Capacitor Charge time / power
Capacitor Charge time / power
(OP)
Hi all!
Im a novice electronics enthusiast.
Im charging a capacitor bank from a 350V supply. The total capacitance is 940uF.
I want to be able to approximately calculate how long this will take with different resistors, then juggle the time/resistance to reach a reasonable power figure (disapation) for the resistor.
If someone can please explain how this is done so that I can substitute differrent capacitor/resistor values.
Thanks,
John.
Im a novice electronics enthusiast.
Im charging a capacitor bank from a 350V supply. The total capacitance is 940uF.
I want to be able to approximately calculate how long this will take with different resistors, then juggle the time/resistance to reach a reasonable power figure (disapation) for the resistor.
If someone can please explain how this is done so that I can substitute differrent capacitor/resistor values.
Thanks,
John.





RE: Capacitor Charge time / power
Yikes! This is not the best way to start out in electronics.
Google 'RC Time Constants'.
RE: Capacitor Charge time / power
RE: Capacitor Charge time / power
RE: Capacitor Charge time / power
Is there an easy way to approximate a series resistor's dissapation? P=IV will only work when the capacitor is fully discharged & the AC is at full wave (rectified mains).
RE: Capacitor Charge time / power
So, if you are charging your 940 uF capacitor to 350 V, you will dissipate .5x.00094x350^2 which computes to near 58 Ws each time you charge it. If you charge it once every second, your dissipation will be 58 watts. If you do it ten times a second, the dissipation will be 580 W.
Simple as that.
Take care. These voltage levels are no playthings.
Gunnar Englund
www.gke.org
RE: Capacitor Charge time / power
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Capacitor Charge time / power
Rate the diode for the peak current, that is the peak mains voltage divided by the resistance.
If you want to charge the bank in a few mains cycles there would be no simple formula. If you charge it over a period of tens of seconds then I think the mains pulsations will all tend to even out and the time constant formula will become applicable again, albeit with a scaling factor. Just guessing at this stage. I would run a SPICE simulation because there is less chance of making a large calculation error.
Tell us what time constant you want and whether or not you are doing half wave rectification of the mains and then we can offer more specific answers.
RE: Capacitor Charge time / power
Depends on his local line voltage. In North America, with 115 Vac input, he wouldn't reach 350 Vdc with a half-wave.
There's lots of AC-powered strobes around. Must be plenty of schematics available on the WWW. Of course, a found circuit plan can be easily adapted and extended.
RE: Capacitor Charge time / power
RE: Capacitor Charge time / power
respectfully
RE: Capacitor Charge time / power
So one time constant is 1-1/e=63.21%
TTFN
RE: Capacitor Charge time / power
Thanks for everyones help.
RE: Capacitor Charge time / power
RE: Capacitor Charge time / power
TTFN
RE: Capacitor Charge time / power
The RC time-constant is 4x what you might expect, and even then the curve isn't exactly an exponential. However it is pretty close.
ht
RE: Capacitor Charge time / power