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 !

In article ,
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'd go with the "experience tells me that many high-tech appliances are
designed by idiots" notion, and just replace the failed devices with
more robust ones.

Isaac

On Mon, 19 Nov 2012 19:50:17 +0100, cLx
put finger to keyboard and
composed:

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

I don't have any experience with these appliances, but my approach
would be to replace both IGBTs and all the capacitors, especially the
two 0.68uF film or polypropylene (?) types.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On 20/11/2012 06:20, isw wrote:
In article ,
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'd go with the "experience tells me that many high-tech appliances are
designed by idiots" notion, and just replace the failed devices with
more robust ones.

I thought about that, but i'm afraid to choose something which would present
more gate capacitance than the originals IRGP4068D. I've closely inspected
the Kapton isolation, but new thermal paste under it already.

cLx

On 20/11/2012 20:24, Franc Zabkar wrote:
On Mon, 19 Nov 2012 19:50:17 +0100, cLx
put finger to keyboard and
composed:

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

I don't have any experience with these appliances, but my approach
would be to replace both IGBTs and all the capacitors, especially the
two 0.68uF film or polypropylene (?) types.

Thanks for your advice. It's polypropylene caps I guess. There is a picture :
http://clx.shacknet.nu/random/IMG_5956.JPG
Any recommended source ?

I'll also change the two "snubber like" 47nF MKP capacitors (mounted from the
common node of transistors and coil to both supply rails).

On Tue, 20 Nov 2012 21:28:14 +0100, cLx
put finger to keyboard and
composed:

It's polypropylene caps I guess.

There is a picture :
http://clx.shacknet.nu/random/IMG_5956.JPG

Any recommended source ?

This appears to be the manufacturer's product page:
http://www.epcos.com/web/generator/W...locale=en.html

Curiously, the construction is "MFP" which is Metallized Polypropylene
Film, but the datasheet for the type, B32669, lists it as "MKP", and
the lowest capacitance is 1uF.

I'd try Mouser, Digikey, Farnell, RS Components.

I'll also change the two "snubber like" 47nF MKP capacitors (mounted from the
common node of transistors and coil to both supply rails).

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On 11/19/2012 12:50 PM, 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 !


Sometimes a call to the company or the service center will get an
answer like, " oh ya, you need to replace #%&#@ or it will keep shorting
the bottom one.
Mikek

"cLx" wrote in message
...
On 20/11/2012 20:24, Franc Zabkar wrote:
On Mon, 19 Nov 2012 19:50:17 +0100, cLx
put finger to keyboard and
composed:

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

I don't have any experience with these appliances, but my approach
would be to replace both IGBTs and all the capacitors, especially the
two 0.68uF film or polypropylene (?) types.

Thanks for your advice. It's polypropylene caps I guess. There is a
picture :
http://clx.shacknet.nu/random/IMG_5956.JPG
Any recommended source ?

I'll also change the two "snubber like" 47nF MKP capacitors (mounted from
the
common node of transistors and coil to both supply rails).


I'm with Franc on this. Replace both devices and all caps near them.

IGBTs are my least favourite power switching devices. I've always found them
hugely over-priced compared to FETs, and extremely fussy about their
operating conditions. I have also been told by a friend of mine that works
with them a lot, that they are *extremely* intolerant of having their gate
terminal touched when they are not in-circuit. He says that they can be
damaged as a result, so that's maybe something else that could have been a
contributory factor in the device re-failing.

Arfa

On Nov 19, 11:50*am, 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 !

From memory, shorting a bipolar structure has significance. Like, over
current blows the 'emitter' wire off - OPEN. And, over voltage
avalanches between the collector and the emitter, welding a small
nonsemiconductor material connection - SHORT. Anything that makes you
have an overvoltage, like a snubber circuit, or ?? might be 'killing'
your part. If the esr goes way up on your DC filter cap...?

Plus, I've had too many designers count on the two components to be
somewhat matched, come from the same lot, have similar switching
characteristics. Thus, replace both, each time.

