Resume from power outage, really only with 24V?
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relevant formulas are
C = Q * V
2 * E = C * V * V
Q = I * tQ = charge in Columbus
C = capacitance in Farrads
V = voltage in Volts
I = current in Amperes
t = time in seconds
E = energy in Joulesalso you have
"usable energy" = "potential difference" * "charge"so in your case Eusable = (10.5V - 6.5V) * Q
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@arhi said in Resume from power outage, really only with 24V?:
relevant formulas are
C = Q * V
2 * E = C * V * V
Q = I * tQ = charge in Columbus
C = capacitance in Farrads
V = voltage in Volts
I = current in Amperes
t = time in seconds
E = energy in Joulesalso you have
"usable energy" = "potential difference" * "charge"so in your case Eusable = (10.5V - 6.5V) * Q
thank you soooooo much!
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you are welcome, you might double-check them, I exited university more than 25 years ago
and it's not something I use every day but I think my memory is still good enough 
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@arhi said in Resume from power outage, really only with 24V?:
you are welcome, you might double-check them, I exited university more than 25 years ago
and it's not something I use every day but I think my memory is still good enough You've been great, thanks! A friend of mine will give me a 22000µF 50V capacitor to try, so I have to buy only the two resistors! The 10.000uF will be used someday for something else....
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@the_dragonlord said in Resume from power outage, really only with 24V?:
22000µF 50V
that one most probably have high ESR so no resistors needed
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I have not thought too deeply about this but -- if there is concern about the initial current surge .... what about something like this -- using an AC SSR ?
The resistor can be chosen to limit the wattage and slowly charge the capacitor. If VIN drops the AC SSR should latch up and remain latched until the capacitors are exhausted.
Of course a diode could be placed in series with the resistor to prevent drain but at the expense of a slightly lower available voltage on the capacitors.
Just an idle thought .... Unlike @arhi -- it's been almost 40 yrs (an NO! not valves)
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@stuartofmt said in Resume from power outage, really only with 24V?:
I have not thought too deeply about this but -- if there is concern about the initial current surge .... what about something like this -- using an AC SSR ?
The resistor can be chosen to limit the wattage and slowly charge the capacitor. If VIN drops the AC SSR should latch up and remain latched until the capacitors are exhausted.
Of course a diode could be placed in series with the resistor to prevent drain but at the expense of a slightly lower available voltage on the capacitors.
Just an idle thought .... Unlike @arhi -- it's been almost 40 yrs (an NO! not valves)
i understand but it's a little too complicated for what's my purpose... I haven't got an ssr and neither electronic components... i'll try with the 22.000 and with 2 1 ohm in parallel each other and in series with the capacitor as you suggested me.... thanks a lot for every precious suggestion!
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@the_dragonlord - I perfectly understand
@arhi - You are obviously much more recently "in tune" with art. What do you thing of the suggestion above? I've not fully thought it through (timimg / race conditions etc) but on the surface it seems like a reasonable way to have a low power (and high R) resistor for initial charging and minimal resistance (max power handling) during the discharge cycle.
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@stuartofmt it depends on the ssr, lot of them have antiparallel diodes on input, that will not allow it to work... they show in datasheed single diode but you reverse polarity and it still work so they have antiparallel ones often...
everything else seems ok, when the cap bank start to discharge the scr/triak will latch and will stay latched till next time you power it on and Vin gets higher than Vbank ... so ideal beh. in theory... in practice - never tried this solution
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@arhi If there are antiparallel diodes on the input then that ought to be able to be circumvented with a blocking diode on the input - yes? I.e. prevent triggering the SSR during the charge cycle. Or am I misinterpreting your meaning ?
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@stuartofmt yes, adding a diode should solve that problem ... there might be some edge cases dunno brain don't work from all the painkillers, but could be a good solution, I might try it out in the morning to see how it behaves on real example. the question is mostly why go with it, decent ssr is around $50, few caps, res and a relay is under $5
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@arhi - I was not thinking a decent SSR
So what if it goes closed circuit ..... 
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@stuartofmt
... dunno I really dislike the PRC stuff when it comes to power ... they are usually cheap for a reason ...anyhow, this is all really only needed if one goes with a lot of low esr caps in parallel, with one big cap the ESR is high enough to not have to worry about this at all
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