Author Topic: WeatherShield + supercap + solar node revisited (only works indoors) [SOLVED]  (Read 710 times)

ltj

  • Newbie
  • *
  • Posts: 19
Hello,

So after some time away I have finally taken up my electronics hobby again :)

I came across this (old) post by Felix describing a setup where the moteino + WeatherShield is powered from a supercap only, and using a small solar panel to replenish energy during the day: https://lowpowerlab.com/2017/09/15/weathershield-supercapacitor-tiny-solar-cell/

I decided to copy this setup using a Moteino R4, the r2 WeatherShield, a 5.4V 7.5F supercap and a 6V/1W solar panel. Now after a lot fiddling with ATC and such I got everything working. The moteino wakes up every two minutes, does a reading and send the payload, no ack requests/retries. This works beautifully...but indoors only.

Running everything indoors at regular room temperature and I see the cap voltage drop ~0.5V over 24hrs with no or very little light hitting the panel. Remarkable. As soon as I put everything out in the cold (~ 0C / 32F) I'm lucky to get two packets through. The voltage on the cap plummets and that's the end of it. After half an hour the cap is at ~2.5V. I have no clue as to why that is, so I would be very grateful if anyone can help understand what could possibly be going on here.

Thanks.
« Last Edit: January 24, 2019, 09:15:59 AM by Felix »

ltj

  • Newbie
  • *
  • Posts: 19
Re: WeatherShield + supercap + solar node revisited (only works indoors)
« Reply #1 on: January 24, 2019, 03:19:14 AM »
Found the issue: condensation. The rapid temperature changes must have caused condensation resulting in a high-resistance short.
By putting everything in a zip-lock bag inside and then leaving it in the cold outside produced no issues at all.

Kind of embarrassing ;D But there you have it. I just haven't really experienced this before (due to different power sources, seasons etc.)

Uncle Buzz

  • Jr. Member
  • **
  • Posts: 96
  • Country: fr
Re: WeatherShield + supercap + solar node revisited (only works indoors)
« Reply #2 on: January 24, 2019, 04:17:34 AM »
6V/1W solar panel

I wonder, as chinese parts (probably) if 1W is a real value, or if it's less than 0.8W because chinese get virtual power from their panel calculated with maximum current (at 0V) and maximum voltage (at 0mA) ? 1W / 6V = 167mA, which should be at the maximum power point about 5.5V and 140 mA ? so 25% less than argued ?
Or is the 6V 167mA the real maximum power point ?

ltj

  • Newbie
  • *
  • Posts: 19
Re: WeatherShield + supercap + solar node revisited (only works indoors)
« Reply #3 on: January 24, 2019, 06:22:12 AM »
I wonder, as chinese parts (probably) if 1W is a real value, or if it's less than 0.8W because chinese get virtual power from their panel calculated with maximum current (at 0V) and maximum voltage (at 0mA) ? 1W / 6V = 167mA, which should be at the maximum power point about 5.5V and 140 mA ? so 25% less than argued ?
Or is the 6V 167mA the real maximum power point ?

I think you are right about the real value being <0.8W (MPP). I rarely do the exact math on this, but rather opt for a lot of overhead in the panel power rating (maybe 3x).

FYI it was this one: https://lowpowerlab.com/shop/product/166?search=solar  :)

Uncle Buzz

  • Jr. Member
  • **
  • Posts: 96
  • Country: fr
Re: WeatherShield + supercap + solar node revisited (only works indoors)
« Reply #4 on: January 24, 2019, 07:14:30 AM »
As we depend of weather which has more variation than chinese promises, 25% less maximum power is not really a concern because you have to choose a panel larger than needed. If we can trust Vmax for overvoltage protection, that's ok