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Solar Charger and Fona
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Solar Charger and Fona

by snoller on Wed Jan 14, 2015 12:36 pm

Hi,
i am running Adafruit Fona with an Arduino and want to combine it with a solar-panel. I connect the battery to the Batt-Port and the Fona to the LOAD-Port as described on the product page of the Solar Charger. In general this setup seems to work, Fona is uploading data etc. - BUT: something strange happens always after a few hours and measurements. The Solar-Charger seems to have a strange influence on the system because it will hang after a few hours. This disappears if i connect the battery directly to Fona. It happens with and without Sunlight. And with different combinations of batteries, hardware etc. - it really seems to be an issue with the power the Charger is providing. Are there any known issues i should be aware of?
Would it make sense to connect the Load-Port of the Charger not with the JST-Plug on Fona but with the Micro-USB on Fona that is intended to be used for charging as well? (in this case the battery would be attached to Fona directly)
Thanks in advance.

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Re: Solar Charger and Fona

by adafruit_support_rick on Fri Jan 16, 2015 11:19 am

Don't use the LOAD port of the solar charger. Use the battery output pads (B+ and gnd) to connect to your FONA

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Re: Solar Charger and Fona

by snoller on Mon Jan 19, 2015 7:45 pm

ok - but do i benefit from the smart load-sharing then or is it the same as if i'd connect Fona to the battery directly/in parallel?

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Re: Solar Charger and Fona

by adafruit_support_rick on Tue Jan 20, 2015 10:56 am

The problem with the load-sharing is that you can feed to full 6V from the panel into the FONA. The FONA is expecting battery voltage levels, and you risk burning it out. If you wire to the battery output, you will only get battery levels.

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Re: Solar Charger and Fona

by marcusbehrens on Tue Feb 10, 2015 4:21 pm

Hi, i have a similat setup working well. One 6600mAh battery hooked up to the solar charger. One 3.4w 6v solar panel hooked up to the charger. A fona and an attiny85 based arduino called olimexino both directly on the battery. And a set of devices connected to the load that are switched on or off by the olimexino.

You would not want to much connected directly to the battery as charging and drawing power to and from the battery at the same time is not a good idea.

The fona however can only deal with the typical lipo voltage range and it draws very short term up to 2 amps - not good to route this through the load part of the charger and/or other circuit.

So how does it work? most of the time my olimexino is sleeping and the fona is turned off. the olimexino is sleeping with the switch for the load turned off. so at tis point i do not consume more then a few microamps which is less then the natural discharge rate of the battery. charging will work fine during these times. when the olimexino wakes up he in many cases turns on the switch for the load as required. between the load output of the charger and the load i still have a regulator which bumps it up from the 3.1 (minimum battery one can still use) and 6v (solar panel working) to 7.7v for the load. only from time to time when the olimexino wakes up i use the key pin on the fona to turn the fona on and once transmission is complete turn it off again. in those short times where fona draws on the battery charging is hampered.

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Re: Solar Charger and Fona

by snoller on Tue Feb 10, 2015 4:39 pm

Sounds interesting. I also let Fona and the (custom) Board sleep most of the time. It's connected to the battery in parallel as connecting to load does not seem to be a good idea. But that way i still get stability problems, sometimes Fona and/or the board will just hang, i guess it has to do with spikes or so, perhaps it's also triggering the brown-out barrier for a short time. But just yesterday i found a solution that seems to work quite well: i just soldered a small 100nF ceramic capacitor into the power wires between the battery and the board/fona. Stability problems seem to have disappeared completely!

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Re: Solar Charger and Fona

by marcusbehrens on Tue Feb 10, 2015 5:15 pm

thx for the tip - my longest run was 8 hours with load on every minute for a second and fona on every 5 minutes for about 40 seconds (complete power up until i got gprs and sent 300 bytes to ubidots.com).

one problem i had with the fona was it would turn off just when it was about to connect. this was solved by putting reset to 5v - before it was floating.

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Re: Solar Charger and Fona

by chipmc on Mon May 11, 2015 1:15 pm

I ended up building a custom board to sit between the Fona / device and the Adafruit Solar Charger. That way, I could control the voltage to the Fona / Device and monitor the LiPo batter fuel level. I have written up the project on Hackster.io and you can build it yourself. Details here: https://twitter.com/chipmc86/status/597811201230376961

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Please be positive and constructive with your questions and comments.