duncan
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Re: Power supply

Sat Aug 13, 2011 6:12 pm

Whats the chances this could run of a 9v (PP3) Battery ? Anyone have an informed estimate of how long it would last ?

AmyS3
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Re: Power supply

Sat Aug 13, 2011 6:27 pm

given that the raspi uses ~1W, just divide 1000mW by 9V and you would end up at ~112mA.
depending on the mAh you´re battery provides it could run some houres.

example: if you take a 9V 350mAh battery you could run the raspi ~3h.. theoretically
but that does not include any additional usb devices...!
you have to put the "current" needs from those into the calculation.

duncan
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Re: Power supply

Mon Aug 15, 2011 3:00 pm

Anyone know if the Coax is going to be standard center positive ?

Dave Duchesneau
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Re: Power supply

Tue Aug 30, 2011 12:14 am

Quote from abishur on August 4, 2011, 19:21
...if you've done this kind of thing and could display a good circuit board that would be to charge the batteries while there's power and then run off the batteries during a loss of power event I'd be interested in seeing those schematics...

Linear Technology (http://www.linear.com/products.....anagement/) has quite a few chips that can do just what you're seeking, but you probably already know that. If you go to that URL, be sure to check out the 15 (or so) headings on the left-hand side of the page (battery management, POE, etc.), rather than just the new products in the main page content. Linear's app notes tend to be filled with excellent circuit diagrams that provide cookbook-style recipes for solving various power challenges, and their chips are available through major distributors (Digi-Key, etc.) until you're ready for really high volumes.

On a separate but related note, we bought a bunch of Tekkeon 58 watt-hour Lithium Polymer battery packs (see the MP3450i R2 at http://tekkeon.com/products-my.....erall.html), and then took them apart (unsoldering various components) so we could reconstruct them into a prototype of a future unit (we don't recommend this be done by amateurs, unless you really know what you're doing). In our case, we needed at least 5X battery capacity in a small space (for an emergency communications node), with multiple regulated output voltages, and we also wanted to have multiple chargers and power sources, all connected together, so that we could use whatever power sources might be available at a particular time, such that the total battery capacity would be shared among all loads (thus, if some loads are shed dynamically, the remaining loads can operate for a longer time). We put one of our prototypes on a sailboat at sea, charged by the boat's internal battery banks (12-16V typical) and/or an occasionally operating diesel engine. The 300 watt-hour Lithium-Polymer prototype's battery loads included 3 radios and CPUs, a switch/router/firewall, and a variable-power high-gain amplier to provide a 3G/4G connection (via an external antenna) up to 50 miles from the nearest shore-based carrier tower. The typical variable loads totalled to 8-30 watts, depending on power-saving modes and distance from shore-based tower. The prototype could operate continuously from internal power for 10-40 hours or more before needing recharging. (Run-times get exponentially longer as the load decreases, and vice-versa).

In your case, however, a single off-the-shelf 58 watt-hour pack may meet your needs as-is (you could expect 58+ hours of run-time for a 1-watt Raspi). Tekkeon allows you to gang one or more battery packs charged by the same internal charger if you need more capacity. Each Tekkeon pack (http://tekkeon.com/downloads/d.....P3450i.pdf) -- with built-in charger and PSU -- is quite compact (3.32"x6.85"x0.89"), and weighs under a pound, thanks to the Li-poly batteries. The add-on battery packs are the same size and weight (slightly lighter due to the lack of connectors and electronics). A two-pack configuration as depicted in the datasheet would give you more than 116 hours of continuous Raspi runtime at full load (Model A). The lithium content of a single pack is 4.8 ounces, so it meets the FAA's lithium battery requirements for carry-on luggage. The datasheet at the cited URL has pictures and specifics. This industrial pack has DIP switches to set the desired regulated output to one of 16 preset voltages (5V to 19V), plus there's a fixed 5V secondary output on a USB-style (A) jack.

The primary output of a single MP3450i can deliver up to 4A (4000 mA) at the selected voltage. At 19V, a current of 4A yields 76 watts, whereas at 5V the same 4A delivers 20 watts. I don't know exactly what a Raspberry Pi will draw, but let's suppose it will be less than 1 watt, which would be less than 112 mA at 9 volts. This is only about 2.7% of the current that the voltage regulator of a single MP3450i can deliver, so there's plenty of reserve for other devices.

