Hello,
I am using Meshcore and mainly boards with a RAK4630. I started with a RAK4631 and I see now that the RAK19007 may be on my way. I like the integration of the L76K and the 3-axis sensor for a starter board but I will drop the 19007 requirement for my later purchases if it is on the way of properly using LiFePo4 cells.
I am slowly going away from LiPo and Li-Ion, gearing toward LiFePo4.
I searched the Forum and don’t see much about LiFePo4 (or I missed some gems).
I found:
- RAK19007 with LiFePO4 18650 but not many answer but using Li-Ion
- Custom Lipo-LiFePO4 RAK3172 node which is not about the RAK4631 but looks nonetheless interesting
The problem
LiFePo4 does not have the same specs that the now common LiPo pouches and Li-Ion cells:
| Battery Chemistry | Low Voltage (Cutoff) | Nominal (Typical) | High Voltage (Full Charge) |
|---|---|---|---|
| LiPo (Lithium Polymer) | 3.0V – 3.2V | 3.7V | 4.20V (4.35V for HV-LiPo) |
| Li-ion (Lithium-ion) | 2.5V – 3.0V | 3.6V – 3.7V | 4.20V |
| LiFePO4 (Lithium Iron Phosphate) | 2.5V | 3.2V | 3.65V |
Why ?
LiFePo4 are much more stable and show less catastrophic outcomes when damaged (in the sun for instance).
The specs
I would like to find a solution that:
- fully runs on LiFePo4 (1sNp)
- ideally without a step-up, or I am considering a split with a path with a step up for sensors that require 3.3V
- can charge via USB
- can charge via Solar, open for now whether 5V or 12V + BMS but leaning towards the 2nd option
- offers a top notch security level for the board and the battery system
I may end up making a custom board if there is no existing project but that would suprise me.
What do you want 
?
As I mentioned, I am sure some people already played (or more) with the topic and I would love to gather feedback, tips and tricks.
I am hoping to gather enough so we define better solutions than “Use 2SNP and a LDO” so we can honor the performance of the RAK modules and the LiFePo4 packs !
I would be grateful if non-solutions (inspired from other posts…) could be excluded from the answer, such as:
- just use a Li-Ion, it works great
- use two cells in parallel so you get 2x3.2V (sic)
Why not the RAK3172 ?
that’s a good question and if I would be chasing the lower consumption, that would be the answer. But the RAK4630 comes very close behind in terms of consumption and adds BLE, USB, packs more RAM and flash.