Battery operation best practice

[Amir Nathoo]

Hi,

I have a mini ultra pro v3 now working all as expected in Low Power (i.e standby mode), but it is currently powered from the USB port (connected to my laptop). The prototype I am building for environmental condition sensing requires the device to be battery powered.
I have chosen to use an RCR123a (rechargeable) Li/Ion battery which is 3.7v (max 4.2) at 750mAh. The idea is that eventually it can be recharged using a solar panel or an USB power bank module. If not using a rechargeable battery (e.g use a RC123a 1300mAh instead) the requirement is for the battery to last around 9 months when the board is awake for about 1~1.5 seconds every 60 minutes. This seems to be achievable given the low power rating of the board.

So this seems reasonable goal given the design of the Ultra Pro V3. What I am currently confused about is the various power management PINs. Remember, I am not a hardware guy :-), so probably these are very basic questions:

1. When I power the board both with USB and the Battery (from the provided connectors), my understanding is the battery will get charged until it reaches 4.2v and while it is being charged, the board is drawing current from the USB power. Is this correct?

2. What is the LED behavior? My understanding is the following:
When both sources are used:
GREEN Led always on when within 5-10.5v
RED Led when charging on, then off after being charge is complete.
When only battery is used:
Both LEDs are off
Additionally the GREEN Led will turn off if the board is supplied more than 10.5V
Is this correct?

3. Now I am very confused as to what the different power PINs mean and their typical usage. Specifically I want to know what pin should be providing power to sensors when the board is power with either USB or the battery. I don’t know if different pin should be used, or not.
My assumption is that I should use the 3v3 pin in both configurations (USB teetered and standalone battery), all my sensors are operating at that level. Is that correct, or should I instead draw power from the Vin PIN in all cases?

Thanks in advance for the help,
Amir.

[LIM PHANG MOH]

1. When I power the board both with USB and the Battery (from the provided connectors), my understanding is the battery will get charged until it reaches 4.2v and while it is being charged, the board is drawing current from the USB power. Is this correct?

Correct.

2. What is the LED behavior? My understanding is the following:
When both sources are used:
GREEN Led always on when within 5-10.5v
RED Led when charging on, then off after being charge is complete.
When only battery is used:
Both LEDs are off
Additionally the GREEN Led will turn off if the board is supplied more than 10.5V
Is this correct?

Correct.

3. Now I am very confused as to what the different power PINs mean and their typical usage. Specifically I want to know what pin should be providing power to sensors when the board is power with either USB or the battery. I don’t know if different pin should be used, or not.
My assumption is that I should use the 3v3 pin in both configurations (USB teetered and standalone battery), all my sensors are operating at that level. Is that correct, or should I instead draw power from the Vin PIN in all cases?

Depending on your sensor requirement, you could tap the power from different pins. If your sensor requires 3.3V, then use the 3.3V. The 3.3V can source up to 250 mA but bear in mind that the radio and the rest of the board components also uses that, so please make sure sensor power requirement is not over that. When not using the 3.3V pin, you could also add external regulator by taking power from the VBUS pin. VBUS pin the recommended pin to further derived whatever power rail you want (VBUS maximum is 4.4V) by using it with conjunction with an additional suitable regulator. The rest of the power pin might not be available depending on the scenario. For example, if VIN takes in power from solar, it is not a recommended place to tap the power. VUSB (5V) is also not always present. So, the best place is to use VBUS or 3.3V.

[Amir Nathoo]

I am having an issue with one of the board. I don’t get any serial unless the battery is plugged in (i.e the port does not show up on my mac). I loaded the board with LED blink script (it blinks every 5 seconds).
The script runs fine when the board is powered by the battery alone and continues to work when I plug in the USB while it is powered with the battery.
And the strange thing is the board is getting power through the USB, I measured 5.05v. But if I remove the battery, the script stops.
There is no low power involve, just the basic LED script.

When I plug in just the USB cable, the green LED turns on and then off and remains off.
Any ideas what is going on?

• This reply was modified 6 years, 10 months ago by Amir Nathoo.

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