OK I NEED HELP - REALLY I DO ...

I AM PLAYING WITH A MICROWAVE OVEN -

WOULD LIKE TO REDUCE THE POWER OUTPUT OF THE MAGENTRON -

AS IT IS - IT IS SETUP FOR 600 WATTS PULSED ERP - THAT IS SHE PEAKS AT 600
WATTS 60 TIMES A SECOND -

ANODE VOLTAGE IS 4500 VAC THROUGH A 125 VAC STEP UP TRANSFORMER.

I WANT TO KEEP THIS VOLTAGE BUT WANT TO REDUCE THE CURRENT TO REDUCE POWER.

BEST WAY I THINK IS TO REDUCE CURRENT ON THE PRIMARY 120 VAC SIDE OF THE
TRANSFORMER.

CAN'T REDUCE VOLTAGE OF 4500 VAC BECAUSE MAGNETRON FAILS TO OSCILLATE AND
DRAWS A LARGE PLATE CURRENT.

ANY IDEAS ? ALREADY TRIED A VARIAC ON THE PRIMARY - IT REDUCED VOLTAGE BUT
DID NOT REDUCE POWER UNTIL THE MAGNETRON STOP OSCILLATING COMPLETELY.

ANY HELP WOULD BE APPRECIATED

- BIZ WDØHCO

WDØHCO wrote:
OK I NEED HELP - REALLY I DO ...

I AM PLAYING WITH A MICROWAVE OVEN -

WOULD LIKE TO REDUCE THE POWER OUTPUT OF THE MAGENTRON -

AS IT IS - IT IS SETUP FOR 600 WATTS PULSED ERP - THAT IS SHE PEAKS AT 600
WATTS 60 TIMES A SECOND -

ANODE VOLTAGE IS 4500 VAC THROUGH A 125 VAC STEP UP TRANSFORMER.

I WANT TO KEEP THIS VOLTAGE BUT WANT TO REDUCE THE CURRENT TO REDUCE POWER.

BEST WAY I THINK IS TO REDUCE CURRENT ON THE PRIMARY 120 VAC SIDE OF THE
TRANSFORMER.

CAN'T REDUCE VOLTAGE OF 4500 VAC BECAUSE MAGNETRON FAILS TO OSCILLATE AND
DRAWS A LARGE PLATE CURRENT.

ANY IDEAS ? ALREADY TRIED A VARIAC ON THE PRIMARY - IT REDUCED VOLTAGE BUT
DID NOT REDUCE POWER UNTIL THE MAGNETRON STOP OSCILLATING COMPLETELY.

ANY HELP WOULD BE APPRECIATED

- BIZ WDØHCO


First, you are missing an important electronic's fundamental: You cannot
reduce the anode current into a magnetron without also reducing the anode
voltage.

The reason your magnetron is quitting oscillation, is you don't have enough
power going into the filament. You need a separate filament transformer.
Be sure that the filament transformer has adequate insulation to handle the
anode voltage of the magnetron. The filament is running full anode voltage
below ground on most ovens.

If you reduce anode voltage, using a variac, the power output will reduce
quite nicely, but will be very nonlinear.

Depending on what it is you are trying to do, a possibly better way is to
build a cycle stealing power controller for the primary of the transformer.

What you do is this, build a triac controller that basically works as a
relay on the main power, and using a zero crossing detector, and a counter,
turn off one cycle of the AC (at the zero crossing), for every 10 cycles,
and you will be at 90% power, 2 cycles, out of 10, and you have 80%, 3
cycles out of 10, and you have 70%, ...9 cycles out of 10, and you have
10%. Because the transformer, and power supply filter capacitor cannot
respond this quickly to the cycle loss, you will have a smooth reduction
in your power, unlike the conventional oven's full power/no power duty
cycle modulation.

For best results, the removed cycles should be evenly distributed throughout
the 10 cycles. If you need finer control, you can use more cycles... for
1% control, 100 cycles... This is a great place for a PIC microprocessor.

-Chuck

Might I suggest that instead of trying to vary power supply conditions,
you change (lower) the PRF (pulse repetition frequency). That will
reduce the average power out to whatever level you wish.

Jeep/K3HVG
ex-NEXRAD-JSPO

WDØHCO wrote:

OK I NEED HELP - REALLY I DO ...

I AM PLAYING WITH A MICROWAVE OVEN -

WOULD LIKE TO REDUCE THE POWER OUTPUT OF THE MAGENTRON -

AS IT IS - IT IS SETUP FOR 600 WATTS PULSED ERP - THAT IS SHE PEAKS AT 600
WATTS 60 TIMES A SECOND -

WD=?ISO-8859-1?B?2A==?=HCO wrote:
OK I NEED HELP - REALLY I DO ...

I AM PLAYING WITH A MICROWAVE OVEN -

WOULD LIKE TO REDUCE THE POWER OUTPUT OF THE MAGENTRON -

AS IT IS - IT IS SETUP FOR 600 WATTS PULSED ERP - THAT IS SHE PEAKS AT 600
WATTS 60 TIMES A SECOND -

ANODE VOLTAGE IS 4500 VAC THROUGH A 125 VAC STEP UP TRANSFORMER.

