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