From: firstname.lastname@example.org (N. Thornton)
Subject: Re: Spark gap q
Date: 16 Nov 2002 14:55:55 -0800
References: <email@example.com> <3DD559C4.340D3BF1@cox.net>
NNTP-Posting-Date: 16 Nov 2002 22:55:55 GMT
Mark Fergerson wrote in message news:<3DD559C4.340D3BF1@cox.net>...
> "N. Thornton" wrote:
> > firstname.lastname@example.org (John Crighton) wrote in message news:<3dd19791.792838
> > Hi.
> > Thanks for the replies.
> > > Is there any combination of material / curent etc that produces a
> > > fixed spacing spark gap that doesn't burn at all, i.e. would be very
> > > long lasting?
> > I am thinking in terms of miniature spark gaps, run at very small
> > currents, more signal than power.
> > > Spark gap design is still something of
> > >an art. What voltage, current, rep rate, etc?
> > V very low, very narrow gap. Below 20v.
> You want the arc to start at 20V, or
> to drop 20V once started
I was wondering if a fixed gap could be made to strike at 20v or less.
> (you say you've
> worked with carbon arcs so you ought to
> know they're negative-resistance
Yup, but I'm not looking for neg R here. It doesnt too much matter
what the characteristics are once its struck, as long as the device
> I agree with others that
> starting an air arc at 20V is gonna be,
> um, difficult.
Yeah, I was hoping with small enough dims it might happen.
I looked at Paschens curve, and maybe I missed something, but I saw
the plotted curve was for a given fixed airgap with different air
pressure, not for varying airgaps. I cant imagine air's dielectric
strength rising endlessly as gap tends to zero. But I'm sure no expert
If it is poss, the kind of airgaps I'd be looking at would be
incredibly small. That is quite doable if such a gap really would
strike at 20v or less.
> > Current ditto, far below an amp.
> > Rep. rate 100Hz. faster rep rates would be attempted later, but aren't
> > a necessity.
> I think somebody mentioned a Diac or
> similar semiconductor as a better
Unfortunately that wont do what I need. Hence the search for a spark
gap. I need to avoid silicon devices here.
> Looked into other
> negative-resistance ideas, like
> Negistors or Lambda diodes?
I havent, I really doubt they'd do what I am after. I'll look up
> > Its difficult to be more precise at this point.
> We ought to have asked earlier; why
> are you trying to build such a
> low-voltage gap? What's it for?
Ah, the tough question :) It needs to breakdown like a diac, but be
non silicon based. I also need to be able to play with it design wise,
a diac would be a closed box for me. It also needs to spark at very
low V. Its hard to believe that a sub min spark gap wont go below
300v: air's dielectric strength can't rise infinitely. I can do tiny
gaps, but the metal surfaces would have to remain unaffected for it to
keep working. I wish I had more expertise on spark gaps; alas I don't.
Thanks for the input!