Timeline for Supercapacitor Bank Wont Charge w RPi Load
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 13, 2017 at 10:32 | vote | accept | user8087995 | ||
| Jun 13, 2017 at 10:32 | comment | added | user8087995 | @jimmyB I placed a 5 ohm resistor and anti-parallel schottky diode (SB120), together in parallel, in series with the s-cap bank and 10k ohm series balancing resistors - it appears to be working. Edited the schematic w the updates. Thanks all! | |
| Jun 10, 2017 at 18:41 | comment | added | JimmyB | Use the diode across the resistor to make the cap charge through the resistor but discharge (into the Pi) via the diode bypassing the resistor. | |
| Jun 10, 2017 at 15:03 | comment | added | Glenn W9IQ | The issue of your USB supply not being able to charge the caps when they are below 4.3 volts is probably still due to the charging current required by the caps is more than your USB supply can handle. When the caps are above 4.3 volts, they require less current to charge. | |
| Jun 10, 2017 at 13:08 | comment | added | user8087995 | @JimmyB any advice? | |
| Jun 8, 2017 at 9:33 | comment | added | user8087995 | JimmyB, you're suggesting adding the 10 ohm resistor in series with the bank and then also adding a Schottky in parallel with that resistor? What is the purpose of the Schottky in that position? I was thinking of placing a 4.7Vf Schottky in series between my parallel circuit and the RPi, to shunt current from the RPi when the s-cap voltage discharges to 4.7V, which would then push all current to charging the s-caps? | |
| Jun 8, 2017 at 9:16 | comment | added | JimmyB | 1) Balancing resistors/circuits are needed, else you will get imbalance and reduced performance from or damage to the caps 2) A 10 Ohm resistor in series with the caps will drop too much voltage to power the Pi; one could try an anti-parallel (Schottky) diode across the resistor though. | |
| Jun 8, 2017 at 9:01 | comment | added | user8087995 | I havent let the s-caps discharge all the way to ~1V or less. During testing, I noted that when the caps fell to ~4.3V (or below) and the 5V power supply was brought back, the s-caps failed to charge and the whole circuit only saw <=4.3V (wherever the discharging voltage was when the power supply was brought back). However, when the caps only fell to ~4.4V or greater, it was still enough to recharge the circuit when the power supply came back. FYI - the 5VDC supply is a 220VAC - 5VDC power supply for a microUSB cable, which has been cut in half and my circuit added. | |
| Jun 8, 2017 at 8:55 | comment | added | user8087995 | Thank you for the notes - the balancing resistors were 1k ohm each and the bank is attached to gnd. Edited schematic. | |
| Jun 7, 2017 at 23:47 | history | answered | Glenn W9IQ | CC BY-SA 3.0 |