Help Understanding Green LED + Charging behavior

zane

I’m having trouble understanding the behavior behind the green LED.

I have several batteries of the same design. 3.7v, 2200mAh 8.14Wh batteries that I’m using with my feather board.

The fresh batteries (unused) that are connected to the feather with a USB-C connection have a green LED that shows. I assume this is a charging indicator.
After some amount of time (₁ day) the green LED goes away, and I can no longer get it to show. I can not tell if the battery is charging anymore.

I then put the feather board on battery power, and it appears to be working for some time though it is powering off prematurely given what I would expect for the 2200mAh rating. I try to recharge the battery through the feather board and it appears that it may be charging since the board will then work again on battery power for another hour or two after a few minutes of charging, but the green LED never appears.

What might be my issue here? Does the green LED go away on a full charge. Does the lack of a green LED with a battery+USB connected mean that it is unable to charge? Might I have defective batteries?

Thanks!

jaredwolff

Hi @zane

What type of batteries are these?

After some amount of time (1 day) the green LED goes away, and I can no longer get it to show. I can not tell if the battery is charging anymore.

If the LED is off, it is not charging.

appears to be working for some time though it is powering off prematurely given what I would expect for the 2200mAh rating

What is the board doing during this time? Have you measured the current?

zane

Hey Jared, thanks for taking the time to reply!

These are Lithium Polymer batteries that we had custom made. I’ll attach a couple of images to show…

Battery Image
Battery + USB-C plugged in, no LED

I’m unsure how to measure current with the tools I have, but what I have done is I’ve measured the voltage at two spots.

At the battery connector I measure to make sure I’m seeing 3.7-4.2 range of the battery
I’m able to measure 3.3v at the 3.3v supply pin, this makes me feel confident that the battery is at least working…

I also know that the board is “working” since the software we load onto it is pinging a webserver, I see the board doing things on my server end so this tells me the battery is powering the board and working. However, plugging in the USB-C I do not see the green LED light up and I’m unsure how to go about testing if charging is happening.

Thanks again, hopefully that explains things a little better.

jaredwolff

zane got it. And you have seen the LED light up when plugging in USB? (i.e. does it charge at any point?)

What is the current of the device in normal running mode? You’ll have to measure that to get us an idea of what’s going on here.

zane

jaredwolff Thanks!
I ordered an Otii Arc in order to help me obtain these measurements as I currently don’t have a way to do so.

As a secondary question, how would we be able to utilize a 2xAA battery configuration (Alkaline battery)?

The specs for the battery requirements state this
Battery Requirements Battery type: LiPoly Operating range: 2.8-5.5V Current/power rating: Able to support at least 2W of power Battery capacity: > 300mAH² Charging current: 294mA ± 10%.

2xAA batteries should get us to the operating range we want, but would we be able to utilize the JST connector since it’s designed for charging a LiPoly battery?

Is there a way to disable the charging? Is there a separate Vin pin we could utilize for a 2xAA battery input that takes the 3V input and boosts it up to 3.3V to operate?

Thanks

jaredwolff

zane 2xAA batteries should get us to the operating range we want, but would we be able to utilize the JST connector since it’s designed for charging a LiPoly battery?

Is there a way to disable the charging? Is there a separate Vin pin we could utilize for a 2xAA battery input that takes the 3V input and boosts it up to 3.3V to operate?

Using primary cells is not uncommon on the nRF9160 Feather. You can use the JST connector but, for safety (especially if you’re going continue using the USB port), you may have to remove the charger. For future revisions I may pop in a jumper so it can be bypassed in the future.

The power supply chip will operate in 100 duty cycle mode and will probably work all the way down to your 2.8V range. You’d have to test and see what your experience is as it’s not a truly supported mode. (Previous boards had buck-boosts which would be supported but since supply chain issues it had to change. 😢 )

zane

jaredwolff
Great, I’ll give it a try.
When you say

you may have to remove the charger

Do you mean de-soldering chip (4) here in this image?.
Can you help me understand how the nRF9160 can operate without the buck-boost with a 3.0V (or even down to 2.8V) supply? My understanding was that there was a 3.3V minimum.

jaredwolff

Do you mean de-soldering chip (4) here in this image?.

Yup the chip right below.

Can you help me understand how the nRF9160 can operate without the buck-boost with a 3.0V (or even down to 2.8V) supply? My understanding was that there was a 3.3V minimum.

For 3GPP compliance, yes, you need 3.3V. The module though works down to 3.0V along with most of the peripheral devices on the nRF9160 Feather. If you do require that 3.3V when your input voltage is below you’ll definitely need a different power supply.