John, and especially Rich (AG6K), I did look up the formula for voltage
multiplier regulation and ripple and a 6x multiplier used to provide 500mA
when driven by a 60 Hz source is an impossibility. Voltage drop per the
formula, assuming 560 uF capacitors are used in a 6-stage multiplier,
exceeds the output voltage target (1500V), meaning that under 1/2A load, a
60 Hz 6x multiplier using 560 uF capacitors would have an output voltage of
zero.
The formula is found here:
http://home.earthlink.net/~jimlux/hv/cw1.htm
I do seem to recall from my old voltage multiplier design days that the only
serious application for multipliers in the 6x range would be at low load
currents, or high operating frequencies, or preferably both. Most
multistage (> 2x) voltage multipliers do operate at >15 kHz, and are used in
applications where regulation and ripple are not particularly important.
There seems to be some reasoning behind the fact that even amateur equipment
containing HV supplies never seems to use > 2x multipliers (doublers); I
would imagine if 3x or greater multiplication resulted in a weight or cost
savings, or allowed reasonable performance at equivalent weight and cost
compared with HV transformers, they would be in popular use.
WB2WIK/6
"If everything seems under control, you're just not going fast enough." -
Mario Andretti
> -----Original Message-----
> From: John T. M. Lyles [SMTP:jtml@lanl.gov]
> Sent: Tuesday, October 15, 2002 9:51 AM
> To: amps@contesting.com
> Subject: [Amps] voltage multiplier shown
>
> We use a voltage multiplier to get about 700 kV DC at work. Its
> large, about the size of a small cottage. To get around using 60 Hz
> iron, we drive it with audio around 5 - 10 KHz, and do the conversion
> at that frequency. Pair of 3CW20,000s used in the audio driver, which
> then drives a step up output transformer, in oil. From this it goes
> upstairs into the voltage multiplier rectifier/capacitor stacks. The
> filter/storage caps are much smaller then, about the size of a humans
> leg (each one). There is a dc feedback loop around the entire supply,
> to regulate it.
>
> One can take a tour at:
> http://lansce.lanl.gov/overview/tour/index_tour.htm
> Place your cursor over the injector area, you see a photo showing the
> size of the voltage multipler, with the man standing beside it with a
> shorting stick.
>
> This is used to charge ions and accelerate them from resting state,
> in a device known as a Cockroft-Walton accelerator. Such was
> developed by Lord Cockroft in UK, in the early 1930s i believe. This
> was the beginnings of ion accelerators in early 'big' science. Most
> particle laboratories have dumped their CW's and gone to a small RF
> quadrapole accelerator at the front end. We still run ours; it was
> shown on an episode of Bill Nye the science guy (kids show) and also
> on the Horizon channel in years back.
>
> 73
> John
> K5PRO
> --
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