Issues when powering thingy:91 from solar panel

[Jonathan E]

Hi!

I am trying to power the thingy:91 from solar panels and have some issues with the thingy:91 restarting when the solar panel receives a medium amount of light. The solar panel charges the device properly in full sun and does not interfere with the device when there is no sun. However, it starts rebooting when there is some light. I assume that this is because the USB solar panel outputs a voltage lower than 5V, but high enough that the regulators turn on so that the nrf9160 is supplied with too low voltage. I have tried with multiple USB-solar panels which most often are used to charge surveillance cameras.

Do you have any tips on how to run the thingy:91 from a USB solar panel properly?

Best regards,

Jonathan

[Kenneth]

Hello,

I would likely have measured the VDD on startup, and made sure it's stable over a few seconds and (sufficient high) before starting to do something useful, also periodically measure VDD and enter power down immediately if VDD start dropping below operating conditions:
https://docs.nordicsemi.com/bundle/ps_nrf9160/page/recommended_op_conditions.html 

Kenneth

[Jonathan E]

Hi,

The issue also occurs when the onboard battery on the Thingy:91 is fully charged.

-Jonathan

[Kenneth]

I will run this by the designers of Thingy:91, but an measurement on what voltage looks like on VBUS (e.g. voltage drops with a timescale) I think would be very helpful here.

Kenneth

[Kenneth]

Can you provide some measurements before I contact them internally? I suspect this is the first they will ask about.

Kenneth

[Jonathan E]

Hi,

I have started doing some tests. The first test I did was powering the USB port with a power profiler kit to test multiple voltages. I did not recreate the problem with this method; the thingy switched between the battery and USB without any issues.

I have observed that using a solar panel makes the input voltage on the nrf9160 drop when it is connected and there is a medium amount of light shining on the solar panel.

-Jonathan

[Kenneth]

Please share the measurements when you have time. Could be interesting to check if a shotkey diode on VBUS made any difference.

Kenneth

[RichM]

I have been testing with several solar panels and looking at voltages today. It seems like the beginning of the problem is that when the Thingy begins doing something that draws more power (like connecting to cell network), the input voltage (VBUS)  from the solar panel which is running at 5 volts, can dip below 4.4 volts.I'm just using a meter on TP12 to watch this.

With the scope I see that Test points 3V3 and 1V8 and Li-Po and nRF52 are stable. nRF91 is bouncing around as the current draw does.

Since we only have high power draw a few moments per hour, is there a way we can disable the power charging before we do the cell transfers. It seems like this is the only time it is a problem.

Rich

p.s. - I am testing this using a 250W heat lamp aimed at the solar panel. That give me a lot of control. Everything works great when the panel is near the lamp or completely dark. Failure is when the panel voltage drops to about 4.7 volts and then drops further when cell is enabled.