Don't forget proper handling of the component when you replace. Static
discharges, especially during winter months, can be pretty robust May
not kill the part today, just weaken it enough to die tomorrow.

Arfa Daily wrote:


IGBTs are my least favourite power switching devices. I've always found
them hugely over-priced compared to FETs, and extremely fussy about their
operating conditions.

The big problem with IGBTs is they are a parallel structure of many
bipolar transistors, with POSITIVE temperature coefficient. So, they
do not balance current across the die well. When driven hard into
saturation, they balance better. So, the secret an IR app engineer
told me years ago is you have to drive them hard into saturation,
and never allow them to stay in the linear region for more than
a few ns, if possible. (You can only do so much of this during
turnoff, however.)

Jon

"Jon Elson" wrote in message
...
Arfa Daily wrote:


IGBTs are my least favourite power switching devices. I've always found
them hugely over-priced compared to FETs, and extremely fussy about their
operating conditions.

The big problem with IGBTs is they are a parallel structure of many
bipolar transistors, with POSITIVE temperature coefficient. So, they
do not balance current across the die well. When driven hard into
saturation, they balance better. So, the secret an IR app engineer
told me years ago is you have to drive them hard into saturation,
and never allow them to stay in the linear region for more than
a few ns, if possible. (You can only do so much of this during
turnoff, however.)

Jon



What I've never really understood, is what supposed advantages IGBTs have
over FETs. A while ago, I had the misfortune to work on a switcher that was
in a Yammy powered speaker. It used a pair of IGBTs that were about eight
quid apiece from memory. Much like the OP's induction heater, it would run
fine for a while, and then the stupid things would just destroy themselves
again - and I mean violently, legs actually blown off, and all that good
stuff. I mend a lot of switch mode power supplies, and for the most part,
their failure modes and what needs to be done to obtain a reliable fix, hold
no mysteries for me. But after about the fourth set of devices that I put in
the Yammy, along with just about every other component in the surrounding
area, I gave up on it. Many switchers of similar size and ratings, use an
almost identical topology, but with a pair of FETs. Typically a couple of
quid apiece, and in my estimation, *much* more robust. So with power FETs
rated to 800 volts and staggering amounts of amps being readily available
almost for pence, why would anyone actually design with IGBTs ?

Arfa

Arfa Daily wrote in message
...


"Jon Elson" wrote in message
...
Arfa Daily wrote:


IGBTs are my least favourite power switching devices. I've always found
them hugely over-priced compared to FETs, and extremely fussy about
their
operating conditions.

The big problem with IGBTs is they are a parallel structure of many
bipolar transistors, with POSITIVE temperature coefficient. So, they
do not balance current across the die well. When driven hard into
saturation, they balance better. So, the secret an IR app engineer
told me years ago is you have to drive them hard into saturation,
and never allow them to stay in the linear region for more than
a few ns, if possible. (You can only do so much of this during
turnoff, however.)

Jon



What I've never really understood, is what supposed advantages IGBTs have
over FETs. A while ago, I had the misfortune to work on a switcher that
was
in a Yammy powered speaker. It used a pair of IGBTs that were about eight
quid apiece from memory. Much like the OP's induction heater, it would run
fine for a while, and then the stupid things would just destroy themselves
again - and I mean violently, legs actually blown off, and all that good
stuff. I mend a lot of switch mode power supplies, and for the most part,
their failure modes and what needs to be done to obtain a reliable fix,
hold
no mysteries for me. But after about the fourth set of devices that I put
in
the Yammy, along with just about every other component in the surrounding
area, I gave up on it. Many switchers of similar size and ratings, use an
almost identical topology, but with a pair of FETs. Typically a couple of
quid apiece, and in my estimation, *much* more robust. So with power FETs
rated to 800 volts and staggering amounts of amps being readily available
almost for pence, why would anyone actually design with IGBTs ?

Arfa



Is there any rules for substituting powerFETs for IGBTs in such situations
that you had there, assuming you are not averse to going against the
designer's wishes?

