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



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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