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Re: Safety gap and first light
Well, after blowing my cap a second time I rebuilt it using 2 layers of 60 mil
poly. I had to leave out some plates to get it all to fit in my enclosure
ending
up with only 1/3 as much as what I started with (10 nF). Not much for all
my work.
Based on the time and money spent in building this cap and it case (a machined
glued and screwed plexiglas case) I'm going to an MMC. I don't think you
can beat
the cost and serviceability. Based on the data presented on this list,
they work
great too.
It's interesting how the discussions about MMC's have changed over the last 6
months since I started my cap. At first there was MUCH of skepticism and many
people saying it would never work, that's why I stuck with the plate cap.
Nothing
like a little experimental data to give a definitive answer!
Bill
Tesla List wrote:
> Original Poster: Alex Crow <user-at-alexcrow.clara-dot-net>
>
> Bill
>
> I would never say that a cap safety gap is needed, unless you are using
> super-expensive brand-new metal-cased Maxwell pulse caps. The other
> safety gaps should be fine here. Your cap is insufficiently rated, and
> your main gap is too wide! There is no other way your cap safety gap
> would fire unless this is the case. For 15kV you need *AT LEAST* two
> layers of 60 mil poly, perhaps 2 caps in series or even 2 of two layers
> of 40 mil. BEFORE YOU DO ANYTHING with your primary circuit make sure
> your main gap fires without anything else connected, ie just the xfrmr
> and the gap, at about 90% of max setting on variac. This is the only
> way to determine the total gap spacing you will need. Also, when tuning,
> close the gap down to, at the widest, 1/4 of this - then you can tune OK
> at low power and not worry about overvolting your cap.
> If your cap is a flat layer type, make sure
> you have left plenty of margin on every side to avoid flashovers.
> Where the poles leave the sides of the dielectric the next foil *must*
> be spaced at least 2" in from the edge of the previous, opposing one.
> Otherwise at even 12kV you are asking for trouble. Also make sure that
> you have rounded the edges on all foils - time-consuming but worth it.
>
> Either get rebuilding or do a MMC like others who got fed up of
> chopping up umpteen pieces of poly and foil! (ouch, those scissor
> burns!!!)
>
> It *will* work - congratulations on 1st light!
>
> Stay safe
>
> Alex Crow
>
snip..........