Jon Elson wrote in message
...
Arfa Daily wrote:


IGBTs are my least favourite power switching devices. I've always found
them hugely over-priced compared to FETs, and extremely fussy about
their
operating conditions.

The big problem with IGBTs is they are a parallel structure of many
bipolar transistors, with POSITIVE temperature coefficient. So, they
do not balance current across the die well. When driven hard into
saturation, they balance better. So, the secret an IR app engineer
told me years ago is you have to drive them hard into saturation,
and never allow them to stay in the linear region for more than
a few ns, if possible. (You can only do so much of this during
turnoff, however.)

Jon



Thanks for the insight, I'll try to remember the warning

On 21/11/2012 22:10, Jon Elson wrote:
Arfa Daily wrote:


IGBTs are my least favourite power switching devices. I've always found
them hugely over-priced compared to FETs, and extremely fussy about their
operating conditions.

The big problem with IGBTs is they are a parallel structure of many
bipolar transistors, with POSITIVE temperature coefficient. So, they
do not balance current across the die well. When driven hard into
saturation, they balance better. So, the secret an IR app engineer
told me years ago is you have to drive them hard into saturation,
and never allow them to stay in the linear region for more than
a few ns, if possible. (You can only do so much of this during
turnoff, however.)

Jon

I did not designed the gate control circuit on that applicance... I hope
there is no problem there.

"N_Cook" wrote in message
...
Arfa Daily wrote in message
...


"Jon Elson" wrote in message
...
Arfa Daily wrote:


IGBTs are my least favourite power switching devices. I've always
found
them hugely over-priced compared to FETs, and extremely fussy about
their
operating conditions.

The big problem with IGBTs is they are a parallel structure of many
bipolar transistors, with POSITIVE temperature coefficient. So, they
do not balance current across the die well. When driven hard into
saturation, they balance better. So, the secret an IR app engineer
told me years ago is you have to drive them hard into saturation,
and never allow them to stay in the linear region for more than
a few ns, if possible. (You can only do so much of this during
turnoff, however.)

Jon



What I've never really understood, is what supposed advantages IGBTs have
over FETs. A while ago, I had the misfortune to work on a switcher that
was
in a Yammy powered speaker. It used a pair of IGBTs that were about eight
quid apiece from memory. Much like the OP's induction heater, it would
run
fine for a while, and then the stupid things would just destroy
themselves
again - and I mean violently, legs actually blown off, and all that good
stuff. I mend a lot of switch mode power supplies, and for the most part,
their failure modes and what needs to be done to obtain a reliable fix,
hold
no mysteries for me. But after about the fourth set of devices that I put
in
the Yammy, along with just about every other component in the surrounding
area, I gave up on it. Many switchers of similar size and ratings, use an
almost identical topology, but with a pair of FETs. Typically a couple of
quid apiece, and in my estimation, *much* more robust. So with power FETs
rated to 800 volts and staggering amounts of amps being readily available
almost for pence, why would anyone actually design with IGBTs ?

Arfa



Is there any rules for substituting powerFETs for IGBTs in such situations
that you had there, assuming you are not averse to going against the
designer's wishes?


I don't know. I must admit that at the time, I *did* consider trying exactly
that, but you know what it's like when you get one of these soul-destroying
jobs. I wrestled for several days with the idea of giving it one more go
with FETs in place of the IGBTs, but in the end, the owner said that if it
was going to be a lot of trouble, and absolute future reliability couldn't
be reasonably guaranteed, then he would just scrap it. I must admit that I
then drew a deep breath of relief, bundled it back together, and cheerfully
gave him it back. Next time, maybe ...

Arfa

On Fri, 23 Nov 2012 01:59:45 -0000, the renowned "Arfa Daily"
wrote:

So with power FETs
rated to 800 volts and staggering amounts of amps being readily available
almost for pence, why would anyone actually design with IGBTs ?

The main reason is that they're considerably cheaper when you need
both high voltage rating _and_ high current rating. That's because
they use less silicon die area. On consumer products the cheapest
component that will do the job acceptably well usually gets designed
in. Try pricing a 30A 800V MOSFET vs. a similar rating in a IGBT.. the
MOSFET will probably be 5x the price.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Spehro Pefhany wrote in message
...
On Fri, 23 Nov 2012 01:59:45 -0000, the renowned "Arfa Daily"
wrote:

So with power FETs
rated to 800 volts and staggering amounts of amps being readily available
almost for pence, why would anyone actually design with IGBTs ?

The main reason is that they're considerably cheaper when you need
both high voltage rating _and_ high current rating. That's because
they use less silicon die area. On consumer products the cheapest
component that will do the job acceptably well usually gets designed
in. Try pricing a 30A 800V MOSFET vs. a similar rating in a IGBT.. the
MOSFET will probably be 5x the price.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com


Assuming there is space to put 2x powerFETs in place and the switching f is
not beyond sensible powerFET territory, other than adjusting the gate drive
, any other considerations ?

On Sun, 25 Nov 2012 08:46:48 -0000, "N_Cook" wrote:

Spehro Pefhany wrote in message
.. .
On Fri, 23 Nov 2012 01:59:45 -0000, the renowned "Arfa Daily"
wrote:

So with power FETs
rated to 800 volts and staggering amounts of amps being readily available
almost for pence, why would anyone actually design with IGBTs ?

The main reason is that they're considerably cheaper when you need
both high voltage rating _and_ high current rating. That's because
they use less silicon die area. On consumer products the cheapest
component that will do the job acceptably well usually gets designed
in. Try pricing a 30A 800V MOSFET vs. a similar rating in a IGBT.. the
MOSFET will probably be 5x the price.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com


Assuming there is space to put 2x powerFETs in place and the switching f is
not beyond sensible powerFET territory, other than adjusting the gate drive
, any other considerations ?


Since IGBTs tend to be rather slow, power fet speed is not normally the
issue. Just the same IGBTs almost may be called IG-GTOs.

?-)

Arfa Daily wrote:



What I've never really understood, is what supposed advantages IGBTs have
over FETs. A while ago, I had the misfortune to work on a switcher that
was in a Yammy powered speaker. It used a pair of IGBTs that were about
eight quid apiece from memory. Much like the OP's induction heater, it
would run fine for a while, and then the stupid things would just destroy
themselves again - and I mean violently, legs actually blown off, and all
that good stuff. I mend a lot of switch mode power supplies, and for the
most part, their failure modes and what needs to be done to obtain a
reliable fix, hold no mysteries for me. But after about the fourth set of
devices that I put in the Yammy, along with just about every other
component in the surrounding area, I gave up on it. Many switchers of
similar size and ratings, use an almost identical topology, but with a
pair of FETs. Typically a couple of quid apiece, and in my estimation,
*much* more robust. So with power FETs rated to 800 volts and staggering
amounts of amps being readily available almost for pence, why would anyone
actually design with IGBTs ?
Below 400 V there is probably no benefit to an IGBT. At 400 V and above,
MOSFETs start to show a higher on-resistance. The higher the breakdown
voltage, the higher the on resistance. IGBTs have a constant Vce drop of
about 2V or better, up to several times continuous rated current. That
starts to look real good in serious power devices like motor drives.

IGBTs in an audio amp sounds really odd to me, I'll bet a set of
FETs could have been dropped into it perfectly.

Jon

"Jon Elson"

Below 400 V there is probably no benefit to an IGBT. At 400 V and above,
MOSFETs start to show a higher on-resistance. The higher the breakdown
voltage, the higher the on resistance. IGBTs have a constant Vce drop of
about 2V or better, up to several times continuous rated current. That
starts to look real good in serious power devices like motor drives.

IGBTs in an audio amp sounds really odd to me, I'll bet a set of
FETs could have been dropped into it perfectly.


** Switching PSUs in many high powered audio amps use IGBTs - often in
parallel groups. The topology is a driven, square wave inverter - no
feedback or regulation is needed.

The dodgiest time is at first switch on, when the filter electros present a
dead short to the DC output. Usually, the drive wave begins with a very low
duty cycle ramping slowly up to full square wave. Drive frequencies are in
the order of 100kHz to 150kHz.

