Possible Raspberry Pi UPS

I was in Lidl today (UK) and noticed that they had AA[A] battery
chargers which have a 12V DC input (wall-wart supplied), a USB power out
(claimed rating 5V at 1500mA) and a "power tank" facility when batteries
are present. The details appear to have dropped off of Lidl's website
(so the chargers may not be available for much longer), but it looks as
though this charger *could*, with the addition of 4 AAs, serve as a UPS
for the Raspberry Pi (as well as as a battery charger).
I'm not sure whether to risk £16.99 to try this it out: I already have
an "intelligent" AA[A] charger, but my Pi is currently running from a
float-charged Power Gorilla, which gives me a UPS with a backup of about
12 hours, but it's rather a waste and the PG may be better freed for use
with my workhorse laptop.
Other tinkerers may want to investigate this possibility.
Reply to
Hils
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Reply to
hamilton
All-Purpose Battery Charger.
The relevant
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page is blank, but this one (at the time of writing) isn't:
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The bad news is that this suggests it will only charge two batteries at a time, so it's difficult to see how the "power bank" will give 5V. (It also indicates that the charger costs £1 less in Norn Iron than in GB.)
I've also found a paper brochure which says
o Charges standard lithium-ion and Ni-MH rechargeable batteries
o Simultaneously charges batteries and devices connected to the USB port
o With Power Bank function, Revive function, Polarity Reversal protection and detects non-rechargeable batteries
o Contains mains power supply, 12V car adapter, 2 x AAA adaptor
So I'm now have major doubts that it can give 5V out in the absence of external power, though it could still be worth a punt if you can use an AA[A] charger.
Reply to
Hils
Have a dig about on the Kompernass site, the product pages are only in German. The English side only has product suppport but you might be able to find the manual to download.
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Cheers 
Dave.
Reply to
Dave Liquorice
It should be able to do the job with Li-ion batteries in it. For all normal interpretations of the term 'lithium-ion batteries' you expect 3.6 to 3.7v per cell fully charged and hence 7.4v from a pair of them. That should be good enough to power almost any 5v regulator, though it would need to have an automatic low voltage cutoff since Li-ion cells have a tendency to die suddenly if you discharge them below 3.0v.
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martin@   | Martin Gregorie 
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Reply to
Martin Gregorie
True, but the charger may contain a dc-dc inverter so a primary voltage of less than 5v may be used.
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Graham. 

%Profound_observation%
Reply to
Graham.
I've been trialing these:
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I got about 50 minutes run-time on a model "B" but there's a glitch when power is resumed, which I have not yet tried to mitigate. the AC plug detatches but I don't know if there's a UK plug option
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Reply to
Jasen Betts
Also true. MAXIM make a big range of them though I can't remember if they make anything that would run off a 3v supply. I'm used to them operating at a higher voltage: my 28v Turn-and-Bank indicator runs off the normal 12v glider battery via a solid state DC-DC converter.
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martin@   | Martin Gregorie 
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Reply to
Martin Gregorie
Only supplies half an amp, so I'd be wary of using it with power-hungry kit. Can't immediately find its battery capacity.
A rather pricier option, but one that works well for me, is the NewTrent IMP120D, intended for iPads and BlackBerrys and such - 12Ah of battery, and a mains transformer to keep it topped up. (I actually got it to run the Pi for GPS logging while walking.)
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Reply to
Roger Bell_West
Interesting. I haven't been able to find any further information on the charger online. It comes with what /may be/ a cellphone-battery-shaped adapter, but it's not clear whether it will charge AA-format lithium ion batteries.
It's tempting to suggest that someone should buy one and report on its real capabilities, but Lidl only make things like this available for a few weeks each year.
Reply to
Hils
4.2v per cell fully charged, falling to 3.7 as average and as low as 3.3 before they puff up and go bang. LiFe is about 3.7 fully charged, but that's not Li-Ion..
3.3 is pretty much 'damaged permanetly' 3.00 is 'likely to explode and certainly useless now'
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Reply to
The Natural Philosopher
The RC model industry has all the stuff you need - mains or 12v chargers, voltage regulators that 'understand' lithium cells and so on. And the lithium cells themselves.
None of it is that expensive.
Viz
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etc.
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Ineptocracy 

