Making my own USB solar charger..need help

[Armin_Balija]

I posted this in the beginner's forum but I think it'd be better suited here:

Hello EEVBLOG,

My name is Armin and I'm a first year engineering student at WSU and during the summer I wanted to do some electronics hobby work for fun. I was watching TV the other day and realized how annoying it is to have to buy batteries all the time, so I figured I could just put a USB jack in the bottom of my remote and charge it whenever I feel like it. So I bought a few parts and was hoping I could do it with the limited knowledge I have and some that I don't, (I haven't taken any classes on diodes and such and I've just been learning what I can from websites.) So I came here because I love Dave's videos and thought a great crowd like yourself could help me.

So here's what I've got so far:
3'' x 4'' 0V-6V solar panel
1N5226B 3.3V 500mW Zener Diode
5.1V 1W Zener Diode
Resistors of all values
1N4001 Diodes

The plan:
My plan is to use the 0V-6V Solar Panel to charge a 3.7 Li Ion rechargable battery to 3.3 V with a Zener diode through trickle charging and then whenever I need to charge my remote I can connect it to the hub and charge it from the battery instead of the solar panel.

Here comes my problem:

So I've read up on Zener diodes and I've got a fairly OK comprehension of how to use them to limit DC output, however I don't know if I'm going about this the right way or the wrong way. Everytime I think I have a good idea I realize that I'm missing something or that I'm not thinking about something that I should. So far I've put a 15 ohm resistor in series with a zener diode that is reverse biased with a 5V source (ambient light in my home during daytime produces 5V in my panel.)

My problem comes in that I'm going to be dropping to about 3.389 - 3.434V because of the Zener diode, so I'm assuming I'm only going to be able to charge up my battery up to 3.434 Volts..unless I need more than that just to create the difference in the battery..

So anyway, after the battery is charge to 3.389 - 3.434V I need to charge my remote's batteries...which are 2AAA batteries.. 3V flat. I need to use a diode (I assume) to stop current from flowing out of the batteries, so that'll drop me another .7V ; So I'll only have 2.689 - 2.734V going to my batteries.. is this ok or will my project fall on it's face?


Is there anything I'm doing wrong and is there a better way to go about this? I was thinking maybe I should be looking into using voltage dividers to set my voltages and using a diode to set current flow after I've selected the voltages I need. Problem is I don't know if they have any zener diodes that would be good for my application?

[sacherjj]

Modern Lithium batteries contain energy on the order of 1/6 of the same mass of TNT.

Do a search for LiPo Fires on YouTube and you will see how flammable to explosive these things are.

There is no way I would think about doing this without a Charge Controller IC.   (Search for "charge controller" on Digikey.)   Lithium batteries are tough to charge correctly.  Ask all the RC pilots that have charged their LiPos into a nice fire.  Some lost houses over it.  You don't screw around with these.

Read some data sheets for the MCP7384X series and see what it up.

[Armin_Balija]

Would it be better then to use some rechargeable NiMHd batteries? Thanks for the reply. What about the rest of the project? Any critiques you could make that would help me? Am I on the right track?

[johnboxall]

Here is a  good example of a LiPo charging circuit from adafruit:
http://www.adafruit.com/datasheets/mcp73861.png from
http://www.adafruit.com/products/280

[sacherjj]

NiMH would be much safer to work with.

[Mechatrommer]

i think you'll wait for a full shiny many days before your battery in solar panel fully charged. and i think you need to study dv/dt to properly charge a battery, esp lipo. but i'm not sure of the fire hazard with this very slow charging rate. and lastly, why usb? are you planning to charge it from pc?

[Armin_Balija]

i think you'll wait for a full shiny many days before your battery in solar panel fully charged. and i think you need to study dv/dt to properly charge a battery, esp lipo. but i'm not sure of the fire hazard with this very slow charging rate. and lastly, why usb? are you planning to charge it from pc?

Yeah, i figured since it's for a remote control it won't be discharging quickly so I figured this would be an ok application for the solar panel. What is dv/dt? USB just because I think it's a nice interface that's used by a lot of things. I figure if I used the main hub as USB, I could potentially upgrade/add to the circuit to make it work for a variety of voltage to charge different things. Plus, it's easy to install on a remote control so it's square and easy to cut

[Mechatrommer]

dv/dt is voltage change per unit time. in depleted battery, when charged it goes to +ve (batt voltage increase), but when the battery full, it will decline to -ve, its the indication the battery is full. but i'm not sure if you can detect this in this slow charging application, and probably it will require a mcu.

[Lawsen]

You will need a diagram of the USB port.  Chose a battery controller chip to prevent over recharging and over heating the batteries.  The Maxim 712 or 713 are good controller chips to based your design than just a basic zener diode design.  The zener diode is used on the output of the controller chip as a safety to prevent over recharging if the chip fails.  Chose the type of battery that your USB solar recharger will be charging.  Most lilkely the solar recharger will be 1.2 V DC NiMH or NiCd AA, D, C, and AAA types.  You will need to buy a battery holder for various sizes that the unit is intended for.  Chose the type of photovoltaic cell from printed thin film by Nanosolar in San Jose, California, USA to tradition silicon based types.  The photovoltaic cell selection will determine the size and weight of the unit.  There is the need to determine the minimum amount of light and time exposed to recharge a set of batteries. 

http://www.maxim-ic.com/datasheet/index.mvp/id/1666

http://www.usb.org/home

I hope this help gives you some ideas.

