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Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
Different Li tech on 09/25/2012 11:57:51 MDT Print View

"Question: Do even AA lithium batteries have the internal circuits you describe? Disposables and/or rechargeables?"

Two different chemistries.

AA and similar disposable nonrechargable lithium batteries use lithium iron disulphide chemistry, and are not the same as the rechargeable lithium-ion technology used in cell phones.

There are no rechargeable AA Li-ion batteries on the market for a few reasons, one being that Li-ion tech gives 4.20V/cell which would kind of smoke your usual flashlight or digital camera, and because without careful charging, Li-ion batteries can overpressure and create messy and embarrassing explosions.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Solar Panel Theory on 09/25/2012 15:19:07 MDT Print View

Hi David

Ah, but which of us is the ' highly opinionated and blunt' person?
Probably me.
OK, definitely me :-) :-)

> if you wire individual solar cells in series [to get a 9-10 V array]
Oh, true. It would work well.
But my gut feel is that the result might be more rather expensive, since you would have to buy a number of them. The 12 V units are really mass-produced, packaged and distributed.

Would you get better results/performance? I am not sure about that. The limiting factor with solar cells is always the area of the cells (and the angle of incidence).OK, and the intrinsic efficiency of the cell. Hum ... interesting question. Dunno.
Would it make all that much difference? Doubtful imho, but I might be wrong.

> Do even AA lithium batteries have the internal circuits you describe? Disposables and/or rechargeables?
My understanding (I could be wrong) is that the 1.5 V AA primaries (Energiser brand) do have that internal circuit.
Don't think I have seen rechargable AA batteries yet. Not sure the chemistry which gives 1.5 V can be recharged.

Are there other brands offering rechargable 1.5 V yet? If I am missing something here I am sure someone will help out.

PS: rechargable 3 V and 3.6 V, yes, they are available. But we are talking about 1.5 V here.

Edited by rcaffin on 09/25/2012 15:21:13 MDT.

Wizard of Oz

Locale: New England
Breadboard and initial efficiency calculations! on 09/26/2012 13:09:46 MDT Print View

So the breadboard was a success in that it gladly accepted 12V and output 5V! I haven't hooked it up to my iPhone quite yet to do any time tests or mode tests. The LED circuit is a no brainer and really nice to see what's going on (no switch in the breadboard, it's just constantly connected and shows when the 5V is coming out). I changed the shutoff circuitry values slightly (I'll post an updated schematic later) to accommodate variation chip to chip better, so that circuit pulls .4mA so it's only a SLIGHT drain.

Solar Breadboard Detail

I also took apart a 30 dollar iPhone specific USB Car Charger from Griffin. I've had it for a while, and I thought it would be fun to do a comparison as it's pretty good quality. It's a 500mA unit so I did my measurements apples to apples with just the 10ohm load, although both circuits do function under the 5ohm load.

So here's how the fight went...
In the red corner, hailing from China, Griffin with an input of 11.93V pulled .287A to generate 5.1V out at .467A. That is a 3.424W use of power to generate 2.382W or a paltry 69.56% efficiency.

And in the blue corner representing the USA, the brainchild of National, Texas Instruments, and the Wiz, the FUCD (Four ounce Usb Charging Device, I crack myself up) at the same 11.93V pulling only .217A, put up 5V at .455A. USA is the clear winner with a 2.589W use of power for a 2.275W output, yielding 87.9% efficiency!!! Just shy of the hoped for 90%, but I'll take it. Technically the LED and shutoff circuit are taking 50mW of power (most of that is the LED), so with the switch that was so wisely suggested, I'd be at about 89.8%.

More to come. Next, the iPhone test, then I'll finally let the sun do the powering and see if it can push a full 1A!!! Let me know if you have any additional optimization ideas!

Edited by wizardofoz on 09/26/2012 13:28:34 MDT.

Wizard of Oz

Locale: New England
Some thoughts on 09/26/2012 13:45:44 MDT Print View

At a few points during this fun, I thought about limiting the system to just the 500mA setting for simplicity sake. But I found this graph, that basically says it really will charge almost twice as fast at 1A and if I can get that much juice from the panel, that's worth while.

Charging graph

And since I destroyed my Griffin Charger, well the case anyway. I might go ahead and pick up one of these as maybe even use it as a test subject!


Edited by wizardofoz on 09/26/2012 13:46:19 MDT.

