3 years ago
They discharge very slowly by themselves
3 years ago
Speaking generally, you can discharge a capacitor by connecting it to some thing that will allow current to flow through it. The voltage on a capacitor is proportional to the charge on it. If charge moves out of the capacitor, in the form of current, the voltage on the capacitor drops.
An easy example is what happens when that thing is a resistor. A small resistor will allow big current, and discharge the capacitor quickly. A large resistor will allow small current, and discharge the capacitor slowly. For ideal capacitor C and ideal resistor R, voltage on the capacitor drops exponentially. More specifically it drops to (1/e) = 0.36788 of its previous value, every R*C seconds.
V(t) = V0*exp(-t/(R*C))
where V0 is the initial voltage on the capacitor, i.e. the voltage at time t=0.
This simple case, of just a resistor and capacitor, is well known, and you can read more about it here:
I am not sure what you mean by "leakage". Maybe you mean your capacitor behaves like it has a large "built in" permanent resistor inside? So the capacitor voltage drops slowly, even with no external thing ( an open circuit) connected to the capacitor.
But there is not much you can do about a "built in" permanent thing, because there's no way to remove a thing that is permanent.
i think he may mean the cap takes a long time to self discharge. Answer Slap a big resistor across it - 1 Meg ohm for example.
If the op doesn't clarify the statement to mean somethng other than was the OP said , then his meaning is quite clear.
It's really hard to say, as is often the case it is easy to use a technical term in the wrong way and change the meaning.
To my way of looking at it discharging with a minute leakage isn't worth while the Cap will discharge itself anyway give enough time.
BUT If the cap has a minute leakage characteristic then maybe it is taking a long time to self discharge and the OP wants to speed this up hence put a resistor across it is the normal practice.
Of course they don't say where the Cap is and what the circuit is which may be a game changer totally.
I hate it when a poster doesn't come back with information or to say thanks guys.
I used a screw driver in my time...
I once discharged the Pulse forming network of a radar using a screwdriver about 50Kv! Unfortunately the Radar was still on and I welded the screwdriver to the back panel of the cabinet - very impressive arc.
After that I was never too lazy to get out the discharge rod with a nice big resistor on it.
50Kv Wow, I was just discharging 400V 500uF caps that would leave sputter marks on the screw driver shaft...
The older radars produced their power pulse by charging a capacitor / inductor ladder - A big one! This was then discharged through the magnatron using a gas filled thyristor producing a narrow pulse of 10cm RF. It was normal practice to ensure the cap bank was discharged by grounding the top of the thyristor (But not whilst it was on - and YES I should have noticed the blue glow but it was late and we had been working a long time..
Lots of whining and singing electronics :-) Exciting times.
We always had to work in pairs and one handed to reduce the chance of electrocution.
To be fair I only had 3 or 4 serious shocks and mostly my fault. Only 1 put me in hospital for a few days and that was because I hit the wall as I reflexively jumped back giving me concussion.
charge it and leave it alone. no added load will beat the capacitors own natural leakage for "very minute"
If you mean, how do you discharge a capacitor slowly?
Use a large resistor like a 1 meg ohm across the leads.