Lawsen

[Armin_Balija]

You will need a diagram of the USB port.  Chose a battery controller chip to prevent over recharging and over heating the batteries.  The Maxim 712 or 713 are good controller chips to based your design than just a basic zener diode design.  The zener diode is used on the output of the controller chip as a safety to prevent over recharging if the chip fails.  Chose the type of battery that your USB solar recharger will be charging.  Most lilkely the solar recharger will be 1.2 V DC NiMH or NiCd AA, D, C, and AAA types.  You will need to buy a battery holder for various sizes that the unit is intended for.  Chose the type of photovoltaic cell from printed thin film by Nanosolar in San Jose, California, USA to tradition silicon based types.  The photovoltaic cell selection will determine the size and weight of the unit.  There is the need to determine the minimum amount of light and time exposed to recharge a set of batteries. 

http://www.maxim-ic.com/datasheet/index.mvp/id/1666

http://www.usb.org/home

I hope this help gives you some ideas.

Lawsen

Lawsen thank you for the huge help. That was really in depth and beginner friendly.

I looked into the MAX712 kit and I want to order the IC from them but I can't seem to find the price. They want a target price range from me? I've never worked with companies that let me bargain with them like this so I don't know what price range to start at.

Currently I was looking to get an LDO and 1n4001 diode to regulate the voltage to 3.7 with resistors and use the diode to prevent current feedback. The thing about using a clip for the batteries is a really good idea. The idea behind my design was to solder the wires from the USB to the + and - of the remote's battery compartment and to feed the voltage directly into the batteries that way.

ANYWAY, I really want to use that IC for my project because it looks like it could add a lot of flexibility and depth to my project; I just don't know where to start with ordering it and such. In the overview of the IC do I just hook it up like it shows without any thinking on my own?

[Zero999]

NiMH would be much safer to work with.

Agreed but they're more complicated to charge, have a lower cell voltage, are heavier and more expensive for the same energy storage.

Lithium batteries should always contain a thermal fuse, just in case.

[Lawsen]

Recharging a Lithium ion battery is a mark of engineering and science.  We are not trying to discourage you, but I think the group is great in letting us know the risk.  What do I know so far from using lithium powered devices in my mother's house?  I have a Hitachi right angle cordless impact that is 10.8 V DC lithium ion electricity powered.  Lithium ion includes a broad range of ionic chemistries that are rarely explained to consumers.  During the charging cycle, there are three parameters that need to be taken into account.
1. voltage
2. current
3. temperature

Power is calculated as a product of current and voltage over time as Watt hour.  

I did not include time, because most powered tools left that out.  IBM Lenovo Think Pad computers have time included into the recharging software.  

LiPO4
LiMn2O4, lithium di manganese tetra oxide cathode and anode is a compound of germanium, silicon, or carbon.  IBM Lenovo computers have these.
LiCoO2, lithium cobalt dioxide are used in some Panasonic cordless tools.  It might be in the $100,000 USD Tesla Sporter two seat car.  
There are more Li ion compounds.  Li ion is just a carrier of electrons that migrates from the anode to cathode during discharging and cathode to anode during recharging.  This is getting complicated, correct or help me here.  

The Hitachi has a red LED to indicate when the battery is getting too hot during discharging and running the tool.  Lithium ion battery recharger will need to continuously measure voltage, current, and temperature to be safe and optimum recharging.  It is more complicated process than NiMH and NiCd.  NiCd is the heaviest battery, because of the Cadmium.  NiMH weighs less, because of the negative hydrogen ion, a hydride.  Temperature can be sensed by a thermistor circuit.  The voltage and current could be sensed by a comparator circuit?  Li ion batteries are available at all ionic chemistry and kinetics characteristics from on line stores, but you really need help from someone closer and with experience.  I never built a battery recharger myself, but I have repaired many battery powered appliances and things around the house from Sony Minidisc to a laptop tablet PC.  It helps to know a little about batteries and their risks and limitations.  

I have electronic technician experience and geology earth science four years type education at an U.  This is my background and I am an owner of my compound Zeiss and Nikon microscopes.  My bedroom work area has a Rigol oscilloscope, Philips PM2505 and PM2518 and Fluke digital multimeter.  I do not have a power supply.  The signal generator is a cheap $60.00 pocket sized one.  

The group has already written their cautions and I do not have to repeat that here.  I assume you know about this, even before posting.

Lawsen

[Armin_Balija]

Here's a really crappy schematic I drew up in paint. It's a quick project and was wondering if I'm doing anything wrong or need to make sure I do before I hook this up. I've used a Dremel to cut out the hole in my hobby box to house my panels, I just need to wire and solder up the project. It's simple but I don't want to do anything wrong and have someone fry :/.