capacitive isolation

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Re: capacitive isolation

Postby Alex555 » Tue Dec 25, 2012 2:13 pm

I ran some simulations and at only 1 khz with a 5 amp load and my monster cap I found no notable ripple. I will probably switch it just above audible frequency. I have one problem though, The resistor I use to limit the current to charge the capacitor forms a voltage divider with the load resistance, making tha capacitor not able to charge past 10v with a 15v input. Also, is it a bad idea to draw 10A surges from a bunch of AA batteris in series?
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Re: capacitive isolation

Postby Alex555 » Tue Dec 25, 2012 2:20 pm

Situation averted. If I do not let the charge voltage-capacitor voltage exceed .125 volts, the cap's resistance would limit the current to ten amps or so. I will just need a relay to charge it through a resistor in the first place, And I'll add some overcurrent circuitry for safety.
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Re: capacitive isolation

Postby Bertho » Tue Dec 25, 2012 3:06 pm

Alex555 wrote:I ran some simulations and at only 1 khz with a 5 amp load and my monster cap I found no notable ripple. I will probably switch it just above audible frequency.


At 1kHz 50% duty, 5A output current and 33mF output capacitance, you will have a ripple of Q=I*t=U*C --> U=5A*0.5ms/33mF ~0.83V.


Alex555 wrote:I have one problem though, The resistor I use to limit the current to charge the capacitor forms a voltage divider with the load resistance, making tha capacitor not able to charge past 10v with a 15v input.


You can never attain the input voltage when a load is attached. The upper bound is always the input minus the ripple voltage.

Alex555 wrote:Also, is it a bad idea to draw 10A surges from a bunch of AA batteris in series?


You'd probably never get that much current out of AA batteries unless you put a lot of them in parallel. The internal resistance is in the order 1-to-50Ohm and dependent on temperature, usage and age.
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Re: capacitive isolation

Postby Alex555 » Tue Dec 25, 2012 5:49 pm

I think I will just limit my load to two amps. I should have far less problems that way. I also calculated the load resistance of my battery pack and it will limit current to 30 amps.
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