The Tekkeon MP3450i pack is well-engineered. I personally carry around 2 or 3 paired packs at 116 watt-hours (2x58 watt-hours) each, so I can work off-grid for quite a while. You can charge the MP3450i by supplying it with any 12-24 VDC source(regulated or unregulated), such as from a 12VDC vehicle or 19V laptop adapter, or even a solar panel. It comes with a universal AC adapter (20V output @ 3A), but other input adapters (e.g., vehicle CLA plug) are available from Tekkeon and elsewhere. The internal electronics will boost the charging source voltage up to whatever is needed for charging its internal 24V battery rail (4-hour charge time is typical for a fully discharged battery, and after charging, the actual internal rail voltage is typically at least 26.4V with the charging source removed). The MP3450i's electronics also exposes its internal 24V rail via an external 6-pin connector that may be used to connect battery packs in tandem (you should see at least 26.4V here also, with a fully charged battery). The 6-pin connector may also used for an external PV panel adapter that will accept 16-30V from a solar panel and charge the internal 24V battery rail directly (although typically at a lower current flow).

You can leave the MP3450i connected to a 12-24 VDC primary power source all the time, and it will charge as necessary whenever power is availalbe. You can also leave the loads connected all the time, and they'll never know when the charging source comes and goes (because the outputs are regulated), which implements a very effective DC UPS. As noted earlier, a fixed 5V output is available at a USB-A jack (great for powering or charging USB devices). A DIP-switch-settable 5V to 19V output is available at a 3-pin jack that hosts a cable which will accept dozens of different power supply tips (the 5 most common tips are supplied with each pack, and one of them will surely fit the Raspberry Pi).

The PSU board inside the MP3450i is relatively small (only about 2"x3"x0.4"), despite its sophisticated charging and power-handling capabilities. It can easily charge Li-ion or Li-poly batteries, and probably other technologies (which tend to be easier). The MP3450i PSU board would make a good OEM board (although it's not currently available as an OEM part, we intend to pursue it; Tekkeon may be open to supplying an embedded version of it, or perhaps licensing the design so the necessary elements could be added to an existing PCB).

Disclaimer: No affiliations with Linear or Tekkeon, except as a customer.

-- Dave

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abishur
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Re: Power supply

Tue Aug 30, 2011 3:16 am

Ah, so the battery device controls the complicated matters of not overcharging and powering the device. Very interesting. Admittedly, I was hoping for something in the 20-30 dollar range :P
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Dave Duchesneau
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Re: Power supply

Tue Aug 30, 2011 4:14 am

Quote from abishur on August 30, 2011, 04:16
Ah, so the battery device controls the complicated matters of not overcharging and powering the device. Very interesting. Admittedly, I was hoping for something in the 20-30 dollar range :P

The largest cost item is definitely the battery pack itself, by far. In smallish OEM quantities (1K), the second battery pack would be on the order of $100. Just guessing at this point, but the PSU's PCB would probably be on the order of $10 if the design was licensed, with some kind of modest royalty or per-unit fee to achieve a return on the NRE. In high quantities this should be a very small number.

-- Dave

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abishur
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Re: Power supply

Tue Aug 30, 2011 5:29 am

So I was actually researching some of this tonight when I came across this little gem it's the DS2715 by Maxim. It claims to be able to charge 1-10 NiMH batteries from either USB or DC power while also providing power for a device. If this is correct, we could use these chips to charge however many batteries we want while plugged in and automatically swap over when unplugged. I don't know how others would want to use this, but I'm thinking of taking an old laptop screen and making me a cheap e-reader!

Here's the official datasheet

Edit: Originally I had missed linked the PDF below. I fixed the link so it points to the right spot.

Here's a PDF with a little better conceptual view on how it works
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frafra
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Re: Power supply

Tue Aug 30, 2011 9:13 am

Very intresting!

Dave Duchesneau
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Re: Power supply

Tue Aug 30, 2011 2:32 pm

Quote from abishur on August 30, 2011, 06:29
So I was actually researching some of this tonight when I came across this little gem it's the DS2715 by Maxim. It claims to be able to charge 1-10 NiMH batteries from either USB or DC power while also providing power for a device. If this is correct, we could use these chips to charge however many batteries we want while plugged in and automatically swap over when unplugged.

This was a good find. I did a quick read of the entire datasheet (http://datasheets.maxim-ic.com.....DS2715.pdf) and it seemed to me that, as described, the chip will switch to DISCHARGE mode as soon as it senses a reverse current flow (i.e., a load). I'm hoping I misread that, because one implication would be that a perfectly usable charging source would stop delivering current as soon as a load is detected, which is not UPS-like behavior (and would in fact kill batteries rather quickly due to frequent deep cycling).

