The GV-5 is a superior board that is built to last.
Feel free to try all the different solutions, and compare them to each other.
You will not be able to charge the 12v battery with the 5v USB input.
If you want to charge the 12v battery you will need a 12v charger like these:
Could any wall charger be plugged into the GV-5 in place of the solar cell input? I think the GV-5 works fine even with solar cells below 12.8 V.
P.S. After reading the article about MPPT my class voted on who’s ideas they liked the best.
I got 3 votes 
@rwb RynaB got 24 Votes 
The GV-5 is a buck regulator, so the input needs to be 1v above battery voltage for charging to begin ideally.
So under normal conditions, the input voltage will need to be 15v - 27v DC to charge the battery. The MPPT will consistently pick the voltage that supplies the maximum current.
You can supply the GV-5's solar input with 15-27 volts from any source, but the solar charge controller will try to pull as much current as it can from that source which can push the supply over its max limit which will cause some power supplies to reset or shut down.
If you have a bench power supply then you can use that, they work fine for me. The bench supply is also a good way to see how the higher voltage it puts out get's converted down to the battery charging voltage with an increase in current compared to the incoming lower current at the higher voltage.
Sweet, glad I could help spread the knowledge! Renewable Energy is the future! 
So I guess I can just use your $28.95 smart charger with a quick disconnect at the battery. Switch from the GV-5 to the smart charger physically.
Yea put some sort of easy to use quick connector on the battery terminals and then a set on the battery terminals on the solar charge controller and a set on the AC charger.
I’ve always liked the Anderson Power Pole connectors personally.
While looking at professional systems, here is something that might be interesting.
@RWB any opinions about this system? Remember that I am trying to power small Wifi controlled Rovers with Solar Trailers. Looking to trickle charge the battery on cloudy days and to fully run the rover on cold sunny days. My single motor is 12V and about 1.4 Amp at stall.
Battery (Li-ion this time) has both 12V and USB Outputs
Solar Panels at 24 W
If you do not want to build a battery then this will provide all you need.
It’s Lithium-Ion batteries but that’s fine.
Another awesome webpage, slight correction the Voltaic System is Li-Polymer, adds a level of complexity to the use and maintenance of it.
In summary the Voltaic System with one solar panel holds more power 20000MAH but charges slower at 17W probably uses MPPT charging for $388 USD. The Talent Cell System might charge faster with 2 x 24W solar panels holds less power at 11000mAH no idea if it uses MPPT for $221 USD but neither are as safe as LiFePO4 batteries.
Like always everything is confusing when it comes to making stuff work.
Looks like there is room for someone to come up with a portable (for the average person) LiFePO4, 12V DC and 5V USB system with power cord for 120 volt charging (or USB charging if possible), as well as trickle (one solar panel) and fast (chain several solar panels) MPPT and balanced charging system using LiFePO4 batteries.
If I wait 6 months there will probably be several systems on the market. Hey Ryan possibly a niche for PortableSolarPower http://www.portablesolarpower.biz/ @RWB? Your company is so close it would fit right in!
A problem is the price of solar panels. Anyone got any opinions on solar panel prices and products for the near future?
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Not sure if any of these are for the near future or have any durability:
BioSolar check out BioSolars Si-Alloy Conductive Polymer battery http://www.biosolar.com/super_battery.php
Neither of these systems use MPPT on the solar input.
If you want MPPT + LIFePo4 in a smaller package your going to need to build it yourself.
I'm building a new line of systems now from pocket size to large enough to run your house.
The smallest system I have right now is a 10Ah system that uses LiFEPo4 batteries & MPPT solar charging.
If you look on ebay there are plenty of options. If you want to save tons of money just use smaller aluminum framed glass solar panels since they can be bought for 80 Cents to $1 per watt these days.
That is the most awesome thing I have ever seen. When you have a large but pocket sized version available, tweet me directly @rocksetta .
The cigarette lighter output is perfect, since so many products will work with it such as USB chargers. Until your pocket version is ready, I think my class will just play around with some simple low voltage solar charging systems more within my school budget. Not sure how I am going to afford yours but I will figure it out somehow.
I hope the general public understands why your system is safer and better than other systems. Good luck with it.
So while waiting for @RWB’s awesome pocket solar powered battery to be developed, I have turned back to my Rover.
A student brought in a 12V, 4W solar panel and it actually turned my rovers wheel slowly (no weight on it). So my next plan is to use solar panels and see how many watts I need to drive my one wheel powered (with one servo) really ugly wifi Rover (The uglier I make it the more the students want to make their own better designs).
12V solar panels reach up to about 14V which is above my motors recommended voltage range so I can get a 12V step down regulator https://www.pololu.com/product/2855 or https://www.pololu.com/product/2834 if that is needed?
I presently have 2 problems:
Solar panel Watts per Kg. Most people do not have to worry about the mass of the panels. For my Class Rover I need as little weight as possible. I am going to use a trailer so actual surface area is not as big an issue as weight. I will put my class onto this problem but if anyone has any suggestions?
We should be able to make 12V solar panels from individual solar cells. We could get used or slightly broken large solar panels and dismantle them. I am not sure which brands of solar panels are easy to dismantle? Any suggestions.
Anyone want to donate some solar panels for a class project?
If you are planning on powering the motors from a 12.8v LiFePo4 battery then ideally you would use a 12v battery to power your wheels during your test so you can get an accurate idea of how much current the wheels will draw when the 12.8v supply is stable and steady.
