Power supply

[DanielSilva]

For now USB charging isn't supported and besides mobiles chargers are far from being standardised. We have something like 5 mobiles at home and none of them have interchangeable plugs as they use different usb ports or have proprietary ports, so imho phone chargers are less than an ideal solution.

DC jacks on the other hand come in hundreds if not thousands of house appliances, and such they are easily available ( things like routers, battery equipped appliances, most externally powered computer peripherals, etc ) and even if you don't have any around the house you can easily find them, any hardware store usually has available universal power bricks that only costs a couple of bucks ( i just bought one for 5€ made by Creative, a "white" brand should cost even less ). The board current accepts 6 to 20v input so it should cover most common bricks out there.

If we could have both and choose which power source to use that would be the ideal solution but if i had to choose between USB and DC jack i would choose the later, if anything else because i would be limited to 500mA ( and you'll find this pretty limiting if you want to add daughter boards to the raspi ).

[kme]

Quote from DanielSilva on September 4, 2011, 14:46
For now USB charging isn't supported and besides mobiles chargers are far from being standardised. We have something like 5 mobiles at home and none of them have interchangeable plugs as they use different usb ports or have proprietary ports, so imho phone chargers are less than an ideal solution. [CUT]
I'm sorry but your information is outdated. In the entire EU no one can sell mobile phones without the EPS plug (micro-USB). This agreement has been made between the EU Commision and Apple, LG, Motorola, NEC, Nokia, Qualcomm, RIM, Samsung, Sony Ericsson, Texas Instruments, Atmel, Emblaze Mobile, Huawei Technologies and TCT Mobile (Alcatel).

It has been adapted in China (modified), South Korea, Japan and several other Asian countries.

It had been adapted by GSM Association, which means it's reasonably common in the Americas too.

Your own experience with five different mobile phones and five different power adapters show clearly why everyone loves the new standard.

And I just think Raspberry should benefit from this, it technical possible in any way.

[DanielSilva]

Yes i know that mobiles are now required to provide a standard port but this ONLY applies to newly manufactured phones, do you really think that represents even 50% of today or even 2 years from now on phones ? Much less in less developed areas ? Bet my entire year salary that it won't.

The point in Raspi is to make it easily available to everyone, do you really think tinkerers and people who change phones every year is the intended target ?

[Johannes]

Only phones which can exchange data with a computer through a wired connection (i.e. have a USB port) are required by the EU to support charging through USB. Many "feature phones" still come with non-USB chargers.

Anyway, standard USB can only supply 2.5W (0.5A at 5V), which is enough for the Raspi itself, but not enough to also supply full power to the USB port(s). While there is a standard which allows USB devices to negotiate more than 2.5W with a power supply that can handle the load, such power supplies are not nearly as commonly available as simple USB chargers which can only handle 2.5W. I've seen some which can handle even less.

Then there's the problem that a 5V power supply, if used directly without further conversion, would exclude other voltages from being used, such as 6V or 12V from lead-acid batteries. Anyone trying to use a different voltage anyway would instantly fry attached peripherals (at least). In order to also accept other voltages in addition to 5V, a buck-boost converter would have to be used, instead of a much simpler and cheaper buck converter.

[kme]

Quote from DanielSilva on September 4, 2011, 15:41
Yes i know that mobiles are now required to provide a standard port but this ONLY applies to newly manufactured phones, do you really think that represents even 50% of today or even 2 years from now on phones ? Much less in less developed areas ? Bet my entire year salary that it won't.
You are missing the point entirely (again). It is *not* a matter if you have one of these new phone chargers (consider yourself lucky if you do) or not. Eventually you will.

It's a question of the price for a PSU for Raspberry PI:
1) Buy a dirt cheap standard phone charger.
2) Buy an expensive non-standard PSU for this particular hardware only.

Is that hard to understand?

@Johannes: The standard phone charger is not a USB device - it is a PSU that use a micro-USB plug physically. You can supply about any amount of power you like (fire hazard etc. still apply). But you are in no way limited by electrical USB standards, the PSU isn't a USB host or anything USB. It's just using the mechanical form factor of the micro-USB plug. Feel free to supply 20W if you like, the Raspberry will still only consume what it needs. Your desktop PC may have a 500W PSU, but it certainly doesn't use 500W.

