My application is primarily portable ham radio operation. I chose a self-balancing, 4.5 Ah, 12.8V, 4s3p LiFePO4 battery pack, a 28W panel and an MPPT solar charge controller with extremely limited knowledge of batteries and solar charging. My choices were based on power requirements (of course), my desire for MPPT and my need for small, lightweight, highly portable components (my controller weighs only a couple of ounces). I had hoped that in sunlight, the controller would distribute power between the battery and the load. However three factors make this impossible:
- The battery pack's on-board PCM disconnects the battery when charging rate reaches 0.02C.
- The charge controller passes panel Voc to the battery and load terminals when no battery is present.
- My load is not rated to handle panel Voc.
As a work around, I keep the load isolated from panel Voc via a DPDT switch with which I manually connect either the panel or the load to the controller. So, instead of a system in which the controller optimally distributes power, I'm forced to alternately charge and and discharge the battery.
I recently conversed with someone who has been using a DIY LiFePO4 battery pack successfully with my controller model, with none of the problems that I described above. It seems to me that the difference between his setup and mine must be that his battery's PCM doesn't disconnect near the end of CC charging.
My questions are:
- Can someone recommend a commercially available, self-balancing LiFePO4 4.5 to 6 Ah battery pack whose PCM has no low charge rate threshold?
- Can someone recommend an MPPT charge controller that has load terminals, is super small and lightweight, and that handles a disconnected battery gracefully?
- I'm considering building a 4s2p battery pack from 26650, 3.2V, 3300 mAh, 2C LFP cells (1C max charge rate, 2C max discharge rate). Can someone recommend a PCM board that would meet my needs?
- If I were to stay with my current controller and battery, would it make sense to place a voltage regulator or some other circuit between the controller and the load to protect the load when the battery disconnects? If so, it should ideally consume little power and only drop the voltage when it exceeds 14.6V. (I'm out of my league with this question.)
- What is the likely reason for the battery's disconnect at 0.02C? Wouldn't it make more sense to remain connected and allow the controller to go into CV mode at it's programmed CV voltage of 14.6V?
- I realize that I haven't provided much detail and that some of my terminology and concepts might be wrong. What additional information would make my quesions meaningful and answerable?