The press release (http://www.maxim-ic.com/compan.....vp/npk/981) seems to indicate otherwise, however: "...this charger can be configured as a switched DC charger, a linear current regulator, or a switch-mode current source..." This may indicate some hope for a useful circuit. I did NOT have time to read any of the application notes, so there may be redeeming info hidden there. Two of the app notes (http://www.maxim-ic.com/app-no.....vp/id/4180 and http://www.maxim-ic.com/app-no.....vp/id/3607) give me hope that the chip may be more flexible than it appears at first glance.

Although the chip COULD be configured to be a linear current regulator or a switch-mode current source, and MIGHT be perfect for the job at hand, I believe it would require altering the example circuit, which doesn't seem to provide smart charging with UPS-like continuous behavior when a load is present. However, since the chip is designed to allow some external control, such as from a microcontroller, a Raspberry Pi is well positioned to directly influence the chip's behavior, in conjunction with a modified circuit.

Three other points to consider:

1. Since the primary goal of the chip seems to be to provide occasional charging service (like after you've used a battery-operated power tool), it does not seem to re-enter charge mode once a full charge is reached. I've seen this as a frustrating problem with battery-operated power tools occurs that become fully discharged even though they've sitting in a charging dock the whole time (due to self-discharge, which is a problem with virtually all battery types, to varying degrees). To me, this is *dumb-charger* behavior (in contrast to a *smart-charger*).

2. Again, due to the chip's primary function as a DC charger, it does not appear to have any support for LVDC (low-voltage disconnect), which prevents battery destruction by shutting down the load when an appropriate voltage floor is reached (threshold varies by battery type and configuration). Again, this isn't UPS-like behavior.

3. Although this chip does a great job charging NiMH batteries, which were still considered fairly advanced batteries in 2005, it cannot be used for the more modern battery chemistries exhibiting high power densities, whereas the reverse is typically not true (chargers for more modern chemistries will often support older ones as well). The second app note listed above does, however, specifically mention Li-ion & Li-Poly batteries, which is encouraging. I just don't have time to actually read it.

For these reasons, and others that could be conjured up with additional effort, I would suggest that the ideal chip for your needs may not yet have been uncovered, and more digging may be called for. In any case, the app notes should be analyzed. Of course, that's just my opinion. Over the upcoming weekend I'll try to find time to look around.

-- Dave

frafra
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Re: Power supply

Tue Aug 30, 2011 3:15 pm

I found some solar panel (33 g / 5.5 V / max 180 mA / 15.5% efficiency) for 5,5 €. Would be cool take four of those, connect them with a battery with Raspberry Pi. With a little usb keyboard it could be easily used as mp3 player :D

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Re: Power supply

Tue Aug 30, 2011 3:46 pm

I looked some more at the data sheet (Specifically, starting at pg 7). I think your concerns could be easily addressed by putting a relay between the chip and the r-pi. The relay control would be attached to the external power device such that whenever the external power was disconnected, the relay would close (a normally closed relay).
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Re: Power supply

Tue Aug 30, 2011 5:57 pm

Quote from abishur on August 30, 2011, 16:46
...I think your concerns could be easily addressed by putting a relay between the chip and the r-pi...

Other than not drawing amps in battery mode, I'm not sure I understand exactly how an NC relay would address my concerns (but then, my brain is fried due to the projects I'm currently working on for two shifts a day).

The self-discharge I mentioned earlier would occur even if the batteries were completely disconnected from all loads. For the Maxim chip, the issue was that it appeared to me that the associated "basic circuit" might provide only a one-shot charging cycle each time battery presence is detected, rather than ongoing on-demand dynamic charging according to the current state-of-charge of an always-present (or usually present) battery. Of course, in my fried-brain condition, I could very easily be wrong.

From my viewpoint, regardless of the chip and circuit selected, the key PSU/UPS functionality should include:

* Ability to fully supply the electrical load with external power present and battery absent

* Ability to fully supply the electrical load & charge the battery with external power present and battery present

* Ability to fully supply the electrical load with external power absent and battery present (i.e., via battery only)

* Ability to disconnect the electrical load with external power absent and battery present (but depleted to some low battery threshold that is preferably settable)

* Ability to maintain output voltage regulation to the electrical load during transitions between external power and internal (battery) power sources

* Ability to properly charge various battery chemistries, to include at least Li-ion, Li-Poly, and NiMH, with appropriate smart-charging behavior that takes battery temperature, voltage, and state-of-charge into account

Electrically, the PSU/UPS connectivity would include:

* Wide external DC voltage input range (ideally 5-20 VDC) with ample current rating to meet specified loads (including simultaneous battery charging)

* Two external power input sources (possibly via a single jack, with a configuration jumper): one for clean, regulated input power (e.g., 5V from USB), and a second that is filtered sufficiently to handle a wide range of dirty input power (e.g., 6-20VDC, which would include typical vehicle power), but would also (of course) accept clean power in that same range

* Optional: Two separate jacks for the two external power input sources above, such that either or both sources may be simultaneously connected and in use.