Of course the phone charger won't give you more than 4-6W, but that has nothing to do with the physical interface. And your 20W PSU with a USB plug won't cost you more than a 20W PSU with a jack plug.

[Johnmennis]

As much as possible, I think that keeping a system where small scale solar and batteries are a potential power source would be best.

[abishur]

I hear what you're saying and it's a very rational point of view, but there's two overriding factors going on with the r-pis decision.

The first is that universally accepted standards are subject to rapid change. It wasn't but a couple years ago when people had finally accepted those little dc jacks for charging cell phones. You can't count on industry standards to remain stagnate. More importantly, however is the desire to provide a device that is powered from a source people already have on hand. Will everyone have it on hand? Of course not, it will be naive to think that *everyone* will have a spare DC jack lying around. But the idea is to hit the maximum amount of people possible with items they already have, not something they might one day obtain.

Now that's just my opinion, I think it's safe to say you disagree and that's okay The second issue is what it actually comes to. The power jack and handling on the r-pi itself is being a tricky issue because of it's price! To keep it down at the $25 dollar mark, the wider voltage range coax jack in necessary.

So why the coax plug? It hits a wider base in what people should already have on hand (even if they have to steal it for a minute any time they use the r-pi) and it's a cost issue.

[Johannes]

I know that the USB standard isn't the technical limit, but many USB power supplies will not supply much more than 2.5W. They are after all designed to supply power to standard USB devices which aren't allowed to draw more than 2.5W. Again, I've seen USB power supplies which won't deliver even 2.5W. USB plug power supplies which are rated for about 5W, which you'll need for the Model B Raspi with its two USB ports and Ethernet, are not as common as you think they are.

The coaxial power plugs that are on external hard disk enclosures are the most common kind and power supplies with these plugs (typically 12V 2A) are widely available and cheap. Most importantly, not going with a 5V power supply opens many more options for powering the Raspi, particularly batteries. You'd need more complicated and more expensive circuitry if you wanted to use a 5V power supply and still be able to use other voltages. Choose: Complicated and expensive circuitry or 5V only or 6V-20V.

[DanielSilva]

Quote from kme on September 4, 2011, 16:27
Quote from DanielSilva on September 4, 2011, 15:41
Yes i know that mobiles are now required to provide a standard port but this ONLY applies to newly manufactured phones, do you really think that represents even 50% of today or even 2 years from now on phones ? Much less in less developed areas ? Bet my entire year salary that it won't.
You are missing the point entirely (again). It is *not* a matter if you have one of these new phone chargers (consider yourself lucky if you do) or not. Eventually you will.


It seems you just diagonal read the posts and disregard everything that doesn't go with your opinion.
DC 3.5mm jack plugs ARE NOT uncommon and are in fact pretty popular in everyday appliances and you do NOT need to buy any expensive non standard power supply since these power brinks are available in any hardware store and/or electronics store for cheap, i just bough a Creative branded universal power brick ( could have gotten a generic brand for even less ) for 5€.

The point with raspi is to give a very low priced educational environment to people and for that we should use what we have *today* and not what we could or not have in the mid/distant future, in fact the best thing is to plan with something we currently or even have had access for quite some time because that's what people in rural and undeveloped areas have.

Besides this is a moot point since using or not usb isn't a matter of ideology but rather something that isn't technically viable with this version of the raspi.

[beatyrm]

So I've been looking at this particular solar panel from PowerFilm.

http://www.amazon.com/Powerfil.....38;sr=1-50

It runs 7.2V @ 200mA and is (contrary to the posting there) ~6"x10" according to the website. At ~$40 it's probably a bit more expensive than some folks are interested in but I feel it's still pretty reasonable. The real question would be could it handle pairing up with a battery and running the pi throughout the evening while charging up during the day. The wiki says that the prototype unit running a hdmi display is using 180mA. Obviously without an output the usage will be lower. Given that the battery/batteries would need to be below the 7.2V/200mA I'm curious if it could work.

