Battery-powered Pi?

Over on http://www.raspberrymod.com/viewtopic.php?f=60&t=640&sid=b006909c691d78e07788ff03dbf8526c I wrote a little piece about Lithium-Polymer batteries and the rising trend to integrate Li-Po chargers on microcontroller boards.

This doesn't help at all with Malcolm's question of course, but I'd like to ask a supplementary question in case someone here knows the answer.  Is there a 2-cell Li-Po charger module (2 x 3.7V = 7.4V) available from anywhere, suitable for integration into 5V-powered equipment?

Over on http://www.raspberrymod.com/viewtopic.php?f=60&t=640&sid=b006909c691d78e07788ff03dbf8526c I wrote a little piece about Lithium-Polymer batteries and the rising trend to integrate Li-Po chargers on microcontroller boards.

This doesn't help at all with Malcolm's question of course, but I'd like to ask a supplementary question in case someone here knows the answer.  Is there a 2-cell Li-Po charger module (2 x 3.7V = 7.4V) available from anywhere, suitable for integration into 5V-powered equipment?

Interesting idea of putting them in series.  I had been wondering how the Duracell Li-ion battery-powered USB chargers I have work.  I suppose it could either have cells in series and then regulate down to 5V or have a boost converter which brings a single cell up to 5V.  I wonder which method, in general, is more efficient.

Alternatively we could ply Pete with crates of beer until he submits and makes future Pi board operable standalone from 3.7V.

Sounds good   I can't remember exactly what post but I recall from RPi forum either Pete or Gert saying that the Pi not designed with battery operation in mind at all (understandably given their goal).  The impression I had is the way it handles power is not super efficient, but it doesn't matter as much when plugged into wall and not trying to squeeze out battery life.

But yeah, I just started using 3.3V 8MHz Arduino Pro from SparkFun and I'm digging it for LiPo operation.  The main embedded project I have in mind for the Pi would unfortunately be battery powered, so I'll be interested in figuring out an efficient solution once Pi's are available in quantities.

By the way there are significant differences between switching power supply modules, if you care about efficiency. I tested two small ones shown below (much smaller than what you need to power a R-Pi). They aren't directly comparable but I found the efficiency of the Pololu one to be higher at *every* output current than the Sparkfun design. And the output noise was also lower. (and the Pololu one was actually cheaper!)

https://picasaweb.google.com/lh/photo/PzArmv5OEmDtBuyC2cBFQ9MTjNZETYmyPJy0liipFm0?feat=directlink

@ Morgaine,

Li-Po batteries are fussy things and you might suffer from tolerance stack up or balance problems if you charge in series (although lot's of battery packs must do this).

Why not use a boost converter to generate the 5V you need from the battery's 4V or so?

Boost converters are simple, small, cheap and quite efficient.

If you can give me a  spec I'll suggest something specific.

Michael Kellett

Many thanks for the suggestions, I guess I'll start with an off-the-shelf charger, I may well get a longer run-time than with my 6V battery.

Now how to change the status here to answered ??

Malcolm,

   At the top of the original post, just under the title, there should be

a link you can click on that says "mark as assumed answered".

Also, at the bottom of each response, there are two boxes you can

click, one for "correct answer" and one for "helpful answer".

Any correct or helpful answer you click on will get automatically mentioned

in the original post.

I'm using this one with Raspberry Pi very successfully: http://www.amazon.co.uk/gp/product/B005JSG7GE/ref=oh_details_o03_s00_i01

Sadly out of stock at Amazon (and all the other suppliers I looked at seem to link back to Amazon!).

@Michael:  Indeed, Li-Po batteries are very fussy in their charging requirements, which is why I shied away from a simple series arrangement with two floating single-cell chargers.  I strongly suspect that there be dragons in that area.  That's why I asked whether anyone knew of a ready commercial module that is specifically designed to keep two Li-Po cells charged up as a unit

I've noticed in 10.8V Li-Ion LED torches (not quite the same as Li-Po, but share some features with them) that the built-in charger has connections to the two inner links between the 3 Li-Ion cells, so there must be something clever going on.

Your suggestion of using a boost converter from a single Li-Po cell up to 5V is an excellent one though.  If the conversion is efficient enough and the component cost less than that of a two-cell charger, it seems the more sensible way to go.

Morgaine.