* One regulated output with low-voltage disconnect (the Raspberry Pi load and/or others are connected here)

* One bidirectional battery connection (to charge/discharge/monitor the internal battery)

Well, that would be my short list of specs. It's not very short. The wide-range (or dirty) voltage requirements could be relegated to a separate module, if it weren't for the fact that the need to accept dirty power appears to be the normal use case for the Raspberry Pi, rather than the exception.

Likewise, you could eliminate the need for battery charging by making it an end-user problem (which is actually what the current Raspi specs appear to do). It all depends on what the real needs are.

My own personal preference would be to go the extra mile and include a maximum power point tracking (MPPT) chip in the dirty power circuit, so that maximum power can be extracted from variable DC power sources like solar panels, pedal-powered or hand-cranked generators, etc. MPPT works by dynamically varying the load seen by the power source to extract maximum power from the voltage*current source available, then converts that power to the voltage*current combination needed downstream (for powering a load, charging, etc.), which can make a substantial difference in the real-world power available for battery charging. Although such features are cheap if designed into a PCB, they would probably need to be relegated to Raspberry Pi configurations with more budgetary headroom, like Model B or later.

-- Dave

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Re: Power supply

Tue Aug 30, 2011 6:56 pm

Quote from Dave Duchesneau on August 30, 2011, 18:57
Quote from abishur on August 30, 2011, 16:46
...I think your concerns could be easily addressed by putting a relay between the chip and the r-pi...

...My own personal preference would be to go the extra mile and include a maximum power point tracking (MPPT) chip in the dirty power circuit, so that maximum power can be extracted from variable DC power sources like solar panels, pedal-powered or hand-cranked generators, etc...


As a courtesy, I'm uploading some MPPT chip-level datasheets from a couple of manufacturers, and reference design info from another. The STMicroelectronics SPV1020 is particularly interesting, since it can directly operate off the same voltage range that it can accept as the wide-range power input to be controlled (0-36 VDC, but effectively, 6.5-36 VDC, since its algorithms kick in at 6.5 VDC). This overlaps nicely with the R-Pi's contemplated 6-20VDC input range.

The SPV1020 is designed to support distributed MPPT, which implements MPPT on a per-PV-panel basis rather than for a whole array. This makes it particularly well-suited for the Raspberry Pi and auxiliary componentry, since virtually any single PV panel can be supported for both battery charging and continuous operation.

IMPORTANT NOTE: To those just jumping into this thread, please see previous posts for context. The suggested use of MPPT here relates to widening the already wide power supply input range of the Raspberry Pi while enabling battery-based operation, backup, and charging. This is merely discussion and does not (and may never) have any effect on the R-Pi's present specifications.

-- Dave

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abishur
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Re: Power supply

Tue Aug 30, 2011 7:09 pm

Ah, yes this chip is more in line what I want for battery backup. For my application I actually want to use it as a mobile device (e-reader) so I would be frequently charging and discharging it. Also, looking at it a little closer I think the relay is unnecessary. I think the chip handles that, my electrical diagram reading skill are a little only so so.

Edit: oh, but take a look at the other chips on that site, they offer a large selection, they just aren't all as cheap as the one I listed.
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Re: Power supply

Tue Aug 30, 2011 7:11 pm

Okay, so uploading datasheets didn't work so well. Here are some URLs instead:

STMicroelectronics -- SPV1020 Interleaved DC-DC boost converter with built-in MPPT algorithm
Press Release:
http://www.st.com/internet/com...../p3031.jsp
Datasheet:
http://www.st.com/internet/com.....275733.pdf

National -- SM72442 Programmable Maximum Power Point Tracking Controller -- Datasheet.pdf
http://www.datasheetarchive.co.....056798.pdf

Cypress.com -- PowerPSoC -- MPPT Solar Charge Controller Reference Design.pdf
http://www.cypress.com/?docID=21164

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abishur
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Re: Power supply

Tue Aug 30, 2011 7:17 pm

I'm not seeing an order option for the chip. Do you know how much they cost?
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Re: Power supply

Tue Aug 30, 2011 7:25 pm

Also, I just noticed that Rev.2 of the STMicroelectronics SPV1020 datasheet indicates that the input voltage OPERATING range is now 0-45V (45V is also the absolute maximum voltage, and always was), with MPPT regulation still beginning at 6.5V. The maximum regulated output voltage is now 40V.

