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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#41
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Induction Cooking Table : IGBT keeping to short !
On Fri, 30 Nov 2012 09:31:06 +0100, cLx
put finger to keyboard and composed: On 29/11/2012 11:23, Franc Zabkar wrote: On Wed, 28 Nov 2012 19:22:28 -0800 (PST), put finger to keyboard and composed: You got 0.68uF and you are afraid to use 1uFs ? Just use them as long as the current capabilities are up to snuff. The value does not mean **** as long as it doesn't go too low. Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50% increase in cooking energy? Also, wouldn't each capacitor take longer to charge, and if the capacitor wasn't fully charged when the IGBT switched off, wouldn't this result in an interruption of the current in the coils, with a potentially damaging back-EMF? Or am I completely misunderstanding how this appliance works? It's a serie LC resonnance driven by a half bridge switcher, if I'm correct. Yes, I see that now. I should have researched the topic instead of relying on the OP's rough circuit diagram. The absence of the flyback diodes from the drawing left me wondering how the coil current would decay after the IGBTs switched off, so I assumed that the current had to be zero when this happened. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#42
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Induction Cooking Table : IGBT keeping to short !
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#43
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Induction Cooking Table : IGBT keeping to short !
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#44
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Induction Cooking Table : IGBT keeping to short !
On Thu, 29 Nov 2012 10:21:43 +0100, cLx
put finger to keyboard and composed: Now i'm stuck at finding the polypropylene caps. They are expensives, and what i found can handle only 17 amps. Seem a bit underrated for such that case. Doing measurements is not easy as, without load or transistors, the drive shuts itselfs (not detecting anything), just trying shorts pulses, and i would not wasting my replacements parts. I would measure the voltage at the junction of the two 0.68uF capacitors, with the coil disconnected, and confirm that it sits at half the DC supply voltage. This might identify any imbalance in the capacitor characteristics, ie leakage, reduced capacitance. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#45
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Induction Cooking Table : IGBT keeping to short !
"I don't understand what triggered your "ground" rant..."
I didn't mean it like it sounded I guess. Anyway I understand what you say about the Xc, but I am assuming that the frequency is much higher than 20 Khz. I'd bet it's somewhere around 75 Khz which takes the tuned circuit out of the picture. The Xc of the caps would be much lower and the Xl of the coil much higher. If the whole shebang was 12 ohms total, one burner would pull almost 27 amps providing the supply is 320 DC. The numbers fall into line at around 75 Khz or so. At that point, there is nothing tuned about it. I didn't mean to offend, I just know that so many have a few misconceptions about these things, actually not even these things pty se, SMPSes that use a similar configuration. If you don't have those misconceptions great. I try to think from the engineer's standpoint. Why would I waste energy on Xc ? There is a reason to do it for example in the horizontal sweep ciscuit of a TV but usually it's all or nothing. Block the DC and pass the AC. J |
#46
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Induction Cooking Table : IGBT keeping to short !
On Fri, 30 Nov 2012 16:20:16 -0800 (PST), put
finger to keyboard and composed: Anyway I understand what you say about the Xc, but I am assuming that the frequency is much higher than 20 Khz. I'd bet it's somewhere around 75 Khz which takes the tuned circuit out of the picture. That Fairchild design note I alluded to in an earlier post discusses several topologies (including the OP's), all of them based on resonance principles. The resonant frequency was chosen as 24kHz while the operating frequency "of the system is set at 28kHz, which is higher than the resonance frequency, in order to avoid noise generated within the audio frequency band". Wikipedia also suggests that 24kHz is a common design target: http://en.wikipedia.org/wiki/Induction_cooking The above article tabulates the skin depth of various materials at 24kHz. However, Wikipedia also states that "Panasonic Corporation in 2009 developed a consumer induction cooker that uses a higher-frequency magnetic field, and a different oscillator circuit design, to allow use with non-ferrous metals." As for some real examples, here are two service manuals for induction cookers: http://www.garland-group.com/docs/up...cs_4521635.pdf http://www.garland-group.com/docs/up...a%20Heater.pdf Both manuals refer to a diagnostic mode whereby the microprocessor is accessible via an RS232 interface. There are several sample outputs which indicate that the operating frequency is 20080 Hz. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#47
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Induction Cooking Table : IGBT keeping to short !
