Hi I'm Dann,
I bought the LTC4041 eval board form mouser to Raspberry Pi power backup. I have tried in first time, it was work properly and could charge the series supercapacitor 10F in 1-2 minutes. But when I'm not using it in one month, and I have tried again, it has a weird issue, the charging time need 10-15 minutes from 0.6V until 4.5V. The other, the board have a ringing in inductor or supercapacitor. I'm analyzed maybe there was something wrong with supercaps performance (ESR) but I'm not sure. Could you help me guys, what's going on with that?
Did anything change on the board to your knowledge? Or is it in its default state?
Do you have a load connected to VSYS when trying to charge now?
I would take a look at how much current is being delivered to the supercaps verses how much you expect. By default, it should be 2A. Make sure VSYS is unloaded during the test or the system load will steal current away from the supercap charging supply and that will result in a longer charge time.
I'm sorry make you confuse, the issue was gone. It was because my bad connection cable from power supply to LTC4041. Right now the LTC4041 could work properly and have 75s to charge the 75F supercapacitor in series.
Thanks for your help,