Step 5: FAQ and additional info

Here's a list of frequently asked questions:

Q: Is it possible to overcharge the Lithium Polymer battery?
A: No- the charger will automatically switch to trickle charging and then shut off.

Q: Is it possible to drain the Lithium Polymer battery completely and damage it?
A: No- the battery has its own low voltage cut off circuitry that will prevent it from completely discharging- the low voltage cut off is around 2.8v

Q: Does the solar cell have a blocking diode to prevent it from draining the Lithium Polymer battery?
A: No blocking diode is necessary- the Lithium Polymer charger prevents the battery from leaking current.

Q: How long will it take to fully charge the Lithium Polymer battery and how long will it take to charge my iPod/iPhone?
A: How long it will take to fully charge depends on the amount of sunlight available but as a rough guesstimate it would take around 20hrs using the small solar cell in direct sunlight. Using a larger solar cell could easily take half if not one third the amount of time. Those same figures would apply if you were charging it over USB or using a wall wart power supply.

Charging your iPod is much faster. How fast it does it depends on your device's battery capacity. An iPod Touch has a 1000mAh battery so it should fully charge it in around 2hrs. A 3G iPhone has a 1150mAh battery so it will take slightly longer and a 2G iPhone has a 1400mAh battery, so it will take around 3 hrs.

Q: The Lithium Polymer charger has an input voltage range of 3.7v minimum to 7v maximum- what if I want to use a higher output solar cell for faster charging?
A: To use a solar cell with a voltage output greater than 7v, you need a voltage regulator to drop the voltage to a level that the charger can handle. You could use a 7805 voltage regulator to limit the output to +5v -they only cost about $1.50 and are very simple to wire up. The 7805 will give you as fixed +5v and is usually good up to 1A current. You could also use a LM317T which is an adjustable regulator, but it would involve a bit more circuitry to use. Some people also use diodes to drop voltage, since many diodes have a voltage drop of .7v

There's a lot more info here: http://en.wikipedia.org/wiki/Linear_regulator

The other option would be to use a 6v/250mA solar panel. This will stay within the current input range and voltage input range of the Lithium Polymer charger. Remember that you can also connect smaller solar cells in parallel to increase the available current- two 5v/100mA solar cells connected together in parallel will give an output of 5v @200mA

Q: What if I want to use a charger with a higher input current limit?
A: Sparkfun does have a Lithium Polymer charger that maxes out at 1A:

Q: How would I connect the more powerful charger- there doesn't appear to be a clear way to do this?
A: To use the more powerful 1A charger you would need to wire a two way switch to the battery so that in one position the battery would be connected to the charger and in the other position the battery would be connected to the MintyBoost circuit.

Q: Will this work with USB devices other than iPods and iPhones?
A: You bet! There's a list here: http://www.ladyada.net/make/mintyboost/

Q: Won't the inside of the Altoids tin short out the circuit?
A: No- using double sided foam tape to mount the circuit boards keeps the bottom of the board from coming into contact with the inside bottom of the tin. If you're really worried you can cover the inside bottom of the tin with clear packing tape.

Q: How much does this cost? Can I build it for less? Is it cost effective?
A: If you buy everything as listed it would cost $70.75 (not including the Altoids tin or shipping.) If you wanted to scratchbuild it using the MintyBoost PCB from Adafruit, building your own charging circuit and supplying your own parts from various sources you can save quite a bit. Both the charging circuit and the MintyBoost circuit are available online- just go to the web pages listed in the tools and materials section- they're also listed at the bottom of this page.

Both Maxim and Linear Technology supply free samples (according to their websites) of their ICs so you just need to provide all the other bits (available from places like Mouser and Digikey.) Using a slightly smaller solar cell and a 2200mAh battery it is possible to build it for a lot less:

2200mAh battery
solar cell
MintyBoost PCB

After adding up the small parts for the MintyBoost circuit, a small blank PCB for the charging circuit (you would have to etch the board yourself) and a mini USB connector, you could conceivably build this for around $21.00 (not including shipping or an Altoids tin.) It wouldn't be exactly the same of course, but it would be functionally the same. I don't know if the 2200mAh battery would fit into an Altoids tin either. It would be a LOT more work of course, and there could be a fair bit of troubleshooting if you're not experienced in building these types of circuits or soldering surface mount components.

So is it cost effective? Absolutely- it just depends on the amount of work you want to do. Either way, you get a very useful and versatile solar powered charger.

Q: How did you calculate the power usage and equivalent CO2 values?
A: Here's the math-
3.7v (LiPo rated voltage) x .1A (solar charge current)= .37W
.37W x 12.5hrs (charge time based on average battery capacity) = 4.625Wh
4.625Wh x 365 days = 1688.125Wh per year
1688.125Wh per year x 30,000,000 units sold = 50,643,750,000Wh total used per year (50.644gWh)
50.644gWh per year x 1.5 lbs CO2 produced per kWh used = 75,965,625 lbs. CO2 produced per year

Granted these are more or less maximum values but they clearly show some potential for some serious energy savings. A 12.5hr solar charge time per day isn't realistic for the majority of the planet but if you shorten the solar charge time to approximately 4.5hrs at a 280mA current the results still remain the same.

General information about the Lithium Polymer charging circuit as well as a circuit diagram and data sheet can be found here:

A complete description and documentation of the MintyBoost circuit can be found here:

Love this setup,<br><br>I plan on building a 12V system for other power hungry applications, but instead of a flimsy altoids can, i decided to beef it up a bit with a pelican project box. If anyone has any suggestions about how to cover ports a little better, that would be great. <br><br>Check it out!<br><br>Love the instructable! Great work.
<p>Love the case. I wonder if you could use sugru around the ports to make secure fittings. http://sugru.com</p>
How much did you pay for yours.
Looks awesome. Pelican cases are great- I have a large one that's over 15yrs old and it's still going strong. Maybe for port covers you could mold some silicone plugs. Try Sugru!
Thanks! They're possibly one of the best made containers of any sort. I've been using them for various things here and there over the past 7 or 8 years. I like the idea of using Sugru for port covers! I was having all sorts of failed trials with grommets, silicon and other failed devices, but sugru might just be the ticket. Thanks Honus! <br><br>
No problem- let me know how it works out!
<p>i love this</p>
<p>where did you get the iron</p>
<p>I purchased that soldering iron from here-</p><p>www.sra-solder.com</p>
<em><strong><a href="http://yoghfgh" rel="nofollow">yes</a></strong></em>
<p>Is this capable of handling an iPhone 6s? I would love to make this for my dad but I'm worried the iPhone 6s is is going to require more power than this would put out. Thanks in advance for the help!</p>
I don't know if it will work with a 6. It will work with all iPhone 5 versions so I'd be surprised if it didn't work with the 6 as I don't believe the charging requirements/protocol has changed. Both of the iPhone 6 versions have greater battery capacity than the 5 series so it just wouldn't charge it as much.
<p>Thanks for getting back to me. I'll give it a shot and see how it goes. Thanks very much!</p>
<p>Should the battery be the polymer version, or can it be a regular lithium-ion battery? I'm noticing a rather substantial price difference between the two.</p>
The charging circuit is suitable for either Lithium Polymer or Lithium Ion.
<p>No problem- let me know how it works out!</p>
<p>Its wonderful</p>
<p>Thats astounding<br></p>
<p>The other issue is that the iPhone and iPodTouch have large batteries in them and will deplete the two AA batteries in the MintyBoost rather quickly so I wanted to increase the battery power as well</p>
<p>Its superb</p>
<p>Its ideal</p>
<p>Hey! I built this for my science fair project and I have a problem with it. Whenever I charge up the battery through USB or solar power, a few minutes later, it doesn't charge at all. It's like the battery doesn't work or something. My setup looks exactly like the one in this picture https://learn.adafruit.com/assets/1482 . Also, I don't know if this matters but what does it mean when I charge this with solar power, the power LED light flickers over and over rapidly. While when I use a USB through a wall outlet, it doesn't flicker at all. This project is due in about a week or a week and a half. I'd appreciate any help if possible.</p>
<p>I'm no genius, but I think the reason for the LED light flickering means the phone is not getting enough power or the solar panel is not producing power fast enough.</p>
So it begins charging and then stops? It sounds like the flickering LED is showing that you're not getting a consistent output from your solar panel. When it does this is it in direct sunlight?
<p>Sorry, I was thinking of something else but what I typed isn't really my problem. What's happening is if I charge the battery with solar power from the sun, the battery only seems to hold onto that energy for a few hours and then it all just disappears . I don't use it while its charging nor after I charged it. Also, when the light flickers, I am using it under direct sunlight.</p>
<p>What solar panel are you using and have you checked its output? If <br>you're using the Adafruit solar charger circuit they recommend a solar <br>panel that puts out at least 6V. As far as the battery charge <br>dissipating that has me stumped- there has to be some load somewhere <br>that is draining the battery. Maybe there is a short somewhere? Check <br>the battery voltage before and after charging and let me know what it <br>is. The battery voltage shouldn't ever drop below 2.8V and at full <br>charge it should be around 4.2V.</p>
<p>Hmm, maybe the solar panel is the problem? I bought the same one put at the top of the website. It has 0.45W and it's rated for a 4.5 open voltage. Here is where I got mine from. <a href="https://www.sparkfun.com/products/7845" rel="nofollow">https://www.sparkfun.com/products/7845</a></p><p>As for the battery, I just tested what I had now since it is dark out, the multimeter showed me 4.17V in the battery. </p>
<p>That could definitely be part of the problem as that panel was what I used for the original charging circuit- Adafruit specifies a higher output panel for their charging circuit. </p><p>It appears that your battery has a full charge. I'd check the battery voltage again in a few hours to see if there is a drain on it.</p>
<p>Okay, so I'll try to buy a different panel. I plan on rechecking the battery voltage in the morning once I leave for school and tell you the results asap. Also, since i noticed that the battery has a charge, I went ahead and tried to charge my phone with it, but it didn't work. But for some odd reason when I plug in my USB power meter, ( I bought it from Amazon. Here's the link : <a href="http://www.amazon.com/DROK-Dual-USB-Voltmeter-Multimeter-Alignment/dp/B00J3JSEG6/ref=pd_cp_pc_1" rel="nofollow">http://www.amazon.com/DROK-Dual-USB-Voltmeter-Multimeter-Alignment/dp/B00J3JSEG6/ref=pd_cp_pc_1</a> ) it showed me 3.9V and 0 amps. Any idea's as to why I can't charge my phone but the USB power meter still shows that there's energy?</p>
<p>What kind of phone do you have?</p>
<p>I have an iPhone 5s that was bought about a year and a half ago.</p>
<p>OK so you have good battery voltage but the Mintyboost circuit output is at 3.9V and the 5s is a supported device according to the Mintyboost specs. I would double check all of your soldered joints on the Mintyboost circuit and make sure all of the parts are installed correctly. If your battery voltage is good you should be seeing a regulated 5V output out of the Mintyboost USB output- it won't charge your phone if the output is less than 5V. I think that's the problem and it would definitely explain why the phone isn't charging.</p>
<p>I plan on building a 12V system for other power hungry applications, but instead of a flimsy altoids can, i decided to beef it up a bit with a pelican project box. If anyone has any suggestions about how to cover ports a little better, that would be great.</p>
<p>Its brilliant</p>
<p>Wonderful project. Thanks for the clear instructable</p>
<p>what size battery and solar panel (and anything else) would I need to mount on the back of an 08 MacBook pro to charge it?</p>
I have no idea. You would have to look up the specs for the battery and figure it out from there.
<p>Wonderful project. Thanks for the clear instructable</p>
<p>Love this Intractable</p>
<p>Hi- love the idea. How would you modify it to make it into an ipad 4 charger?</p>
You would just need to figure the pinout for the thunderbolt connector. It would take it an awfully long time to charge an iPad though since the batteries in those are much larger.
Would I be able to add a higher wattage solar panel to get more energy quicker, and what would I have to do to do this? Also, would I need to add more batteries to the pack to increase capacity?
<p>You can certainly do that. Have a look at the FAQ section- there is a charger listed there than can handle up to 1 Amp. You absolutely can add a larger capacity battery and you don't need to change the circuit at all.</p>
<p>good project. well done!</p>
<p>interesting, and the solar parts looks small and nice.</p>
<p>i have a 7.2v Ni-Mh rechargable battery would this be effective with a 6v 1Watt solar cell?</p>
No it wouldn't work. The charging circuit is designed to work only with single cell LiPo batteries.
Hhmm...'ok thanks.<br>
<p>I made one out of an old Shrek DVD case because I have a bad sense of humor. I also made an adjustable stand with Velcro that allows me to adjust the angle of the solar panel. Works very well, but do be conscious of the casing you pick out. Because this case is black, it can heat up rather quickly, which reduces performance and risks damaging the circuitry and battery inside. I always make sure to hide the case from the sun, which can be a bit inconvenient since the panel is on a short leash.</p>

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Bio: I'm a former bicycle industry designer turned professional jeweler. I like working with my hands and am happiest when I'm in the shop ... More »
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