On Sat, 01 Dec 2012 16:27:24 +1100, Franc Zabkar
put finger to keyboard and composed: On Fri, 30 Nov 2012 16:20:16 -0800 (PST), put finger to keyboard and composed: Anyway I understand what you say about the Xc, but I am assuming that the frequency is much higher than 20 Khz. I'd bet it's somewhere around 75 Khz which takes the tuned circuit out of the picture. I found this interesting application note: http://www.st.com/internet/com/TECHN...CD00115561.pdf "Induction cooking functions based on the principle of the series L-C resonant circuit, where the inductance L is the cooking element itself. By changing the switching frequency of the high voltage half-bridge driver, the alternating current flowing through the cooking element changes its value. The intensity of the magnetic field and therefore the heating energy can be controlled this way." It describes the OP's circuit as a resonant circuit consisting of an L-C resonant tank. It states that "the IGBTs are driven by high frequency complementary square waves with 50% duty cycle", and that the frequency of "the PWM signal applied to the driver input pin ... varies in a range between 19 kHz and 60 kHz". The two capacitors are 680nF 600V types, and the IGBTs are STGY40NC60VD. The design has 9 power levels, with a frequency of 60kHz for lowest power, and 25kHz for highest power. At 60kHz the plate current appears to be roughly triangular, while at 25kHz it appears sinusoidal. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#48
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Induction Cooking Table : IGBT keeping to short !
On Sat, 01 Dec 2012 17:12:28 +1100, Franc Zabkar
put finger to keyboard and composed: It describes the OP's circuit as a resonant circuit consisting of an L-C resonant tank. It states that "the IGBTs are driven by high frequency complementary square waves with 50% duty cycle", and that the frequency of "the PWM signal applied to the driver input pin ... varies in a range between 19 kHz and 60 kHz". The two capacitors are 680nF 600V types, and the IGBTs are STGY40NC60VD. The datasheet for the STGY40NC60VD states that the IGBT is good for "high frequency operation up to 50kHz". Hmmm ... http://www.st.com/internet/com/TECHN...CD00003462.pdf - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#49
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Induction Cooking Table : IGBT keeping to short !
Very interesting Frank. You do good research. However there is no real contradiction. The inductance must be higher than we assumed because if the Xl is only 6 ohms, it would pull a hell of alot more current. It had to be one or the other.
Even more interesting is how they're making it work with non-ferrous vessels. Technically it should work with anything that conducts electricity, coils in a transformer are not ferrous and you can induce current in them right ? It actually does work on non-ferrous I guess, just extremely inefficiently. They aimed to increase the efficiency. It says reduced efficiency and I saw a chart, but it wasn't boiled down to just HOW inefficient a given unit will be on specific cooking materials - as if the layman would usually even know. It would still be trial and error. Now if they can make it work on glass cookware, they get my vote for the Nobel prize. Very interesting, thanks for bringing that in. |
#50
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Induction Cooking Table : IGBT keeping to short !
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#51
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Induction Cooking Table : IGBT keeping to short !
Actually if they can really penetrate the non-ferrous they can heat the food directly. I gues an upside down microwave or something.
Hell, it might be all the rage range now because your steak heats the pan, not the other way around. By now you know most of that "Visions" type cookware got recalled right ? The stuff exploded on a few folks and they went back to metal pots and pans. Funny what it takes to induce common sense sometimes eh ? My Mother had them but got rid of them over that ****. Really, they would probably be alright for boiling and casseroles etc, but I think trying to fry crispy chicken in a glass pan might not be the smartest idea. But then lead could be put in the glass, or barium. Maybe it would glow or something. Colored glass I guess in a way could be considered "doped". A study of the various types' reaction to bombardment like this would be intereasting. |
#52
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Induction Cooking Table : IGBT keeping to short !
On 01/12/2012 06:27, Franc Zabkar wrote:
On Fri, 30 Nov 2012 16:20:16 -0800 (PST), put finger to keyboard and composed: Anyway I understand what you say about the Xc, but I am assuming that the frequency is much higher than 20 Khz. I'd bet it's somewhere around 75 Khz which takes the tuned circuit out of the picture. That Fairchild design note I alluded to in an earlier post discusses several topologies (including the OP's), all of them based on resonance principles. The resonant frequency was chosen as 24kHz while the operating frequency "of the system is set at 28kHz, which is higher than the resonance frequency, in order to avoid noise generated within the audio frequency band". When it was brand new, i've measured the frequency at ~35KHz, modulated by 100Hz (double rectification of the mains' frequency). See: http://clx.freeshell.org/view.html?f...n/img_0809.jpg http://clx.freeshell.org/view.html?f...n/img_0812.jpg http://clx.freeshell.org/view.html?f...n/img_0813.jpg Wikipedia also suggests that 24kHz is a common design target: http://en.wikipedia.org/wiki/Induction_cooking The above article tabulates the skin depth of various materials at 24kHz. However, Wikipedia also states that "Panasonic Corporation in 2009 developed a consumer induction cooker that uses a higher-frequency magnetic field, and a different oscillator circuit design, to allow use with non-ferrous metals." As for some real examples, here are two service manuals for induction cookers: http://www.garland-group.com/docs/up...cs_4521635.pdf http://www.garland-group.com/docs/up...a%20Heater.pdf Both manuals refer to a diagnostic mode whereby the microprocessor is accessible via an RS232 interface. There are several sample outputs which indicate that the operating frequency is 20080 Hz. - Franc Zabkar |
#53
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Induction Cooking Table : IGBT keeping to short !
