Solar powered Lipo (Li-ion) charger

[kje]

My plan is making a solar powered usb charger like this one: http://www.youtube.com/watch?v=rxQ6LZyOK1w I`m thinking of using a Lipo (Li-ion) battery connected to a 9v solar panel. I have ordered a LM7806 voltage regulator so the voltage will be 6v. What kind of battery would be suitable? Will a 3,7v Lipo battery do the work, or is 6v too much for a 3,7v battery?

I also wonder how I can make it automatically stop charging when the lipo battery reach full charge and protect from overcharge? For more power I could also use a 2 or 3 cells lipo battery. 2 cells has 7,4v and 3 cells has 11,1v. With several cells it`s important to balance the charging.

Any tips or ideas how to build this?

[kje]

In order to increase current to reduce charging time, I ordered two 9v, 220mA solar panels so I can put them in paralell connection. In paralell circuit total current is 2 * 220mA = 440mA

Maybe this is my solution: http://ladyada.net/products/usbdcsolarlipo/ but here they used 6v battery...
What do you think?

[MJLorton]

I think you are onto a great project here that will turn out far better then mine did. I like the idea of using lipo but a charger in this case is critical. I think you have stumbled onto quite a handy device in the link you posted.

I will take a closer look in the next day and feedback.

I also plan to post a video on building little solar projects like this and how to go about it.

Thanks for posting.

Martin.

[MJLorton]

In order to increase current to reduce charging time, I ordered two 9v, 220mA solar panels so I can put them in paralell connection. In paralell circuit total current is 2 * 220mA = 440mA

Maybe this is my solution: http://ladyada.net/products/usbdcsolarlipo/ but here they used 6v battery...
What do you think?

I think their solutions looks great...if you are using 9v panels have a look at their other option: http://www.adafruit.com/products/280

[kje]

I think you are onto a great project here that will turn out far better then mine did. I like the idea of using lipo but a charger in this case is critical. I think you have stumbled onto quite a handy device in the link you posted.

I will take a closer look in the next day and feedback.

I also plan to post a video on building little solar projects like this and how to go about it.

Thanks for posting.

Martin.

Thank you Martin. I`m excited about using lipo battery because of its strong power, low weight and almost no self-discharge.

The power from the solar panel is not steady enough to charge a 5v item (smartphone), but the battery in the circuit will give the charge. A step up converter is needed to get the battery voltage back up to the 5v expected by the item, so I ordered this: http://www.ebay.com/itm/220648409360?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649. But I don`t know how to make it automatically stop charging when the lipo battery reach full charge and protect it from overcharging.

[kibi]

You need to be very careful when charging LiPo batteries. If you overcharge them or charge them incorrectly, they can catch fire in a big way, very dangerous.
Charging LiPo's with just a 7806 is not good, especially with no charge cutoff.

Martin's video that you link to details the charging of NiMH a battery, this is a completely different animal to LiPo.

I would advise that you use a proper LiPo charger. Microchip make a versatile chip, easy to use and nice and cheap. Its their MCP73113 device.
It accepts a wide input voltage range, low external component count and has timers if you want to use them. More importantly, it includes Over Voltage Protection for the battery. You can choose from different versions depending upon the charge voltage of your particular battery.

Check it out. http://ww1.microchip.com/downloads/en/DeviceDoc/22183c.pdf

[kje]

You need to be very careful when charging LiPo batteries. If you overcharge them or charge them incorrectly, they can catch fire in a big way, very dangerous.
Charging LiPo's with just a 7806 is not good, especially with no charge cutoff.

Martin's video that you link to details the charging of NiMH a battery, this is a completely different animal to LiPo.

I would advise that you use a proper LiPo charger. Microchip make a versatile chip, easy to use and nice and cheap. Its their MCP73113 device.
It accepts a wide input voltage range, low external component count and has timers if you want to use them. More importantly, it includes Over Voltage Protection for the battery. You can choose from different versions depending upon the charge voltage of your particular battery.

