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Voltage Multiplier Problem

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Dragon64

Thu Aug 07 2014, 03:31AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

I recently replaced the flyback on my voltage multiplier but the output seems to be almost nothing (Less than 1mm discharge as seen in this video)

I've tested the ZVS driver which seemed to be working fine although I am unable to test the output frequency because of a lack of oscilloscope. Also checked both the capacitors and diodes for the multiplier but all of them are in working conditions.

Here is the output of the ZVS driver itself without the multiplier.

The 6 stage multiplier should be able to produce a minimum of 40+ kV (As it did previously with my older ZVS/flyback combo. Assuming that the change in the zvs driver changed the output frequency (decreased), it should still charge up to several kV though with a much larger Vripple but since it isn't, I'm at a loss to what the problem could be.

Here's the schematic

And some pictures the multiplier

Any help to problem solve this multiplier would be greatly appreciated

Sigurthr

Thu Aug 07 2014, 04:17AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

I doubt there is an issue with the multiplier; just the application of it. Most modern flybacks are DC output (integral diodes), and voltage multipliers work on AC output.

Dragon64

Thu Aug 07 2014, 04:48AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

Sigurthr wrote ...

I doubt there is an issue with the multiplier; just the application of it. Most modern flybacks are DC output (integral diodes), and voltage multipliers work on AC output.

The flyback that I used is a AC old disc style flyback with no internal or external diodes.

In fact, here's a picture of it out of the mineral oil

GrantX

Fri Aug 08 2014, 07:01AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Hmm. Just to clear things up with regards to the photo of the multiplier: The red wire on the right-hand side is grounded (based on the connection of diodes and caps), the yellow wire is AC input and the lone wire on the left is the HVDC output, correct?

Honestly, I don't know, I'm extremely tired at the moment. During operation does the ZVS circuit draw a lot of current when the multiplier is shorted (close to the amount drawn when the flyback alone is shorted), or does it sit near it's idle open circuit current?

Dragon64

Sun Aug 10 2014, 02:19AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

GrantX wrote ...

Hmm. Just to clear things up with regards to the photo of the multiplier: The red wire on the right-hand side is grounded (based on the connection of diodes and caps), the yellow wire is AC input and the lone wire on the left is the HVDC output, correct?

Honestly, I don't know, I'm extremely tired at the moment. During operation does the ZVS circuit draw a lot of current when the multiplier is shorted (close to the amount drawn when the flyback alone is shorted), or does it sit near it's idle open circuit current?

Yup, the red wire is grounded and the yellow is the hot.

Here's the data for various operating conditions

Voltage Multiplier (not shorted) - 30.4W
GFDUTfp

Voltage Multiplier (shorted) - 24.9W
5ljiHmj

ZVS Driver Idle (Disconnected from multiplier) - 18.7W
LbuSzJe

ZVS Driver (Maximum arc drawn) - 236.4W
KkG6jaR

Steve Conner

Sun Aug 10 2014, 10:03AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I know you said that you tested all of the diodes and capacitors, but it sounds like one of them is bad. Maybe it tests OK with a meter but breaks down under high voltage.

Dragon64

Mon Aug 11 2014, 06:57AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

Steve Conner wrote ...

I know you said that you tested all of the diodes and capacitors, but it sounds like one of them is bad. Maybe it tests OK with a meter but breaks down under high voltage.

Hmm, you were right. I tested each diode and capacitors again but in high voltage conditions and found one capacitor at the foot of the multiplier to be shorted.

After replacing it, I managed to get the old sparks I used to get however another capacitor at the foot of the high voltage input shorted out a few second after (arcing with a resistive load). Seems like these Chinese caps cannot hold up to the output of the flyback.

Proud Mary

Mon Aug 11 2014, 11:21AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Generally, operation of a C&W without a matched load is likely to lead to trouble.

Steve Conner

Mon Aug 11 2014, 01:11PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Pulling arcs off the output is about the worst thing you can do. The sudden short circuits cause violent oscillations that put a lot of stress on the diodes and capacitors.

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