Cockcroft-Walton Voltage Multiplier

[jimctr]

I am driving a microwave transformer with a > 3000 Continuous Watt Voltage Inverter. The Secondary of the transformer is part of a Cockroft-Walton Voltage Doubler, to take 2.1kV to 4.2kV DC.  When I powered up the "current charger,"  the Inverter seemed to go in and out of limit and there was no apparent high voltage at the output storage capacitor.  The 15A fast blow in-line fuse to the Primary did not blow.  Nor did the fuses in the Power Inverter blow.
After the device was depowered and discharged (if there ever was any residual charge to begin with), I ohmed out the voltage doubler and was not able to locate any shorts to ground.  When I ohmed out the secondary winding coil, I got an O.L. reading on my DVM, whereas before it had read 65 ohms or thereabouts.  Apparently, I had blown my secondary winding.
I noticed on the microwave transformer - for which unfortunately I had no schematics - that part of the secondary winding is tied to the core itself.  I am
wondering if the secondary of the microwave transformer is polarized, and that I had therefore hooked the secondary backwards.  I had actually hooked the connector typically used for the magnatron to ground reference - earth ground - and connected the other end to HV DC blocking cap.

 

[BrianG]

I assume by "microwave transformer" you mean one from a microwave oven? You later mention that part of the secondary is connected to the transformer frame, i.e. at ground potential and that you connected the magnetron connector to ground.

Normally magnetron anodes are at ground potential and it's the cathode that has a high negative potential on it with respect to ground. It's possible that the magnetron connector assembly included a diode to give a negative-going voltage for the cathode. If this is the case and if I understand you correctly, your setup would have connected the diode across the secondary winding thus causing very high currents to flow in the winding on negative cycles.

 

[hacksaw]

you really need to post your schematic.

such transformers are single ended with one leg tied to case ground and the HV end to the diode and filter cap to produce negative dc.

puzzled by your use of a "dc blocking cap" .

the secondary of such transformers is rated for quite a bit of current so it is difficult to see how it would of opened up without causing greater problems in the primary.