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Reflow Fred Style! :-) 
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Some notes on using them to best effect: viewtopic.php?f=9&t=1621

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Thu Mar 01, 2012 2:09 pm
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I've been performing more heat distribution testing with the Rommelsbacker speedy BG 950 by cooking pizza. Putting it on the lower shelf with a flat metal plate under it produces very even heating, which is good. Maybe I won't need to mod it. We'll see what the temperature profile looks like once the K type probe arrives. Pizza pics soon :-)

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Thu Mar 01, 2012 10:55 pm
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Update! Pizza pics from the other day! Mmmmmmm, pizza! :-)

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It tasted great! Don't worry, the grease came off the door easily enough. Though once I put it into production the food cooking may have to stop!

This morning I performed another test and did a from cold to tstat click off at ~230C test. 7 minutes exactly:

Quote:
fred@cheetah:~$ date
Sun Mar 4 15:21:28 CET 2012
fred@cheetah:~$ date
Sun Mar 4 15:28:28 CET 2012

That might be a bit on the slow side. I also melted my EEE in the process, which wasn't ideal.

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So, the next step is to strip it down and add some fibreglass insulation to the sides, back, top and bottom. This will reduce the danger of damaging other items on the desk by careless placement of it while baking. The back is the worst and gets pretty hot pretty fast. I might look into putting some sort of insulator under any screws that join the layers too.

The detailed plan:

  • insulation on the back panel, glass and washers
  • insulation in the top, glass only
  • insulation in the sides, glass only
  • another layer of metal on the bottom cover and glass fibre in between. Zinc coated sheet steel for that.

Then I'll test the room -> cutoff again and likely it'll be about 2 minutes faster.

After that I'm going to replace the cooking tray and wire rack with a 1.5 or 2mm aluminium plate suitable for resting PCBs directly on. This will serve two purposes:

1) A smooth flat level surface for placing the PCBs
2) Distribute the heat from the bottom element across the width of the oven more evenly/quickly.

In tandem with that, I'll likely rivet or screw another partial sheet of alloy on the top of the lower element to force more heat to the outsides. I may do that to the top one too, or I may add more elements for a faster heat up ramp time.

Fred.

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Sun Mar 04, 2012 4:34 pm
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Woops! I just realised why the back gets so hot so fast, it's single skin! I thought I had checked that and found it to be double skinned, however I was clearly wrong. I'll add another layer of metal and some glass fill to that too.

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Sun Mar 04, 2012 5:54 pm
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Nice work, but I think some of the tomatoes are tomb stoning. :lol:


Wed Mar 07, 2012 6:56 am
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Spudmn wrote:
Nice work, but I think some of the tomatoes are tomb stoning. :lol:

ROFL :-)

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Wed Mar 07, 2012 9:52 am
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^ ROFL again! :-)

Update! Got K type thermocouple from a man appropriately named Ding Dong in China (that took some restraint!) along with tweezers and ordered some break out boards to attach thermocouple amplifiers to. So decided it was time to do more investigation of the mighty Rommelsbacher with respect to insulation and promptly pulled it apart. It's pretty cheaply made, but will be easy enough to improve thermally. I made a cutting list and insulation list and took some pics:

Control side (right):

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Other side (left):

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All laid out:

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Thermocouple:

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Tweezers, just LOOK at that quality!

http://stuff.fredcooke.com/toaster.oven/IMG_5959.JPG
http://stuff.fredcooke.com/toaster.oven/IMG_5969.JPG
http://stuff.fredcooke.com/toaster.oven/IMG_5970.JPG
http://stuff.fredcooke.com/toaster.oven/IMG_5971.JPG
http://stuff.fredcooke.com/toaster.oven/IMG_5972.JPG
http://stuff.fredcooke.com/toaster.oven/IMG_5973.JPG

More progress as it comes to hand, or oven, as the case may be.

Fred.

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Fri Mar 09, 2012 9:54 pm
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Insultation? Are you nuts? Unless you're trying to make back the 50 cents you'll spend on electricity, I'd recommend against it. You want to be able to CONTROL the temperature, which means either you need a high speed powered cooler you can rapidly and controllably switch on and off, or you need the natural heat sink of the oven to be high. Unless you can't overpower the cooling (i.e. you're trying to get much hotter than the oven was designed for) or you can't heat up fast enough to meet your profiles, I don't think this is something you want to do.

For that matter, have you timed how long it takes for the oven to drop in temp? Perhaps you'll have trouble meeting your profiles as is (this I doubt, though. If you did, it would be awesome, because I'd like to see this have a fan in it. Actually, you might want that anyway, it'll help keep things even in there.

Of course, you could just mean electrical insulation, but I rather enjoy typing. :-) A case in point: Any professional environmental equipment I've used generally has a high power, always on cooler, and a cycled heater, since it's just easier and more responsive and more predictable. Adding insulation is like putting a huge air leak into the engine who's idle you're trying to control. You're moving up the floor quite a bit, and doing so asymmetrically.
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Fri Mar 09, 2012 10:33 pm
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Understood, Abe, though a solenoid to crack a leak in the front wouldn't be bad, and you can't get anything remotely close to the back of it without it catching fire, so insulation is a safety thing at the least. The glass stays cold. I know what you're saying about the cooling down, though that's easy with a DC fan on the bottom to cycle cool air under the alloy plate the PCBs will be sitting on. The main thing is getting the ramp up fast enough and not catching fire to fabrics 17 meters away.

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Sat Mar 10, 2012 1:08 am
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To Quote Tim Taylor: Needs More Power!

Perhaps a heating element in your plate - that's going to be your big thermal capacitor. I like the idea of a fan, but it's a heavy job for a fan if it's in there. Perhaps a junked toaster and blow the fans through it, or a hair drier.


Sat Mar 10, 2012 1:16 am
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