1
\$\begingroup\$

I'm going to start with a picture to illustrate my question: Circuit Falstad

The resistor on the far right is my load (which will eventually be an Arduino or a battery which will then be connected to an Arduino) and I haven't bothered to fill in the proper values yet (and I'm also still missing a voltage regulator), but I'd like to understand how to deal with my problem first.

I'm planning to connect a solar panel as the main power source, which, upon switching off (due to the sun going down or the sky becoming cloudy), will cut the DC circuit and connect the device to the AC power socket. It should also be able to switch back and forth between AC and DC power as the light outside increases or decreases.

I've tried multiple solutions using switches, transistors, inverters and everything I could think of (in this specific case, I was about to try using inverters and an ADC to "switch" the SPDT switches, which failed miserably), but I can't for the life of me figure out how to make this work.

I'm still learning, so I'd love it if someone could help me figure this out while also explaining their solution, as I'm trying to learn and simply applying a solution given to me online won't really help me understand this stuff better.

Thanks in advance for your help!

\$\endgroup\$
1
  • \$\begingroup\$ There are specialized devices like the LM66200 (if you do not want to waste power with real diodes). \$\endgroup\$
    – CL.
    Commented Sep 17, 2023 at 14:43

3 Answers 3

2
\$\begingroup\$

Arrange the solar panel to deliver a higher voltage than the rectified AC source.

Wire-OR the two supplies with diodes.

Then, whenever the sun is shining, it will supply all the current the load need. Automatic, no-break, switching between the two supplies, with not a relay in sight.

The load will need to accept a voltage that varies between the high of your solar and the low of your AC backup. However, you've said that you're missing a voltage regulator. So make the first item after the diodes a DC-DC switching converter, that can accept the voltage range, and deliver the right voltage to your actual load.

\$\endgroup\$
2
  • \$\begingroup\$ You might not even need diodes. Solar panels act as diodes - you can't push current the wrong way through them - and the rectifier already consists of diodes. \$\endgroup\$ Commented Sep 17, 2023 at 15:26
  • \$\begingroup\$ I tried using your solutions and came up with something like this: pastebin.com/rLKJMh20 (had to shorten the url because it was way too long. It does seem to work both with and without diodes, although I may need to regulate the current, but it makes Falstad go wonky and only switches the input source automatically if I press the reset button, so I'm not sure if this would work as intended. \$\endgroup\$
    – Meika
    Commented Sep 17, 2023 at 16:07
0
\$\begingroup\$

For a very simple solution, just wire the solar panel in parallel with the rectifier, capacitor, and Arduino.

You don't need to prevent rectified AC power from going into the solar panel, because solar panels don't work like that. And you don't need to prevent solar power from going into the AC transformer, because the rectifier is made of diodes which only allow power to flow in one direction.

Make sure the solar panel's actual voltage is higher than the peak of the rectified AC. That way, when the sun is shining, the transformer won't be able to push current through the rectifier because the output voltage from the rectifier is higher. If the solar panel's voltage is too low, you'll be using wall power, or a mixture of wall power and solar power.

Make sure the capacitor and the Arduino are able to handle the solar panel's open-circuit voltage - I expect you already knew that. With bright sunlight and a small load, the voltage you get will be close to the open-circuit voltage. If it's too high, you could consider adding a shunt regulator. In this case, the regulator voltage must be higher than the peak rectified AC, or it will waste power from the wall.

P.S. If your solar panel is big enough, you can power an Arduino even when it's cloudy.

\$\endgroup\$
2
  • \$\begingroup\$ Pasting here the same comment I left on the previous answer. I did add in a second voltage regulator to account for the voltage fluctuation in solar panels :) I tried using your solutions and came up with something like this: pastebin.com/rLKJMh20 (had to shorten the url because it was way too long. It does seem to work both with and without diodes, although I may need to regulate the current, but it makes Falstad go wonky and only switches the input source automatically if I press the reset button, so I'm not sure if this would work as intended. \$\endgroup\$
    – Meika
    Commented Sep 17, 2023 at 16:08
  • \$\begingroup\$ Realized I made a mistake putting that voltage regulator before the diode on the solar panel so I inverted their order. I still looks like I have a problem though, since the solar panel current passes throught he load and proceeds towards the bridge rectifier rather than the negative terminal on the solar panel. I don't think it makes much of a difference, but I'm not too sure about that. \$\endgroup\$
    – Meika
    Commented Sep 17, 2023 at 20:31
0
\$\begingroup\$

It looks like I was able to find a solution in the end!

I realized I hadn't set up the transformer properly and I was making the job way harder on myself than it had any right to be.

By setting up the proper number of coils in the transformer, I was able to reduce the voltage before the rectifier, making it so it's slightly below that of the solar panel. This way I only have to use a rectifier on the solar panel to account for voltage fluctuations (although I may as well use a capacitor, if the conditions allow for it) without the need for any diodes.

Circuit

This should be the final result (with the diodes still in, since I forgot to delete them).

Does anyone have any suggestion to improve this, or does it lookd good?

Again still learning so any comment is appreciated :)

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.