Just saw in last week's NewScientist (Jan 18 p.19) that someone is coming out with a fuel-cell powered USB phone charger. Wonder if that could be used to power a Pi -- and for how long per canister?
-- Pete --
How big a battery does the average phone have? The range of capacities would seem to be 1000mAh (Samsung B2100) to 2100 mAh (Galaxy S4) and the charge/discharge efficiency is 80-90%, so lest say that the hydrogen charger is designed for 5 charges per cartridge and the charge/discharge efficiency is 80%.
IOW the charger outputs 1250 - 2625 mAh per charge and so the cartridge must store 6250 - 13125 mAh of electrical energy.
Not lets assume the charger is only supporting the Pi, i.e. it is NOT also being asked to power a screen, mouse or keyboard and doesn't have any PiFaces, etc. added to it. This means it will be supplying 500 mA or
500 mAh per hour that the Pi is running, so should be expected to run the RPi for between 2.5 and 5.25 hours. Not a lot, is it?Then there's the little matter of cost: Amazon will flog you a 13000 mAh 'portable phone charger', i.e. a Lithium battery plus a bit of
at least 3 portable chargers (the Pi needs a new battery every 5 and a bit hours but the batteries take just over 8.6 hours to charge at 1.5
If you replaced the Li power packs with 12v SLAs the cost stays about the same.
You see where I'm going: the hydrogen charger had better cost less than that or its a waste of money *and* that excludes the cost of a set of hydrogen cartridges, the ongoing cost of getting them refilled and the probability that refills won't be available at your local Maplins, Car- phone warehouse or anywhere else that's handy.
Of course, I may have missed something: Dave Ackerman and his chums are regularly flying PIs into the statosphere on met balloons for pretty long flights, so I'd be interested to know how they do it: use a Model A and somehow make it hibernate for a lot of the flight?
-- martin@ | Martin Gregorie gregorie. | Essex, UK org |
I meanwhile did a web trek, and managed to find the specs (it's the 'Upp'
It outputs 5V at 1000mA and has a 25Wh capacity per canister. I measured my model B (with K/B and mouse connected) at ~2.5W, so it should be able to power it for about 10 hours. The price (from a press release somewhere) is $199.
... and the specs indicate 5000mAh, so I guess they're being optimistic!
Eh? If it's taking 500mA (as mine seems to -- 2.5W @ 5V), your max of
5.25 hours is only 2625 mAh! As I say, I calculate about 10 hours.If the Pi only needs to run for up to 10 hours, you'd only need the one 'Upp' at ~£120 or so at current rates. Plus the (unknown) cost of the hydrogen. So yes, at the moment it isn't really competitive, but prices will probably come down.
Well, that 13000mAh unit should power it for about a day, by my calculations...
-- Pete --
I didn't say quite what I should have there...
The thing is, presumably changing a canister is very quick, so you will *never* need surplus Upps, whatever the duty cycle of the Pi -- just a supply of hydrogen canisters. (Even with a supply of Li units, you presumably have to power down/up at each change.)
Maybe in Darkest Africa, where there's no mains supply...
-- Pete --
One of these:
will run a Pi for over 24 hours with no peripherals attached.
(I have one and have tested it)
Available today. This whole fuel-cell thing sounds good, but will it be better than a "traditional" stored charge system?
Gordon
In a mad moment - Pete mumbled :
Just like the Hindenburg ? Touchy stuff is Hydrogen.
-- |)ryn [vans mail to - BrynEvans@bryork.freeuk.com
Someone was working on a mini propane/butane fuel cell a couple of years back, using similar cartridges to those in gas curling tongs, that should have hit the market by now ...
Yes, I was wondering about that, but decided to assume that they had looked at current spartphone specs and designed for that.
Yep. If you assume 80% efficiency you need to supply 2526 mAh to fully charge a 2100 mAh battery once..
Yep, I see where I messed that up - my only excuse was that it was late.
So, that means 2 x 13000 batteries (one is running the Pi while the other
interbank rate) vs $199 for the hydrogen charger.
Did you see any prices for full canisters or refills?
Meanwhile, I did some measurements on my 512MB model B using a Maplins watt-meter between the wall-rat and the mains. My Pi has no connections except the power input and a wired Ethernet cable in the RJ-45 socket. I run it headless. It has no extra hardware and nothing connected to the GPIO lines. I fitted a switch in the 5.v line to minimise wear on the micro-USB socket.