You could just use the 12v AGM battery that you have in the picture you posted and measure the current draw from the motor when it's connected while you put it under different pulling conditions.
I have a Laser cutting machine and a CNC router so if you guys want to draw up some rover designs and save it in a DFX file I can cut them for you so you have something unique to work with. I can cut wood or clear acrylic sheets. I just don't have time to do any design, I can just cut and ship to you.
Normally what is labeled as a 12v solar panel will have a voltage in the sun with no load of 18-24 volts. The voltage where the solar panel will produce the maximum current will be approx 70-75% of the solar panels output voltage under no load. So the voltage that the motors actually see could be in the 18-24v range.
If your planning on having a battery on board then just plan on feeding the motor 12-13 directly from the battery.
The only regulator you should need is a 12v to 5v-3.3v regulator to power the Photon. Plus what ever equipment you want to power on the rover that could also require a regulator.
How large of an area are you thinking about for the solar panels?
I have some 18w solar panels on 1/8 inch thick FR4 circuit board material that would work just fine for your project. I had them made for me many years ago but I no longer need them. They are using Sunpower solar cells which are about 21% efficient.
I think that is a waste of time considering how quickly prices for solar panels are coming down. You can't really make a high-quality solar panel for less than you can buy them for these days. I say spend your time on making something cool or useful vs building solar panels. I can supply you with some solar panels.
As always @RWB great replies:
Presently I am planning on running my Rover directly from the solar cells, no battery until @RWB has a small LiFePO4 solar charging battery ready.
That is very, very kind of you. I teach 3D Printing so we should be good for all small parts.
Presently no battery plan except for when testing. So I will probably need a 12V step down regulator for the motors with a 5V step down regulator for the Photon and Servo. Presently the Photon is rebooting when the Servo moves so I may have to separate the two on their own 5V regulators.
I have two panels that will not work for my project: The left one is too heavy at 0.500Kg (8 Watts per Kg), the right ones are too fragile but are a great weight at 12 grams. (333 Watts per Kg).
It looks like I need about 18 Watts to get my vehicle moving with a surface area of around 1500 square cm (233 square inches)
Wow that would be great. those look perfect. Can you give me some measurements, weight, volts and max current for that 18 Watt panel? From the website video https://us.sunpower.com/home-solar/solar-cell-technology-solutions/ it looks like those panels are less breakable than my wafers. I can message you my address on your website or with twitter.
This is exactly why you will need to use a battery as a power supply buffer.
When you try to pull more power from the solar panel than it can supply the voltage will drop out down to zero or close to it. This voltage drop-out will shut down the Photon or Electron and anything else you have connected to the output of the solar cells. Having dual 5v regulators will not prevent the photon from resetting.
Good point, but I am presently using a battery, so the rebooting must be some other reason. I think my 5 Volt regulator 1 Amp max current is a mismatch for my servo stall 2.4 Amp current. Will test it tomorrow.
That makes sense. Overloading the converter which causes voltage drop and then the Photon to reset.
Quick question: I have been reading about marine solar installations and they mention that the small amounts of shade from rigging and sails kills the solar power gain since the other solar cells are drained by the few shaded cells.
Why are the cells not connected in parallel with schottky diode protection to deal with any shaded cells and then have the voltage stepped up? Is the extra wiring a problem, the diode drain or is the solar cell series connection voltage increase needed for efficiency? I assume it is just easier and thus cheaper to attach solar cells in series.
This $15 regulator could step the voltage up to:
12V at 2.0 Amps https://www.pololu.com/product/2577
or for 5V at 2.0 Amp https://www.pololu.com/product/2574
Some factors
The forward drop of the diodes reduces efficiency considerably when dealing with single cell output voltage (ratio between 0.2V forward drop over single cell output voltage).
The extra cost of the diodes (either as extra components with additional assembly steps or during production as completely different production step).
If you have all the minute voltages in parallel all the power needs to go into the current, hight current means more power lost as heat, which reduces efficiency again.
This product is 30W and 1.6 Amps (Ideal conditions!). It is light weight, slightly flexible and strong. Dimensions about 1 foot by 3 feet. I could easily fix wheels to it and pull it behind my Rover. Bit pricey at $200 CND, but it is available in a nearby store.
http://www.canadiantire.ca/en/pdp/noma-30-watt-semi-flexible-solar-panels-0112032p.html
I am just trying to get proof of concept that my Rover will move with only the Solar Panel (12V Step down regulator if needed.). I am trying to run a 12V motor with stall current of 1.4 Amps. Not really sure what voltages and currents to expect with the motor connected under normal conditions. Anyone have any idea what to expect?
I think my motor needs about 400 mA to move the Rover, probably a bit more current with the extra weight. I would really like it to be able to move slowly on a cloudy day and move fast on a sunny day.
The individual solar panels are protected by a diode and some panels have mutiple diodes in them for shading. You will not see them on individual cell connections because they are a pain in the ass to assemble/ manufacturer that way.
I have panels like that and they are really good and light panels plus they use the Sunpower solar cells. I would pick those up if you think they are the perfect size for your project. I have a 30w panel just like that but in a more square shaped that I have had outside under the sun all year now and it's holding up great.
Using MPPT on that 30w panel in the summer yields 21-22 watts power output so don't expect that unless you have ideal conditions and your using a MPPT solar charge controller.
Put a multimeter on the motor and see how much current it pulls under normal and stressed operation and then you will know how much power to expect.
Here is a good, cheap, bluetooth multimeter that would allow you to view the current and voltage measurements wirelessly. I use one of these all the time when testing stuff.
