I am not much experienced with electronics. But I am aware that supercapacitors must be charged with lower voltages than rated. I want to make a simple spot welder using this capacitor.

I have the following things. Can someone tell me what is needed (resistors/Schottky-diodes) and how to connect them?

  1. 100F 2.7V super capacitor
  2. 5V 1.0A mobile charger, non branded
  3. multimeter for measurements

I want to charge the capacitor at 2V and then short it over nickel strip to weld the strip to 18650 battery terminal.

  • 2
    \$\begingroup\$ This is a bit of an XY-problem, so could you please post the datasheet to the supercap? \$\endgroup\$ – pipe May 25 '18 at 14:01
  • \$\begingroup\$ Sorry, but i bought this supercap at aliexpress and unaware of datasheet. s.aliexpress.com/NBB7J3eU \$\endgroup\$ – dudul May 25 '18 at 14:05
  • \$\begingroup\$ Watch out for fake caps. \$\endgroup\$ – Long Pham May 25 '18 at 14:07
  • \$\begingroup\$ Heh yeah, I would not plan on getting 100F out of those :). But that's merely a diversion, let's assume that you can. I was mostly wondering about the maximum currents, but that's not listed. \$\endgroup\$ – pipe May 25 '18 at 14:18
  • 2
    \$\begingroup\$ The recommendation here, as always, is, "No datasheet? No sale!". \$\endgroup\$ – Transistor May 25 '18 at 14:18

The simplest solution would be to use a linear regulator (LM1117) set to 2V. This pair with a current limiting resistor would prevent the regulator from blowing up.

The next step would be to use a 555 timer to drive a PWM signal to a mosfet in between the LM1117 and the cap. This way you can limit the current without the need for a big current limiting resistor.

  • \$\begingroup\$ Thanks. This answer can be useful to other people who are familiar with electronics. But for me, can you tell how to charge cap of given specifications and power adapter of 5V 1A with simple resistor and schottkey diode (if necessary). I need to know their specs and arrangement in the circuit \$\endgroup\$ – dudul May 29 '18 at 21:21
  • \$\begingroup\$ You could use a power resistor of anywhere between 1 to 20 ohms. You could use this one mouser.ca/ProductDetail/ARCOL-Ohmite/…. It is pretty cheap and will get the job done. \$\endgroup\$ – Meozaa May 29 '18 at 22:20
  • \$\begingroup\$ i used 2 ohm 10W ceramic resistor. Thanks! \$\endgroup\$ – dudul Jun 7 '18 at 3:53

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