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I have an Arndale octa board which itself needs 5V 3A power supply. Then I have four (4x) DC 5V motors and a 5V servo, and a number of other peripheals. So I think 5V 5A is safe to assume?

I want to power all of this with Solar, which if there's not enough light I will switch to a backup battery (that the solar also charges, during idle time)

I tried doing some research but I'm just so confused. I know I will need like 12 or 24V rechargable battery and a buck regulator, perhaps a board that regulates between solar/battery and such, and solar panels. But I am really in over my head trying to figure out the pieces. Can someone please help point me to some good products to do what I want?

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  • \$\begingroup\$ fix your ideas on the solar panel, decide what sort of wattage you need to run the system then ask yourself how much daylight you need to keep this running on an average day. Don't assume you live on the equator I.e. be realistic. \$\endgroup\$ – Andy aka May 27 '14 at 22:22
  • \$\begingroup\$ How much current do your motors and servo consume? Data sheets would be nice. \$\endgroup\$ – WhatRoughBeast May 27 '14 at 22:22
  • \$\begingroup\$ How much surface area do you have available for solar panels? \$\endgroup\$ – Ignacio Vazquez-Abrams May 27 '14 at 23:45
  • \$\begingroup\$ The DC motors are Rated voltage: 3-24v (6-9V best) Current: 250mA. Power: 1W. Servo I have data sheet for: parallax.com/product/900-00005. Surface area is ~200*140mm (7.8*5.5in). I live in New Mexico, lots of sun. I will have robot seek out sun spots when battery runs low, save known ones, and lie dormant until it has a good charge. \$\endgroup\$ – Sean Nall May 28 '14 at 1:17
  • \$\begingroup\$ The solar/battery switching maybe doable with some Schottky diodes. Don't overcomplicate it. \$\endgroup\$ – Kaz May 28 '14 at 3:09
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The problem with solar power is that it is not a consistent or constant source of power. I.E. The current that solar panel will supply will fluctuate through out the day. As a result it is a good idea (pretty much a necessity) to use a battery as your power source and the solar panel to charge the battery.

And because of the fluctuating power output of the solar panel you will need a solar charge controller that goes between the battery and the solar panel. The solar panel feeds power into the charge controller and the charge controller carefully feeds that power into the battery. The charge controller makes sure that the battery does not get overcharged and many charge controllers also make sure that your load does not over discharge the battery.

So the battery powers your device, the solar panel charges the battery and the charge controller controls the charge and discharge of the battery.

In general, the solar panel needs to have an open voltage of about 18 volts for a 12 volt battery.

The hardest decision will be how large a panel and how big a capacity battery you will need. The answer to that will depend on how many watts your device uses and how many hours of sunlight you get. so you will need to calculate how many watts per day you will use, then you can determine the size of your battery (will it be big enough just for one day or for two or three days in case of rain?). Then you can determine the average amount number of hours of sunlight you get (there are websites that can help) then you can decide on how big a solar panel you need. For example, if you need 100 watts to power your device for an entire day and you get one hour of sunlight per day, you might want a 100 watt panel or even 150 watt panel in case you get a lot of clouds. (this example is extreme, and trying to charge a battery in only one hour would be pushing it, but I used these numbers because they are easy to understand). Also, in this case you would want a battery that can provide 100 watts per day(or maybe a 300 watt battery to account for rainy days, in that case you might want a bigger solar panel also. A 300 watt battery at 12 volts is 25 amp hours(amp hours is usually how these lead acid batteries are reported for capacity).

I am ignoring the fact that you would need a buck converter to get the battery 12 volts down to the voltage of your device.

Hopefully this will get you started. If you have more questions feel free to ask. Good luck!

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  • \$\begingroup\$ You seem to have some useful practical solar experience. You may wish to say hello via email - address on my profile page. You may be wasted as a Physician :-). \$\endgroup\$ – Russell McMahon Jun 9 '14 at 13:33

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