How best to find the "best" small solar panel of a particular size?

[NeverDie]

Back to the OP, here's a screen scrape of what had been the "good" small solar cells:

Here's a closeup photo of one:

It may not show so well in the photo, but what I think may be key is that it wasn't pieced together out of scrap solar cell fragments (like the "bad" one was) but rather appears to be a single piece. So, that may be a clue on what to look for in the future.

[NeverDie]

Here's a schematic for the ideal diode that is pictured above:

[gohan]

Do those solar panels handle outdoor weather?

[NeverDie]

Not sure. There's probably a risk of UV damage to the epoxy, but that's just a guess.

At the moment, I'm focused on indoor use, which is a largely ignored category. I think outdoors is easier because, well, it's a lot brighter. For instance, novicit (above) reported "The solar panel is from China, Ebay, 110mmx70mm, 5V, 1.25W. The panel works great also. It reaches 4V in the smallest amount of light, and 5.45V (no load) in modest indirect light. In fact, it will fully recharge the supercapacitor in the morning before the sun even rises above the horizon, just from the sky brightening. (From the ~20% overnight discharged state.) It seems to charge a fully empty supercap in ~10 minutes under average light."

[NeverDie]

If anyone has a favorite buck converter chip, or one they want to recommend, I could possibly make a PCB for it and post it on mysensors.org. Suggestions anyone?

[NeverDie]

I received the 0.7v to 3.0v boost converter module from Aliexpress whose link I had posted earlier above. Can anyone identify the chip which is on it?

[Nca78]

@NeverDie it is a ME2188 from MicrOne
http://www.sz-hxdz.com/uploadfile/pdf/201605111221584282.pdf

[ceech]

Anyone interested in super capacitors.
I'm working on a backup super capacitor storage board. It connects directly to the power rail and charges and balances super capacitors bank. When and if power fails the board steps in and provides power to the circuit.

It is based on LTC3110 super capacitor bi-directional charging IC.

[alexsh1]

@ceech interesting board. Is it available that order or not yet?

[ceech]

@alexsh1 Boards will be most likely available by the end of the week.

[Tmaster]

why use supercaps on an arduino tha consumes so low current? that caps will not discharge during night,when solar panels are not producing energy.?

[gohan]

They will not discharge during just one night

[NeverDie]

@ceech
Isn't it more economic to buy just one much larger supercap, with say 16x the Farads of the supercaps in your photo? Or does a capacitor bank have some other advantages besides just higher Farads?

By the way, have you found supercaps that you like which also have very low self-discharge? I've been using leakage as a proxy for self-discharge--because self-discharge data is hard to come by--but they are actually defined differently.

[ceech]

@Tmaster They will slowly discharge. And depending on quality discharge times can vary a lot. The ones I'm using have a leaking current of 6uA.
Of course not always is a super capacitor a suitable replacement for a battery but where batteries are not available, suitable or safe, super capacitors can take their place. They also have some advantages - high cycle life of more than 100.000 cycles comes to mind.

[ceech]

@NeverDie Not necessarily. Larger super capacitors tend to be more expensive than smaller ones. Anyway, the board on the photo is a proof of concept. I would like to see how balancing and bi-directional charging/discharging work. Besides, I have some super capacitors left from other projects.

[gohan]

If you could make one the smallest as possible just for 2 supercaps, it would be a nice thing to have to integrate into an existing project to give it a little backup power.

[NeverDie]

@gohan said in How best to find the "best" small solar panel of a particular size?:

If you could make one the smallest as possible just for 2 supercaps, it would be a nice thing to have to integrate into an existing project to give it a little backup power.

But I'm guessing you want them in series, not parallel. Am I right? I suppose that might be useful actually. Ceech's seems to be parallel, though I can't say for sure whether or not it connects two banks of parallel caps in a series configuration or a parallel configuration.

@Ceech What voltage does it supply? Are they 2.7v supercaps, or something else?

[gohan]

of course I want them in series :D

[NeverDie]

You know what would be interesting? A capacitor bank that accepts charge in parallel but gives it back in series after a voltage threshold has been reached. That way you could charge it with very weak voltage (e.g. from a solar panel in very weak light), and still get a useable voltage out of it without the huge efficiency losses you usually get from a boost converter running at very low currents. Of course, the ESR might be very high (since it adds) if it wasn't very low in the supercaps to begin with. Low ESR supercaps are certainly available though.

@Ceech What do you think?

[wallyllama]

@NeverDie you mean a like battery from a hybrid car? Cells form a pack, but monitored(at least) and [possibly] charged individually. I believe that is how they are set up. It might be a way to find a reference on how to do it.