Hi Dale,
Thank you for your excellent reply.
I think i now understand what you were concerned about,
and what you thought might address your concerns.
Not really a test, but a way to gauge what was bothering you.
I think you were concerned about the contacts shorting out the cap.
You are correct to check that out.
Shorting out charged up electrolytic capacitors is not a good idea,
unless they are quite small values, and the charge voltage is low.
In this case, below ten micro-farhads, and twenty four volts will do
no harm. After testing the time interval the cap will probably turn
out to be less than five micro-farhads. That is just a guess, it will
depend on the R1 needed to push the transistor into saturation.
There is no resistor in that discharge loop because that is intended
to discharge the capacitor fairly quickly, so that if the supply is
plugged in live by someone wiggling the plug, or gets switched off
then back on quickly, then it will still do the ramp-up that you want.
A relay is a mechanical device, but the delay caused by its inertia
is very small, and is at the start of a small deliberately induced
rise-time, i don't think it is a concern. The rise-timing would not
start until the relay has operated, and opened its contacts, allowing
the cap to charge. Its job is not really to drain off the capacitor,
it is to ground it out quick.
Significantly, it is the absence of a supply feed that closes the
contacts, which can be done quite simply using a relay, but could be
complicated to design using electronics.
And you are quite correct, R1 will draw more current with the contacts
closed, i can only guess at a likely value for R1 for i don't know
the transistor (or FET) that you may be using, it could be around 300
ohms to push the transistor into saturation. (just a guess)
Which means that it would take around 80 milliamperes initially.
Once the relay operates, and the cap has settled, the base current
comes through the load anyway. Actually 300 ohms sounds a bit low,
you will have to check your data sheet.
The transistor is not used as an amplifier, it is used like a switch.
The value of R1 has to put the transistor into maximum conductivity.
But it is used a bit like an amplifier briefly, for the rise-time.
During this time the transistor has to handle significant wattages,
fortunately this time is brief, and the transistor should not get hot.
You quite obviously have a better grasp of what is involved than you
say. Which is why you have picked up on the apparent problem of the
contacts shorting an electrolytic. With these low voltages, and low
capacitance values, it should be Ok.
If there are others looking in, perhaps they would care to guess at
a capacitance which would give about twenty milli-seconds rise-time
for that transistor .... and it would only be a guess without the
number of the transistor. My guess is about five micro-farhads.
I did not mean to go into so much detail on my reply, but i am very
impressed by your grammar. Which appears almost faultless.
And i am impressed by your spelling, which is at least as good.
And your correct syntax, you were wondering, not wandering.
Only one slip, which shows you weren't using a checker system.
Regards, John