I’ve been spending the weekend researching this topic and bumped into this topic which seems to have raised similar issues to those I raise below. BTW, my electronics skills are close to zero. My objective is to have load sharing capabilities to allow me to build (I have already built one) a series of Sonos type WiFi speaker using the Pi Zero and the Hifiberry mini Amp.
All of these will be based on recycled 18650 cells that are assembled in parallel to allow me to have large autonomy of these portable speakers.
My current solution is a TP4065 (3x chip based one) which then has a 3.3-5V booster (I was going to add the link but its my first post on this forum so only two links are allowed ) on the load end to allow me to power the Pi Zero. I thought I had nailed this until I realised that I hadn’t done my research properly. I discovered that I had three problems:
a) I had taken a big risk by parallelising 3x 18650 cells. Luckily they all came from the same laptop battery and were all charged to approximately the same voltage (+ or - 0.1V). The connection went smooth and nothing caught fire. The internet has mixed messages on this topic: some say these cells should never be connected in parallel, other say you can as long as you do it in mindful manner. I’ve concluded that the latter it true, and that any charging circuitry current would simply be shared based on the number of cells (in my case, the TP4065 1A charger provides a 0.33A current to each cell. I’m not concerned about this anymore and I think the prevailing opinion is that it can be done. Clearly, he more cells in parallel, the less convenient the TP4065 becomes (I understand that the TP5000 has a 2A charge current so could be a good alternative).
b) The TP4065 has a low voltage cut-off of 2.4V, which apparently is not good for 18650 cells. This is the thing that annoys me most about the TP4065, suggesting that the best usage of these circuits is to have them as charge only function (i.e. manually add them to a charger and then removing the cells and transferring them to the load units). The prevailing opinion seems to be that the low-cut off should be at 3V for 18650 cells. These units seem to resolve this issue, so I’m already leaning to substituting the TP4065 units with this circuit.
c) The above circuitry has load sharing capabilities - the TP4065 doesn’t seem to have proper load sharing capabilities. Would people agree? The TP4065 units don’t’ seem to have this load sharing capability from what I understand, even though they have the mosfet (not sure what this actually does if it doesn’t do the load sharing bit …). The alternative would be to use 2 way power switch on my speakers (i.e. load ON means USB charger input off and vice-versa … this would take load-sharing out of the equation for the device).
These MCP73871 units seem to be the answer to the need of having load sharing 5V power supply that has proper Li-Ion 18650 recharge/discharge management. Would people agree? Of course, the alternative is to use the $20 Adafruit units. Apart from the huge difference in cost, these Adafruit units are not advertised for 18650 Li-Ion chemistry cells but only for LiPo. From what I understand this doesn’t make much difference but would appreciate to be enlightened on this matter.