Re: Bleed resistor AND Led

I agree that if all you want to do is bleed the cap off and speed is
not an issue then the LED/resistor is the simple fix.

Using Mariss's notes (boy I wish he sat beside me in High School) we
can figure the resistor size.

I would use 40 volts just to throw in some elbo room. we know v=ir
so 40/0.02=2000 so I would use a 2k resistor. there is not a big
deal here between 1.6k and 2.6k at the LED should work all the way to
less than 1k (but not recomended)

Using 2k (did I mention I like to use round numbers too ?)
we can calculate the time constant t=rc

c= 0.025 farafs
r = 2k

t=0.025*2000 = 50 seconds.

At this point I would lean over and pffffft ...mariss....does the LED
in the circuit have an effect on the circuit ???? er... the time
constant... er... how long it would take to drain the cap one time
constant ?

but since he wasn't sitting there and Kimberly was, my mind was
somewhere else.... : )

Of course I could easily do the math and figure the watts will be
just over a half watt, so you would need a 1 watt resistor.


Dave

--- In CAD_CAM_EDM_DRO@y..., JanRwl@A... wrote:
> In a message dated 25-May-02 21:05:06 Central Daylight Time,
js3mc@a...
> writes:
>
>
> > By Mariss's explanation at the third time
> > constant the CAP will be at 5% or 2.5v Now by Daves explanation
the
> > LED needs 1.7 v to light. Sooo will the LED glow dimmly for some
time
> > after the third time constant?
> >
> >
>
> Jay: No, you will still have the 1800-2200 ohm resistor in series
with the
> LED, so it will not be conducting much current, if any, when the
cap is below
> a few volts.
>
>
> [Non-text portions of this message have been removed]