I own several Seeedstudio XIAO nRF52840 and am loving them so far. I just have two questions regarding the battery compatibility of the boards, which I hope you can help me with.
First, I would like to know which batteries are compatible with the BAT+ / BAT- connector at the bottom of the board.
I know that 18650 Lithium-Ion batteries (3.7 V) are compatible, but I don’t know whether Ni-MH batteries work and if Ni-MH batteries can be safely recharged with the board.
Second, I couldn’t find any information as to what the voltage range of those BAT+ / BAT- pins are. How high of a voltage do I have to supply for the board to work properly and how high of a voltage can I supply at most?
If you know of any official specifications or documents that show these values, that would be great as well!
Thank you, the PDF in the linked post was very helpful.
So if I understand correctly, the charging circuit in the nRF52840 only supports Lithium batteries.
The bq2510x is a highly integrated family of single cell Li-Ion and Li-Pol chargers
This means, that I cannot charge Ni-MH batteries with it, but presumably I can still use them to power the board. Is there a way to disable the charging mechanism of the battery pins so that if I accidentally connect the board to USB-C, the battery is not charged?
The PDF also says “30-V Input Rating; with 6.5-V Input Overvoltage Protection”, so that would mean I should supply at most 6.5 V to it to not trigger the protection, right? Does that mean that the nRF52840 can also handle these 6.5 V?
And what is the minimum voltage I need to supply for the board to function? Is e.g., 3 V enough?
Sorry if these questions seem obvious, but I am pretty new to electronics overall and am still learning.
Hi there,
All very good questions,
No mechanism that I know of for disabling the battery charger.
No, Those a maximum rating not suggested.
Albeit 3.0 vdc is below the standard some Lipo battery will go down to 2.8 b4 they LDO shuts down. Not advisable and especially if your using the BLE radio
I use a Round 3.85vdc 450maH battery to power very thin and light., pictured in many of the demo’s I post.
i.e.
for a non rechargeable (NO USB) small footprint but enough Power to go for a short time.
a CR2450 coin cell(pic) and yes it’s 3.0 volts, does work.
HTH
GL PJ
So in summary, I could use 4 AA rechargeable batteries (Ni-MH, rated at 1.2 V each) for a total voltage of 4.8 V.
The 4.8 V should still be okay for the chip and the batteries should supply enough voltage, even if they are almost empty.
Then I can just let them run dry and recharge them in an external battery charger.
One final question:
To prevent the batteries getting charged, could I simply include a diode between the batteries and the board? Or do you see any problems with that?
Side note:
My project is to create a small box that measures the humidity and temperature inside a dry box and sends it via Bluetooth low energy to an ESP32 (which is connected to power) that sends the data to a dashboard.
So my nRF52840 are in deep sleep most of the time, but I still want as much battery capacity as possible (so no coin cell sadly) so that the sensor lasts as long as possible before I have to recharge the batteries.
Hi there,
Yes I like the Diode in those cases. You can skip it if you add a small power switch to
the battery pack and turn it off when using the USB connection.
HTH
GL PJ
PJ
