Would anyone be able to share their experiences running the Fin on battery power of any kind?
Can the Fin run on 5V USB power?
In our deployment context, we cannot rely on mains power, and we are wondering whether we can power a Fin with a USB phone charger battery.
Thank you so much!
Hello, can anyone on the Balena team answer this basic question? Thank you!
Hi @zestyping !
you can power the Fin from the 5V HAT pins and use any battery pack that comes in the HAT form factor, as long as it provides ~2A @5V. Another option that is possible thanks to the wide input voltage range from the DC and phoenix power input on the Fin, is to run a battery with external charging/regulation circuitry and connect it to the Fin via the phoenix connector. That would allow you a big choice of battery technology and cells count
Hi @curcuz, thank you for helping me out!
Are there any products that the Balena team recommends (and ideally supports) as battery power solutions for the Fin? I imagine I must not be the first person to want to use a Fin with a battery 
— what are the most popular ways to do this?
I am wondering what products you have in mind when speak of “any battery pack that comes in the HAT form factor.” I’ve spent a while searching for such a thing, and so far have only turned up two HAT power supplies (https://www.sparkfun.com/products/14803 and https://uk.pi-supply.com/products/ups-pico-uninterruptible-power-supply-hat). These only have tiny batteries and I’m uncertain of their reliability, as they appear to be made in low volume and are only sold to hobbyists.
On the other hand, USB battery packs are ubiquitous, mass-produced, sold with warranties, available in a wide range of sizes, and so on. I am looking for a solution that can be purchased in quantity and relied upon (just like the Fin), so a USB battery pack seems very appealing. Is there any reason why one cannot power a Fin simply by connecting the 2A output of a USB battery pack to the HAT pins? It seems like the obvious solution, so I wonder if there might even be a cable designed specifically to do this that is sold as a product; are you aware of any such thing?
Thank you!
@zestyping I suppose it depends on your use case. The PiJuice is quite advanced and includes programmable functionality alongside battery monitoring and charge circuitry as well as an API you can use to access battery information via the host. I know you can also connect much larger batteries and the board will continue to monitor and charge them as well. I have a couple of these on the test bench and would recommend looking into them if you need a fully featured solution.
However if you just need to run the Fin from a battery for a period of time without having to worry about charging etc. then you could definitely do that from a USB power bank via the HAT pins.
Thank you, @chrisys! I really appreciate you making the effort to explain this to me.
What did you mean by “without having to worry about charging”? Is there something different between the PiJuice and a USB power bank with respect to charging capability?
My knowledge of the situation currently looks like this:
For use cases that don’t require an API, these points seem to weigh very heavily in favour of USB power banks. Given what I currently know, I can’t explain why USB power isn’t the primary recommended off-grid solution, and I’m mystified by the design decision to omit a micro-USB power port on the Fin. I’m a complete beginner in this realm, and obviously your design team must have made this decision for a good reason, so it seems likely that I’m missing something important. Could you help me understand what I’m not getting?
Thanks so much for your time!
I don’t know what USB power banks you’re planning to use but the ones I have experience of typically don’t allow charging at the same time as you are discharging, which is what I meant with my comparison with the PiJuice which instead works the same way as a UPS does.
The Fin accepts a wide DC power range allowing it to be used with a much wider variety of power sources, for example various battery types and voltages. The micro-USB connector wouldn’t support this, plus is very fragile in comparison to the phoenix connector or barrel jack; it’s a common point of failure on the Raspberry Pi.
As I said, it’s going to be absolutely fine to power the device from a USB power bank via the HAT pins if that works for your application. To me, an off grid solution still needs some way of charging the batteries, as they aren’t going to run forever, and so unless you can charge whilst discharging or have some power controller (as the PiJuice does) to handle that for you, you’re going to be manually swapping batteries out all the time when they run out.
If you could share more of your intended use case perhaps others may chime in with some different views! 
Thanks @chrisys! That clears up the confusion. There are several USB power bank products that support pass-through charging, which is why I think of them as performing the same function as a UPS or the PiJuice. You’re right that most don’t, but some do.
