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Simple Day/Night Solar Circuit
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Simple Day/Night Solar Circuit

by sokbok on Sun Jan 23, 2022 4:38 pm

Hello Forum.
It has been too long since I posted. I have missed all my blinky experiments
and its a joy to return to making after a hiatus.

I am trying to make a simple setup with a small solar panel (probably 6V), 3.7V LiPo Battery, and an LED
I am thinking of using the Adafruit sold White LED Backlight module: https://www.adafruit.com/product/1626
or the warm white sequins.

What I need is for it to turn on at night and off to charge during the day.

I have seen a variety of schematics online that I can try but wanted to see if there was any integrated
LiPo charging board that could also do this. I know I could use a full board and run it Arduino style, but
I want to keep this a simple as possible.

I keep taking apart Solar Garden Lights and perhaps that may be cheaper then building myself.

Any input appreciated.
sokbok
 
Posts: 12
Joined: Thu May 17, 2012 12:15 am

Re: Simple Day/Night Solar Circuit

by adafruit_support_bill on Sun Jan 23, 2022 5:02 pm

LiPo cells are finicky and require a charge controller to safely control the charge cycle. And since solar cells are not the most stable of power sources, it is best to use a charge controller designed for that purpose such as the bq24074: https://www.adafruit.com/product/4755

For a smaller - lower-cost option, NiMH cells are much less fussy to deal with. Our Evil Mad Scientist friends have a nice post on the subject here:
https://www.evilmadscientist.com/2008/s ... -circuits/

adafruit_support_bill
 
Posts: 83814
Joined: Sat Feb 07, 2009 10:11 am

Re: Simple Day/Night Solar Circuit

by sokbok on Fri Jan 28, 2022 11:40 pm

@adafurit_support_bill
Thank you for the thoughtful response.

Yes that Evil Mad Scientist post is a great resource.

NiMH cells are 1.2V and from what I can read online, they prefer to charge at 1.45V

I want to use the Voltaic 1W, 6V panel, offered by Adafruit:https://www.adafruit.com/product/3809
Peak Voltage is 6.5V.
VoC = 7.7V
Imp = 180 mA

and 4 of these NiMH batteries: https://www.batteryjunction.com/tenergy-nimh-aa-2000-tabs.html?gclid=Cj0KCQiAxc6PBhCEARIsAH8Hff30BOalGdADN0u4qf0TwErRQ9QRQ_fOfuEBhBLi2FRlVCu0wD9d3n0aAjMREALw_wcB

4 x 1.45 = 5.8V which I think is probably ok for that 6V panel.
The C/10 value of those cells is 200mA and that 1 W panel puts out 180mA so that also seems good.

If I put 2 of the adafruit sold LED backlight strips in series I should be ok I think. Their forward voltage is 3.2 but should work under 4.8V or should I do 2 LEDs in parallel with some resistors? https://www.adafruit.com/product/1626#technical-details ??
sokbok
 
Posts: 12
Joined: Thu May 17, 2012 12:15 am

Re: Simple Day/Night Solar Circuit

by adafruit_support_bill on Sat Jan 29, 2022 7:24 am

Best to add some current limiting resistors. One in series with each of the two backlight modules. 100 ohm resistors should work.

adafruit_support_bill
 
Posts: 83814
Joined: Sat Feb 07, 2009 10:11 am

Please be positive and constructive with your questions and comments.