Solar gadgets + AA's

[andygates]

This is a muttering-and-sums-out-loud thread.  I really want to display my Rugged Individualist stripes by not begging a power supply from pubs and campsites, yet I am, alas, gadget boy.

Kit to charge: phone (1540 mAh, micro USB), camera and GPS (2x AA each, will run on mini USB but won't charge), head torch (3xAA).  I can't imagine my LED tail light running out, so let's ignore the awkward AAAs that it uses. 

The nice folks at Power Monkey do a Powerchimp AA charger/gadget-feeder, which one could stack with their solar panel (reasonably robust, folding) to do most of that job in one go.  £45 or thereabouts, piecemeal from their site.

Adafruit Industries do geek kits.  The MintyBoost is effectively a Powerchimp, and there's a nice how-to for hooking up a beefy 2W (!) robust panel to the lot.  You'd need to change the lipoly charger for a NIMH charger, and waterproof your unit yourself (I think a Mentos Gum tube will do nicely, to be explored).  HOW TO – Make a solar MintyBoost, a solar power charger for your gadgets! «  adafruit industries blog for the how-to; the MintyBoost pages start here http://www.adafruit.com/index.php?main_page=product_info&cPath=10&products_id=14 .  Super solder fun!

...and there's the slim but non-zero possibility that an Energizer Energi pack will take on charge if one reverses the polarity (of the neutron flow, Captain!).  Probably dioded out.  To test.

Does any other manufacturer do an AA-carrying unit?  Freeloader and Solio have integral lipoly cells; so do the new (and very well priced!) Maplin ones. 

Aha! A Freeloader add-on Freeloader AA/AAA Battery Charger ... but the Freeloader's construction shouts "break me! drop my bits in the road!" to me.

Looks like generic USB AA/AAA chargers work fine with the Solio et al USB AA/AAA battery charger by Targus model TG-CHUSB

...or go hardcore homebrew: Solar Battery Charger With LM317T - Solar

[andygates]

Discussion of exactly this View topic - Green or SpearmintyBoost? • adafruit industries • Customer Support Forums, DIY Electronics, Open Source Hardware, Arduino

[Kim]

As you probably know, I'm going down the hardcore homebrew route with a view to integrating everything into one box.  I've got a working prototype of the insanely efficient active rectifier - no voltage drop *squee* - (for extracting useful power from a hub dynamo at the sort of pace I could expect to manage fully loaded back when I spent more time breathing solder fumes than riding bikes) and USB charging sections.  I've used this successfully to keep my ageing smartphone in power on various trips this summer.

The next stage is to add some logic to deal with excess voltage from the dynamo at speed (it's currently dissipating excess power as heat, which is wasteful and tends to toast the zener diodes on fast descents) and a battery pack.  While my Nokia is happy with an intermittent charging source, other gadgets seem not to be, and it makes things more flexible to be able to store a couple of phones worth of charge.

Adding solar and mains/12V inputs should then be straightforward.  I think I do want a solar panel for days that involve more camping than cycling, but I've yet to work out what to use.  Depends on whether I'm aiming at small devices, or running a netbook (which I reckon is just about doable, assuming it's mostly going to be used for short GPS and photo wrangling sessions, rather than prolonged spodding).  There are some utterly droolworthy flexible 5W panels out there.

I was considering using AA NiMH cells as the battery pack, with a view to being able to charge the ones from my GPS/torch/etc.  But it seems that building the sort of multi-channel NiMH charger that entails is going to mean a lot of inductors and stuff that add weight and complexity.  It seems better to have a large lithium-ion/lithium-polymer battery pack with a single charging channel, and deal with AA/AAAs externally with an off-the-shelf charger.

I discovered the SCH600F charger, which meets the fairly restrictive requirements of running from a 5V supply at dynamo/solar-friendly currents while having independent charging channels for the cells - nearly all USB-powered chargers charge cells in pairs for simplicity, which is useless when you've got devices that run from 3 AAAs.  It's cheap and plastic, but is surprisingly lightweight and does what it says on the tin.  It needs minor fettling to make it touring-ready, in the form of disconnecting the 'refresh' button internally, as that's just going to get knocked and waste all your valuable charge, and the addition of a Mk 1 elastic band to hold the battery compartment flap shut.