Check it out. http://ww1.microchip.com/downloads/en/DeviceDoc/22183c.pdf

I`ll be ordering the USB/DC Lithium Polymer battery charger 5-12V http://www.adafruit.com/products/280 wich monitors the charge on the LiPo battery and regulates the output voltage accordingly. I also discovered that the charger stops automatically when the battery is fully charged. It uses the MCP73861. I don`t know so much about the difference of MCP73861 and MCP73113 (I think MCP73861 have temperature monitoring wich MCP73113 don`t have). Before I order, is this Lithium charger difficult to make myself?

Do you think this DC-DC converter http://www.ebay.com/itm/220648409360?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 will do the same job as the "mintyboost"? http://www.adafruit.com/products/14

[kibi]

OK cool, the Adafruit charger will be fine. The circuit is pretty simple, but it is surface mount, so if that puts you off, then you would be better off buying the assembled one from Adafruit.

As for the ebay DC-DC convertor, it looks like it is pretty much the same as the Minty Boost, just doesn't have the fancy case and battery holder etc.

[kje]

OK cool, the Adafruit charger will be fine. The circuit is pretty simple, but it is surface mount, so if that puts you off, then you would be better off buying the assembled one from Adafruit.

Thanks. I ordered the Adafruit charger and waiting with excitement. 

As for the ebay DC-DC convertor, it looks like it is pretty much the same as the Minty Boost, just doesn't have the fancy case and battery holder etc.

I also ordered the ebay DC-DC convertor, but I discovered a similar DC-DC convertor with 1A current output. Would the charging be faster, or is it a USB limit on 500mA?

[kibi]

I also ordered the ebay DC-DC convertor, but I discovered a similar DC-DC convertor with 1A current output. Would the charging be faster, or is it a USB limit on 500mA?

Some devices will charge faster with a 1A charger. A computer will usually limit it's output to 500mA even if the device is able to charge at higher currents. iPhone for instance will charge at 1A from it's wall charger. iPad will charge at 2A from it's wall charger but will barely charge at all via the computer.
Some devices, like the i devices, rely on resistor settings within the chargers to enable them to charge at full chat.
Limor (LadyAda) has a video covering the subject.

http://www.youtube.com/watch?v=FW72sDTYi1k

[MJLorton]

kibi...kje,

Thanks for sharing info and helping out.

I'm looking at the LadyAda video and the adafruit channel now....very interesting...I'll link to them from my channel.

Thanks again,
Martin.

[HappyMike]

Hi Mr Lorton,

I was looking at a forum about Tim Nolans MPPT charge controller. When I wanted to post, I had to sign up, and that was a very arduous and error laced process. Once I finally managed to walk that minefield and get registered, now I can't find the forum about the Tim Nolan MPPT project again. I searched for "Tim Nolan" and only found one post, that wasn't related to what I wanted How can I get back there.

Also, I see I have to jump through all the stupid hoops again just to post a message. That Pi question is the dumbest of them all, because there is a decimal point in there, and it is unclear as to whether that is part of the answer, as it's not strictly a digit, and then does that count towards the total number of digits. On top of that, at school I seem to remember that Pi = 22/7 or 3.142856.... but that didn't work, so then I had to research Pi. Surely you could simplify the process a little. I really felt as if I wasn't welcome on the forum, and you had done everything to make it hard to join. And now that I find I have to go through this huge verification process every time I want to post, it is doubtful I will return very often,

Cheers,

UN HappyMike

[tillt]

I also ordered the ebay DC-DC convertor, but I discovered a similar DC-DC convertor with 1A current output. Would the charging be faster, or is it a USB limit on 500mA?

Some devices will charge faster with a 1A charger. A computer will usually limit it's output to 500mA even if the device is able to charge at higher currents. iPhone for instance will charge at 1A from it's wall charger. iPad will charge at 2A from it's wall charger but will barely charge at all via the computer.
Some devices, like the i devices, rely on resistor settings within the chargers to enable them to charge at full chat.
Limor (LadyAda) has a video covering the subject.

http://www.youtube.com/watch?v=FW72sDTYi1k

You can actually modified system on computer to have more than 500mA for USB ports, and on USB 3.0 it's 900mA