David Lowry
(huskyrunnr) - F
Re: Some thoughts on 09/26/2012 22:30:09 MDT Print View

Oz, fantastic! I'll probably copy your work sometime, although I don't have the intestinal fortitude to surface mount the mods on the eval board. Two questions, the specs are a bit picky on coupling to the inductor, which should not be a problem if I take the mods off board. Do you not see that as a problem? That's probably much ado ... What is the 2V rail for? I know nothing about charging smart-phones.

Thanks for documenting your progress.

Wizard of Oz

Locale: New England
Re: Re: Some thoughts on 09/27/2012 07:14:57 MDT Print View

David, so the inductor pretty much takes up one end of the board, and the spec sheet details some of the proper component placement and routing on a PCB to help with noise. I'll put the mods on the other end of the board (or maybe on the backside beneath a ground plane) to reduce the probability of issues, but I really don't think it'll matter in full sun. My only real concern is the shutoff pin, and I may add a diode and capcitor to give just a bit of hysterisis to minimize (though it won't eliminate) oscillation in low light conditions.

I talked a bit about the 2V/2.5V rail on the USB Data lines in my original post, but basically they are an iPhone specific requirement to ensure that the charger is 'proper' and also it tells the iPhone which charging mode to use. The iPhone won't necessarily charge without it, you'll get a "not a compatible charging device" message if you don't add the Data Line voltages. In addition, the level of those voltages changes the internal charge controller in the phone and allows it to charge in 2 different modes depending on the capacity of your charger.

I still need to check if I need or want an additional diode if the phone discharges when the solar panel output too low of a voltage and shuts the IC off. So more to come!

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Cheaper sources of 5-volt sources on 09/27/2012 09:10:12 MDT Print View

Rather than a $15+shipping, one-port charger from Thinkgeek, how about a $1.50+free shipping, two-port car charger off ebay? Or a 1.0A + 2.1A dual-port charger for $3.60+free shipping:

They're all made in China, right? Might as cut out the middleman (middlemonkey?) and have it shipped direct. That's been my approach for years now on camera batteries, chargers, etc.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: Re: Re: Solar Panel Theory on 09/27/2012 09:26:13 MDT Print View

Roger: I was observing that neither of us holds back in technical realms.

Agreed on the mass-produced aspect of 12-volt PV panels. has this chart:PV volts versus amps

Here's a link to another chart:

with a less flat curve as you approach short-circuit current, but again, max power is at 18 volts and near-max power is in the 15-19 volt range. Instead of 36 cells in series, 12 cells in series would give max power at 5.5 volts and a max voltage of 7 volts. Such a panel producing 1 amp or less could be hooked directly to a phone for charging (give or take that 2-volt, iPhone-specific signal WofOZ speaks of).

Ideally one would rewire a 3-row, "12-volt" array of 0.3 amps into a 5-volt, 0.9 amp array by changing the rows of cells from being in series to being in parallel while utilizing as much of the mass-produced packaging as possible.

(jordo_99) - M

Locale: Midwest
...just awesome on 09/27/2012 10:09:55 MDT Print View

This just might be my favorite MYOG thread I've seen yet.

Some of this still goes over my head (realizing I remember less of my electronics course from years ago than I thought) but it's definitely encouraging me to give something like this a try. I don't think it would take long to refresh my memory of this stuff.

Edited by jordo_99 on 09/27/2012 10:47:25 MDT.

Wizard of Oz

Locale: New England
'Chinese' knockoffs on 09/27/2012 11:52:44 MDT Print View

Yea, not so much on the ebay one...I see your point, but if you take a few apart, the knockoffs (from china, or wherever) are generally assembled poorly with very bad quality control. If they don't have oversight of a good company, they buy the cheapest parts possible (which may be seconds or fakes), and monkey's often put them together. You can get great leftovers and surplus on ebay and for some electronics you can even do the knockoffs, but $15 bucks for a quality part designed by thinkgeek is well worth it to me.

An aptly timed comment though :) How un-american of you David.. :)

Wizard of Oz

Locale: New England
Sun Power!!! YEA! on 09/27/2012 13:27:17 MDT Print View

So I had intermittent clear skies here so I got outside with the actual solar panel to see how it all came together. I forgot to bring the iPhone cable that I could hack up so I didn't implement the .5A/1A mode switch yet, or test it out with a real phone but i used dummy loads purposefully made just under 5 and 10 ohms to make sure I reached full current draw.

So what do you want first, the good news or the bad news...