[mattc]

This is a muttering-and-sums-out-loud thread.  I really want to display my Rugged Individualist stripes by not begging a power supply from pubs and campsites, yet I am, alas, gadget boy.

Can't you just use the lighter socket?

[andygates]

That's a dirty trick in that rectifier.  Did you invent that?

[rogerzilla]

What about a folding wind turbine as another option?  Wind often works on days when solar doesn't, although you get plenty of days when neither are any good.

[andygates]

I think Kim and I are thinking along the same lines, with a "universal battery and gubbins" that will take a variety of inputs and give a variety of outputs, all at the same time.

The main difference is that I'm thinking the gubbins should be AA batteries, and Kim's going for more storage with a mighty lipoly so as to run bigger kit.  Also, she's hardcore, I'm a shopper.

So, yeah, any old bit of chargey kit, so long as it was within spec, would do nicely.  Riding to camp and pitching a windmill might draw some eyebrows.  Hmm, folding fabric windmill?  Savonius or VAWT blades..? 

[Kim]

That's a dirty trick in that rectifier.  Did you invent that?

God no!  It's a fairly standard technique for avoiding prohibitively silly diode losses where Rich Chunky Amps are involved, and crops up occasionally when efficiency is more important than cost or complexity.  I saw a post on CandlePowerForums or somwhere in which someone dismissed the associated control electronics as being too involved to be practical on a bicycle.  Fair enough if you're building a light, but I reckoned it was worth a go for a gadget that's going to live in a pannier.

Combined with the frighteningly efficient Recom switching regulators (if you're homebrewing this sort of stuff, they beat the pants off linear regs), it'll run an eTrex at about 3mph.  What's not to like?

[Kim]

What about a folding wind turbine as another option?

I haven't tried it, but the mad science part of my brain likes the idea of clip-on vanes to go between the spokes of your dynamo wheel.  Just invert the bike and point it in roughly the right direction.   

(I'm also reasonably certain that you'd need a complete bastard of a wind to get any useful power out of such a contraption, and any cyclist can tell you that those only happen when you're trying to ride the bike.)

[andygates]

Y'know, I made a scrappy windmill exactly like that, using alu tape to make a lot of angled, slim blades, kinda like an American water-pump windmill.  It definitely turned -- but it was a junk wheel I was playing with, so no idea on genny potential; it turned lightly, not with mighty gusto.  Blew down a week later.    On-bike it won't be able to rotate to track the wind, and that's probably a showstopper.

The hardcore camper-van types will use a yacht turbine, which are routinely available (even in Maplin, though the Rutland ones are the de facto standard) and go up on a high pole for clean air.  They're usually rigged to charge a 12v deep-cycle lead-acid battery in the camper's leisure circuit.  Memo to self: next leisure circuit, don't forget the shunt!

I think for cycle-camping, a wind turbine is overkill: well before that comes "a good dynamo".  It comes into its own for base camp somewhere cloudy.  Still, there's no reason not to try one, or a micro hydro based on a prop in a drainpipe, or a campfire stirling engine, or anything else bonkers. 

[Kim]

or a campfire stirling engine, or anything else bonkers. 

Now that I like.

Paging Charlotte to the red courtesy phone...   

[andygates]

Thought you might.  I'll spin up the Mamod... 

A thought occurred to me about solar: to work best, it's got to be sun-tracking, and the control mechanism for that is quite fancy.  But there's flowers to copy: if the panels are arranged in a shallow bowl, then the voltage is higher in the sunward petal.  All I need is a memory-elastomer that varies stiffness across voltage, and I can plant fields of sunflowers!

/dried frog pill

[Kim]

Not really worth it for cycle camping, thobut.  You're either there to give the panel a tweak every couple of hours, or you're on the road, in which case it's either flat across the rear rack or tucked away in a pannier.

Or you're hiding in the pub, where there's mains.

[andygates]

I just love the idea as a bit of Make art.  One for the mothballs.  Now, if I've just got three items and I wire them in parallel with a Y-shaped cable, I think it should Just Work:


Circuit sketch by andygates, on Flickr

With sun and empty batteries and no gadget, the batteries would charge.  With the gadget, it would draw on both.  With the gadget and no sun, the diode will stop it peeing away power into the panel, while it can draw on the batteries.  (assume they're well-matched, as per MintyBoost kit)

It can't be that easy, surely? 