Readily available, low cost mosfets are not in the game.



..... Phil

Phil Allison wrote:


"Jon Elson"

IGBTs in an audio amp sounds really odd to me, I'll bet a set of
FETs could have been dropped into it perfectly.


** Switching PSUs in many high powered audio amps use IGBTs - often in
parallel groups. The topology is a driven, square wave inverter - no
feedback or regulation is needed.
OK, in the off-line DC power supply section, this makes perfect sense!
Not in the audio amp section. (You can probably tell I rarely get into
late-model consumer audio gear.)

Thanks,

Jon

"Jon Elson"
Phil Allison wrote:
"Jon Elson"

IGBTs in an audio amp sounds really odd to me, I'll bet a set of
FETs could have been dropped into it perfectly.


** Switching PSUs in many high powered audio amps use IGBTs - often in
parallel groups. The topology is a driven, square wave inverter - no
feedback or regulation is needed.

OK, in the off-line DC power supply section, this makes perfect sense!
Not in the audio amp section.

** But no body said that they were used there, you misread Arthur's post.

" A while ago, I had the misfortune to work on a switcher that was
in a Yammy powered speaker."

The "switcher " is the PSU.

..... Phil

I am not responding to you here Phil, but the whole bunch.

Everyone wants to get into all this esoteric **** here and really an induction top doesn't run at microwave speeds. Simple RF. I mean television SMPS RF.

The bottom keeps shorting, well lessee here, what can cause one transistor in a totem type pole circuit to short ? This is a switcher. Can an imbalance cause a problem ?

First of all the drive. Now you might not be able to compare the drive to the top transistor without diff inputs or all that, but yuo should stil be able to tell. If the duty cycle is 50/50 then the E-B or S-G voltage will read the same on a voltmeter, which can be floated easily.

Once a 50 % duty cycle is conformed then the DC reading confirms equal drive. I ASSUME both transistors were changed at the same time. If not, shame on you.

There will be some snubber caps, and then there are the coupling caps. If it ain't drive it is load, PERIOD.

You got the bottom Xstr shorting, look at the TOP coupling cap. Leakage there would never bother the top Xstr. But the bottom might have a problem with it. The capacitor decides to be a resistor. C'mon you old folks, tell everyone about it.

Know what else ? If you can't get the same rating caps, so what ? Most likely they were chosen by price. Engineers might even make adjustments in the operating frequency to accomodate lower value caps, if it saves the company money.

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.

Use whatever, within reason, just make them equal. They must be equal, otherwise the engineer would have just used one cap instead of two.

Kapeesh ? Think of it from their end.

J

To add;

The top snubber cap (or transistor) is just as likely to be a problem. This cap's value is a bit more critical. For snubbers I would use the original value. The couplers don't matter.

J

I am not responding to you here Phil, but the whole bunch.

Everyone wants to get into all this esoteric **** here and really an
induction top doesn't run at microwave speeds. Simple RF. I mean television
SMPS RF.

The bottom keeps shorting, well lessee here, what can cause one transistor
in a totem type pole circuit to short ?


** An intermittent fault ( ie internal short) in the load.

That induction heating coil is a non- trivial device running at high voltage
& frequency.

The briefest short or arc between adjacent turns would take out one or both
IGBTs instantly.

BTW:

Stop being such a PITA jerk.



..... Phil

"An intermittent fault ( ie internal short) in the load. "

Of course it would. But not always the same transistor. As a matter of fact, if it is the final load doing it, both transistors would usually short. You saw the circuit. Or are you all talk and no analysis ? Can you REALLY read the ****ing schematic to a basically clipping SASEPP audio circuit from the 1970s ?

Now if there is an imbalance in the coupling or snubbers or even the devices, the device on the good side will usually fail first. Do you disagree ?

I want to know if both devices were replaced. Don't you ? Before you battle with me that is. I would hate to find out later I was right. It's not all that fair because it has happened so much on my life.

