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I want to find a way to use a solar panel to power an old iPhone running a single app to continuously collect temperature and humidity data in remotely located beehives. The iPhone must be continuously charged in order to run the app. I have tried a small solar panel with the iPhone plugged directly into it, but it doesn't keep the iPhone charged if there are a few days of clouds/rain. Once the phone runs out of power the app shuts off and does not restart once power is supplied again by the solar panel. I have also tried a 7500mAh battery pack plugged into the output USP port of the solar panel (to bank electrons from the panel). The battery pack is also simultaneously plugged into the iPhone to keep it charged. This arrangement seemed to work but only for a day. Finally, I've tried various solar powered battery packs but they shut off once the battery is full and don't provide a continuous charge to the iPhone which then runs down and the app shuts off. I'm not sure if I need a bigger solar panel, a bigger battery pack or if this arrangement is not compatible and there is another solution. This is proving to be a harder problem to solve than I thought, but I keep wondering if I am missing something. Thoughts much appreciated from this community of experts!

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    \$\begingroup\$ The place to start is with an energy budget. How many Watt Hours per day does the phone actually use when there is no solar available? After that, you can decide on how many hours or days of dark you want to survive. This will tell you how big the battery needs to be. Then you pick the solar panels and charge controller to charge the battery (plus run the device) in one good day of sun shine. \$\endgroup\$
    – mkeith
    Dec 19 '20 at 3:34
  • \$\begingroup\$ I would simply make another setup like that one that almost worked, then lookup how to wire one as redundant. Since the phone has a battery, even a relay would work, but don't use a relay, they waste power unless it's a latching relay. That will give you twice the capacity as before. You might be able to omit some parts in the 2nd one, not 100% clear what your setup is. Maybe also add a cheap wind turbine (eg <$50 on amazon); even a small one should be plenty for a phone. \$\endgroup\$
    – dandavis
    Dec 19 '20 at 4:00
  • \$\begingroup\$ Also, is your phone staying awake between readings? are you connected by data to upload the readings? if so, you could use push notifications to wake the phone rather than keep it live. (I believe iOS has no cron jobs). But maybe you've thought of this already. Interesting project by the way, we have a bee keeper in the family. \$\endgroup\$
    – P2000
    Dec 19 '20 at 7:43
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I am working on a very similar project with a Samsung S4 phone. We use a 12 Volt 15 watt solar panel, a 3 amp PWM charge controller, a 7 Ah SLA battery, and a 2 amp DC/DC converter with 5 V USB outlet.

Right now we are running the app (which takes photos and uploads them to an ftp site once every hour) continuously. This works fine if the weather is sunny, but the SLA battery discharges after ~2 days of overcast weather. Running the phone continuously wastes power, so my intention is change the app so it sleeps most of the time. According to my calculations it will have no problem staying charged if we can get the average power consumption down to 1/4 of what it uses now.

If you can get your app to sleep between taking readings then your existing setup may work OK. If that is not possible then the only solution is a bigger panel and more battery capacity. A 60 watt solar panel, 5 amp controller, and 30 Ah SLA battery will probably be enough.

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