Hi, I have tried to post this in one of the older threads, but not have an answer yet.
If anyone is using Lipo Rider Plus or similar with a 5V boost output on usb-A or board pins: I have the following:
I’m using the Lipo Rider Plus with relatively small Li Ion/LiPO batteries (250-350 mAh) and Arduino Nano Matter connected to a 5V booster output on type A connector in my projects. I have also a a physical (latching) switch to turn the power on/off to Arduino after 5V output. All batteries I have, include integrated PCM/BMS modules (they all do) providing all sorts of protections. However, after a while batteries stop charging. On the board only 4th green LED blinks with 3 solid LEDs which hints on almost fully charged battery.
However, after testing the batteries - they all have discharged below 3V cut-off, when the circuit is left to rest for couple of days to a week and some even discharge to 0V completely, without any load - the switch is off. When this happens the battery “refuses to be charged” - when connected to usb-C external charger again, Lipo Rider board applies 4.2V at the battery pins but no/trickle current is flowing for charging. Which is not surprising as battery is now in over-discharged state and PCM stops it from charging.
My question, how is this possible (discharging below 3V safe cut-out) with no load connected (switch is off on Arduino and even if nothing is soldered to the output)? Battery protection circuit should stop discharge at 3V. How it is possible for Lipo Rider to slowly discharge it over time to below 3V? I tried many different batteries and I have 20 different Lipo Rider boards - they all do the same.
PS. My guess it is a 3V-5V booster has something to do with that as our internal toggle board switch for 5V is always on.
Since I don’t have a Lipo Rider Plus, I checked the circuit diagram and the ETA9740 datasheet. The datasheet lacks detailed operational descriptions, so the following is my speculation.
Even if no load is connected to USB-A, if the switch is ON, it generates 5V and supplies about 3mA to the 5V output enable indicator on the board. However, when the battery voltage drops below 3.2V, the BOOST mode should stop, and no current should be supplied from the battery. The phenomenon of the battery fully discharging is very strange.
What is the function of the built-in over-discharge protection circuit in the battery?
thanks. I’ve spent some time on this since then. So, if anyone has similar, here is some information.
Firstly, yes 5V buck-boost converter self-draw even without load is significant to discharge the permanently connected battery below cut-off within a week or so. We had tried to overcome this by re-soldering the external power switch to the 5V ON switch contacts on the board itself. While onboard switch stays at 3V the external enables the 5V output. It isolates boost more in off condition. It solved 95% of cases of failing batteries, but not all.
There is also an issue with “refusing to charge” batteries - no recovery mode. ETA9740 sees protection latch on battery PCM, i.e. open circuit, mis-recognises it as battery full at 4.2VDC and no actual charging occurs even over long time. When charger is disconnected, the battery reads still below 3V.
- There is still self-draw from Lipo Rider Plus ETA9740 (below 1mA range) with 3V always active and some other bits which could cause over-discharge below 3.0-2.8V with time if battery is permanently connected. There is of course also a self-discharge in the LiPO battery as well, before PCM barrier even.
- The ETA9740 itself has no hysteresis 3.0V cut-off and 3.0V enable for battery charging, so with PCM cut-off on battery also at 3.0V it can cause oscillations and instability.
- Small batteries like 350mA with max charging current of 380mA are not a good match for Lipo Rider with max 2A charging/discharging. I’m not sure how it handles the battery current with PCM together, but it might cause too harsh charging and no-recovery possibly. Some AI chats suggest resoldering ETA9740 R1 ISET resistor on pin 5 from 56kOhm to higher (e.g. 560kOhm) to limit charging current to match with PCM on battery, which might help with softer current and recovery of over-discharged batteries. This is not documented in the ETA9740, but I might try that, as there are not many alternatives to Lipo as I need also 5V out supply from a battery source.
- I’ve noticed that charging Lipo+Battery via USB port on PCs rather a wall plug charger or similar can provide more gentle charging and helping to reset the latched battery. Which points to possible issues of matching high current input on USB-C with high charging current limit of Lipo Rider with low max charging current of Li battery we need to use.