Hi All,
I am finalizing the design for my first Blues based device. I need to ship a prototype from the UK to the USA for testing. The person doing the testing is not able to connect the battery, so I can’t ship it disconnected. I have done the course and I am fully up with the shipping of LiPo cells.
I want to ship the device with the battery connected to the Notecarrier B, but I don’t want the device running while it is in transit. It is also preferable to ship it with the battery mostly discharged. Ideally, the user will connect it to a USB power supply on receipt and it will just start working.
Is there a cutoff battery voltage, below which the Notecarrrier B does not try to start? If so, I will discharge the battery to just below that votage.
Thanks in advance,
Rob
Hi @rlkeith,
The Notecard requires a minimum of 2.5V, but you can’t feasibly draw a LiPo battery down that low. Anything lower than 3.2V can permanently damage the battery. If you don’t want the Notecard to try to connect in transit, you can set the "mode":"off" in your hub.set request, but that would require updating the value on the other end.
Rob
@rlkeith,
It’s my understanding that many (most?/the ones I use) LiPo battery packs contain circuitry from discharging the LiPo below around 3.2 volts. When the battery voltage drops to the that level, the battery is shut down and voltage goes to zero. Once you plug in the USB and start charging the battery it should recover. This has worked for us, though sometimes I’ve had to unplug and replug the battery in. That may be one alternative, but you definitely need to test it with your battery before shipping.
In our application we run the notecard in minimum and have to force every sync. The mcu spents most of the time in deep sleep. We set an environment variable to determine the wake interval. For shipping we set the wake interval to 1440 minutes (1 day) so we can track where the devices are but we could set it to a week or more.
A couple of other alternatives,
Karl
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Hello Karl,
Thank you for your reply. I have been thinking about a number of possibilities, but I can’t rely on the people at the receiving end to operate a switch. I thought I could add a pull tab but the solution may be much easier.
Regards,
Rob
Hi Rob,
I thought I was being smart and using an 18650 cell. I could put a pull tab to isolate it, but that adds another point of failure. I will see if the built-in cutoff works.
I am currently testing a prismatic 1850 mAH LiPo cell, drawing 700 mA, so I will know in a few hours.
Regards,
Rob
Conclusion:
The rig pictured ran for a few hours, longer than I expected, and abruptly cut out. The battery showed no voltage and would not even light a 2 mA LED.
I applied the charger for a few seconds and the battery came back to life, showing 3.6 volts. When the 5 ohm load was applied it quickly sank to 2.9 volts and then cut out.
It looks like I can safely discharge the battery until it cuts out and then connect it to the prototype. When the users receive it, they will plug it in to the USB supply and the Notecarrier, Swan etc. will start up within a few seconds.
I can buy a suitable PKCELL 2,000 mAH cell from a local supplier in the UK. It would be much easier in the US and EU.
Rob
