[circuit design] Solar power for Arduinos

[Spuriosity]

I recently had the idea to build come kind of a solar-powered Arduino robot. I have a (relatively) powerful solar panel I'd like to use, but obviously it's nowhere near powerful enough to drive a motor in continuous operation.

The design I had in mind was a low-voltage solar panel (~2V on a good day) in conjunction with some form of DC-DC boost converter to charge a 6V rechargeable battery, which (once charged) wakes the control circuitry, then shuts it off again once discharged for more sun collection.

I was thinking of using a Joule thief to boost the panel voltage to charge the 6V battery pack, but I'm not sure what the best way of building the microcontroller-activating circuit is. I though I'd ask someone more experienced so I don't go and solder-ruin a perfectly good transistor.

 

[MikeMl]

You can put an Arduino in a very low-power-down sleep mode where it draws only a few 10s of uA at 3.3V (See the Narcoleptic library, for example). Put the Arduino to sleep such that it wakes up once every few seconds, powers up, does an AD conversion to see if the battery has accumulated sufficient charge. If yes, do something, else go back to sleep.

I would get a second panel, or one that is capable of >5V open-circuit, and charge a battery directly, with no intervening SPMS, and then use the battery to power the Arduino, either while it sleeping or doing something useful. A fully awake Arduino is a real power hog, so you only want to wake up the parts of it that you really need to do something useful...

 

[ericgibbs]

hi.
If you prefer the mini boost PSU route, these units from Amazon work well, check when they are back in stock.

£1.0 GBP for 5 pieces.

E

 

[Spuriosity]

Thanks for that! I know that those cheap modules are going to be better than anything I can build myself, but I'm a big fan of scratch-building my own circuits out of salvaged parts for the hell of it. Can you recommend a boost converter circuit that'll work off the meager power generated by a solar panel?

 

[spec]

Hi Spur,

To get the most power from your solar cell, with varying amounts of sunlight, you will need to use Maximum Power Point (MPP) techniques and to get maximum energy transfer you should use a lithium Ion (LiIon) battery rather than lead acid, because LiIon has a better charge efficiency than lead acid. Provide that you use the appropriate battery management, LiIon is also better for the wide charge states likely with a solar energy source.

Two LiIon batteries in series will give you 2 * 3.6V = 7.2V. If you could use just one LiIon battery and operate your motor off 3.6V that would be much better. You could get around 3.4A/Hr from a single 18650 size LiIon battery and you can connect them in parallel to increases the capacity.

Here are links to a few energy harvester chips that may be of interest:
(1) LT, LTC3105 (£4.00UK from DigiKey)
http://cds.linear.com/docs/en/datasheet/3105fb.pdf
(2) TI, bq25504 (£4.10UK from DigiKey)
http://www.ti.com/lit/ds/symlink/bq25504.pdf
(3) ST, SPV1050 (£2.20UK from DigiKey)
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.DM00100984.pdf
(4) Cypress, MB39C831QN (£1.50UK from DigiKey)
http://www.cypress.com/file/216476/download
(5) LT, LTC3108-1
http://www.linear.com/product/LTC3108-1
(6) LT, LTC3526-2
http://cds.linear.com/docs/en/datasheet/3526llb2fa.pdf

And an ETO thread which has some information that may be a help: https://www.electro-tech-online.com...teg-output-into-something-i-could-use.148521/

spec