Re: Rectification and asundry Shtuff.
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Thursday, May 11, 2000 5:16 PM
Subject: Rectification and asundry Shtuff.
>Original Poster: "sundog" <sundog-at-timeship-dot-net>
> What is the easiest (read cheap too!) way to rectify the output of an NST?
>I surmise using diodes in sequence/parallel (MMD!), but what parts work
>for this? I have only 1 microwave for, er, "Research", and it still works,
>so cannibalizing that is out.
You don't need diodes in parallel, because the NST is a current limited
source (just about any old diode will handle 60 mA). The basic idea is to
string diodes in series. I use the 50 cent 6kV units from All Electronics,
and string together enough for a safety factor of 1.5-2 timesthe voltage I'm
going to work at (for instance, for a 15 kV NST (21 kV pk) I string up 6 of
them (36 kV nominal PIV)). Why so many extras? In case one is slow turning
off, or fails shorted, or has a bit higher reverse resistance, so it picks
up more voltage in reverse. I do NOT use equalizing resistors or
I either immerse the string in oil or pot it in HV electrical silicone
(epoxy would also work) because the diodes are pretty small compared to the
voltage across them, and I don't want surface flashovers.
You could also string up a whole bunch of 1200V diodes.... They're much
cheaper, but you've got to buy a whole lot more, and, more important, solder
a lot more, and after all, time IS money.
> And can I skimp on the voltage rating, or do I have to run it at 2x the
>NST voltage because of the non-polarized caps I'll be using? Would it see
>more than the rated voltage on the reversal?
Caps being polarized or nonpolarized makes no difference on the rating
required. What you DO need to be aware of is that on the reversal, a bridge
rectifier will be forward biased and it will destroy the diodes in short
order. Use a resistor or choke to limit the current (or just build a
standard "fullwave rectifier" and the transformer impedance will limit the