Jetracer (Jetson Nano) battery charging

Help & Support Robots & Kits
1

Hi,

The Jetracer requires three 18650 batteries. I see the Jetracer has battery protection, and a 12.6V barrel plug. Does it also allow charging over this plug, or do you need an external battery charger?

Thanks,
Maël

P.S.: Link to the product: https://www.robotshop.com/en/waveshare-jetracer-ai-racing-robot-powered-jetson-nano.html

2

Hello @maelh and welcome to the RobotShop community,

The 12V power adapter is used to charge the batteries but DO NOT directly connect it to Jetson Nano Developer board.

You can find this information and more on the product’s Wiki available under the Useful Links section on the product description.

Let us know if you have further questions!

1 Like
3

Thanks for the reply and the welcome (although I am not new, a welcome is always appreciated :slight_smile:

I saw the Wiki, but rereading it again “The 12V power adapter is used to charge the batteries.” seems to also mean that it is used to charge over the expansion board, and doesn’t require an additional charger.

I mostly wondered, because it did not explicitly mention how you know when it is done charging.

Your confirmation encouraged me to look at the schematic, and indeed it has a HY2213 chip which the datasheet claims as “Cell Li-ion/Polymer Battery Charge Balance IC”, so it does balancing and charging.

There was no LED to be seen on the schematic, but there is an OLED-display, so I assume it is used for displaying the charging state.

Thanks.

4

Oops, I’m used to newcomers haha :sweat_smile:

Well, it seems like you have it all figured out!

Thank you for posting what you discovered because it might help other people with the same questions

5

After lots of searching I found a vendor’s description that explicitly answer what I was looking for:

https://www.amazon.com.au/Waveshare-JetBot-Kit-Recognition-Green/dp/B081LF98T8

Strangely, Waveshare’s own site does not answer these questions clearly. The useful points are:

  • Adopts 3x 18650 batteries (NOT included), high battery capacity, up to 12.6V voltage output, more powerful driving force
  • Integrates S-8254AA + AO4407A lithium battery protection circuit, provides protections for over-charge, over-discharge, over-current, and short circuit
  • Onboard APW7313 voltage regulator, provides stable 5V voltage for the Jetson Nano; Onboard TB6612FNG dual H-bridge motor driver
  • Onboard 0.91inch 128×32 pixels OLED, allows to display robot IP address, RAM, battery life, etc.; Onboard ADS1115 AD acquisition chip for monitoring the battery in real time

Edit: it’s the JetBot, not the JetRacer, but they have very similar electronics and the same OLED screen, so I assume the battery life is indicated the same way. Fingers crossed.

6

Further investigation of the source code for the JetBot shows that Waveshare added code to show the battery voltage and current on the OLED:

The relevant code is in __main__ of jetbot/ads1115.py and jetbot/ina219.py

For JetRacer the relevant changes are NOT in the jetracer github, but in jetcard github:

The relevant code that displays battery voltage and current is in jetcard/ads1115.py and jetcard/ina219.py this time.

So only when the Jetson is running, the Python code that checks the battery has a chance to run. Therefore, the battery charge display is somewhat inconvenient, as the Jetson cannot be off for it to work.