Regarding the use case—yeah, good idea.
The intended use case is a server for a medical record system at a remote facility (possibly even a mobile clinic or temporary structure in an emergency context) that has only unreliable mains power or a generator. We are trying to maximize the ratio of battery capacity to system power consumption; the Fin is attractive as a low-power server. And we want the parts to be easily sourced and replaceable; hence USB power banks are attractive as mass-produced products.
We are also seeking an overall configuration that is simple enough to be communicated to IT staff (not engineers), such that they can easily set it up correctly and, should a part malfunction, easily obtain and install a replacement part. Thus, we’d love for our instructions to say “plug this USB power bank into your power source, and plug the USB cable from the Fin into the power bank”—which everybody knows how to do because everybody has a phone. There are only two parts, the power bank and the Fin, and anyone can figure out how to put them together. If they lose the power bank then they can just use a wall charger or a non-passthrough power bank as a stopgap; it will even run on a car charger or in an airplane because there are 5-volt USB sources everywhere and everyone knows how to use them. We’d be pretty nervous if our instructions sounded like “take this naked LiPo battery and connect these tiny cables to some pins on a naked circuit board, mount that onto another naked circuit board and be sure to line up the pins correctly or you might destroy it, put the circuit boards in a case, assemble the case with four screws and a screwdriver, then plug this special DC adapter into the wall and plug the cable into the barrel jack, and if you lose the DC adapter, you won’t find another one within a 100-mile radius.” Especially if they don’t speak English.
A device with a micro-USB port is something that almost anyone in the world can plug in and power up with zero electrical engineering knowledge. A device with a DC barrel jack can only be powered up by someone who has specialized knowledge of how to get their hands on a DC adapter of an acceptable voltage with a cable whose plug has the correct inner and outer diameter to fit the barrel jack.
I hope that helps paint the picture! Thanks for helping us figure out the best way to do this—it has the potential to really help some people in need.
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@zestyping it sounds like your use case is quite well formed. If you’d like to discuss it in more detail with us, and investigate the possibility of supplying preassembled units with additional hardware as you suggested I can put you in touch with our solution architecture team. It would likely depend on the number of units required but that’s something we can investigate with you.
@zestyping, it sounds very interesting.
Have you got any experience with any pass-through USB power banks? Can you suggest one?
I investigated some time ago, but I never bought one. At that time, I also needed something that will not will turn off when the load doesn’t draw enough current (e.g. while powered off via RTC). That is, something like the “dummy load” found on the Witty Pi 2 by UUGear or the Always On Mode by Voltaic was needed.
I’ve also tried the UPS PIco and even others in the past. Not the PiJuice, yet.
The UPS PIco may be a good product, but I run into problem with its engineer, because of other features, being “sold” as implemented, why they were not. The S.USV can be a better choice.
What about a small DC UPS with 12V or maybe 24V output? You can have one being powered via a main, recharging a small battery and powering the balenaFin at the same time.
Hi @zestyping,
There are a couple of things you need to keep in mind when using standard power banks for powering boards (the balenaFin in this case).
As @daghemo mentioned, many power banks will shut down when current falls below a certain threshold, mostly to avoid draining the battery on an already charged device.
From what I can see in your use case, having a way of identifying the health of the battery would be beneficial to communicate the IT staff what might be the issue.
If you were to embed the balenaFin + Pi-Juice (or similar) in a case and only expose the micro usb from the HAT you could tick all the boxes. They will be able to use any phone charger and you can monitor the health of the battery that could be replaced as you would replace a phone’s battery (or at least how it was done back then when phone batteries were removable ).
Cheers,
Nico
Thanks for the feedback and ideas everyone! I appreciate your patience with me—this has helped me understand the picture much better. Thanks in particular for pointing out the low-current shutdown feature; I hadn’t thought of that.
@daghemo The one I’m trying is a Jackery SuperCharge. I picked this one because it has a 45W USB-C input; for pass-through charging to realisticallly work, the input has to supply enough power to the battery and the output at the same time, and typically power banks use USB-C PD input to achieve this. I don’t have test results for you, though.
I think these may be of interest: