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:
http://www.sparkfun.com/commerce/product_info.php?products_id=8293
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:
http://www.sparkfun.com/commerce/product_info.php?products_id=726
A complete description and documentation of the MintyBoost circuit can be found here:
http://www.ladyada.net/make/mintyboost/
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:
http://www.sparkfun.com/commerce/product_info.php?products_id=8293
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:
http://www.sparkfun.com/commerce/product_info.php?products_id=726
A complete description and documentation of the MintyBoost circuit can be found here:
http://www.ladyada.net/make/mintyboost/
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I just bought the v3.0 kit and I bought the new USB LiPoly Charger-single cell at sparkfun electronics as suggested by the Instructable website. The older charger circuit board seem to have connections for the battery, the mintyboost PCB and for the solar panel. I'd like to connect the solar panel to circuit board without the barrel plug ( or is the barrel plug more efficient? ) but don't know where to connect the solar panel wire to...And lastly I'd like to know if the LED for the charger turns off when the battery is fully charged.
Thanks again Honus!
http://ladyada.net/make/solarlipo/
It really doesn't make any difference what type of connector is used as far as efficiency is concerned. Since the charger has a mini USB port that's the type of connector you want to use.
I believe the LED should turn off when the battery is fully charged but I'd have to do some more research to make sure that is the case.
I was able to assemble everything and seemed to be working fine. The other day I wanted to see how much it would charge in 1 hr so I firsts got the new battery and used up all the charge on my iphone4, which charged my phone 68%. Once I checked that it no longer was charging my iphone battery I unplugged the iphone and left the solar charger out in the sun for an hour. Then I brought it in to charge my phone but it only charged 2% of my iphone4 battery....Is this about right? Because based on what I have been reading, it takes 20hrs to fully charge the Lipo battery which means the fully charged Lipo battery will only charge 20% of my iphone battery?
Just a side note. I measured the voltage of the Lipo battery after the 1hr charge and it read 3.4V. The capacity of the battery is 3.7 which is the same capacity for the iphone4 lithium ion polymer battery, so shouldn't it charge the battery up to 100% theoretically? Please correct me if I'm wrong.
Thanks again.
Also I left the charger outside without the case when I was charging since the case was not ready at that point ( just the naked LiPo battery, PCB, charger and solar panel all connected). Could this have been the problem?
I really want this to work :(
To a certain degree the time it is left out in direct sunlight is irrelevant as that isn't a good indicator of the charge the LiPo is getting- there are simply too many variables regarding quality of sunlight. The best way to check your solar cell is to use a multimeter to check both its current and voltage output while it's connected to the charging circuit in direct sunlight. I had to move mine to several locations during the course of a day to get the best sunlight.
I'm a little worry about the current limit of the Minty boost (400ma?). I'm a newbie at this; any thought or advices would be much appreciated.
Thank you!
I know a big question regards charging apple products. I looked at some of the sites regarding soldering together the middle two prongsof the USB adaptor on the MintyBoost board, or some sort of voltage divider. But I tried charging my 64 Gb Itouch with and without the center prongs being soldered, and the Itouch still said it didn't recognize it as a charger. I did have it charging my Samsung Vibrant Droid though, so I know it works. Any thoughts on getting through to the Itouch?
Thank you
This is why iPods take 4 hours to completely charge. This will also be the case through the MintyBoost circuit. I hope someone can provide some insight into this issue.
The standard rate for charging a LiPo is 1C (2000mAh cell @2A, 1800mAh cell @ 1.8A, etc. but some newer fast chargers and LiPo cells can easily exceed this) and the charger will charge at that rate (constant current) until the cell reaches 4.2V and then it switches to constant voltage charging. This charges the battery at a gradually decreasing amperage holding the battery at its maximum rated voltage (4.2 for a single cell) usually until the amperage drops to 10% of the initial charge rate. The LiPo will usually reach 4.2V before it switches to constant voltage charging so you are probably adding only around 5% capacity by waiting for the full constant voltage charge cycle.
Charging a fully discharged LiPo at 1C rate should take about an hour (actually about 1.4 hours to reach 100% capacity if it's fully drained), no matter what capacity the battery is. I don't see how it can take 3 hours to charge a 2000mAh cell @1C rate and I don't personally know anyone that has had that experience. It's also not a good idea to completely discharge a LiPo cell anyway- most everything I've read says to charge cells when they reach 80% discharge. My iPod Touch has never taken 4 hours to fully charge, but I never run it until it is completely dead.
I calculate that with 1200mAh @ 350mA rate it should take you about 4.8 hours to charge it 100% but I'll bet you reach 95% charge @4.2 V in about 3.5 hours. That CV cycle adds a lot of time. It'll be interesting to see what you come up with!
The tools and materials page says the barrel plug connection can only handle 280mA max - but the LiPoly Charger's MAX1555 "internally limits this to 300mA" on the barrel plug according to the Sparkfun product page.
If THREE 5v 100ma panels is too much for the circuit, what modifications would need to be made/added to make it work?
I'm a noob, but just assembled the kit (w/ 1 5v 100mA panel) and it seems to be working great!
I guess I made the mega mighty minty boost? I used your instructions and the FAQ here to charge the 6ah LiPo battery (http://www.sparkfun.com/commerce/product_info.php?products_id=8484) with the same charging circuit, and hooked it up to the 2.5 W large solar panel (http://www.sparkfun.com/commerce/product_info.php?products_id=7840).
I took your advice and used a 7805 voltage regulator, and hard spliced it in to the same input that you used on the charging board. Worked like a champ on the first go-around! For those that are interested, pin 1 on the 7805 is the input (solder to red wire from solar panel), pin 2 is ground (solder black wire from solar panel and solder into GND port that Honus used on the charging circuit for his panel), and pin 3 is the +5V out (solder to the 5V port Honus used)
I am mounting it inside a pelican case (waterproof) with a clear lid, so it can be left outdoors at camp all day long without fear of rain ruining it. There is room for a couple of phones and a camera in the case, so you can store most of your gadgets in it for safe, waterproof storage while in the outdoors.
I still figure about 20 hrs to fully charge the battery, but I think we should get 4 to 5 charges from it easy once its charged.
Thanks again for the great instructions!
Thank you so much for the great project. I am trying to get my working solar charger to charge my HTC google phone. The wall charger outputs 5 V at 1A. I know that the Solar Charger does a little less than this.
So far, I have charged the LI battery to full (the light goes off) and then plugged the phone in at the USB jack. The charge light on my Google phone lights for about 15 minutes (have tried it twice) then shuts off. Then I can't turn on my phone. After plugging it into the wall, it still charges and turns on. It starts at zero power.
I'm thinking there's some kind of short. Is it possible that it is short circuiting with the Altoids tin? I'm trying it tonight with new electrical tape lining the tin.
Thanks again,
On a Journey to Solar power,
Nate
It doesn't really sound like a short to me. If that was the case I don't believe you would be able to charge the LiPo or get your phone to light up at all. I don't know anything about the HTC Google phone, but there could be an incompatibility issue with the MintyBoost circuit. Have you tried different resistor values or checked the Adafruit forums?
forums.adafruit.com/viewtopic.php
http://forums.adafruit.com/viewtopic.php?f=15&t=13206&start=15#p73057