I WANT TO KEEP THIS VOLTAGE BUT WANT TO REDUCE THE CURRENT TO REDUCE POWER.

You can't do that. From the supply side, the magnetron is basically a big
diode. There is no grid. All you can do is adjust the voltage across it,
and the current will follow.

ANY IDEAS ? ALREADY TRIED A VARIAC ON THE PRIMARY - IT REDUCED VOLTAGE BUT
DID NOT REDUCE POWER UNTIL THE MAGNETRON STOP OSCILLATING COMPLETELY.

Right. It's not really intended to operate over a very wide range.

There _is_ an article from Radio-Electronics in the mid-nineties on
those things... they give some methods to modify them and to get them
operating well out of their normal regime. Detuning it may be the
easiest way to reduce the output level.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

REDUCE THE POWER BY REDUCING THE DUTY CYCLE BY VARYING THE ON-OFF TIMES.
YOU SHOULD NOT BE PLAYING WITH MICROWAVE OVENS IF YOU DONT UNDERSTAND PULSE
OPERATION. WHEN YOU DROPPED THE VOLTAGE, YOU ACTUALLY HURT EFFICIENCY. IF
YOU HAVE LIMITATIONS ON THE MAINS SUPPLY, GO WITH A SMALLER MAGNETRON. I.E.
CHECK THE LABELS BEFORE YOU BUY. MOST CONSUMER MODELS PULL BETWEEN 8-15
AMPS DURING THE ON CYCLE. i SAW A CLAMP ON AC AMMETER FOR 20 BUCKS
RECENTLY. TRY BEFORE YOU BUY.


JIM, ac6tk
Technical Consultant
http://tekstuff.freespaces.com


"Scott Dorsey" wrote in message
...
WD=?ISO-8859-1?B?2A==?=HCO wrote:
OK I NEED HELP - REALLY I DO ...

I AM PLAYING WITH A MICROWAVE OVEN -

WOULD LIKE TO REDUCE THE POWER OUTPUT OF THE MAGENTRON -

AS IT IS - IT IS SETUP FOR 600 WATTS PULSED ERP - THAT IS SHE PEAKS AT
600
WATTS 60 TIMES A SECOND -

ANODE VOLTAGE IS 4500 VAC THROUGH A 125 VAC STEP UP TRANSFORMER.

I WANT TO KEEP THIS VOLTAGE BUT WANT TO REDUCE THE CURRENT TO REDUCE
POWER.

You can't do that. From the supply side, the magnetron is basically a big
diode. There is no grid. All you can do is adjust the voltage across it,
and the current will follow.

ANY IDEAS ? ALREADY TRIED A VARIAC ON THE PRIMARY - IT REDUCED VOLTAGE
BUT
DID NOT REDUCE POWER UNTIL THE MAGNETRON STOP OSCILLATING COMPLETELY.

Right. It's not really intended to operate over a very wide range.

There _is_ an article from Radio-Electronics in the mid-nineties on
those things... they give some methods to modify them and to get them
operating well out of their normal regime. Detuning it may be the
easiest way to reduce the output level.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

K3HVG wrote:
Might I suggest that instead of trying to vary power supply conditions,
you change (lower) the PRF (pulse repetition frequency). That will
reduce the average power out to whatever level you wish.

And since the filament winding is on the same transformer, it will
also lower the filament power proportionally, just like with the variac.
You still need a separate filament transformer.

-Chuck

Guys,

How do the "new" inverter technology microwave ovens operate?

Pete

Uncle Peter wrote:
Guys,

How do the "new" inverter technology microwave ovens operate?

Pete

They work in a manner that is very similar to the way the old
60Hz transformer style ovens operate.

They convert the mains AC to DC using a voltage doubler (US),
and convert the DC into a 100KHz square wave that feeds a small
ferrite cored transformer that contains a HV winding, and a
filament winding.

"Power" is controlled by cycling the oven on and off over a
10 second cycle: 10% = 1 second on, 9 seconds off, 20% = 2 seconds
on, 8 seconds off, ...

-Chuck

Probably switch mode inverter for HV.
73, Steve, K9DCI

" Uncle Peter" wrote in message
news:3UQIf.64002$bF.21387@dukeread07...
Guys,

How do the "new" inverter technology microwave ovens operate?

Pete

Hello again - Thanks for all the responses ! I talked with an EE at work and
he said just about the same thing.

I have decided to keep the microwave oven. For $33 dollars where can you
find a 600 watt 2.7 gig source ??? - I have already taken out the good parts
and are drilling and tappin them into a slab of aluminum. Lots of
experiments are planned !!! I feel like the mad scientist in a really bad
movie!

But I'm not the only one - check out this link from scientists in Israel who
claimed to have an instrument made from a microwave oven than can produce
balls of lightning.


http://www.livescience.com/forcesofn...lightning.html


Jeeze - I have already done this (many times - some even on purpose HI HI)
and I guess many of you have as well. It's called RF arcing. Still its bad
form in science these days to let a little thing like facts get in the
way.... after all these guys have PhD's and we hams... well...

As for me - I'm gonna create a web site showing all my mad experiments...

So when will the ARRL have a mad scientist section in the handbook??

Thanks all - Biz WDØHCO