This extended input range means that the SPV1020 chip can accommodate even the very largest solar panels (250+ watts) with high open-circuit voltages (e.g., Voc > 36V). Basically, you can supply power from whatever you can get your hands on.

-- Dave

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Re: Power supply

Tue Aug 30, 2011 7:42 pm

Quote from abishur on August 30, 2011, 20:17
I'm not seeing an order option for the chip. Do you know how much they cost?

Sorry, I don't know, except for budgetary pricing. For minimum orders of 1K, the SPV1020 chip was priced at about $5 in 2010. Unit pricing (1-10) from a distributor might be on the order of $6-7, but I don't know off-hand who the distributors are, or if they have them for this chip, since I don't normally deal with them. UPDATE: No distributors. Contact ST directly. See: http://www.st.com/stonline/con.....index.html. By the way, ST may provide bona fide design/engineering groups with free or nearly free samples.

Also, you might be able to get your hands on a demo board directly from ST (for a price), and possibly avoid buying chips while prototyping. A demo board is pictured in a January 2011 product flyer FLSPV10200111 (http://www.st.com/internet/ana.....250769.jsp), in a PDF with the following URL:

http://www.st.com/internet/com.....pv1020.pdf

Out of time. Gotta get to it.

-- Dave

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Re: Power supply

Wed Aug 31, 2011 1:24 pm

Should I be able to run a raspi off a setup like this?

http://seeedstudio.com/wiki/Li.....Rider_V1.2

DanielSilva
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Re: Power supply

Wed Aug 31, 2011 1:54 pm

Quote from poeee on August 31, 2011, 14:24
Should I be able to run a raspi off a setup like this?

http://seeedstudio.com/wiki/Li.....Rider_V1.2

You *could* use it to power the raspi *if* the raspi ends up being able to be powered from the usb port. If not you could still use that stuff if you build a step up dc converter to bump the 5v to something that the raspi can use ( at least 6v ), which isn't hard to do by itself but it would be yet another thing to buy/build.

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Re: Power supply

Wed Aug 31, 2011 2:03 pm

Quote from poeee on August 31, 2011, 14:24
Should I be able to run a raspi off a setup like this?

http://seeedstudio.com/wiki/Li.....Rider_V1.2

Not at this point in time. Right now the r-pi requires a 6-20V DC input. That only gives a 5V DC output :(
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Re: Power supply

Sun Sep 04, 2011 11:31 am

I think it is a very unfortunate design decision not to go with the new universal mobile phone charger standard as power supply. Every household has - or will soon have - these and probably several units and you (the project) wouldn't have to even think about this part anymore.

Going for a jack plug is equally troublesome as there are so many different brick units around. You better make the on-board power system *very* robust as kids will plugin anything that fits physically, AC or DC at whatever voltage.

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Re: Power supply

Sun Sep 04, 2011 12:01 pm

We're targeting the product at the developing world as well as the developed world. Not everybody has a universal mobile phone charger - a lot of our customers won't even have a mobile phone. The demographic which we hope to be taking up the device isn't just the one with you in it!
Director of Communications, Raspberry Pi

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Re: Power supply

Sun Sep 04, 2011 12:46 pm

universal phone charger is micro usb i believe, i don't think it provides the correct voltage which is why this isn't charged via usb as far as i'm aware.

If it is possible then it would be better using a plug with a usb connection on and a usb cable as you can get chargers for £1 and a cable for very little. Even with the chip(s) needed on the pcb for this it would almost certainly be cheaper than a power adapter and you could use the usb charger for other things and power the board via a usb port off another computer.

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Re: Power supply

Sun Sep 04, 2011 1:09 pm

Quote from liz on September 4, 2011, 13:01
We're targeting the product at the developing world as well as the developed world. Not everybody has a universal mobile phone charger - a lot of our customers won't even have a mobile phone. The demographic which we hope to be taking up the device isn't just the one with you in it!Thank you for your answer. Yes I do realize many people in less developed areas of the world may not have mobile phones (although they are surprisingly common in large areas of Africa). But as you also know from your own project, mass production is crucial to the price and these new adapter are being made in hundreds of millions and hence is very inexpensive.

A custom Raspberry PSU (or any other DC-adapter) will be much more expensive anywhere in the world. And will leave you with a non-working unit it you forget to bring the PSU with you. With the standard mobile phone adapter you can borrow one anywhere.

But of course there may be technical hassles that I'm not aware of to prevent this solution, but I failed to spot anything requiring more than 5V and 1W.

Mike

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