BQ25798: Solar Panel Charging not working consistently

James Berck

Part Number: BQ25798

Hello,

We are attempting to utilize this part as a part of a power system with solar panels connected. We are not always charging when an external solar source is applied to our panels.

We've done tests outdoors as well as with a large stage lamp. We have not seen outdoor tests work reliably. Indoors with the stage lamp, we've observed an interesting pattern. When we quickly apply the stage lamp to the panels, the system is able to start charging and we register current on our scope on the panel line. However, if we slowly bring the stage lamp over the panels, we consistently see no charge state activating. A small bump in current on the scope is observed in this condition which quickly dissipates. This is non-charging condition was also observed when we brought the lamp over smaller to larger sets of panels on the same system. So even with a large array of panels, when we bring it slowly over them, it does not activate charging.

We also did this test at suggestion of the forum: slowly applied the lamp to solar panels, observed no charge. left lamp over panels for 8 minutes (to prompt the 7 minute reset timer) no change in charge state

We've done a lot of debugging, we look at each of the states and recorded some states of interest below from the GUI:

trying to look for something suspicious in the GUI when we do light charging
- no light
  - no fault interrupts
  - chip config
    - enable charge, enable adc
- not charging with light
  - fault interrupt flags
    - pgflag int, acpresent flag int, vbus flag int, poor source flag int, vbuss present flag int
  - chip config single bit registers
    - enable charge, enable adc,
  - charger single bit
    - enable ibatt discharge with batt ovp,
    - enable termination
    - ignore ts
    - enable ilim pin
  - adc ibuss reading 4mA, adc vbatt 3584mV, acdvac2 7006mV
- took light away
  - all fault interrupts cleared
- light with fast charging
  - fault interrupts
    - flags light up when there is a change, doesn't indicate status of flag
    - power good interrupt, charge flag interrupt, vbatt ovp flag, vidnipm flag, ac2 present flag, vbuss flag, vbus present flag.
    - when we took it away
      - power good, charge, ac2 present, vbus, poor source ,vbus present
  - chip config single bit
    - enable acdrv2, enable charge, enable adc
  - charger single bits
    - enable ibatt discharge with ovp, enable termination, ignore ts, enable ilimb. same as not charging with light case.
  - noticing enable acdrv2 is going away when we take the light away and poor source is changing.
    - so it seems like taking away the light is disabling this.

Here are some images from the GUI associated with these different states:

default state with no light and no charging:

State where a stage light is slowly applied, resulting in no actual charging in the system. You'll notice HIZ is enabled in these faulty charge states:

State where a stage light is quickly applied, resulting in adequate charging in the system.
TODO getting this pic from a coworker.

For our configuration by default, we do the following: