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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Andy, you're not using enough words to be unambiguous. I'm too far away to read your mind at this time of night. Pictures or diagrams would be even better.
Let's tackle "connecting two 1uF microwave caps at 90khz and reading the voltage across one, it shows 0.1volt from a 150volt source". Is this in simulation or in the real world? Are the capacitors designed for microwave frequencies, or for the power circuits of microwave ovens? Is the microwave attribute relevant? Are you connecting and disconnecting them 90,000 times per second? How are you reading the voltage? Is the 0.1 volt value an AC or DC or mixed reading? Same questions apply to the 150 volt source -- and where is that in the circuit?
In any case, if you put two identical capacitors in series, with identical initial charges, then their voltages should always be pretty much the same (note 1). So when you see 0.1 volt across one, what do you see across the other?
Note 1. In practice, the DC voltages won't generally stay matched, because of net leakage currents to the floating node.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Hi, Its real world not in simulation. The below picture is the setup that is showing 40volt approx, and being read with AC on the multimeter. Using the same setting on the multimeter but using 1uF caps, is only showing about 0.1volt on both measuring across the cap,and also showing that measuring across both caps. The source is ac at approx 90khz measured from the secondary of the transformer with just the wires connected reading 150volt. Adding a high Dconstant(barium titante) to the picture below increases the volts on the meter(larger capacitance, shouldn't it drop the voltage?), and putting a space between the top two and bottom two increase it as well.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
If the field falls off with distance, but the two inner plates are closer to the two outer plates it becomes one capacitor? You said that there is no charge inside the metal conductor, if I link up the two inner plates there shouldn't be any voltage, but the current should be the impedance of the one cap? Is it correct that for a 1uF cap at 90khz the impedance is 1768ohms(I thought it would be lower)? If I wanted to heat up some nichrome or copper powder inside the two plates with a 50/50 mix of nonconducting substance would it still follow the four plate method, one cap?
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
You can consider it one capacitor anyway, with a plate distance 2s and thus a capacitance of c/2. It doesn't matter how far apart the two caps are, so long as they are connected. Ignoring inductance of course.
However, connecting the two plates with nichrome would put current through the wire, and it would behave as one very lossy capacitor.
1.768 ohms, not 1768. But no, that's pretty much spot-on.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
However, connecting the two plates with nichrome would put current through the wire, and it would behave as one very lossy capacitor.
Thanks gren, with lossy capacitor, what part would be bad, the distance or permittivity. Was thinking that it would be a good way to joule heat the dialectic, at 1.7ohm it should be doable. Why would the capacitance increase or voltage on the two inner plates, when it moved farther away, but the outer and inner plates are close together, in your picture the field is related to distance, summonsing that the field wouldn't double in strength, but still have 1X in a local area? and shift more to two caps and a voltage divider? I used for the calculator, so I guess its not accurate to a degree.
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capacitor theory