[Kim]

Sort of.  That's certainly how you'd do things with lead-acid batteries and appropriately matched panel and gadgets - usually 12V stuff, which for compatibility with vehicle electrical systems has a reasonably flexible definition of 12.

It's a bit trickier when you're talking USB (which has a fairly strict voltage tolerance) and NiMHs (which don't like being float charged).  There's going to be at least some electronics between the battery pack and the USB-powered gadget to give it the nice clean 5V supply it needs, and that's only going to let the current flow one way.  If the solar panel's voltage and current spec are appropriate it can probably be connected directly across the NiMH battery (ie, behind the regulator) without cooking anything, but if there's a charge controller involved (as you'd probably need for a decently big panel), it'll need to be feeding that.

...and of course there's a voltage drop across the diode.  At USB voltage that matters, even with a Schottky diode.

[andygates]

Sort of.  That's certainly how you'd do things with lead-acid batteries

Indeed it was.  Replace the panel with the alternator, add in a relay which closes when the engine is running, and I had just such a beast.  Lovely too, apart from the lack of a shunt which, at those power levels turns out to matter in a "boiling battery acid" kind of way.

So to do the all-three-connected trick, we're looking at going hardcore.

I can start to see the appeal of KISS - charge the storage battery, then charge the devices ad hoc.  If that's the case then there's a twenty-quid Maplin charger-n-battery in an iclone-sized box that becomes "slip me under the map trap" appealing.

[Kim]

So to do the all-three-connected trick, we're looking at going hardcore.

Or an integrated panel-and-battery thinger.  Not sure if they come in AAbatteries-and-USB-output flavours, though.

[andygates]

They all seem to be lipo. Mmm, soap.

Ooh! Look what I found! How likely is this to be any good at all? HY Mini Wind Turbine at Firebox.com it even comes with an ARMBAND! Welcome to HYmini Online
Store - Green power is in your hand

[Kim]

To give you an idea of its impressive capabilities, a 20 minute charge (at 19mph wind speed) should give 30 minutes playing time on an iPod, 4 minutes talk time on a mobile, or 20 snaps on a digital camera.

..yeah, impressive.   

[Cunobelin]

I know that the ideas here are well thought out, practical and effetive, but I have found the one big flaw in the whole solar process:

The lack of sun!

[plum]

I took a freeloader on a summer tour in France last year. Strapped it to my handlebars, was travelling north to south so it got full exposure most of the time. That was for about 5 or 6 hours riding each day then it was out on a table or wherever for the rest of the time. Provided plenty of power to keep either my mp3 player going or to charge the batteries for my HCx but not both. Was overcast most of the time, if there had been full sunshine it would have done both for sure. Not at all fragile, I was dropping it and bouncing it around non stop for four weeks, has a few scratches but nothing to impair its operation. I took a mini AA charger and often used the usb cable that came with the freeloader to charge batteries from the campsite booking computer. I'd definitely recommend the things for small devices, but not enough to guarantee power for a bunch of devices unless you can also guarantee full sun.

[Charlotte]

or a campfire stirling engine, or anything else bonkers. 

Now that I like.

Paging Charlotte to the red courtesy phone...   

*Arrives breathless in thread*

New Solar Dish Stirling Engine - From Gyroscope.com -

[andygates]

 

[Wombat]

Being a model engineering type, I've been aware of these things for some years, but the project has never got anywhere near the front of the build queue!  (Its behind several articulated railway engines and a fart powered gas engine).

I have seen a site with info on a massive one in the USA, it was humungous, and brought on a serious case of technofrenzy on my part, dribbling and drooling....

Here is a much smaller one... SES :: Technology

[mrcharly-YHT]

I know that the ideas here are well thought out, practical and effetive, but I have found the one big flaw in the whole solar process:

The lack of sun!

I lived on a boat for 18months with no source of power apart from a solar panel.

I can assure you that decent 3-junction panels generate power even on cloudy days. Just sod all power compared to sunny days (when the battery would be fully charged and the controller dumping spare power through the heatsink).