Toaster Oven dimmer ?

It's the same effect. The only difference is between the built-in thermostat on the oven vs. the electronics to do the switching, well, electronically. Or standing there watching the thermometer.

Although, I haven't used a toaster oven in quite some time - they _do_ have a knob, don't they? As opposed to just an on-off switch?

I think a heater is pretty much a heater. I have no idea what's so special about a "quartz heater", unless the envelope protects the element from corrosion. Watts in == watts out, after all, and the inefficiencies show up as heat anyway - what's the benefit to some high-tech heating element? Marketing hype?

Thanks, Rich

Reply to
Rich Grise
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Sounds interesting

Use a SSR (Solid State Relay). These come with opto isolated, logic level inputs which can be safely driven by any micro processor.

Dave

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Reply to
Dave

Hello,

To try to approximate the temperature profile of a reflow oven, I'd like to make a computer controlled dimmer for a toaster oven.

Does any one here as a schema / base where I can start from for the Hipower part (digital and pc interface is ok). I found some dimmer schema but they where all for light and a power of 500W max. Here, the heating element is more like 2500W. Is it just a matter of putting a bigger triac, that can handle that load ?

Thanks,

Sylvain

Reply to
Sylvain Munaut

Hello Martin,

And the author can sometimes be found on this newsgroup as well as on fr.sci.electronique.

To be honest I didn't even know that there were toaster ovens with quartz top heaters. Guess I am barbequeing too much (ribs yesterday).

Regards, Joerg

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Reply to
Joerg

this was in circuit cellar

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martin

Reply to
martin griffith

I have done this with some success. I used a Sunbeam oven that cost $20 and had the quartz elements. The oven is somewhat slow heating (less than 1 degree C per second and slows down the hotter it gets). I am considering moving the bottom element to the top and/or purchasing a second oven for more elments. I just used a relay to control it. That is all it should take. I used a MAX6675 thermocouple to SPI converter to measure temperature. The board I ran was a complete success including the 1mm pitch BGA. I simply used thermostatic control, and it was nearly perfect. Note that the pink line is the goal temp, and it is covered up by the fuzzy blue line (measured temp).

There are temp profile from the oven linked at:

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Darrell Harmon

Reply to
dlharmon

I would say that you were way above 220 degrees C on the board that seperated.

I have noticed that most of the heating takes place by infrared. If the thermocoule was not in contact with the board, there could have been large temperature differences. I saw a 50 C difference between a piece of copperclad (very reflective of IR) and a board with green soldermask in testing. I placed my thermocouple directly on top of the board near the BGA.

Your heating speeds seem reasonable. Mine is about 2C/second at room temperature and 0.5C/second at 200 C. Xilinx recommends ramping up to the peak temperature at 2-3 degrees C per second if I remember correctly. I believe I would be in that range with the second element since the decrease in speed is probably due to the poor insulation of the oven.

Darrell Harmon

Reply to
dlharmon

Yes, thanks. I've seen similar article. But I was wondering if using a a dimmer to for example be able to set the heaters to 50% of it's nominal power would be better/worse than just turning it on/off bruptly.

Is it really necessary to have top quartz heaters ? I just did 3 stores and none of them had quartz heater. They all had classical resistors (either in S shape, or several straight line ).

I'm more a merguez type of guy ;)

Sylvain

Reply to
Sylvain Munaut

Hi Joerg

I've only just bought my first blender, ever, I dont even have a microwave. It is not advisable to light a BBQ here, serious drought problems/fires

I'll stick with Tapas in the local bars, less washing up

martin

Reply to
martin griffith

That's an option. Another one is to use two MOSFETs in "anti-series." Tie their sources together, and also their gates together. Effective total switch between drain1 and drain2. Excite between gate and source with Vgs > Vgs_th. The advantage of this over the TRIAC is that it consumes nothing, from the excitation circuit, while in static conditions. In your application, you have very few transitions, so this makes sense.

Reply to
Mochuelo

Could be the wavelength of the infra red,and absorbtion factors of the solder gloop rather than just wattage.

martin

Reply to
martin griffith

There's a difference in heater control units and light dimmers. Light dimmers use an SCR or triac that turns on at different places during each half wave to get varying power and varying light. (Electronic) Heater controls turn on and off at zero crossings, and thus don't put a noise spike on the power line as dimmers generally do. I looked at the referenced Circuit Cellar reflow oven, it uses a mechanical relay to control the heating element! That probably produces spikes, but probably just one (or a few, depending on how bouncy the contacts are) every couple of seconds or so, or however fast it switches the relay. Someone else mentioned a solid-state relay, and that sounds like the solution, ISTR that some (or perhaps all nowadays?) only switch off and on during zero crossing, and that's what you want to keep from dumping spikes on the power line.

