Hi Phillip,As the top toroid is raised above the first, the total top load C will increase with distance (both indoors or outdoors). As the two toroids are separated, Ctop increases and frequency will lower. Normally in a toroid stack (with no separation between the two), the total capacitance will be an average of the stacked toroids individual capacitances in situ. So, if your looking for "max capacitance", you would have to separate the two beyond practical limits. Maximum stack height is based on what is practical to operate both mechanically and for breakout (preference is usually the top toroid, but doesn't have to be).
You'll never reach the capacitance of the individual sum of both, but you can come to about 85% of the combined individual capacitances with ridiculous heights. The two toroids directly on top of one another above the coil is about 34pF. With the top toroid 85" above the bottom toroid, about 52pF. Practically, you'll likely not go beyond 40pF (20" above).
I'm not sure how you plan to connect the two, but Ed Sonderman used a cylinder of sheet metal between the two.
http://members.aol.com/esondrmn/index.html Take care, Bart Phillip Strauss wrote:
Hi all, This subject has been discussed some years ago but I wonder if there might be some new insight, I would like to maximize the total capacitance of two stacked spun Al toroids, one 24"x8" (26.5pF) and a 34.5"x8" (37.8pF) unit. I intend to use a spacer to separate the toroids but what would be an optimum length and diameter of the spacer to extract max capacitance in total, The secondary diameter is 12.4" and winding at 4.3 to 1 H/D., Any suggestions much appreciated, Phillip.
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