How to Calculate Capacitor Discharge Resistor Values?

Some info on "RC time constant" for capacitor charge and discharge time.

http://www.tpub.com/neets/book2/3d.htm

It seems all RC calculations are made for R+C connected in series. How to calculate parallelly connected discharging resistor? It doesn't work the same way, does it?

A single parallel-connected resistor acts as a set resistance in an AC circuit (assuming your frequency is not too high that it starts to interact with the small inductive component of the resistor). The interaction gets a little more complicated when other capacitors and inductors are placed around it, but if you keep in mind that it is a fixed resistance in basic AC circuits (rather than a variable resistance like inductors and capacitors) you can simplify the circuit into fixed resistances and calculate for various fixed frequencies.

Information on more complicated frequency analysis is to extensive to be covered here and is available on the internet.

Thanks, in my case, there's 385VDC five elkos parallelly connected + these discharging resistors parallelly with them. There's three such "packages" in series and I'm trying to trace why one designer has used for instance 6.8k and an other one has used 10k resistors (in both cases three pieces) parallelly connected to discharge them. There's plenty of variations of voltages, amounts of elkos and their capacitances and resistor resistances (above just one example), but I haven't been able to follow any logical line how they have got into these design/component decisions. It really puzzles me.

Possibly the capacitors in the different designs are different sizes, run at different voltage (both of which affect the RC discharge time), or it could just be designer variation. Generally the resistance value of discharge resistors is not to critical, especially if there is an additional load connected to the capacitor output to help discharge them.

شي جيد أخوي

الله يوفقكم

Capacitor discharge is exponential decay in time, hence, you need to know the final value of charge or voltage to which you want to decay. Select the time constant from the graph below. Whether it is to go up or to go down, the time constant plays the same role.

Taken from http://www.tpub.com/neets/book2/3d.htm

How on earth did we manage to post the same obscure web page reference at the same time?

I have been working over the years on a unifying theory (based on experience) that relates increasing probability of occurance to increasing size and/or population base (which is actually the opposite of what you would expect), but it is not particularly interesting to anyone else. Stay tuned next week when I may very well manage to break the probability curve by walking into you while coming out of a resturant.

LOL.

Perhaps, when our time segments are large on work, simultanious hits are possible else there is nothing is simultanious in time-space events.

I think you were first to help the person. I felt that image may help better. I need to specify reference tp the link as it is information of some one else that need respect to this level.

T=RC (time = resistance times capacitance) is a basic rule of thumb, but not as accurate as Shyam's graph.

How about an experimental circuit and an oscilloscope?

That is Taguchi way.

You sure can reach the goal and may discover much more. For example we have ignored the leakage resistance in a very cool way. We also did not talk about the capacitor polarity where it will charge only with one polarity.

In this world communication is never complete and one finds more if does all by hand and we thank Taguchi for all that. I am admiror and follower of Taguchi way and put hands on things as far as possible.

Listen to the Indian, they are always right

The discharge / discharging resistor is used to discharge / discharging capacitors, reactors and superconductive magnetic coils.

What is the Log 10 value