Turns ratio change

[me]

HV power supply...160kV/15mA
400vdc pfc rail;
Multiplier, 10 stage:
I've changed my primary turns from 19 T to 15 T and changed secondary
turns so ratio stays the same, yet I am unable to acheive same output
voltage- It's a 10 stage cockroft-walton multiplier. I would have
thought that I would not need to change tuning, just to expect larger
Ipri.
HV switcher f=25kHz.
I'm only able to get 140kv at this current. I believe I am within my
'resonance' window... Can someone give a clue?
(I'm a tech, not an engineer... )

TIA

 

[Paul Hovnanian P.E.]

HV power supply...160kV/15mA
400vdc pfc rail;
Multiplier, 10 stage:
I've changed my primary turns from 19 T to 15 T and changed secondary
turns so ratio stays the same, yet I am unable to acheive same output
voltage- It's a 10 stage cockroft-walton multiplier. I would have
thought that I would not need to change tuning, just to expect larger
Ipri.
HV switcher f=25kHz.
I'm only able to get 140kv at this current. I believe I am within my
'resonance' window... Can someone give a clue?
(I'm a tech, not an engineer... )

TIA

You might be saturating the transformer core.

I can't guess enough about the system topology to tell how other
parameters (frequency) might have changed due to your modification. But
a quick rule of thumb is that a transformer core is good for a certain
number of volts per turn (assuming a fixed frequency).

 

[me]

You might be saturating the transformer core.

I can't guess enough about the system topology to tell how other
parameters (frequency) might have changed due to your modification. But
a quick rule of thumb is that a transformer core is good for a certain
number of volts per turn (assuming a fixed frequency).

Thanks, Paul

I got diverted to another 'emergency'... Primary current usually shows
a large increase when saturation occurs, and I don't see that. Give
me a few days to get over this situation and will try to get more
clues. One thing I have done before is increase secondary tuning
capacitance, but I don't like doing that... (Too many HV gotcha's,
physically)

The front-end seems robust enough, staying at 400vdc. freq is rock
solid. Right now I am leaning toward some insufficiency in the
brick(multiplier). Mebee AC caps or something... sigh

Thanks!

 

[Paul Hovnanian P.E.]

Thanks, Paul

I got diverted to another 'emergency'... Primary current usually shows
a large increase when saturation occurs, and I don't see that. Give
me a few days to get over this situation and will try to get more
clues. One thing I have done before is increase secondary tuning
capacitance, but I don't like doing that... (Too many HV gotcha's,
physically)

Post some more details on the power supply. When you mention 'tuning'
there are lots of things that can interact to affect performance. There
are a number of power supply wizards lurking here that might spot the
problem.

The front-end seems robust enough, staying at 400vdc. freq is rock
solid. Right now I am leaning toward some insufficiency in the
brick(multiplier). Mebee AC caps or something... sigh

Did you by any chance measure a few points before and after the
modification? The input voltage to the multiplier would be an
interesting point.

Change in operating frequency (if any) might also be of interest.