# pulse capacitors [duplicate]

I've got a Polypropylene 630V capacitor.

Wikipedia says this about polypropylene in capacitors: "Very thin sheets of polypropylene are used as a dielectric within certain high-performance pulse and low-loss RF capacitors."

So, it is likely a "high performance pulse capacitor".

Wikipedia says this about pulsed powre: "Pulsed power is the science and technology of accumulating energy over a relatively long period of time and releasing it very quickly, thus increasing the instantaneous power."

Does this mean that: if I charge this capacitor with , say: 12V DC power supply 7Ah (my sealed lead acid battery) for long enough time, It could store enough charge to release hundreds of volts of electricity quickly?

• What's the capacitance? What's the size? Where did you get it from? – starblue Nov 16 '14 at 15:13
• The size is: 2.5 cm in width. No idea about the capacitance; its old. – milo64 Nov 17 '14 at 3:42

## 2 Answers

Then energy stored in a capacitor is

$$W = \frac{1}{2}CV^{2}$$

So, when you give it a DC, the voltage on the capacitor finally goes to the same voltage with your source, can't be more than that, and the energy stored on the capacitor is fixed, no matter how long.

In http://en.wikipedia.org/wiki/Pulsed_power, it says:

By releasing the stored energy over a very short interval (a process that is called energy compression), a huge amount of peak power can be delivered to a load.

So, the key is the very short interval, and peak power, not volts. According to http://en.wikipedia.org/wiki/Power_(physics)

$$P = \frac{d W}{d t}$$

So, your total power is fixed, then the peak power depends on how sooner your power is released, has no matter with your capacitor. Of course, your capacitor should can tolerant the peak power releasing.

Titanium is used to make high-performance aerospace components, but not every chunk of titanium is an exotic component- maybe it's just a keychain.

Your capacitor is more-than-likely a pedestrian part used for snubbing mains voltage or something of that ilk. The energy density of reasonable size PP capacitors is very low (worse even than mylar film capacitors), and by charging it at 12V you'll get no more than 12V, and only about 0.14% of what little energy storage capacity it has (since energy storage is proportional to the square of the actual charge, and your capacitor is capable of 630V).

The peak power you could get from a capacitor is highly dependent on the construction and capacitors designed to produce very high currents quickly need sturdy connections and plates and very low inductance. Most PP caps use aluminized film that is very thin (in fact this is an advantage in some applications because a minor defect (short) in the dielectric can be blown away by a sufficiently high current-- which may occur naturally, so the product keeps working).

For high pulse capability the film capacitor should use foil plates rather than metalized plates: