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Project: 4oz 1A USB Charger
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Wizard of Oz

Locale: New England
Project: 4oz 1A USB Charger on 09/18/2012 13:11:20 MDT Print View

So I'm planning a Grand Canyon Corridor R2R2R for early November, and in an effort to save weight, my Iphone 4S is my GPS, music player, camera, camcorder, etc. It's a 6 day trip, so even in airplane mode the whole time, I'm pretty sure it won't make it all the way through. I plan on enjoying music in the evenings and morning, and doing lots of videos and photos. A few years ago I made a 3.2oz USB charger that worked with my old HTC droid and iPod, but it doesn't generate enough juice for my iPhone.

My new design will use a waterproof flexible panel by Powerfilm. Power Film 12V 5W Solar Panel

I'm modify the F15-300($60)to eliminate the heaviest parts which is the connector that is hanging on it and the velcro closure. I believe that the panels themselves on the nylon fold-up backing will be 3 oz. and that gives me 1 oz to work with to interface to my USB.

Since I used 6V panels before, I used a linear regulator design on my previous solar panel. But this one will be a 12V panel design, a linear regulator would be very inefficient and I want to harness as much of the 5W power generator as possible. I'm going to use a buck regulator switching design based around a National LM2675-5.0 Eval Board to the heavy lifting.LM2675-5.0EVAL

This should be about 90% efficient which is about as good as I can get and it has great regulation so I don't hurt my iPhone. There's an updated design called the LM22675 with wider input specs, but I couldn't get an eval design and I'm short on time. So I'll be adding the circuitry required to charge the iPhone in both the 500mA (car charger mode) and the 1A (wall charger mode) to hopefully be able to adapt to overcast sun conditions. It should charge it from dead to 90% in 60-120 minutes. I'll also design in an auto shutoff if the sun goes behind a cloud of I leave it out and LED that indicates whether it's outputing the 5V. I found on my old design that if I left a device plugged in when the sun wasn't strong enough, the panel would actually discharge my phone/iPod.

IPhone USB Connections

So I know there are other options such as a spare battery or emergency power plug in, but I thought this would be fun and useful. And I'm a geek so I enjoy this stuff. Plus it's fun to try to make the 4oz goal!

I've got alot out of this site, so I thought it would be fun to post progress here, and get input along the way. Your thoughts and ideas would be much appreciated! I'll keep you posted...literally.

Eric Lundquist
(cobberman) - F - M

Locale: Northern Colorado
Re: Project: 4oz 1A USB Charger on 09/18/2012 13:19:13 MDT Print View

Is this a Rim to Rim to Rim or Rim to River to Rim trip?

If you're staying at Phantom Ranch you could buy batteries there and use them in a AA iPhone charger.

GPS is unlikely to be needed as the corridor trails are very well marked.

Wizard of Oz

Locale: New England
Re: Re: Project: 4oz 1A USB Charger on 09/18/2012 13:33:47 MDT Print View

It's a Rim to Rim to Rim in November...BRRRR....

GC Snow

We'll be eating at Phantom Ranch on both ways through but alas I couldn't get a night in the dorms there. Plus I'm planning on spending my money on beer and snickers instead of batteries there :)

LOL, GPS isn't for finding my way on the corridor. I like to mark my picture spots with GPS sometimes, so I know exactly where they were taken.

I looked at some AA Iphone charger, and that's def a great option. I love the flexibility of using this for 12V devices as well though. Do you know of a particular good brand/model of AA Phone Charger? Thanks!

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
Do Keep Me Posted on 09/18/2012 13:34:25 MDT Print View

Dear Wiz,

Keep the technical details coming, and I'm waiting to see how the final design works out.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Project: 4oz 1A USB Charger on 09/18/2012 13:46:03 MDT Print View

It might be helpful to you to get a schematic on a full blown solar charge controller. That is what is used on a big solar panel, and it takes care of all sorts of things like blocking the reverse current during a cloud. If you could scale that down to small charging like you need, it might be helpful.

All I have are the big solar charge controllers, so I can't help much. They really make life easier in a big rig.

In a lot of rigs, there is a rechargeable battery between the solar panel and the load. That adds weight, but it also regulates the charge properties. It might be worth looking into.


jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Project: 4oz 1A USB Charger on 09/18/2012 13:56:13 MDT Print View

What if you connected panel directly to iphone? Would it blow it up?

If you did linear regulator you'de be 83% efficient, which is pretty close to your 90%. Maybe a 1 ohm resistor would be good enough. What if you put in less than 5 volts?

Spare batteries would probably weigh less, but less fun : )

Franco Darioli
(Franco) - M

Locale: @Tarptent
Project: 4oz 1A USB Charger on 09/18/2012 16:52:51 MDT Print View

When I was fiddling with the power Pot and the Bio Lite stove I came across this battery :
12000mAh batt
2000mAh , output 1000mA/2100mA for $26 .
Oddly the manufacturer of that battery ,totally unrelated to my search, sent me a price list of that and several others.
I can tell you that the 1000 price is not all that much better than the one from this eBay seller
No experience with the seller nor the battery or the manufacturer but it may be worth having a look.
I think that it is about 350g, 12oz.
If the link does not work is listed under
12000mAh Dual USB output charger external battery power bank pack
To add.
I did order that.
I have only tested that by charging my AA and running LED lights, it works for that.
225g for the battery , about 150g with USB cable and adaptors.

Edited by Franco on 11/05/2012 22:08:11 MST.

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
Beer and Snickers on 09/18/2012 17:29:18 MDT Print View

Wizard writes, "Plus I'm planning on spending my money on beer and snickers instead of batteries there."

I see you think like me. Very good!

Franco -- that 12 A/h 12 oz battery pack looks like a beast, and at a very reasonable price. Someone, other than me, will need to try it to make sure it's properly-regulated and won't $moke an iPhone.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: Project: 4oz 1A USB Charger on 09/18/2012 18:00:29 MDT Print View

WOZ*: I've long wondered about the approach Jerry mentioned: Directly connect the solar cells to the iPhone. If they max below one amp, won't they be fine (until the iPhone battery is full)? If so, then you just need to disconnect them before the iPhone is fully recharged. Since the iPhone pretty accurately reports its state of charge, you can disconnect at 85-90% and skip all the weight and complications of the circuitry.

An early generation iPhone could serve as a test bed for anything you cobble together.

If you want music, bring a Nano. An iPhone is going to use a lot more power to play music than a Nano (that does nothing but music). Yes, base weight is up, slightly, but there's much less time spent babysitting the batteries in the iPhone.

*I once sold him an Apple II, of all things.

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
12+ volts on an iPhone on 09/18/2012 19:22:19 MDT Print View

David, can the iPhone survive 12 or more volts -- which is what a solar panel can put out -- on its 5V input line?

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: 12+ volts on an iPhone on 09/18/2012 19:55:44 MDT Print View

Most small 12 volt solar panels actually put out 13v-15v. They have to to overcome the resistance of battery being charged. A regulated 5v charger is probably able to put out close to 7v. Too many volts (and amps) will cook a battery. I have a 250w 12 volt system on my tent trailer and open circuit voltage is over 17 volts.

I played around with a Goal Zero Nomad 7 this summer while camping in our trailer. In perfect sun during optimum sunlight and orientation it took 2.5 hours to bring an iPhone 4 from 0% to 100% at 6,000 feet in the Southern Sirras. If I were inclined to bring electronics backpacking I would opt for spare batteries, which doesn't work for an iPhone and the batterie packs to recharge the phone are too heavy for what they do.

We camp for weeks on end self contained in our trailer without any energy conservation tactics. I am a solar fan. But for backpacking I wouldn't consider it. Of course I never really have a need for battery operated devices, except for an occasional trip where I carry a camera.

Wizard of Oz

Locale: New England
Re: 12+ volts on an iPhone on 09/18/2012 20:14:53 MDT Print View

Franco, That looks really awesome! I'll look into that for sure. Thanks! But definitely not as much fun.

David, no you can't connect a solar panel or 12V directly to the iphone. It will not charge it and will likely ruin it.

So I wanted to try to test my weight goal tonight, so here's what happened...

First I tested to make sure each panel to makes sure they worked, because I'm PRETTY SURE what I did later voids the warranty...

I weighed the 'manufacturers suggested setup' using a mini Cigarette to USB converter which has a 500mA output. (The final version will be a 1A output)
original setuporiginal setup weightoriginal panel weight

I took the plug apart and found a circuit board inside. The small board included a diode on the +V line to eliminate discharge of the device when there's not enough sun and a automatically resetting fuse rated at about 1.33A at room temperature (no clue what the is actually for).
plug disassembled

After I removed the heavy plug, , circuit board, excess fabric, metal eyes, and velcro, I reweighed the panel.
panel modded
modded weight

So with a modded panel, stripped down voltage regulator, and mini iPhone cord, I'm at 3.8oz. So it'll take me a while to get the parts and make the final circuit board and waterproof everything, but it seems possible!!! And it's a serious upgrade from my previous .6W version! Over 8 times the power and only .6 oz heavier, that's a good day in the sun! If it works :)
theoretical weightold vs new

Wizard of Oz

Locale: New England
Re: Re: 12+ volts on an iPhone on 09/18/2012 20:30:29 MDT Print View

I'll look into more commercial solar charger circuitry designs to see if I can glean any more ideas, that a great thought!

Yea, this panel will also output about 17V when unloaded, which is very common for 12V solar panels. Solar Panels need regulation to do just about anything.

A linear regulator basically dissipates the 'excess' voltage into heat, which is why you usually see those little three prong black ICs with metal tabs on the back.linear regulator That is what I used for my old panel with 6V panels. It's basically a Zener Diode. So the 1V overage at 100MA was dissipating 100mW into heat. I could deal with that. Although that means that it was only .5/.6 efficient or 83%. However using an appropriate linear regulator on a 12V 5W system would dissipate the 7 V overage or 2.9W, which gives me a 2.1/5 efficiency or 42%. pretty crappy, plus Linear regulators don't up the current on the lower voltage, so I'd only get the 400mA to my 5V device, or 2.1W. Using a Boost Regulator is MUCH more efficient, and hopefully will give me 4.5W to my USB port,or .9A. The Boost Regulator basically stores the charge in an inductor and is able to send it back out in little packets as it switches, so there's much less loss and less heat buildup.

Please keep the ideas and thoughts coming! I'm hoping to get the parts in this weekend and be able to do some tests and weights!

Wizard of Oz

Locale: New England
Solar Panel Theory on 09/18/2012 20:51:00 MDT Print View

One more note while I'm thinking of it. The voltage out of a solar panel (before the regulator) will decrease as more current is pulled (lower resistance load).Solar Panel IV Plot
So this example is a 7.2V 100mA spec'd panel. So as you over draw current (i.e. larger load or lower resistance), the voltage will go down a bit.

So there are two nice thing about the design I'm hoping to use and the iPhone charging feature. First, the Switching (Boost) Regulator only needs 8V to run, so I might be able to squeak a bit more current out of the Solar Panels than they are spec'd to since I can pull them right down to 8V and still have a solid output for the USB port. BUT that assumes solid full sunlight! That's why I'm going to try to include a switch so I can change the iPhone charging mode from 'wall' to 'car'. Basically, if I don't have enough sun to keep the 5V going in 'wall' mode (the phone pulls 1A or has a 5ohm charging resistance) which may cause too far of a drop of the panel output voltage in lower light conditions, I'll disconnect it, switch my solar charger to 'car' mode, and reconnect it which will change the PHONE to 10ohm charge resistance or .5A draw allowing my solar panel voltage output to rise hopefully high enough to continue to charge even in poor conditions.

As I mentioned before, I also plan to include a small 3mA LED to let me know when the 5V is being output properly (iPhone is charging), and I will include a circuit that will turn off the regulator output if the panel voltage drops below 8V. I think this combination of features will make it really usable in the field and allay some of the normal concerns and hassles with solar chargers. But, as has been mentioned, I will still have to babysit a bit,hopefully for only an hour or so a day if I'm blessed with clear skies, and hopefully while taking in SPECTACULAR inner canyon views, and a crazy expensive Phantom Ranch Beer! So I won't complain too much for the privilege of tunes, pics and videos to my hearts content! If it works...

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Solar Panel Theory on 09/18/2012 21:06:43 MDT Print View

A couple of comments. One is the 3mA LED. That is small, but it will be burning all of the time even when you know that charging is happening. Instead, drop some teeny tiny switch in series with it. That way, you can push the switch button and see what you have, but then you release it and there is no 3mA drain.

If you are getting about 17V open circuit in a big solar panel, that is pretty good. As a general rule, only the fairly good solar panels will get you 17V, and many of the cheaper and lighter panels get you only 15 or 16V open circuit. I guess this thing you are doing now is aimed more for 7.2V.

Everything that I have done is with a big panel, so I think only in terms of nominal 12V, so I don't want to steer you wrong about this smaller scale rig.

I was trekking in Nepal, and I was eating dinner in a Sherpa lodge that was candlelit. The proprietor went into the back room and then carried out a 12V car battery. He sat it down on the table and set up a battery operated slide projector. After showing slides of himself on Mount Everest in 1972, he explained the problem to me. He had a good solar panel on the roof, but his charge controller had failed, so he was trying to do things the hard way. I studied it and agreed that it was a charge controller problem. So, when I got home, I ordered up a perfect-size charge controller, received that, and then sent it to San Francisco to his employer. They sent it over to Nepal in a satchel, he hooked it up by my diagram, and it worked. So, now they show more slide shows, solar powered.


Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
Thanks for update on 09/18/2012 21:09:26 MDT Print View

Thanks for the update, Wizard. Sounds like you're on the right path here.

Next step: make a version to sell.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Solar Panel Theory on 09/18/2012 21:13:57 MDT Print View

I just connect 12 V solar panel directly to car battery - a controller just adds inefficiency.

Like in Wizard's chart, the voltage drops by itself to reasonable voltage for battery.

You have to disconnect it at night.

This may or may not be applicable to Wizard's problem - but I wouldn't try it on my ipod - if I had one

It would be better if it was a 6 Volt panel

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
3mA is Tinkertoys on 09/18/2012 21:14:53 MDT Print View

Bob, I think the added complexity and possible decreased reliability by adding a switch isn't worth it. 3mA compared even with "car" (0.5A) mode is only stealing, like, 0.6% of the regulator's output.

Jack Elliott
(JackElliott) - F

Locale: Bend, Oregon, USA
USB spec on 09/18/2012 21:32:31 MDT Print View

BTW, the iPhone is a USB-powered device, and the spec for USB power is 5.00 ±0.25 V

So it's likely not designed to be connected to a 6 or greater voltage source. Unlike a big ol' lead acid battery, which can soak up a lot of current, overvoltaging the iPhone's DC input circuitry is likely to end up badly.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: 3mA is Tinkertoys on 09/18/2012 21:32:35 MDT Print View

"Every little bit helps" said the woman who p!ssed into the sea.