[Lob0426]

Many of the phone chargers will supply enough amperage to run the RasPi. Most of the older phones charged at something above 6v. Almost none of the phone chargers were below this, though there were exceptions. 5v is becoming the standard in europe but as AFAIK not in the U.S. or anywhere else so far. But I do live in California or as I call it the PRC (Peoples Republicof California). So we could see a standard enforced here. I do know they are pushing for auto shut off on all Wall-warts.

[Dave Duchesneau]

I'm just blasting this out, so it's kind of long (sorry, no time to edit). An easy way to look at this problem is in terms of energy (e.g., joules or watt-hours). Since the r-pi consumes about 1 watts of power (i.e., 1 watt-hour of energy per hour), let's use watt-hours. Running an r-pi (and nothing else) on a 24x7 basis would thus require 24 watt-hours per day, and 168 watt-hours per week.

So, if you want an r-pi to run on batteries alone for 1 day, you would need 24 watt-hour battery pack. If you were to obtain 10 rechargeable AA NiMH cells (such as the Energizer or Durcell 2500 mAH batteries available at most grocery stores), and put them in series, you'd have a 12-volt lead-free power source (rechargeable AA batteries are 1.2V rather than 1.5V). The total energy in such a pack would be 2.5 AH (2500 mAH) x 12 V = 30 watt-hours. If fully charged, this would be sufficient to run an r-pi for 24 hours (24 watt-hours of energy) without totally killing the battery pack (20% reserve). To extend this to a week you would obviously need 7 such packs.

Now, for the solar part. To operate continuously with a solar panel only, you need a panel that can deliver AT LEAST 24 watt-hours every day, all day, and the sun must sufficiently direct and bright to deliver the necessary light energy ("insolation") that was used as a reference for the solar panels specification. This is where the problems start. First, it's tough to find a terrestrial location where the sun shines brightly on a 24x7 basis, with no clouds, etc. Even if we did, most panels assume insolation levels of 1000 watts per square meter in their specs, per lab conditions, but in reality, it's rare to get even 80% of that due to atmospheric interference, time of day, etc. However, for the sake of argument, and because I like round numbers, let's assume a panel that claims 10 watts of output in bright sun will actually deliver 10 watts.

Brief but relevant digression: I live in Seattle. According to aclassic song, "The bluest skies you've ever seen are in Seattle." According to a post card I once saw, entitled "Seasons in Seattle," the four seasons were simply depicted as four shades of gray. From this you can glean that if you pick just the right time to look at the sky, it's a very blue sky. On average, however, it is apparently some shade of gray. My hypothesis is that the frequent-but-usually-light-rain keeps the sky so smog-free that you can sometimes catch a glimpse of blue sky.

The reason this is relevant is that insolation levels for most locations on earth are available either as statistical measurements or predictions. If I recall correctly, the annual AVERAGE daily insolation in Seattle is on the order of 2 hours per day, whereas in a smog-free area of the southwest USA, it might be 6 hours per day (I might be remembering seasonal averages though). That's good enough for back-of-the-envelope calculations, to make my point. If you need 24 watt-hours of energy to run an r-pi, and you want to use solar to power it in Seattle, then you'll need sufficient PV capacitity to collect all of that daily energy (plus overhead due to inefficiencies) within a 2-hour window, on average. Thus, in a perfect world, you would need at least a 12-watt solar panel (24 watt-hours / 2 hours = 12 watts). The problem is that it's not a perfect world, and 2 hours of insolation is only an average, and there are many inefficiencies.

There are periods of abundant sunlight, and long periods with none at all, so many off-grid PV-solar-powered systems typically provide perhaps a week of ride-through, which is why I mentioned earlier that it would take 7 10-cell battery packs to last for 7 days. At about $10 for a set of four such batteries, that's about $25 for 10 of them (1 day's worth), and $175 for 70 of them (a week's worth). Of course, that's with consumer NiMH batteries. If you don't mind SLA batteries (sealed lead-acid), you could just get a pretty big deep-cycle battery for under $100, and end up with 3X the capacity (which is good, because you can't fully deep-cycle them very often, or they die).

