefaction sink, application the supplied bore grease and screws, and assignment some holes in the aback awning to arise it with apparatus screws. I would accept army the bore to the attic of the oven, but that was area the ability band came in. Be accurate of the fan shroud—there’s aloof abundant allowance to install the SSR.
Use some abundant barometer wire and wire basics to affix the top- and bottom-forward boiler elements together. Wire them to the actual AC wire that you cut apart earlier—string off addition wire to accumulation the controller. Cull the ambassador base through the ascent bezel (but not the thermocouple wires), and affix them to the ambassador alfresco the unit. Slide the ambassador into the chassis, affairs the aing affairs up and out of the way of the fan. Install the thermocouple affairs on the controller—blue on pin 5, red on pin 4. Install the ascent bezel. Finish base the guts, if necessary.
Reinstall the cover. (Make abiding you accurately reinstall all the screws and feet.) After a abbreviate self-test, the ambassador should appear up as declared in the apprenticeship manual. If you did aggregate correctly, no breakers will cruise and no blaze or smoke will appear aerial out. You can chase the ambassador instructions to set a steady-state temperature and again analysis the control. If it works, you’re done!
Corrected on 13 April 2012 to apprehend “When the SSR is energized, it will accumulation a aisle to aloof [not ground] acceptance the elements to be powered.”
Tom Burke is a Senior Systems Engineer at Oceaneering. He’s originally from a baby boondocks in the Midwest, but still managed to acquire a BSEE, MSEE, and an MS in Systems Engineering from Johns Hopkins University. He now lives in Pasadena, Md.
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