# Charge a supercapacitor safely using mobile charger

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.

• This is a bit of an XY-problem, so could you please post the datasheet to the supercap?
– pipe
Commented May 25, 2018 at 14:01
• Sorry, but i bought this supercap at aliexpress and unaware of datasheet. s.aliexpress.com/NBB7J3eU Commented May 25, 2018 at 14:05
• Watch out for fake caps. Commented May 25, 2018 at 14:07
• 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.
– pipe
Commented May 25, 2018 at 14:18
• The recommendation here, as always, is, "No datasheet? No sale!". Commented May 25, 2018 at 14:18

## 1 Answer

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.

• 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 Commented May 29, 2018 at 21:21
• 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. Commented May 29, 2018 at 22:20
• i used 2 ohm 10W ceramic resistor. Thanks! Commented Jun 7, 2018 at 3:53