Using a 6V solar panel to charge a 6V rated supercapacitor, will capacitor explode/get damaged?

[knightridar]

@Wawa

Not all supercaps are made equal.
You seem to have a lab supply and a DMM. Why don't you see for yourself.

I recall Nick Gammon's post saying they seem to get better at reducing leakage after being charged a few times. I noticed this before with the 6V, 5F and 3V, 10F supercapacitors. I get what you mean now, I mentally kept track of how much voltage drop I'd get over a 24 hour period.

C*V / t = I

This formula should give a rough idea of the leakage.
Thanks to johnerrington's earlier post.

[knightridar]

@Wawa

Which boost converter are you planning to use with your single supercap.
Very few work down to 1volt.
That includes an LM2596 and S7V8A (2.7volt minimum).
I copied this NCP1402 board for a supercap project, with a Chinese/clone NCP1402.
Because the chip manufacturer (not Sparkfun) decided to retire it.

Right now this is what I've been using:
Pololu 3.3V Step-Up Voltage Regulator U1V11F3

Features

• Input voltage: 0.5 V to 5.5 V
• Fixed 3.3 V output with 4% accuracy
• True shutdown option that turns off power to the load
• Automatic linear down-regulation when the input voltage is greater than the output voltage
• 1.2 A switch allows for input currents up to 1.2 A
• Good efficiency at light load: <1 mA typical no-load quiescent current, though it can exceed 1 mA for very low input voltages (<100 μA typical quiescent current with SHDN = LOW)
• Integrated over-temperature shutoff
• Small size: 0.45″ × 0.6″; × 0.1″ (12 × 15 × 3 mm)

[knightridar]

@Idahowalker

My weather station has been buried under the snow for the last 6 days.

That would be a good environment to test in for me.
I'm in southern California so yes, get plenty of light throughout days on average.
Right now we're getting some heavy rain

I just wish someone can make a 2.7 or 3 V max Voc panel with like a 3 or 4 amp rating.
My next setup will be the 0.5V, 250 mA panels in series to ~3V.

Here is my latest spreadsheet calcs. Thanks to Nick Gammon's site post about charging a supercapacitor. This is with theoretical output of 100 mA from solar panels, it's unreal since all devices consume near ~130 mA right now.

Solar Panel Charging Super Capacitor and Powering MCU Calculations, R2.zip (48.5 KB)

[Wawa]

I still think you need to use a 4volt solar panel for a 2.7volt supercap.
And a shunt regulator that can take the current of the panel.
That can be as simple as soldering this board on top of your supercap.
Leo..

[knightridar]

@Wawa

And a shunt regulator that can take the current of the panel.

@Wawa

The LM431, with it's 0.4mA idle current, is on the solar panel side of the backflow protection diode.
And the reference voltage divider that measures/sets max battery voltage is on the battery side, so battery drain after dark is only about 10uA.

I'm trying to find a better one that can handle more current.

LM431 Datasheet
Continuous cathode current 150 mA
(I think this is the spec. that points out its current limitations).

Meanwhile I tested out the 0.5v, 100 mA panels in series and this time got ~2.8 volts on a bright sunny day (~2.8V, 100 mA?).

It took about 7.5 minutes to charge from 0.4 volts to 2.8 volts for a 3V, 10F supercapacitor.
Next I'm waiting for the 250mA, 400 mA version of the 0.5V solar panels to arrive so I can solder them together in series to get near ~3V ( will take about a month to arrive otherwise there were some ridiculous shipping costs ) so I can try them out too.

I don't doubt the lithium batteries or lead acid batteries have greater capacities.
I was going to use the supercapacitor with the intent of deep sleeping the MCU and peripherals.
(Main reason I'm considering it for use is the fast charging rate and life cycles it can take and maybe overall lifetime use cost (1 supercapacitor versus changing out batteries and batteries discharge/overcharge controls)
Will I have to swap it out after 6 months, 2-3 years like batteries or 10 years?
Cost versus LiFePO4, AA, AAA regular batteries, and Li-ion.

Other reasons are the potential cost of lithium going up over the years i.e. evs etc and is a supercapacitor made more easily (in terms of environmental impact) with less costly materials?
Sure 1 person using lithium batteries won't make a big difference but 1 million people using them combined may make a huge difference. How many people even recycle them properly or do they just trash them after use? What ever components I get for my projects I try to get RoHS compliant components as much as possible.

Now I'm not sure if the LiFePo4 will last longer or can take more current, but based on this article it seems like they can. It also seems like they can last a few thousand cycles depending on use.
https://www.powertechsystems.eu/home/tech-corner/lithium-iron-phosphate-lifepo4/

[Wawa]

@knightridar

I'm trying to find a better one that can handle more current.

I gave you the option in post#64.
That board has a low idle current SMD 431 and a 2-transistor amplifier for up to 1Amp (maybe Chinese amps) solar current. The board will probably drain less than 40uA@2.7volt (the cap itself leaks waaay more), and it fits directly onto your 450F cap (or your 10F cap).
Leo..

[knightridar]

I managed to find these and they are difficult to find elsewhere.
They are 2.5V, 200 mA solar panels. With a Voc ~3.03-3.06 volts.

I soldered and wired them in parallel, so in theory they should be getting ~3Voc and 600mA.
Link below has 3d models in case anyone wants to 3d print the case that is holding them and links to panels and supercapacitor.
2.5V, 600 mA Solar Panel Soldering Fixture and Case

The 3V, 10F supercapacitor went from 0.14V to 2.82V charge in about 2 minutes in full sunlight.
I noticed a slight drop in previous Voc maybe due to solder or wiring? Good thing is it doesn't exceed 3V.

I noticed a slight drop in voltage as a cloud passed by and it was a good example of voltage drop from 2.8 volts to ~2.6 volts.