1A mode is not possible with this panel! At least least not with the sun this time of year. The sun was very string about 1:30PM today, but try as I might with angle and waiting patiently for zero cloud cover. I could not reach full 1A output! So I think that, as is way too common, the manufacturer is just a little optimistic. Looking closer at the powerfilmsolar website, it's supposed to output 15.4V at .3A, which is actually 4.62W and at a clean 90% efficiency of my converter in perfect sun, that's only 831mA. Now I didn't see just how much I could have pulled, but suffice to say, my circuit CAN handle 1 full Amp, the panel couldn't provide that much power in the sun today. (BTW, the open circuit voltage on these little panels is 19.4V!)

So I've decided to nix the 1A/.5A mode switch option. Oh well, there something to be said for simplicity

500mA output was fantastic. even with the sun behind a very descent cloud such that I could stare at it without getting fully blinded, it was still able to pump out the .5A! So yea, you need sun to charge, but I won't have to worry about perfect positioning and babysitting too much, which is good news for me, even if it's not quite as fast as a wall charger.

I also found a pretty cool little device to help with the low sunlight turn-off oscillation issue. I played with capacitors and such, but they didn't really fix the problem. So another Texas Instrument special (seriously, I'm not affiliated in any way, they just make great stuff), a TPS3808, come to the rescue. It's a supervisory circuit that draws VERY little power and can be set up to have a 10s delay on the Step-Down Converter On/Off pin. So I ordered that and I think it'll really help solve that issue! Basically if the sun goes behind a big enough cloud that I love panel power below some level that I can choose (8V), it'll shutdown the converter circuit for 10s, then try to power it back on again, and see if the sun is back. I'll keep you posted on that, but it looks very promising.

THE UGLY: well currently the state of the my breadboard...since it's all in test setup mode right now, but it's been a great tool in figuring out little details. I really want to have a custom PCB made for final version of this as a nice icing on the cake.

THE FUTURE: I'm running a 'drain' test right now to see if the circuit will kill my battery if accidentally let plugged into the solar panel over night or something. I really don't want to add diode to block back current and it looks like I won't have to. Preliminary measurements say that it is drawing no current backwards at all! but I'm going to leave it for a hour and half or so in airplane mode and see what happens.

So other than figuring out the detail on the low power shutdown circuit, all the testing that remains is to do a charge time test. I should be able to drain my phone enough by tomorrow to do a full charge through the circuit and I'll let you know.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Sun Power!!! YEA! on 09/27/2012 13:42:59 MDT Print View

You ever buy components from

I've bought stuff from them and they have more selection and cheaper than local "brick and mortar" places

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
The Bad, The Good, The Ugly, The Future on 09/27/2012 16:13:28 MDT Print View

Pity about the panels not being powerful enough for 1A operation. Are we married to 0.5 or 1A options? Could you try for .75A?

But anyway, nice job -- and good idea about using that supervisory IC.

Once you get the thing debugged, maybe you could post schematic and BOM?

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Re: Re: Solar Panel Theory on 09/28/2012 01:44:35 MDT Print View

Hi David

Ahhh, techie stuff :-)

> Ideally one would rewire a 3-row, "12-volt" array of 0.3 amps into a 5-volt, 0.9 amp array
> by changing the rows of cells from being in series to being in parallel
Um - that's not quite as easy as it sounds. One can have problems if the cells are significantly mismatched. However, putting a Schottky diode in series with each one can solve that problem. The voltage drop is small.
Yeah, that's a thought, but the 12 V panels I have seen here seem to be rather integrated, so that rejigging them might damage them. But I know I have not seen anywhere near the full range of what is commercially available.


Wizard of Oz

Locale: New England
Parts and determination on 09/28/2012 05:55:34 MDT Print View

Yea, I definitely love digikey! newark online is my other favorite if I actually have to break down and 'buy' parts. My favorite is the free sample places :) TI and other big names are great at sending samples of 1 or two chips out, then I just have to find or buy the small caps and such that go around them.

Jack, you've motivated me to try a bit more. Unfortunately there's no sun today...But I did hook up both the 1A and .5A modes on the bench with the actual iPhone 4S and they worked great. The current draw on each is right on spec by less that 10mA difference from expected. Of course this is using a lab power supply for my 12V rather than the panel.

I let my phone die this morning, so I'm running a full charge up time test in .5A mode right now. It's been 25 minutes and I'm already up to %21 percent. so I'm guessing it'll be an hour and a half.