You wouldn't believe, but I got witnesses all over the place. Now be nice.

Look Man, on a ****ing TV I solved a greyscale problem by adjusting the vertical height. This is no bull**** I got witnesses. It involved a Sony, need I say more ? Want the technical details just ask, but I am sure you, nor anyone else on this forum would have been able to solve it. Anyone.

I will admit I am a PITA, but I recommend you do not engage me. You are good, but if you want to take me on, pack a lunch. I can design the **** you try to fix.

J U R B Yeah that's me. Back from the 1990s and ****. Think I been forgetting **** all this time ?

T

An intermittent fault ( ie internal short) in the load.

That induction heating coil is a non- trivial device running at high voltage
& frequency.

The briefest short or arc between adjacent turns would take out one or both
IGBTs instantly.

I've got a look at the coils, seem OK, not a trace of burn, and the
turns are isolated by section to distribute the voltage equally.


On 29/11/2012 07:45, wrote:
I want to know if both devices were replaced. Don't you ? Before you
battle with me that is. I would hate to find out later I was right.
It's not all that fair because it has happened so much on my life.

On my first and only test, I've changed only the shorted IGBT, ie. the
bottom's one. Worked, but the top got tripping two or three times and
failed again. Now I've removed the both IGBT, the 3 polypropylenes caps,
and the both MKT snubbers for replacement. I've also inspected the
kapton isolation behind the IGBT, saw no damage here.

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 solved a greyscale problem by adjusting the vertical height.

When this issue has calmed down... I want to hear about that.

I grew up reading the "Model Garage" stories in Popular Science and the ones
about an electronics technician (Art Margolis?) in Radio-Electronics. These
usually revolved around a difficult problem that did not have an obvious
cause.

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?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

"An intermittent fault ( ie internal short) in the load. "

Of course it would. But not always the same transistor.

( snip loads of puerile **** )


** ********.

You have thoroughly worn out you welcome here - pal.

****wit GG posters are tolerable in small doses only.

Sooooo - YOU are now fair game.

Watch out.



..... Phil

You have thoroughly worn out you welcome here - pal.
****wit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game.
Watch out.

For what? You're going to throw a tub of spicy hummis at him?

"William Sommerwerck"

You have thoroughly worn out you welcome here - pal.
****wit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game.
Watch out.

For what? You're going to throw a tub of spicy hummis at him?


** That joke is tad obscure.

My remark is fair warning that the GG poster has crossed the line and needs
to pull his head in.

Or I will bite it off .....



.... Phil

You have thoroughly worn out you welcome here - pal.
****wit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game. Watch out.

For what? You're going to throw a tub of spicy hummis at him?

** That joke is tad obscure.

It is obscure. It's a line from a movie I haven't seen, "Paranorman".


My remark is fair warning that the GG poster has crossed the line
and needs to pull his head in. Or I will bite it off ...

If you mean figuratively... You won't be doing much actual damage.

William Sommerwerck wrote:

You have thoroughly worn out you welcome here - pal.
****wit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game. Watch out.

For what? You're going to throw a tub of spicy hummis at him?

** That joke is tad obscure.

It is obscure. It's a line from a movie I haven't seen, "Paranorman".

My remark is fair warning that the GG poster has crossed the line
and needs to pull his head in. Or I will bite it off ...

If you mean figuratively... You won't be doing much actual damage.


All Phil will ever do, is bore people to tears with his juvenile
whining.

All Phil will ever do, is bore people to tears with his juvenile whining.

Internet Turet's syndrome maybe. But I am not going to dwell on that. The only real power Phil has is that every once in a while he has something to say so people don't completely ignore him YET. Whatever.

"Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50%
increase in cooking energy? "

No, that is a common misconception in the business. Do you remember the formula for capacitive reactance ? Apply it and just guess the frequency is over an octave above the sonic range.

The fact is that those caps are not being used as reactive components like in a tuned system, they are being used as coupling caps.

