I used the capacitor as a bypass capacitor or decoupling capacitor. Let me know if you have any further questions!
Hi all, I'm also trying to figure out if I can recharge the LiPo through Vin with a low current power source. @mohit, could you or anyone else comment on how long the supply needs to sustain ~100mA @5V to be able to charge the LiPo through the bq24195? Is it possible to supply this in short bursts (say 250ms each second?) or is there perhaps a bit of the delay switching to charge the battery that would make this intermittent current supply not useful?
Alternatively, if I were to opt to try to find a separate charging IC that is optimized for low-current/intermittent charging (maybe this LTC4071?: http://cds.linear.com/docs/en/datasheet/4071fc.pdf), could I connect this between GND and the Li+ pin to bypass the BQ24195 for charging purposes?
Thanks for any tips!
I too am trying to charge the battery on an electron from a small solar panel. Like others on this thread, my electron will need to wake up only a few times a day to transmit a small amount of data.
From what I see on the datasheet for the battery management IC the electron comes with, itās not intended to work with small solar panels. TI doesnāt even bother to document its behavior at less than ~500mA: http://www.ti.com/product/BQ24195/datasheet/specifications#SLUSAW59898 500mA is still a pretty big solar panel, at least compared to the electron.
Iāve been considering completely swapping out the battery charging IC the electron comes with with this one http://www.ti.com/product/BQ24230/ and then doing a small batch run via http://www.4pcb.com/ or some competitor. If Iām reading the BQ24230 datasheet correctly, this should allow the battery to charge at input currents down to 25mA (assuming of course the electron is in deep sleep mode). Thereās some complication as the pins donāt match up exactly between the two ICās, but I think I can figure it out (said the software engineer doing hardware for the first time).
I donāt suppose anyone out there has done this yet, but if so, Iād love any brain dump you can give hereā¦ or if anyone at particle has some thoughts. This seems like a pretty standard use case for the electron (remote, infrequent monitoring) but maybe Iāve gone off the rails somehow. Thanks.
The current PMIC charging chip will work just fine with small solar panels so there is no need to replace anything.
Here are the specs for the Electronās input:
When the charging current drops below 50mA the red charging LED on the Electron will turn off and this means charging has stopped since the battery should be at the fully charged voltage of 4~4.2v.
Any of these panels would work wired to the Vin pins.
thanks @RWB
Do you know how the electron will react to being charged with a solar panel that maxes out at 50mA? Specifically, I was considering this one http://store.sundancesolar.com/5-0v-50ma-solar-cell/ I need basically the smallest form factor I can get to, and the electron only needs to wake up 1-3 times a day to transmit a few bytes of data.
@mfogel I would say the solar panel youāre looking at is too small because under ideal conditions in the summer you can only expect approx 70% of the solar panels rated power output which puts you at 50ma x 70% = 35mA and thatās under ideal conditions. If you do not have the solar cell angled towards direct sunlight then that 35mA charge rate will be lower than 35mA and the same goes for clouds or less than ideal weather.
If youāre using the 2000mA battery that comes with the Electron, then youāll probably going to need to supply it with more than 35mA to properly charge the battery. The battery wants a certain amount of charge current for proper charging.
Youāre going to need a larger solar panel if you want the Electron to stay charged up and online under real-world weather conditions.
Feel free to test and report back if you do want to try the smaller panel but I would suggest the 3w panel since itās only going to provide 3w x 70% = 2.1 watts under ideal summer conditions.
Keep the Electron and battery behind the shade of the solar panel since direct sunlight on the enclosure will cause high heat and that is not good for the battery or the Electron, and I have heard of the SIM cardās melting on people when not shading the Electron enclosure.
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@mfogel : I have been using .5w/9v solar panels from Radioshack. You can find them on amazon for cheap. My electron only runs on a voltage change between pins. Maybe 4 or 5 times a day. These solar panels seem to do the trick. I have noticed that in decent sunlight, the red led on the electron does light up, indicating that it is getting the necessary 50mA, but I havenāt done much testing aside from that as this was only a temporary solution. Hope that helps.
I use a 5 volt/ 25 mA solar panel with great success but you have to bypass the IC by connecting the panel directly to the battery. Then add a small piece of code that keep the
modem on for one hour if the battery volt goes higher than 4.2 volt and if not go directly to sleep again.