When I get some more sunny days, I'm going to try the solar panel in 1A mode with the actual phone, just to see what happens, but my guess is that since my circuit is a voltage source and not a current source, it won't work. The StepDown regulator is trying to output 5V and when the phone tries to draw the 1A, it will shut off, not just fold back the voltage. Not knowing exactly what the internal circuitry is on the iPhone, you never know though.

It's a rainy weekend here in MA, so I probably won't get to test out the new shutoff circuit till next week. I'll definitely be posting a schematic and material list in the end with whatever I find works best. I'll likely have some left over ICs and maybe a few extra custom PCBs as a minimum buy if anyone wants to claim them for a few bucks.

Wizard of Oz

Locale: New England
Realworld Results! on 09/28/2012 08:03:11 MDT Print View

Two updates:

1. Started from a completely dead iPhone 4S with the charging circuit on .5A mode. 100% charge reached in 94 minutes!

2. I forgot to post this before, but this circuit does NOT drain the iphone when it's not powered (i.e. no sun), so no diode is needed!

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
Only two choices? on 10/01/2012 11:24:35 MDT Print View

So Oz, does the iPhone only give two options, 1A and 1/2A, and won't recognize or use 3/4A?

Great results so far.

Wizard of Oz

Locale: New England
And the winner is... on 10/08/2012 06:18:35 MDT Print View

Received that last IC I was waiting for to help with the low light issues. The TPS3808 works like a charm! It completely takes care of the oscillation and gives a variable 7-12 sec pause when the panel voltage drops below 7.6V before trying again, but ONLY once the panel voltage comes back over 8V! Really nice! So the circuit is highly efficient (90% measured!), has a very bright 'output check' LED and a 1A-.5A switch onboard. Even though my panel isn't powerful enough to actually power the 1A mode, I figured I could use this in the future with another panel or if someone develops a better lightweight, flexible, and weather resistant photo panel :)

I did go ahead and keep the USB output port, so I can charge other devices or a AA batter charger with that port. i was going to hard wire in an iPhone connector to save a few grams, but figured the versatility was worth it, plus I suppose this will now work with the iPhone 5's new connector since you can just plug a different cable into it. Or a Droid, Samsung, BB, etc.

Anyway, the final board size is 1.275" x1.725"!

Here's the parts I used:
USB A Female Connector
C1 6.8uF Sprague 594D685X9050D
C2 68uF Sprague 594D686X9010C
C3 10nF 50V Ceramic
C4 1.75uF 1.75uF ceramic
C5 1nF 1nF ceramic
D1 Diodes Inc B120B
L1 47uH Coilcraft D03316P-473
R1 58k 58.5kohm
R2 12.5k 12.5kohm
R3 49k 50kOhm
R4 98.1k 98.1kOhm
R5 47.9k 47.9kOhm
R6 8.1k 8.1kOhm
R7 1M 1MOhm
R8 330 340ohm
SW1 NC Momentary ON
U1 LM2675 National LM2675-5.0
U2 TPS3808 TI TPS3808G

And the Schematic:
Final Schematic

I have 6 board being made and have enough SMD parts for at least 2 of them. here's the board layout! Soldering will be TOUGH!
PCB layout

I should have everything by Thursday and I'll let you know my progress. I've got a 16 mile training hike this weekend, but I should be able to find time to get started. Let me know what you think. I'll throw some pics up of the work in progress. And if anyones wants to buy a board off me (bare or assembled), just let me know! Where else can you get a sub 4oz 5W Solar Charger :)

Edited by wizardofoz on 10/09/2012 07:22:38 MDT.

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
Of or or? on 10/09/2012 05:18:28 MDT Print View

Wiz, you wrote, "And if anyones wants to buy a board off me (bare of assembled), [...]

Is that "bare of assembled" or "bare or assembled"?

'Cause I'd buy an assembled board.

Wizard of Oz

Locale: New England
Re: Of or or? on 10/09/2012 07:28:30 MDT Print View

Good catch Jack! Fixed that typo...

What, you don't want to do all that miniscule soldering, haha! Yea, I had to buy the board in a batch...well it cost the same whether I got 1 or 6, so I got 6. I can definitely assemble an extra one for you. I'll just ask for the cost of PCB and parts, which is about $30. I hope to have mine done early next week if everying arrives as expected and I'll get it tested to make sure everything works. Then I'll get another one together for you. The only thing you'd have to do is to solder in your solar panel wires right to the board, or if you want I could put some small 6" wires on there hanging with bare ends so you can connect by whatever means to your panel if you don't solder.

Who else! 1 is spoken for, 4 more available :)