There are several different ways to power your NVIDIA Jetson Developer Kit using a battery. Let’s go over some of the more popular. Looky here:
Background
After working on several projects recently that require Jetsons to use battery power, I want to share with you some of the lessons I learned.
Let’s divide the Jetson family into two camps. The first will be the Jetson Nano and Jetson Nano 2GB. Both of these Jetsons require a 5 Volt (5V) power source. The second group is the rest of the Jetsons, including the Jetson Xaviers, Jetson Tx1 and Jetson TX2. These Jetsons run in a wider range of input voltages, typically 9V to 19V.
As you know, you can think of a battery as electrochemical device which can provide electrical power. Batteries can consist of different chemical makeup, you are probably familiar with some of the common ones, such as alkaline (zinc manganese oxide, carbon), lead acid, nickel metal hydride, and lithium-ion polymer.
Here, we will focus on lithium-ion/polymer types of batteries because of their high power density to light weight. Also, they are rechargeable which make them convenient for long term use.
Note: The video is pretty extensive and covers the things listed here in more detail. Some things are more easily shown than written!
Packaging
We look at two different package styles for batteries here. A power bank is a popular style of battery people use for recharging their phones. Some power banks provide multiple voltages, but almost all provide 5V through a USB connection.
The NP-F style battery is in common use by photographers and videographers. The NP-F battery was originally invented by Sony to power their cameras. The battery uses 18650 lithium-ion cell batteries in pairs to provide a 7.4V nominal battery. The type of 18650s and the number of pairs of cells determine the capacity of the battery. Quality NP-F style batteries have built in battery management systems (BMS) to prevent over-discharge.
Some Project Parts you might need
Here’s a list of affiliate links to some items from the video, available on the JetsonHacks Amazon Storefront:
- SmallRig NP-F Battery Adapter Plate Lite (ABS)
- SmallRig NP-F Battery Adapter Plate (Aluminum)
- Power Bank for Jetson Nanos
- Neewer NP-F550 Battery Packs
- Neewer NP-F750 Battery Packs
- Buck Converter
- Cables and Connectors
- Tools
- JetsonHacks Amazon Storefront
Jetson Nano and a Power Bank
You can power a Jetson Nano through the designated USB port. For the Jetson Nano 2GB, this is the USB-C port. For the Jetson Nano, this is the micro-B USB connector. Simply connect a USB cable between the power bank and the Jetson, and turn on the power bank. Some power banks have multiple USB outlets, which allow you to run more than one device at a time. This can be useful if you are using multiple devices.
Powering a Jetson using a NP-F Style Battery
As we note earlier, a NP-F style battery provides 7.4V nominal power. Nominal defines the class of battery. Batteries run in ranges during their use cycle , a fully charged NP-F battery is ~8.4V, a discharged battery is 6.6V. Note: You should not run an individual cell under 3V, as this may damage the cell so that it cannot recharge. A NP-F has two in series, so that means do not run it under 6V. The Jetsons other than the Nano run in a voltage range of 9-19V.
For our application, we use a SmallRig battery adapter plate which helps us in two areas. First, the plate has a built in boost converter which converts the 7.4V to 12V and outputs it to a jack. Note that the raw battery voltage is also available on a secondary jack.
Second, the plate provides an affordance for attaching the battery to our project. There are two 1/4″-20 threads (a standard in the camera world) which we can utilize. Also, the plate captures the battery and holds it securely. Here’s an example, the battery adapter plate and the battery are towards the rear of the vehicle, attached to the platform plate:
The 12V output on the adapter plate is available on a 5.5mm outer diameter (OD), 2.5mm inner diameter (ID), center positive jack. Remember that the Jetson Nano barrel jack is 5.5mm OD, 2.1mm ID, center positive. The other Jetsons are 2.5mm ID. The video covers a couple of ways of making cables and how to make a simple power distribution block.
To power non-Nano Jetsons, create a cable to connect the adapter plate from the 12V output to the Jetson barrel jack. Plug in the battery, and you should be ready to go!
Buck/Boost Voltage Converter
Another useful device is a voltage converter. The converter takes an incoming voltage and converts it to a different output voltage. A boost convert (step-up converter) takes a lower voltage and converts it to a higher voltage. A buck convert (step-down converter) takes a higher voltage and converts it to a lower voltage. A Buck/Boost converter does both. Note that for efficiency there is expected to be at least a 1.5V difference between the input and the output voltages. Here we are using a buck converter to convert 7.4V to 5V.
This device takes the input from a battery, and converts it to a regulated voltage. This is useful when you have a voltage source outside of the range of acceptable voltages for the Jetson, or you need a more specific voltage like 5V for a Jetson Nano.
Powering a Jetson Nano from a Battery and Voltage Converter
As an example, we can take the 7.4V output from the NP-F battery, and convert it to 5V using the converter to power a Jetson Nano. Because the battery adapter plate that we are using has two outputs which we can use simultaneously, we can power both a Jetson Xavier NX and Jetson Nano:
Battery Run Time and Such
Battery manufacturers list the capacity of batteries in two ways: Amp Hours and Watt hours. You can use this information with the current draw of the Jetson and devices to determine the length of time the battery will last. This can be an extensive calculation, as the draw of the device(s) tends to be quite variable depending on the task.
In addition, there usually is some inefficiency in voltage conversion and such. You can do a quick back of the napkin calculation to get you in the ballpark of run time. However, to get more specific you will need to do testing. You might be surprised to find out that manufacturer claims may not match the observed results!
Conclusion
The methods above are just a few ways to power the Jetson with a battery. There are all sorts of clever solutions out there. Hopefully you find these tips useful.
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