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microwave oven power cooking levels?

N

NSM

Jan 1, 1970
0
| in article XpNtd.5335$Ya4.1531@edtnps84, NSM at [email protected] wrote on
| 12/8/04 4:57 PM:
|
| > Mine has a big ass inverter transformer wound with what looks like 1/4"
| > thick Litz wire (multiple strands to prevent surface effects).
| >
|
| 1/4" litz seems crazy to me! A layer of litz 1/4" in diameter or thickness
| made from finer litz would make more sense. How many turns are there of
this
| litz?

It's not Litz wire, it's about 20# wire wound Litz fashion. It's two or
three layers and it looks like the primary? Actually 1/4 is a tad large, 1/8
might be closer, but I've never seen multiple strands used on a SMPS like
this.

N
 
F

Frank

Jan 1, 1970
0
I would never trust what the shops told me, have far to many times received
completely wrong advise, in fact I would be hard pressed to think of 1
occasion where they did not give completely wrong facts.



But if say 9 out of 10 say one thing, I would think that it wold be correct
 
F

Frank

Jan 1, 1970
0
1/4" litz seems crazy to me! A layer of litz 1/4" in diameter or thickness
made from finer litz would make more sense. How many turns are there of this
litz?

Bill



Its a Mains transformer..
 
J

Jim Yanik

Jan 1, 1970
0
NSM said:
| in article [email protected], wave at wave@waving wrote on
| 12/8/04
2:38

| I was intrigued by this and other posts on the subject. Here is what
| I conclude off the top of my head. I may be wrong in part. It sure is
| difficult to glean specific information from the Panasonic web pages.
...
| Running transformers at high frequencies, what the inverter does,
| reduces the size and weight required to handle large powers. The cost
| of
electronic
| devices such as transistors has dropped as manufacturing techniques
| improved. Magnetic components such as transformers have not dropped
| much,
if
| any, in price. To a large extent, cost and size for these components
| vary together.

Mine has a big ass inverter transformer wound with what looks like
1/4" thick Litz wire (multiple strands to prevent surface effects).

N

"inverters" take rectified and filtered line AC(DC) and chop it at high
frequencies (multiple KHz,maybe 25-50 KHz) thru a non-iron(ferrite) core
transformer,then rectify and use for the magnetron supply.This requires a
inverter control PCB.

Ordinary iron core,low freq transformers run on 50/60 hz line AC.and weigh
a lot more than an inverter transformer.
 
N

NSM

Jan 1, 1970
0
....
| > Mine has a big ass inverter transformer wound with what looks like
| > 1/4" thick Litz wire (multiple strands to prevent surface effects).

| "inverters" take rectified and filtered line AC(DC) and chop it at high
| frequencies (multiple KHz,maybe 25-50 KHz) thru a non-iron(ferrite) core
| transformer,then rectify and use for the magnetron supply.This requires a
| inverter control PCB.
|
| Ordinary iron core,low freq transformers run on 50/60 hz line AC.and weigh
| a lot more than an inverter transformer.

Yes? What's your point? This Panasonic has the biggest ferrite inverter core
I've seen.

N
 
R

Repeating Rifle

Jan 1, 1970
0
It's not Litz wire, it's about 20# wire wound Litz fashion. It's two or
three layers and it looks like the primary? Actually 1/4 is a tad large, 1/8
might be closer, but I've never seen multiple strands used on a SMPS like
this.
Although it is not clear from you description, there are ways of winding
coils to minimize stry capaciatance.

Bill
 
R

Repeating Rifle

Jan 1, 1970
0
Its a Mains transformer..
That is not a surprixe if true. But that would not be used in an inverter
device if low cost were important.