- with the Pi powered off the wall-rat draws 0.0w, i.e.
Is that a model B? I assuming it is.
cartridges and refills will cost. Though you would need two batteries for continuous operation away from the mains.
I reckon batteries will rule for a few years yet.
-- martin@ | Martin Gregorie gregorie. | Essex, UK org |
["Sale price", I noticed. The original cost was more than the hydrogen unit...]
I imagine... But I also imagine that fuel cells will continue developing. Here in the San Francisco Bay Area, more and more hydrogen-fuel-cell buses are showing up on the roads; looks as if the 'test period' is over, and they're an effective option. (Of course they store pressurized hydrogen, rather than the hydride storage used in the 'Upp', so I suppose their energy density is much higher.)
And, as I said in the other fork, it might already be worth it for use-cases where the mains is not handy. On safari, or even a long camping trip [if you insist on taking your Pi along... (:-))]
-- Pete --
Big fuel cells are or were an interesting example of stalled technology. Seven or eight years ago I was talking to Bob Parks, who knows a thing or two about them, or ought to, since he's an aerodynamicist at Aurrora and was working on high altitude, long duration aircraft and Mars planes. I remember him saying that the heavy duty (40 KW) hydrogen fuel cells that were available were virtually identical to the ones used on the Apollo program 40 years previously.
I suppose that depends on the fuel cell's housing etc. It would be a bit limiting if it would only accept small 5-charge cannisters, simply because for reasonable untended operation it would be much more convenient to hook up a decent sized hydrogen cylinder, but those do get heavy, which is why I'd prefer to see affordable liquid fuelled fuel cells appear on the market. Sure, there's an issue with keeping anhydrous methanol anhydrous, but carrying a few litres of that in a lightweight alloy tank has to be a lot easier than lugging a hydrogen cylinder and may even have a better energy density in terms of watts/kg once you include the container in the calculation.
-- martin@ | Martin Gregorie gregorie. | Essex, UK org |
You can also turn off the USB hub on a Rev B Pi which takes the power down to the same as a Model A.
Don't have the rune to hand, but it's a simple echo 0 > /sys/come/path/to/usb/device will look it up if anyones interested.
Gordon
How and where are they getting all this hydrogen from?
I think the big problem with hydrogen is that it's not just lying about in *easy to access* amounts. There is a lot of water about but you have to shove just as much energy in to free up the hydrogen as you get back when oxidising it...
-- Cheers Dave.
Can I assume that you then have no USB at all, unlike an A?
Yes...
echo 0 > /sys/devices/platform/bcm2708_usb/buspower
to turn it off, and
echo 1 > /sys/devices/platform/bcm2708_usb/buspower
turns it back on again.
Gordon
Err, won't that kill the ethernet as well? I thought the Pi ethernet was bodged onto the USB rather than a standalone thing.
-- Regards Dave Saville
Yes it does, but I'm under the impression this thread has veered slightly towards the low power stuff that Dave is using on the baloon Pi's where he's using Model A's to reduce power (which don't have Ethernet).
And there's no "bodge" about it - it's designed that way. The USB chip on the Pi is effectively a 3-port USB hub with one port being hardwired to the internal Ethernet interface..
However yes - if you want Ethernet, then don't do this. (And don't get a Model A either!)
You could use this for a lower-power data acquisition system - so get it to turn the USB off, gather data (via GPIO) then push a button, enable the USB and Ethernet (or Wi-Fi) upload the data, lather, rinse, repeat...
Gordon
According to Wikipedia the common source of industrial hydrogen is burning natural gas with water at high temperatures:
CH4 + H2O -> CO + 3H2 and CO + H2O -> CO2 + H2
a process called Steam Reforming. I guess this is cheap while it lasts, but you can see the carbon footprint. Later on hydrogen fuel cells will revert to being a way to make electrical energy portable.
Mel.
Thanks for that, very useful - I was thinking of getting a Model A plus camera for mobile use, but can now use a Model B as effectively with greater versatility.
Interestigly, when I tried it over ssh I got "access denied" even with sudo. By design, I guess, because usb/ethernet in use? But that made me realise you would obviously need a non-keyboard/network way to re-enable the hub... As you say:
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.