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Hello electronics experts,

I am basically a computer engineer but because of a robotics project i am in a need of designing small ups for few seconds backup ( Approximately 8-10 seconds ) but facing following problems -

  1. Capacitor not charging up to 5 volt even if connected to power bank without using any resistor and without any load at the output.
  2. Is a resistor is always needed if we wants to use a capacitor?
  3. Is a load is always needed and then only capacitor will start conducting?

I am just a beginner in electronics, so please Help. Thank you all in advanced

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  • \$\begingroup\$ 1) Find (by reading its spec) the current your supply (V1) can provide. (if V1 is a power bank, remember your capacitor can't negotiate over USB! ) 2) Use Ohm's Law to calculate R1 to provide that current from 5V. 3) Calculate the RC time constant ( R1 * C1) 4) Charge C1 for 5x that time constant. 5) measure voltage across C. \$\endgroup\$ – user_1818839 Apr 5 at 11:49
  • \$\begingroup\$ How are you determining the Supercap is not charging up? \$\endgroup\$ – StarCat Apr 5 at 12:05
  • \$\begingroup\$ @StarCat I am determining it with checking the voltage across the super capacitor terminals while the circuit is connected using multimeter \$\endgroup\$ – Rushikant Pawar Apr 5 at 14:03
  • \$\begingroup\$ @Brian I didn’t get your point number 4. Can’t I keep the circuit as it is above and keep it on forever? I am going to use raspberry to output of above circuit. Does super capacitor just keeps sucking current and keep storing it even if it’s tummy is full to it’s capacity? \$\endgroup\$ – Rushikant Pawar Apr 5 at 14:08
  • \$\begingroup\$ Is your supercapacitor rated for five volts? Many can't handle that much voltage, and would be destroyed by it. \$\endgroup\$ – Hearth Apr 5 at 14:57
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  1. Powerbanks are not meant to be connected to charge large capacitors. If the capacitor is empty, it will draw as much current as it can, more than what the powerbank can deliver, and the powerbank may protect itself from the overcurrent by turning the output off.

  2. Not necessarily, but in this case it will help to limit the current to what the powerbank can deliver.

  3. No, a load is not needed to charge the capacitor.

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  • \$\begingroup\$ Sir kindly note my power bank and my super capacitor both are 5 volt ratings and my super capacitor is just 1 farad. Where the mistake is then? Please help. \$\endgroup\$ – Rushikant Pawar Apr 5 at 9:50
  • \$\begingroup\$ I already explained that the capacitor connected to powerbank will try to take more current than the powerbank allows so it will not work. \$\endgroup\$ – Justme Apr 5 at 9:52
  • \$\begingroup\$ My power bank allowed the current rating is 2.5 amperes at 5 volt. So can i use limiting current to 2.5 amp = 5 volt / 2 Ohm resistor ? So that power bank will not turn off itself as we have limited the current drawing from it to its ratings? \$\endgroup\$ – Rushikant Pawar Apr 5 at 10:18
  • \$\begingroup\$ You can try that. \$\endgroup\$ – Justme Apr 5 at 10:21

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