Bill
 
N

NSM

Jan 1, 1970
0
| in article %YRtd.7047$Ya4.4814@edtnps84, NSM at [email protected] wrote on
| 12/8/04 10:07 PM:
|
| > It's not Litz wire, it's about 20# wire wound Litz fashion. It's two or
| > three layers and it looks like the primary? Actually 1/4 is a tad large,
1/8
| > might be closer, but I've never seen multiple strands used on a SMPS
like
| > this.
| Although it is not clear from you description, there are ways of winding
| coils to minimize stry capaciatance.

I've seen copper tape windings, but this looks more like an effort to avoid
surface effects rather than avoid capacitance.

N
 
J

Jim Yanik

Jan 1, 1970
0
NSM said:
...
| > Mine has a big ass inverter transformer wound with what looks like
| > 1/4" thick Litz wire (multiple strands to prevent surface effects).

| "inverters" take rectified and filtered line AC(DC) and chop it at
| high frequencies (multiple KHz,maybe 25-50 KHz) thru a
| non-iron(ferrite) core transformer,then rectify and use for the
| magnetron supply.This requires a inverter control PCB.
|
| Ordinary iron core,low freq transformers run on 50/60 hz line AC.and
| weigh a lot more than an inverter transformer.

Yes? What's your point? This Panasonic has the biggest ferrite
inverter core I've seen.

N

I didn't know you had a Panasonic.(with inverter tech)

But for 1 KW power levels,of course you will have a large transformer.
Think how big (and heavy) a 1 KW+ iron-core xfmr would be.
 
J

Jim Yanik

Jan 1, 1970
0
NSM said:
| in article %YRtd.7047$Ya4.4814@edtnps84, NSM at [email protected] wrote
| on 12/8/04 10:07 PM:
|
| > It's not Litz wire, it's about 20# wire wound Litz fashion. It's
| > two or three layers and it looks like the primary? Actually 1/4 is
| > a tad large,
1/8
| > might be closer, but I've never seen multiple strands used on a
| > SMPS
like
| > this.
| Although it is not clear from you description, there are ways of
| winding coils to minimize stry capaciatance.

I've seen copper tape windings, but this looks more like an effort to
avoid surface effects rather than avoid capacitance.

N

I wonder what switching freq it runs at?
Higher freq inductors require more elaborate windings.
 
R

Repeating Rifle

Jan 1, 1970
0
I've seen copper tape windings, but this looks more like an effort to avoid
surface effects rather than avoid capacitance.

I think that you will find that tapes are used more to reduce leakage
inductance rather than capacitance.

Bill
 
N

NSM

Jan 1, 1970
0
| > Yes? What's your point? This Panasonic has the biggest ferrite
| > inverter core I've seen.
|
| I didn't know you had a Panasonic.(with inverter tech)
|
| But for 1 KW power levels,of course you will have a large transformer.
| Think how big (and heavy) a 1 KW+ iron-core xfmr would be.

This oven outputs 1200W. I'd probably get a hernia lifting it onto the
special uWave shelf if it had iron instead of ferrite. I suspect my Sharp
(1200W) may have the same inverter system without the modulation.

N
 
W

wave

Jan 1, 1970
0
Thanks everyone for the advice, considering the advice I decided to not
worry about the inverter technology and bought a Sanyo microwave,
unfortunately there is no way I am going to fit this or any other microwave
in my microwave space without breaking the clearance rules laid out in the
manual, obviously a lot of people must ignore these, same goes to people who
build home kitchens as my kitchen as a space designed for microwaves but in
practice it will not do the job, bummer. I guess my question is if there is
a person who fixes microwaves or has some other reason to know what minimum
standard clearances are acceptable, i.e are the manufacturers clearances
over engineered? The manual for the sanyo says 20cm above, 10cm at the back
and 5cm on the sides.
 
N

NSM

Jan 1, 1970
0
| Thanks everyone for the advice, considering the advice I decided to not
| worry about the inverter technology and bought a Sanyo microwave,
| unfortunately there is no way I am going to fit this or any other
microwave
| in my microwave space without breaking the clearance rules laid out in the
| manual, obviously a lot of people must ignore these, same goes to people
who
| build home kitchens as my kitchen as a space designed for microwaves but
in
| practice it will not do the job, bummer. I guess my question is if there
is
| a person who fixes microwaves or has some other reason to know what
minimum
| standard clearances are acceptable, i.e are the manufacturers clearances
| over engineered? The manual for the sanyo says 20cm above, 10cm at the
back
| and 5cm on the sides.

