Re: [TCML] DIY Tank Capacitor - Plate configuration confusion

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Gary,

Last night I did an autopsy of construction on a 942C. I wanted to check 
the series situation first hand (I wasn't smart enough to go to the 942C 
pdf first which showed the layered construction until after I had made 
my observations). The metallized polypropylene layer serves as an 
unconnected middle plate and forms two series capacitors with the two 
foil plates. I then thought about what is gained. Well obviously, the 
voltage divided across the two caps. The surface area is still about the 
same as would be seen with a standard two foil roll, but the voltage 
seen across each dielectric is now divided in half. Pretty smart 
construction!

As you know, Grants D4 or D5 construction is performing this division if 
measured from center plate to either end terminal, but his construction 
does not stop the inception voltage issue as the 942C construction does 
because the voltage across the terminals is seen as the full voltage 
across the two layers of dielectric. In the 942C construction, the gap 
between the 2 foil plates is large compared to the thin polypropylene 
layer, so the voltage across each layer will be half the total voltage. 
So in Grants case, if the inception voltage is reached, the dual layer 
won't help prevent corona which could lead to a breakdown.

But, Grant could build a plate cap in similar construction as the 942C 
to take advantage of the voltage division as long as the gap between the 
halved plates is large enough (I think).

Take care,
Bart
>
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