Re: diode protection

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Wells Campbell by way of Terry Fritz <twftesla-at-qwest-dot-net>" <wellscampbell-at-onebox-dot-com>

Hi DB, comments interspersed, 


---- "Tesla list" <tesla-at-pupman-dot-com> wrote:
> Original poster: "Daniel Barrett by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <dbarrett1-at-austin.rr-dot-com>
> 
>     Hi!
>     My setup is similar and in about the same stage as yours. I'm not
> sure
> what type of diodes you are using, but let me share a few things that
> may
> help. My exuberance and outpouring of funds has been running unclamped
> on
> this PSU for a couple of weeks now ;)
> 
>     1) Go ahead, break down and put the reactor under oil. It's messy,
> and
> doesn't sound like fun but It's worth the trouble. Home depot has these
> great waterproof electrical junction boxes with no holes in them. My
> reactor
> fit in a 8x8x4 inch model, about $20. If your reactor flashes over
> you have
> just toasted a lot of magnet wire, diodes and time. So invest the time-
> You
> will get good results.


yeah, I figured that was inevitable. 


> 
>     2) Use fast-recovery rectifiers for the de-queing diodes. 1N4007's
> will
> not survive if used much above 60Hz. I have burned up about 400 of
> them
> learning this. I'm having good luck with Gen Semi UF4007's from Mouser.
> These are $.19 each, I use a string of 20. This is a 100v, 1amp, 75nS
> unit.

I've been using microwave oven diodes, I got a bunch surplus at a buck
per, I think they are rated 12 KV -at- 500mA, 7 v forward drop, I'm not
sure of the recovery time, but the only reason I can see that microwave
ovens would need a fast diode would be to survive kicks from the transformer
as the unit was shut off mid-cycle or something, so I doubt they are
anything but "normal recovery".  I would like to keep using these, so
I don't have to do the "MMD" thing (my ps would only use six), but it
looks like that ain't gonna happen. 

> 
>     3) you can use a series resitor, but it's not necessary if your
> inductors are not flashing over and your caps are not exploding. It
> just
> burns power and acts as an expensive slow-acting fuse. The silicon
> fries
> faster than the resistor...
> 
>     I'm running a single MOT feeding a quadrupler feeding a 9H reactor
> for
> 20kV at 90mA. Streamers are about 4.5 feet at 1100VA input power as
> of last
> night, power supply is running cool and no fryodes. No protection or
> filtering of any kind. Just a lot of mineral oil all over the place

Wow, sounds like quite a performer. That must be a chunky MOT you've
got. is it one of those Advance Transformer co. rated 4000 volts?

Also, if you wouldn't mind, could you tell me about your reactor? Do
you use another MOT, or did you wind your own? This is another area where
my coil needs work. Unfortunately, I don't have an L meter, so this may
have to be done by estimation and trial, so info on yours would help.
I've toyed with the idea of using an MOT core wound with 22ga magnet
wire (heavily shielded, of course) or even a winding on a pvc pipe with
a core that could be pulled in and out to add adjustability. All just
ideas now, my cobble up used three MOT's in series and seemed to work
ok. 

>     Hope this helps!
> db

absolutely, thanks!
uh oh, there goes the exuberance again <<CLAMP>>

Wells Campbell
wellscampbell-at-onebox-dot-com