Upupa Epops said:
That's really neat to use a digital delay.
I want to try this circuit to soft starting of a power SMPS.
Tell me, please, the trafo's secondary voltage is enough
to produce the pull-in of the relay?
If nominally secondary voltage is 15VAC, it become about 20VDC.
Relay is Re-24VDC.
Thanks,
Emil.
Ultima Thule said:Hi Zero_Cool,
just a thought, if your auxiliary winding is from the same transformer fed by a variac at 30-40 VAC (as you said in your first post) you can't have much more than some 3 volts BEFORE the voltage regulator to your 555 timer, will it work then...
Cheers Michael
Right, of course the 555 is not working at that time, the voltage does need to be higher before it will kick in. I understand that.
My curiousity lies in the fact that so much current is being drawn and that without the soft start no current is drawn when the voltage is raised with the variac. I was suprised to see the amp meter up around 3 amps as i was bringing up the line voltage when i had just run the same test with the soft start bypassed. I kept looking for something to be shorted, not thinking it was the caps that looked shorted to the transformer. still puzzles me, never thought they would draw that much current. i figured the charge rate would be fast enough to keep up with the transformer as iwas bringing the voltage up so slowley. or at least that if i stopped moving the knob that the amperage would fall quickly as the caps charged up but it didnt. at least not before the resistor complained!
Feeling a bit under the weather today, dont know if i will make it down to the shop tonight....
Zc
Hi,
ok I see.
But the series resistor is not there to limit the inrush current due to uncharged capacitors but rather because a transformer has initially no magnetic field and will it self draw many times higher current which may be well more than the cap-bank would cause.
The cap-bank is kind of "isolated" in the beginning of the power up because when theres no magnetic field in your transformer primary doesn't see what's on the secondary.
So everything is in order, just that the series resistor will probably burn up if you level up the input voltage slowly because the relay doesn't short it, it's kind a bug in that design I would say.
Cheers Michael
ok I see.
But the series resistor is not there to limit the inrush current due to uncharged capacitors but rather because a transformer has initially no magnetic field and will it self draw many times higher current which may be well more than the cap-bank would cause.
The cap-bank is kind of "isolated" in the beginning of the power up because when theres no magnetic field in your transformer primary doesn't see what's on the secondary.
So everything is in order, just that the series resistor will probably burn up if you level up the input voltage slowly because the relay doesn't short it, it's kind a bug in that design I would say.
Cheers Michael
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