In that circuit they are effectively in parallel. Ground and the power supply rail are effectively at the same AC potential, so it's not 0.68, it's aready 1.36 uF. That is almost a piece of wire at 20 Khz. Almost, but we are dealing with a quite higher frequency here.

I got some pretty beefy 1 uF/400 V here but they are old and I can't be sure they can really handle the current. Actually I would like to use them in speaker crossovers someday.

Anyway, people also make this mistake working on SMPSes. Some use a coupling cap to keep DC off the transformer, OK, but that is a coupler. Think about it a sec., it LOWERS frequency to produce more output. Letting the capacitive reactance curve into that would fight against what you want to accomplish.

"Now i'm stuck at finding the polypropylene caps. "

Digikey doesn't have anything ?

What are you dealing with here, rectified 240 volts ? At 320, 17 amps is 5,440 watts. Four burners would add up to 68 amps. What size breaker does this thing take ?

It is possible that they are special caps of course. Manufacturers love using special parts.

Either way, lots of that type of cap fail by exhibiting leakage under stress. Same with the snubbers.

When you get a circuit like that, treat is like a bridge rectifier. Balance.. You change all four diodes in a bridge right ? You change both outputs in an audio amp right ? Same deal here.

Also everybody think about why SMPSes with the "totem pole" configuration usually use full wave rectification on the secondaries. Because balance is as important as it is in an audio amp. It may not seem so, but it is. If not they would save money on diodes.

On Thu, 29 Nov 2012 09:31:06 -0800 (PST), put
finger to keyboard and composed:

"Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50%
increase in cooking energy? "

No, that is a common misconception in the business. Do you remember the formula for capacitive reactance ? Apply it and just guess the frequency is over an octave above the sonic range.

The fact is that those caps are not being used as reactive components like in a tuned system, they are being used as coupling caps.

In that circuit they are effectively in parallel. Ground and the power supply rail are effectively at the same AC potential, so it's not 0.68, it's aready 1.36 uF. That is almost a piece of wire at 20 Khz. Almost, but we are dealing with a quite higher frequency here.

Here is an induction cooker design where the capacitors and coil are
said to form a "resonant tank":
http://beaversource.oregonstate.edu/...ki/IGBT%2BCoil

The second IGBT's body diode allows the coil current to decay
gracefully when the first IGBT switches off. I forgot about that.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Fri, 30 Nov 2012 13:54:20 +1100, Franc Zabkar
put finger to keyboard and composed:

Here is an induction cooker design where the capacitors and coil are
said to form a "resonant tank":

http://beaversource.oregonstate.edu/...ki/IGBT%2BCoil

The above design references the following document:

Induction Heating System Topology Review:
http://www.fairchildsemi.com/an/AN/AN-9012.pdf

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

"The second IGBT's body diode allows the coil current to decay
gracefully when the first IGBT switches off."

No. Don't you understand that ground is a human thing, not an electronic thing ? There is no up and down.

The only possible difference is if one side of the coil has more capacitance to ground, which would make an inbalance. This COULD happen, but if it did, the bottom Xsistr failing would be such a common failure mode it would be on Fox ****ing news. Switching the leads to the inductor could prove it, because then the top Xsistr would fail first.

We are talking about a ground fault condition here, without that, no anomality in the load could be imbalanced after it is running. Failing on startup is a different story, and this ain't it.

Get a grip, or a firm base of theory. Somehting. I'm surprised people can tie their shoes,,,, oh wait, they can't.

So much for that.

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.

I've been following this with curiosity and amusement.

I suspect this product is a marginal design that fails more-often than it
should, but not often enough to be considered outright "defective". (The
NuWave product advertised on late-night TV seems to be plagued with similar
problems.) There is probably no way to "fix" it, short (hmmm) of a complete
bottom-up redesign. It's a shame, because a counter-top induction "burner"
is a good idea. (I almost ordered the NuWave until I learned how unreliable
it -- and its seller -- are.)

The Infinity "SWAMP" switching amplifier from the late '70s is an example of
such a marginal design. It blew its output transistors far too often. The
designer later found the problem, and admitted that adding two cheap diodes
per channel would have prevented it.