Unless it's a convection combo, 25mm all round is plenty. More is nice, but
what can you do?

N
 
A

Adder

Jan 1, 1970
0
I was intrigued by this and other posts on the subject. Here is what I
conclude off the top of my head. I may be wrong in part. It sure is
difficult to glean specific information from the Panasonic web pages.

The inverter substitutes high frequency electronic switching and a SMALL
transformer for a much heavier magnetic transformer to provide the high
voltage necessary to operate a magnetron. The switching also allows varying
the voltage applied to the magnetron. In turn, that varies the magnetron's
output level. A conventional transformer's output voltage is not easily
changed. The down side is that efficency is reduced somewhat, especially at
low cooking level. That is, a larger fraction of the electrical power you
pay for ends up heating things other than food you are trying to heat.

Running transformers at high frequencies, what the inverter does, reduces
the size and weight required to handle large powers. The cost of electronic
devices such as transistors has dropped as manufacturing techniques
improved. Magnetic components such as transformers have not dropped much, if
any, in price. To a large extent, cost and size for these components vary
together.

This is how all switchmode supplies (like in your PC) work. Transformers
can be made much more efficient at the higher frequencies. It's probably
the reason why aircraft power runs at higher than ordinary mains
frequency.
 
J

James Sweet

Jan 1, 1970
0
Jim Yanik said:
I didn't know you had a Panasonic.(with inverter tech)

But for 1 KW power levels,of course you will have a large transformer.
Think how big (and heavy) a 1 KW+ iron-core xfmr would be.

They're quite big and heavy, at least in the old ovens. Still not as big or
heavy as a 1KW metal halide ballast, and even those are much smaller and
lighter than 1960's vintage 1kw ballasts, those were absolute monsters.
 
J

James Sweet

Jan 1, 1970
0
Jim Yanik said:
I wonder what switching freq it runs at?
Higher freq inductors require more elaborate windings.


Could find out easily, hold the probe of a frequency counter near the power
supply with the oven running, might even be able to just poke it in the vent
in the back.
 
J

James Sweet

Jan 1, 1970
0
wave said:
Thanks everyone for the advice, considering the advice I decided to not
worry about the inverter technology and bought a Sanyo microwave,
unfortunately there is no way I am going to fit this or any other microwave
in my microwave space without breaking the clearance rules laid out in the
manual, obviously a lot of people must ignore these, same goes to people who
build home kitchens as my kitchen as a space designed for microwaves but in
practice it will not do the job, bummer. I guess my question is if there is
a person who fixes microwaves or has some other reason to know what minimum
standard clearances are acceptable, i.e are the manufacturers clearances
over engineered? The manual for the sanyo says 20cm above, 10cm at the back
and 5cm on the sides.

Depends on the unit, note where the ventilation grills are and try to allow
some airflow, particularly to the fan. I've seen some installations that
used a small duct to a vent located above or below the oven.
 
N

NSM

Jan 1, 1970
0
| This is how all switchmode supplies (like in your PC) work. Transformers
| can be made much more efficient at the higher frequencies. It's probably
| the reason why aircraft power runs at higher than ordinary mains
| frequency.

Actually they ran 400 cycle for weight long before they came up with solid
state, let alone switchers.

N
 
F

Frank

Jan 1, 1970
0
This is how all switchmode supplies (like in your PC) work. Transformers
can be made much more efficient at the higher frequencies. It's probably
the reason why aircraft power runs at higher than ordinary mains
frequency.



That is to get Smaller Transformers, war time planes use 80hz, and IBM main
frame computers I think from memory used 400hz
 

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