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Reply to
The Natural Philosopher
I thought it was overcharging of a bare unprotected cell that would result in an explosion.
The thought that they might just explode all on their own if left unused due to their self discharge is rather alarming.
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Brian Gregory. (In the UK) 
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Reply to
Brian Gregory [UK]
In the world of RC model aircraft most of the fires in undamaged batteries happen during charging, often due to using a cheap charger, not using a balancer when charging a multi-cell battery or exceeding the recommended charge rate. Almost all the rest are the result of crash damage.
The self-discharge rate of a disconnected Li-ion or Li-poly cell is much lower than any other common rechargeable apart from, possibly, lead-acid batteries. Its a lot higher than NiMH cells and higher than that of NiCds. Of course, if the battery is installed in something that has a so- called soft-touch power switch, it will need charging at more frequent intervals because soft-touch switches are electronic components and so will use power while waiting for you to turn the device on.
Apart from that, if you run a Li-ion or Li-poly battery down below 3v/ cell it will self-destruct (the references I've seen say this happens below 2.9v/cell). The ones I've seen ruined this way have never caught fire or caused any damage to the devices they are installed in - and this includes balsa structures. They merely and quietly become ex-batteries.
The exact discharge limit depends on the chemistry being used, but 3.2v is usually considered a safe minimum.
They don't explode or catch fire that I've seen, and this includes several cases of the high discharge rates, as in using the battery to run an electric motor which was drawing something near its maximum discharge current. The models they were powering were fitted with a timer to shut off the motor. The timer failed to stop the motor, so it sucked the battery dry, which ruined the battery but did not cause an explosion or fire.
NOTE: it goes without saying that if you charge or discharge a Li-ion or Li-poly battery at more than its rated for it may suffer thermal runaway and catch fire no matter how good the external equipment is. However, if you do that you're a fool and deserve the outcome.
Permitted discharge rates are typically a lot more than permitted charge rates: for Li-poly batteries a max discharge rate of 25C is typical, while the max charge rate may be only 1C. 'C' is the battery capacity, so for a 1000 mAh battery with these ratings (I have one: these are read off it) you can draw 25 amps without causing damage but must not charge it at more than 1 amp.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
.......................LOWER - dammit ............LOWER again - dammit
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
no, they normally just die that way. maybe get a bit puffy.
BUT they can explode spontaneously.
A few years back someone left a pack on the dash of a car in Los Angeles. IN the sun.
The insurance did pay for the car eventually. :-)
TBH modern packs have moved away from such volatile organics and its only normally overheating (for whatever reasan) that makes em catch fire. As in Dreamliners where I THINK they said 'someone had taped over the ventilation holes'.
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Ineptocracy 

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Reply to
The Natural Philosopher
Yes, all as I thought. (once you corrected a small error in your next post).
I think I read that the main reason they become totally useless once they discharge below a certain level is that the protection circuits prevent any more charging because of some level of risk that the cell could no longer cope and would become dangerous.
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Brian Gregory. (In the UK) 
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Reply to
Brian Gregory [UK]
The user manual suggests that it can provide 5V out from one Li-ion or two Ni-MH batteries.
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Reply to
Hils
Its possible with some of the more elaborate batteries, e.g. the ones that look like 12v SLAs and contain both a collection of cylindrical SAFT cells and the electronics needed to manage balanced charging and to protect against over-discharging. Some removable phone batteries may alao be like this too. However, the ones usually used to power models tend to be simply a collection of serially connected cells in a shrink-wrap package. There's no electronics in these batteries, just the main pair of leads sticking out along with a collection of much thinner wires terminating in a polarised multi-pin plug for connecting an external balancer during charging.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
Its interesting to find the NTSB report, which has photos of the damaged pack. There are almost no ventilation holes to tape over: the packs were simply a steel case containing six rectangular cells and some management circuit that was primarily concerned with current limiting during both charge and discharge, together with a balancer, though with a abbreviated cycles there batteries are expected to deal with you do wonder how much good the balancer would do unless it somehow splits the pack into separate cells during charging. The main problem looked to be that the batteries were packed pretty tightly, with no obvious space between the cells to allow cooling air to circulate or to provide thermal isolation between the cells.
Here's a link:
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The full "Interim Factual Report" is linked from that page just below the pictures.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie

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