For my arduino project I'd like to use two power sources: as main power a 6v 10w solar panel and, for backup, two 18650 batteries in series, and I have some difficulties in elettronica:
I'd like to automatically switch the power source to batteries if solar panel output drops below 5v, how should I do? I think I have to use mosfet, but is there some out-of-the-box circuit?
if solar panel output is >=6v I'd like both to power arduino and to recharge my 2s 18650 batteries (with a step up converter), I know there is a recharge/control circuit for only one 18650 (tp4065) but for two or more batteries in series I found only bms circuits, are those a right choice?
From my experience, the TP4560 will require 5 to 8V. I found supplying 6V to be the best charge solution on solar.
With 12V solar cells the 12V can be dropped down to 6V and fed to the TP4560.
With 6V solar cells you'll be lucky to get 5V, over time.
With 2 LiPo batteries in series you'll want to use a BMS. SO you'll need into the BMS 2X4.7V, 6V solar cell falls short.
You'll find your LiPo's will last about 4 months or less and if the LiPo's get down to 0C, throw them away.
Frankly what you are stating you want to do is better done with the proper equipment.
12V 10/20W solar panel, a PWM Charge controller, a 12V lead acid or LiFePo4, and a voltage regulator to turn the 12V into something useful for the MCU.
For the lipo the best route is a battery management IC , which can charge it properly and handle a load at the same time . Not easy as most are surface mount .
thanks for your precious suggestions but i haven't had the answer to my questions, that is
i have to power sources (main and backup), i'd like to switch from main to backup in certain conditions (when main falls down a known voltage), how should i do?
when main source is on, can I both power the load and charge the backup source, which is made up by 2 18650 batteries in series
is there a circuit to safely charge 2s 18650 batteries like the tp4065 which works for one 18650?
A diode switch automatically selects the highest voltage source (see below).
For questions 2) and 3), a professional balanced charger design is required and there are no simple, safe modules on the market that support a two cell solar charger. Hobbyists should stick with NiMH or lead acid batteries for solar projects, as these tolerate abuse. Lithium based batteries do not.
Thanks for your kind reply: and if it were a little more difficult and main source gives always a lower voltage than the backup but I want to use backup only when main drops down a certain threshold ? With the diodes only backup source were always on, so what can I do?
