VOISS - Power HATs
Written by Rich Morin.
Precis: a discursion on USB power HATs
Note: As of early 2020, the VOISS project and F123Light were discontinued. For details, see VOISS - Status.
A variety of Hardware Attached on Top (HAT) boards can be used with the 3B+. One of the most useful types, which I’m calling a Power HAT, contains one or more Lithium-ion batteries and some associated circuitry. So, like a USB power bank, it can act as a dedicated uninterruptable power supply (UPS) for the computer.
However, because it is connected to the 3B+ using the General purpose input-output (GPIO) connector, it can report its status to the operating system. This information can then be used to support power management functions (e.g., alerting the user, shutting down the computer).
Unfortunately, most of the units I’ve found to date lack documentation and/or software, have too little power for a 3B+, etc. However, the “Pi-UpTime UPS 2.0”, from Alchemy Power seems quite promising. I’m still in the process of setting this up and evaluating it. Meanwhile, I’ll stay on the lookout for other alternatives.
The models I’ve found fall into two categories. The first uses one or more cylindrical batteries; the second uses a single, rectangular battery. See below for a discussion of each approach.
There are several common formats (e.g., 18650) for cylindrical Lithium-ion batteries. Their primary advantage is availability: finding a replacement should be very easy. Their primary disadvantage is bulk: the cylindrical format wastes quite a bit of space, making the HAT larger than it would otherwise need to be.
The 18650 is 18 mm in diameter and 65 mm long. Cells can be optimized for maximum current or maximum capacity, but not both. Making matters more difficult, there’s a number of liars in the industry. The Best 18650 Battery and How to Avoid Buying Fakes covers a number of issues and pitfalls associated with purchasing 18650 batteries.
Pi-UpTime UPS 2.0
Alchemy Power’s Pi-UpTime UPS 2.0 is designed to work with full-size Raspberry Pi computers. It holds two (e.g., 3600 mAh) 18650 Lithium-ion cells, wired in parallel. This is a substantial amount of capacity, making this unit attractive for a system that will be used heavily on battery power and/or left in an idle state for many hours at a time.
I’ve been setting up a prototype VOISS system, incorporating this board. For details, see VOISS - Pi-UpTime UPS 2.0.
This HAT, which costs $70, appears to be the Alchemy Power Pi-UpTime UPS (as opposed to the Pi-UpTime UPS 2.0). It includes a pair of (3000 mAh) 18650 Lithium-ion cells. The maximum current is said to be 1.7A, which is a bit low… OTOH, Vetco may actually be selling the current model, so YMMV.
This HAT is available for $20 from Seeed). It includes an Arduino, a real-time clock, a case for two 18650 batteries, and miscellaneous hardware. The wiki indicates that a fair amount of technical information is available for it.
This HAT costs $19. It holds one (800 mAh) 14500 Lithium-ion cell (not included). It seems to be the same unit sold by AliExpress, et al. Similarly, very little technical information is available for it. Again, YMMV…
This HAT (sold via AliExpress by “XINLINDA KEJI CO., LTD Store”) costs $19. It holds one (800 mAh) 14500 Lithium-ion cell (not included). So far, very little technical information is available for it. YMMV…
None of the models listed below appear to have much in the way of documentation, so I’m skipping them for the moment. If you get one and have information you can share, please get in touch!
The batteries used in the listings below are all a bit smaller than the RasPi in height and width and about a centimeter thick. They have no mounting fixtures and connect to the HAT by means of a short cable and a plug. So, you should use something (e.g., a cable tie) to keep it from falling out. The other advantages and disadvantages of this battery format are the converse of those mentioned above for the cylindrical format. They are efficient in terms of space, but finding a replacement may be hard.
Alibaba UPS HAT
This HAT costs $19. It contains a flat, 2500 mAh Lithium-ion battery, sandwiched between a pair of circuit boards. It comes with example code to detect and display the battery current, level, voltage etc. The maximum current is 2A, which is a bit low…
This HAT costs $26. It contains a flat, 2500 mAh Lithium-ion battery, sandwiched between a pair of circuit boards. It comes with example code to detect and display the battery current, level, voltage etc.
This HAT costs $15. It contains a flat, 3800 mAh Lithium-ion battery, sandwiched between the RasPi and another (lower) circuit board. There is a wiki page and a Python script, but no English explanation or schematics. Also, apparently, there is no way to monitor the battery level. Again, YMMV…
This HAT costs $7. It contains a flat, ? mAh Lithium-ion battery, sandwiched between the RasPi and another (lower) circuit board. It comes with example code to detect and display the battery current, level, voltage etc. So far, very little technical information is available for it. Again, YMMV…
VILROS PiJuice HAT
This HAT costs $70. It contains a flat, 1820 mAh Lithium-ion battery and a real time clock. It comes with a “guide”, but I don’t know what information that contains.