help me hack the infrawave

[ag3c]

I just picked up a Black & Decker Infrawave FC300 oven, based on way too little research and some positive references on SparkFun and this thread:
viewtopic.php?f=42&t=13259

I've been using a little super cheapo GE toaster that I picked up in a thrift store for $8. (Terribly uneven heating, but it worked well enough to get me hooked on toaster oven reflow.) If I recall correctly, the GE oven's elements were around 10 ohms, which were easy to connect in parallel. Short 120V through the elements (what the external controller is doing when "on"), and it makes a good little oven. Well, a bad little oven, but it mostly worked.

As I'm hacking the much larger FC300 Infrawave for closed-loop control by my temperature controller, one thing that's confusing me: the FC300's top element is 1.7ohms. Feeding that 120V would be... dramatic. Does this element rapidly increase its resistance as it heats up?

Have other people hacked this oven? Are you using the built-in controller somehow, or did you cut it out of the loop and use an external controller? In which case: How do you have the elements configured/powered?

Thanks!

A

[Mackle]

I have the FC150 which has a single 1000w element on top, and two 250w elements wired in parallel below. The controller simply drives two mechanical relays which gate 120vac to the elements. The control board connects to the elements with standard quick-disconnect terminals which made it real convenient to eliminate the controller and run the wires out to a pair of 10A solid state relays. Does the "300" in your FC300 mean 3000w (more elements), or just indicate the additional rotisserie?

So far I have only driven the SSRs manually to get a profile of the oven's thermal behavior; top element only, bottom elements only, all elements, with trays, without, etc. It looks like "top only - with tray", along with manually opening the door for cooling, is the sweet spot

The oven controller at http://www.rocketscream.com looks like a tidy little design and something I can emulate with parts on-hand. It uses Brett Beauregard's PID library, http://www.arduino.cc/playground/Code/PIDLibrary, and includes a front end written in Processing.

I'm undecided whether I should spend today playing with that software and twiddling PID parameters, or just reinstall the oven's original controller and go the route I just discovered here...

http://www.youtube.com/watch?v=8j0impc6ebQ

... five minutes on "Re Heat" followed by a brief "Toast". That's pretty straight forward and would assure plenty of time to get ready for tonight's New Year's Eve festivities. But then again, spending the day poking at PID loops sure has a lot of geek appeal.

Cheers!
Mike

[ag3c]

I think the FC300 is just larger -- it's a "six slice" toaster. (The rotisserie feature shows up in the FC350.) Anyway, my FC300 is still a household banned appliance, meant to work on a standard 15A circuit, so it's definitely not 3000W. Its elements sound similar to what you describe in your FC150. Do you happen to know the resistance of any of your FC150's heating elements? (Particularly the top one.)

I'll be reusing the existing temperature controller I have. It reads from my high temperature K-type thermocouple, already has my solder's preferred temperature curve programmed into it, etc etc. It uses a hefty SSR to switch on the oven, which kind of requires that I disable the toaster's built-in controller. So, control isn't the concern, it's more that unless the 1.7ohms of that top element changes quickly, it seems like it's going to draw a pretty enormously large amount of current and blow fuses/trip breakers. Just trying to avoid electrical drama.

Just for fun, I measured two 40W incandescent household bulbs with my multimeter; one was 17ohms, one was 28. Pretty sure they aren't mislabeled 840W and 513W bulbs. So maybe this incandescent top element really is meant to receive 120V...

[Mackle]

I get 1.8 ohms for the top element. Ohm's law says it will draw 8.3A which won't blow any household breakers, but as you guessed in your previous post, it is "dramatic": it's gets wickedly hot in there which is, you know, the whole point. If it makes you feel any better your SSR is very likely turning on at zero-crossing so that cuts the electrical drama (and noise) a little bit For what it's worth, the bottom parallel elements measured about 25.7 ohms.

I was going to use my old industrial controller on the oven as well, but I loaned it to a glass blower buddy to drive his auxiliary annealing kiln (an "oven" the size of a washing machine) for a big holiday production run. But once he got his stuff made he split town for the holidays with my equipment locked up in his studio, so I'm left bit fiddling with the Arduino.

I'd say you've got everything you need for the project. Get over that fear of sparks and just do it!

[ag3c]

Is my math wrong or is yours? 120V into a 1.7ohm load is more like 70A, no? Hence my concern about drama.

But I assume the design is like a lightbulb filament, where the resistance rises rapidly as the heating element/filament becomes incandescent -- and the top element won't draw 66.7A any more than the aforementioned 40W incandescent lightbulb will draw ... well, 120V into 17 ohms would be 7A (->840W) ... but we know it's a ~40W bulb, so that's 0.3A, meaning it rises to around 360ohms once lit. (wikipedia)

I'll turn the oven on sometime ahead of midnight so that any drama isn't mistaken for new year's revelry.

[ag3c]

Ah, sorry, I see now. You were working back from the fact that you know (think?) it's a 1kW element. So, 8.3A. Got it.

[Mackle]

Right. It's printed on the tube body, but you have to get behind the side sheet metal to see it.

[t00ts]

Hi and thanks in advance,

Sorry for bumping such an old post.

I just got my FC300 but I live outside the US (Europe) and thus here mains are 220V @ 50Hz.

On the bottom of the oven it explicitly says to feed it with (standard) US mains: 110V @ 60Hz. Usually, most household equipment support either 50Hz or 60Hz, but I'm not sure if this is the case for this oven, as the infrared/infrawave cathodes are wired directly to mains, and I've read that in the case of microwaves it could harm it. I don't know if this is the case with the infrawave oven as well.

I've also looked for AC frequency inverters/changers/converters and I think it's probably not the way to go. I might as well return the oven if I have to modify AC frequency to suit its needs. Bringing the voltage down shouldn't be a problem. My only concern is if I will harm the infrawave if I run it at 10Hz less than what it says it needs.

Thanks again.

[Mackle]

I don't know how the oven's existing controller would like 50Hz, but I don't think it would be a problem for the resistive heating elements themselves. So if you're dropping the voltage and replacing the oven's controller with your own SSRs and intelligent control, I think you'd be ok.

Once you get out your trusty screwdriver and void the warranty, see if the heating elements have a manufacture's model number printed on the glass. It's *possible* they are rated to handle 220V (for the global market), which would make your project even easier.

Cheers!

[t00ts]

Hi Mackle,

First of all, thanks for replying.

My actual concern is about the heating elements themselves, as I plan to replace the controller with my own stuff. I contacted customer support to see if they've got an answer, although Black & Decker have it outsourced (Applica - Fox International) which kind of sucks because the people there don't seem to get the point, as I'm probably the first person ever to ask such a technical question. Anyways, I'll wait a few more days and see if I get a decent answer, as I have to be sure before opening it up and voiding a 130€ warranty without being sure that I'm not going to burn it.

I'll appreciate anyone else's comment or opinion on the subject.

Thanks once more.

[t00ts]

Hi,

So, I got an answer, but as I expected it's a really lame answer which just suggests not use it at 50Hz because it's not stated in the manual....

So, Mackle gave me some confidence, and I really think that nothing should happen if the heating elements work kind of like a light bulb (which I don't really know if is the case), but they look similar.

I'm not sure if I want to burn 130€ just like that, but I'm closer to trying it than to returning it. Any thoughts just to make me feel better about doing so?

Thanks once again.

[Option7]

Where can I buy the replacement 1000 watt element (top) and the 250 watt elements (bottom) for Infrawave Oven FC150R?