Scenario: Arduino Uno is powered from the 5V pin and GND pin with a 3.7V Li-po battery. (Note: no USB).
The solar panels provide from 0V to 10V on full Sun. I got 4 cells on total 2 connected on series and then the two pares in series connected in parallel. (is not clear with this just ask).
I want to charge that Li-po battery with the solar panels but I do not want to connect the cells with a diode and then to the battery. So I realized that if I put the battery on the pins powering the Arduino directly the 5V input regulator act as a diode. What if I hook the solar panels in the 5V Arduino Input?
If the cells are giving only 1V that should help extend the battery life. If the solars are giving 8V, that should be charging the battery and powering the arduino at the same time.
Is there any problem in doing this? any better and simple solution for this?
Thanks!
LIPO batteries must not be overcharged, which is around 4.2 V per cell.
Theres nothing in your diagram to stop the battery being overcharged by the Solar Panels.
Otherwise it will work.
LiPo batteries are very fussy about how they're charged (and dangerous if misused) so for any solution that can charge the LiPos you will need to use a battery controller. There is an Arduino clone that has an integral LiPo controller. If you don't use that, you'll need to research how LiPo controllers work and design/build/test your own. Note that some LiPo failure modes can be very dangerous and it's usually recommended that LiPos should not be left unattended while charging.
Other types of rechargeable battery such as NiMH and NiCd are far more tolerant and could be managed with a current limited supply and a simple peak voltage detector.
If you only want the solar panels to be used in preference to the LiPo when available (and revert to LiPo power when there is no solar power available) with no recharge capability, you could do that by arranging for the solar supply to provide a higher voltage than the LiPo, with diodes on both of them to prevent either source discharging through the other. You will suffer some voltage loss from the diodes, and if you're going for maximum efficiency that could be important. Also, it sounds as if your solar cells are producing a far higher voltage than you need and if efficiency matters to you then you would need to choose an efficient way of dropping this down to your required output voltage. For example, you might be able to use a switched mode power supply/buck converter to produce a low voltage regulated output from a high voltage unregulated input. If you use the right type of converter, this could step the solar feed up to 5V even when the solar panels are producing less than 5V, as long as they're producing enough current. (You'd need to look at the voltage/current characteristics of your solar panels to decide whether this was worth doing.)
Also ensure that you isolate the LiPos when the voltage drops below the critical thresholds as they can be damaged by over-discharge.