By now you know most of that "Visions" type cookware got recalled,
right? The stuff exploded on a few folks and they went back to metal pots and pans. I've been using Corning glassware and Corningware for years, and have never had a piece break while cooking. Dropping them is a different matter. |
#54
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Induction Cooking Table : IGBT keeping to short !
"When it was brand new, i've measured the frequency at ~35KHz, modulated by
100Hz (double rectification of the mains' frequency). " So they don't bother filtering, like a microwave. Hmmm. "I've been using Corning glassware and Corningware for years, and have never had a piece break while cooking. Dropping them is a different matter. " Visions were different. Some sort of superglass. The commercial showed them melting a conventional metal pan in their glass pan. I would imagine it was not stainless, IIRC the melting point is quite high compared to aluminum or steel, or cast iron. But these things didn't just break, they exploded. They are no longer on the market, at least with the old formula. It is pretty cool to be able to see what you're cooking like that. There was always Pyrex as well. One of the things visions touted was an extremely high thermal mass. In most cases if you wanted to cook say spaghetti, once it came to a boil again with the pasta in the water, you supposedly could shut the heat off and it would cook fully. |
#55
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Induction Cooking Table : IGBT keeping to short !
William Sommerwerck wrote: By now you know most of that "Visions" type cookware got recalled, right? The stuff exploded on a few folks and they went back to metal pots and pans. I've been using Corning glassware and Corningware for years, and have never had a piece break while cooking. Dropping them is a different matter. The older stuff was real 'Pyrex'. Now they use 'Soda Glass' and call it 'Pyrex'. Soda glass will explode if heated unevenly. |
#56
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Induction Cooking Table : IGBT keeping to short !
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#57
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Induction Cooking Table : IGBT keeping to short !
I've been using Corning glassware and Corningware for years, and have
never had a piece break while cooking. Dropping them is another matter. The older stuff was real "Pyrex" [borosilicate glass]. Now they use "soda glass" and call it "Pyrex". Soda glass will explode if heated unevenly. I complained about this a few years ago, and was told that the newer glass was as good. I doubt it. Several years ago I dropped a Visions baking dish and it shattered like you wouldn't believe. (I'm still finding the pieces.) Corning paid the postage to return it, but they never told me what they found (if anything). They made no offer to replace it. See the Wikipedia article on Pyrex, section on Composition. |
#58
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Induction Cooking Table : IGBT keeping to short !
"When it was brand new, i've measured the frequency at ~35KHz, modulated by 100Hz (double rectification of the mains' frequency. " So they don't bother filtering, like a microwave. Hmmm. ** Microwave ovens have similar line frequency modulation and for the same reason. The high voltage PSU is not filtered. Electronic transformers for 12v halogen lighting are the same too. .... Phil |
#59
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Induction Cooking Table : IGBT keeping to short !
William Sommerwerck wrote:
By now you know most of that "Visions" type cookware got recalled, right? The stuff exploded on a few folks and they went back to metal pots and pans. I've been using Corning glassware and Corningware for years, and have never had a piece break while cooking. Dropping them is a different matter. beware that anything made in the past some years isn't what it used to be. it's just some sort of cheapo fake stuff and not the real pyrex as used in labware. You can even tell from the color of the stuff that it's nothing more than melted bottles and windows. |
#60
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Induction Cooking Table : IGBT keeping to short !
