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Mydesign
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Platinum
Re: Panasonic “Inverter” microwave
Mydesign   2/10/2014 4:47:41 AM
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1 saves
"To get more power to the magnetron you need to use a PFC converter "Inverter" power supply therefore (120V*15A*0.9η  = 1620 W input power) with the magnatron efficency of 65% ≈ 1050 watts in to the oven cavity!"

PFC, thanks for the clarification and I think your valuable info may be useful for our community members. Thanks for sharing your knowledge.

PFC_Switcher_Engr
User Rank
Iron
Re: Panasonic “Inverter” microwave
PFC_Switcher_Engr   2/6/2014 1:23:44 PM
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    When someone uses the term "Inverter" when refering to a microwave (μwave) oven they are usually refering to the power conversion circuitry. Originally, most μwave ovens used a simple transformer/bridge rectifier followed by a storage capacitor (Capacitor Input Power Supply). This results in a terible power line current distortion from a sine wave! These power supplies can supply at most about 0.6 of the available power from the AC line to the Magnetron (120V*15A*0.6η  = 1080 W input power), due to the large peak currents generated during charging the storage capacitor, only when the input Voltage excedes the capacitors Voltage. Additionally, you have the loses associated with the transformer et cetera.

    Newer μwave ovens now use a Power Factor Corrected (PFC) Switched Mode Converter. This consists of the standard bridge rectifier followed by a Boost or "Flyback" Switched Mode converter controlled by the rectifed input Voltage. The resulting current wave from is much closer to the Voltage sine wave, and thus most of the power con be presented to the Magnetron.In a microwave oven, for instance, a 1.1 kilowatt input will generally create about 700 watts of microwave power, an efficiency of around 65%. (http://en.wikipedia.org/wiki/Cavity_magnetron)

    To get more power to the magnetron you need to use a PFC converter "Inverter" power supply therefore (120V*15A*0.9η  = 1620 W input power) with the magnatron efficency of 65% ≈ 1050 watts in to the oven cavity!

tekochip
User Rank
Platinum
Re: Inviting company response
tekochip   7/16/2013 10:36:42 AM
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Ratsky;
 
Your exploding components reminded me of an issue we had with our first surface mount lab.  In the Summer we suddenly had a soldering problem in the lab and it turned out that moisture inside the circuit boards was rapidly boiling out of the boards during soldering and blowing the little surface mount parts right off the boards.  It looked like someone was blowing compressed air across the boards.


Cadman-LT
User Rank
Platinum
Smell
Cadman-LT   7/16/2013 10:09:32 AM
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As far as the smell goes, my microwave does that too. I always just assumed that that's how they are. So no?

Cadman-LT
User Rank
Platinum
Re: Is unscrewing the Torx screws the only way?
Cadman-LT   7/16/2013 9:26:16 AM
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At least someone who didn't know how to replace the bulb could take it in for repair. Imagine if they did that to a refrigerator bulb! lol

armorris
User Rank
Platinum
Re: Is unscrewing the Torx screws the only way?
armorris   7/13/2013 4:04:48 PM
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LarryM,

No, I'm sure that removing the outer jacket is the only way to replace the bulb. Besides being a retired electrical engineer, I repaired TVs and later, VCRs for most of my adult life, in addition to my day job, until they got too cheap to repair. I know what I'm talking about. 

Ratsky
User Rank
Platinum
Re: Inviting company response
Ratsky   7/12/2013 4:13:45 PM
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Here's another moisture/carbon comp story. Back in the mid '70s, I worked for the "batwing" company in South Florida.  I was designing what became the first low-cost "consumer" UHF paging receiver; minimizing power consumption was absolutely critical as all we had room for were a pair of N cells.  Thus, the logic (custom IC) was implemented in low-voltage CMOS (a new proprietary technology at the time). To keep power consumption down, we used a watch crystal for the clock, with an internal oscillator circuit. I used a 10 megohm carbon comp for the bias resistor across the crystal.  Everything worked quite well, and went into production in very high volumes.  After the first few runs, we began to have a significant drop in first-pass EOL test yield.  After a lot of head-scratching, we found that the oscillator circuit sometimes wouldn't start.  The root cause: unfortunately, the factory floor and the stockroom were not climate-controlled, and in South Florida, that meant the humidity was really high most of the time.  It turned out that the carbon comps (especially the high-resistance ones) were absorbing moisture, and the "megohm-plus" ones were becoming either "kilohm-plus" (which just increased the current drain) or were exploding when that moisture was turned into steam duing the wave-soldering process!  The ultimate fix was requiring all carbon comps to be stored in a climate-controlled area until they would be pulled for immediate insertion and soldering into the PCBs.

OLD_CURMUDGEON
User Rank
Platinum
Re: Inviting company response
OLD_CURMUDGEON   7/11/2013 2:46:12 PM
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Larry M:  What I related is a policy that was in place from the 1960s through when I left the company in the latter 1970s.  So, while the case you made MAY be technically & scientifically correct, it didn't affect our products which were in widespread use from the North Pole atmosphere to the super-saturated S. American rain forests to the deserts of Africa.  The product line consisted of mobile & stationary radio communications equipment, and was found wherever one went, from the NY Harbor to the shores of Tripoli to oil rigs in the North Atlantic to wherever humans inhabited the earth and wanted to communicate with each other.  And, since many of these products were the assembly of vacuum tubes AND solid state devices, the heat dissipated by the tubes I'm sure served a very valuable secondary purpose....... demoisturizing the chassis.

The chief engineer was directly responsible for many circuit patents that either he and/or the company held, so I'm sure that IF moisture entrapment was a problem, he would have been very concerned with addressing the issue.

Larry M
User Rank
Platinum
Is unscrewing the Torx screws the only way?
Larry M   7/11/2013 1:59:32 PM
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Is it possible that the author has overlooked another way to access the lamp? Perhaps the cover snaps off from inside the oven, but takes more force than he has applied?

We had another Made For Monkeys article about two years ago where that author complained about how difficult it was to clean the filter in his washing machine and boasted about how he had cut a hole in the side of the cover to facilitate its reinstallation.

Another posted pointed out that had he removed the access panel plainly visible at the base of the front panel he would have had easy access to the filter.

Larry M
User Rank
Platinum
Re: Inviting company response
Larry M   7/11/2013 1:52:00 PM
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Actually, MIL-HDBK-217 (versions B through the current one) point out that using oversized carbon comp resistors degrades reliability. Carbon comp resistors need to run warm to cook off absorbed moisture. If they are oversized their resistance gradually drops as water is absorbed into the carbon, lowering resistance. Bad move on the chief engineer's part.

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