Alternatively, because our gear gets sealed in radio-tight and air-tight containers (where SLA batteries cannot be used), I rather like the industrial Lithium Polymer power packs from http://Tekkeon.com. Each has a built in charger and regulator, and can deliver 58 watt-hours at a range of voltages between 5V and 19V (DIP-switch-settable), at currents up to 4A. There's also an aux USB power port that operates in parallel. It accepts many types of charging power, including solar, vehicle DC, and AC. Multiple packs can be daisy-chained.

When sunlight is abundant, a larger battery capacity provides a place to store it, and when it's not, the larger battery capacity provides ride-through until the sunlight returns.

I like to seriously de-rate off-grid systems, since their usual focus is often related to survivability. Use the insolation available for your area (search Google for an insolation map, etc.), assume no more than 80% will be available at the PV panel, then account for the inefficiencies. PV panels only output their rated values when directly pointed at the sun, and less otherwise. The open-circuit output of a PV panel will be dragged down by the batteries (which present a load on the panel), so a voltage which is sufficient to charge empty batteries will no longer be adequate to top them off. To solve that problem, and extract maximum power from a PV panel, you need a maximum power point tracking (MPPT) circuit. An MPPT circuit is essentially an any-to-any DC-to-DC voltage and current converter, which essentially converts whatever power the PV panel can provide to the optimal combination of voltage and current that is needed (such as for charging). While MPPT chips are available for a couple of bucks, the smallest MPPT converter I've ever seen was on the order of $250 for one that would handle a modest 60 watts (e.g., up to 3 20-watt panels). This is 10X the proposed r-pi price, and it doesn't even include a PV panel.

Gotta go.

[Mr.What]

Quote from AmyS3 on August 4, 2011, 19:19
...the raspi is going to be the cpu of my uav, i also have to think about the motors, servos, gps, camera and other sensors.
i´m lucky that the uav is helium backed so the motors don´t have to run all the time...

Will the RasPi have some sort of efficient buck converter on it's input. Hence if you supply higher voltage, it will draw less current, keeping power use near 1W.

BTW: Is somebody doing time-aloft RC flight competitions. Sounds great!

[Mr.What]

Quote from Lob0426 on September 21, 2011, 06:09
Many of the phone chargers will supply enough amperage to run the RasPi. Most of the older phones charged at something above 6v. Almost none of the phone chargers were below this, though there were exceptions. 5v is becoming the standard ...

5v is pretty standard for cell phones, which is convenient to charge a 3.7v nominal LiPo battery. I guess the RasPi may want more, in order to drive the 5v lines for USB, HDMI? Any chance for a small buck/BOOST converter on the RasPi 3

[Gert van Loo]

WARNING! WARNING! WARNING!
As I already mentioned in several places: the power supply is the last thing we are looking at in the re-design. We are struggling with keeping the cost down and it looks like we have to compromise on consumption to keep the price promise.
For now please assume nothing about power!

[Lob0426]

I have a 7805 waiting just in case!

[mexicodirk2]

For now USB charging isn't supported and besides mobiles chargers are far from being standardised. We have something like 5 mobiles at home and none of them have interchangeable plugs as they use different usb ports or have proprietary ports, so imho phone chargers are less than an ideal solution.

DC jacks on the other hand come in hundreds if not thousands of house appliances, and such they are easily available ( things like routers, battery equipped appliances, most externally powered computer peripherals, etc ) and even if you don't have any around the house you can easily find them, any hardware store usually has available universal power bricks that only costs a couple of bucks ( i just bought one for 5€ made by Creative, a "white" brand should cost even less ). The board current accepts 6 to 20v input so it should cover most common bricks out there.

If we could have both and choose which power source to use that would be the ideal solution but if i had to choose between USB and DC jack i would choose the later, if anything else because i would be limited to 500mA ( and you'll find this pretty limiting if you want to add daughter boards to the raspi ).

The board current accepts 6 to 20v input ?
its not 5V on the PI Board? or i misunderstanding something ?

Dirk

[rurwin]

Look at the date on the thread. This was well before the design of the board was finalised.

The power requirement of the RaspPi is 5V +/- 5%.

[mexicodirk2]

sorry