A 4" x 5-1/2" x 1/16" piece of double clad copper glass-epoxy PCB has 975 pF between the sides. Now you know.

You're welcome.

 

Is there a linear relationship between the capacitance and the area? In other words, if the piece was 2' x 5 1/2", would the capacitance be 487 pF?

 

Is there a linear relationship between the capacitance and the area? In other words, if the piece was 2' x 5 1/2", would the capacitance be 487 pF?

The basic equations for how to make a capacitor seem to confirm that idea.

That means, "yes" (but my supper was beeping so I had to run away for a minute.)

 

Interesting.... never thought of a PCB as a substitute for a capacitor... what would be its advantage, higher voltage capability?

 

Interesting.... never thought of a PCB as a substitute for a capacitor... what would be its advantage, higher voltage capability?

Two conductors divided by an insulator is the definition of a capacitor. Circuit board capacitance is an inescapable fact caused by its shape. Area and distance were provided in the first post. The only thing missing to write the complete equation for circuit board capacitance is the dielectric constant of fiberglass.

 

Two conductors divided by an insulator is the definition of a capacitor. Circuit board capacitance is an inescapable fact caused by its shape. Area and distance were provided in the first post. The only thing missing to write the complete equation for circuit board capacitance is the dielectric constant of fiberglass.

Yes, I understand all that, thank you. It's just that I think it's very easy to get a commercial capacitor of 975 pF (almost 1 nF), but it would probably have a voltage rating of a few hundred volts at most.
What I'm wondering is if using PCB's as caps could maybe work with much higher voltages. After all, when caps fail it's mainly because their insulator breaks down due to over voltage, isn't it?

 

What I'm wondering is if using PCB's as caps could maybe work with much higher voltages.

Better than some, worse than others. For even higher voltages, try a Leyden jar.

 

I think it's very easy to get a commercial capacitor of 975 pF (almost 1 nF), but it would probably have a voltage rating of a few hundred volts at most.

Not true. I have a drawer full of 1000 pf ceramic caps rated at 1000 volts.

Here's a page of 1000 pf caps rated for 15Kv to 30Kv
http://www.mouser.com/Passive-Compo...Z1ykkklbZ1ykkklaZ1ykkkjcZ1ykkkjb&Ns=Pricing|0

 

Not true. I have a drawer full of 1000 pf ceramic caps rated at 1000 volts.

Here's a page of 1000 pf caps rated for 15Kv to 30Kv
http://www.mouser.com/Passive-Compo...Z1ykkklbZ1ykkklaZ1ykkkjcZ1ykkkjb&Ns=Pricing|0

MMMhhh.... a ceramic disk capacitor of 1,000 pF, rated at 15kV, for only $24.81 ... I'd still like to know how much voltage a makeshift PCB on could take ...

Edit: and temperature stability would be interesting to know too

 

Better than some, worse than others. For even higher voltages, try a Leyden jar.

Man, what a memory... the Leyden jar was my first love in electronics when I was a kid. I just loved to play with it.

 

I'd still like to know how much voltage a makeshift PCB on could take ...

You can figure it out yourself.

 

Man, what a memory... the Leyden jar was my first love in electronics when I was a kid. I just loved to play with it.

I think joeyd helped invent them.

 

You can figure it out yourself.

​

Question answered, thank you.
I still wonder about temp stability, though.

 

View attachment 108901
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Question answered, thank you.
I still wonder about temp stability, though.

You need to use dielectric strength. The breakdown voltage is a function of board thickness.

 

I think joeyd helped invent them.

If I should only be so famous.

 

If I should only be so famous.

I very much doubt that's what you really want... you've (wisely, imho) done everything possible to protect your privacy in this place

 

Hello,

Jan sells capacitors that are rated upto 50 kV:
http://askjanfirst.com/dindex.htm?/k3.htm

Bertus

 

Yes, I understand all that, thank you. It's just that I think it's very easy to get a commercial capacitor of 975 pF (almost 1 nF), but it would probably have a voltage rating of a few hundred volts at most.
What I'm wondering is if using PCB's as caps could maybe work with much higher voltages. After all, when caps fail it's mainly because their insulator breaks down due to over voltage, isn't it?

Wondering if not too prone to unpredictable variations due to changes in temperature, depending of next of what you assemble them, fans, etc. Maybe not hard to test, now that I think of it...

 

Man, what a memory... the Leyden jar was my first love in electronics when I was a kid. I just loved to play with it.

I made a few of those but most of what I played with required higher capacitance at lower voltages so I used whatever paper I could find and aluminum kitchen foil.

Oil soaked newspaper was good for at least a few hundred volts per layer.

 

Question answered, thank you.

The board might be good for 50KV, but don't forget the path around the edge of the board. That tiny air gap is not good for 50KV.