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Reply to
Ben Bradley

Hello Sylvain,

The reaction time of a heater element is so slow that I'd guess it doesn't matter. Except that a dimmer for such power levels would be quite expensive. Small triacs are cheap because evey dimmer in the hardwares store contains one. Not so for the big ones.

Email Robert Lacoste about it. There must be a reason why he ordered one via the web for $150 where he probably could have gotten a regular oven for $30 or so at Carrefour.

AFAIK those have to be cooked in oil at the end. They say the same about bratwurst which should be pre-cooked in beer. But we didn't find much of a taste difference versus just slow cooking them on charcoal.

Regards, Joerg

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Reply to
Joerg

Hello Martin,

Same here but we do not use any fossil fuel products. The charcoal is started in a "starter chinmney". Just a couple of crumpled newspaper pages in the cavity underneath is enough, you just have to wait 1/2 hour. The typical American barbeque grill is a "Weber". It is a completely enclosed round thing with adjustable vents on top and bottom. Quite safe if you are careful.

Tapas are more healthy, too. You aren't presented with a chock full plate of food that in the end is consumed much too fast. Do they still place the saucers on top of the beer or wine glasses?

So, are you permanently lving in Spain?

Regards, Joerg

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Reply to
Joerg

Before I bought the toaster oven, I had thoughts of making a very small reflow oven using 4 500W halogen bulbs.

I would try to raise the floor, but the heating element is a single

300mm long quartz tube, and I am afraid that I would not get even heating. I don't think any chickens would fit in this toaster oven. It was the smallest one the store had and I chose it for that reason. The label says 1350 watts, and I assume that would be with both elements on. I have been using just the top element (broil setting). The oven has no insulation (just 2 layers of thin sheet metal). The outside gets really hot.

Assuming I have 675 watts of power going in whenever the element is on, I would estimate that I am losing about 500 watts of heat when the oven is at 200 degrees C based on the difference in ramp rate. So I effectively have about 200 watts going to heat the oven and its contents. If I double the power to 1350W, I will still be losing about

500W, but 850W will be going to heat the oven which should result in a ramp rate of around 3 degrees C per second. Maybe I will test that theory out tommorrow if I have time.

Darrell Harmon

Reply to
dlharmon

Hello Darrell,

It could also be because of the large volume of the oven chamber versus limited heater power. Just like it takes twice as long to heat a room of twice the volume with a space heater of a given power, almost regardless how good the house is insulated.

Unless you are talking about a different beast usually they design these ovens so that one or two regular size chickens will fit. I don't know if that would be safe: What if the oven were somehow modified to maybe a quarter of its usual height?

Regards, Joerg

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Reply to
Joerg

Yes, I've seen that. Actually it's when I saw you successfully soldered BGA that I decided to try it by myself ;)

I've just bought a oven, it's not quart element, just 2 heating resitors on the top and 2 heating resistors on the bottom. 1500W total power. The inside looked exactly like

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To do a quick heat speed test, I placed a thermocouple inside. However, it was near the back panel, not really centered (it's a multimeter probe so i inserted it trhu a screw hole). And at posteriori the real inside temp must have been quite hotter than that.

It heats at about 1-1.5 °C at the start and at 0.2 °C/s when above

200°C. However these measure might be flawed see what follows.

As a quick test, I just took a PCB where the silk screen was failed and where I did some solder test. I took some pads where there was a solder "bubble" on the pad and applied flux, then some 0805 and 1206 components. Then I turned on the oven till I read 130 °C, maintain that for 2 min, then heat up till 220°C and maintain that for 30 s. However the temperature in there must have been higher as the pcb itself kindof melted ;) (the different layers separting themselves, bubble appearing inside) Guess I have to get a better reading than that. The solders looks ok though, even if the components and the pcb are near burnt ;)

Sylvain

Reply to
Sylvain Munaut

Unless the process is very tolerant of wide swings in temperature, you can't control a quartz heater effectively with zero-voltage switched time proportioning because of the fast response-- you have to use something like phase control (which is normally considered undesirable).

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Quartz supposedly gives off more infrared heat, vs. convection heat. This would allow for quicker thermal responses.

Reply to
Jeff

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