William Sommerwerck wrote:
I've been using Corning glassware and Corningware for years, and have never had a piece break while cooking. Dropping them is another matter. The older stuff was real "Pyrex" [borosilicate glass]. Now they use "soda glass" and call it "Pyrex". Soda glass will explode if heated unevenly. I complained about this a few years ago, and was told that the newer glass was as good. I doubt it. Several years ago I dropped a Visions baking dish and it shattered like you wouldn't believe. (I'm still finding the pieces.) Corning paid the postage I wattched a Visions lid from the large pasta pot get dropped recently onto a wooden floor. I would not doubt there was more energy stored in that lid than just it falling into the ground. It din't break, it became hundreds of pieces, but sharp ones unlike a windshield. We noticed that those 1980s white corningware plates with the yellow printing on the edges were unbreakable when new, but became extremely brittle over the years. They seemed to heat in the microwave oven, so maybe that has something to do with it. The extra plates and bowls from the set that never really saw use can survive a kitchen floor drop test. The rest just shatter. to return it, but they never told me what they found (if anything). They made no offer to replace it. Did you send it to the real corning or the fake place called "world cookware" or something like that that now just licenses the corning name? See the Wikipedia article on Pyrex, section on Composition. |
#61
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Induction Cooking Table : IGBT keeping to short !
Corning paid the postage to return it, but they never told me
what they found (if anything). They made no offer to replace it. Did you send it to the real Corning or the fake place called "World Kitchen." The latter. It's not actually fake. According to the Wikipedia article, World Kitchen was originally Corning's Consumer Products division. I'm bothered by companies buying up trademarks, then applying them to products that have no connection with the trademark's original usage. Pyrex is a good example of this bad practice. So is Accutron. Modern Accutron watches do not use a tuning fork. |
#62
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Induction Cooking Table : IGBT keeping to short !
Phil Allison wrote:
wrote: cLx wrote: "When it was brand new, i've measured the frequency at ~35KHz, modulated by 100Hz (double rectification of the mains' frequency. " So they don't bother filtering, like a microwave. Hmmm. ** Microwave ovens have similar line frequency modulation and for the same reason. The high voltage PSU is not filtered. Electronic transformers for 12v halogen lighting are the same too. No big DC filter capacitors means you'll not have huge peaks two times by mains cycle. Better power factor, in fact, it's almost itselfs a PFC |
#63
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Induction Cooking Table : IGBT keeping to short !
Actually I have a pretty novel idea I am thinking of trying to implement. An audio amp with only one output device hopefully, if I can find a fast enough triac type device (a few kinds would work). Would advance the phase of the triggering pulses according to input and switch off automatically when the HF power cycles. No filters or even rectifiers. If I can't do it a triac I can use a bridge rectifier and do the same thing with a fast SCR, or even a tansistor. The only advantage to a transistor though is that it would be switching off at zero crossing all the time. Still no filters.
It would have all the problems of a class D amp but less components and you could probably use slower output device(s) or a higher frequency. I almost decided to patent it but I found some things that are just too damn close. Convertors for VFDs running off three phase mains, with no recitification. It was interesting anyway. I might take a crack at it one day, the problem is designing the trigger circuit, there is not going to be a chip that'll do what I want - yet. But we are talking more efficient than class D if I can pull it off. Also in my [discouraging] research I found there is another type of class D amp out there now, it uses active filters almost instead of analog outputs. The class D part always keeps a pretty constant voltage across the analog devices keeping their dissipation down. The manufacturer claims efficiency nearly as high as class D but without the sonic anomalies that those golden ears dudes can hear. The days of linear operation may really be at an end. Don't even bother to rectify or filter ? Chop chop chop, nary a watt dissipated. Enough commentary now, we can start a thread for that. I would never mention my idea except I DID find out that it is unpatentable. If perchance I ever do build the thing I will get a provisional patent and see which way the wind blows. It's only a hundred bucks. Of course I think in that case every Eurasian engineer out there will look at it and by the time I get to market there will be three products like it, two challenges to the patent and more legal bills than I could ever make on one product. Such is life. I need to look for something even wierder to build. Speaking of which, I happen to own one of those induction cooketops and I would like to do something with it. Maybe I could make a weapon ? I got some microwave parts hanging around for the same reason. |
#64
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Induction Cooking Table : IGBT keeping to short !
On Tuesday, November 20, 2012 at 12:20:17 AM UTC+5:30, cLx wrote:
Hello, A day my induction cooking table did not work anymore (an Brandt TI302BS1). Opened it, saw a couple of IGBT in bridge configuration (two IRGP4068D), and the bottom one was shorted. Got some spares, replaced the shorted one, power on : OK. Two steaks later (in fact, 1 1/2 uses), got some unsuspected shutdowns, and sooner, the same IGBT shorts again. What I need to check before daring to replace the transistor and to retry to power on the beast again ? I've traced a bit the schematics, but it's obviously incomplete : http://clx.shacknet.nu/random/IMG_5802.JPG And a little picture of the board : http://clx.shacknet.nu/random/IMG_5803.JPG Thanks ! There are couple of transistors for drive the IGBT. replace those transistors and your problem will be solved. Thanks |
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