I know a blocking diode of some type should be used to prevent current flow back into the solar panel, but I found this instead and was thinking of using it to see if it would minimize losses in low light conditions.
It's a smart bypass diode. SM74611 Smart Bypass Diode
It has a low forward voltage drop of .026 volts @ 8 amps.
So my main concern with this is lets say the panel reads 7v (open circuit) and it drops to 6.98 volts. Will the supercapacitor below get damaged/blow out? 6 volts, 5 farads, DSF505Q6R0JBG, tolerance of -10%, +30%
Based on my understanding the tolerances affect the capacitance values, so I'm also wondering if it will cause the rated voltage rating to deviate from it's nominal value?
It's been a while since I read the post,but thanks for the voltage info.
I found this post on the forums
It mentions the voltage of the solar panel being lower once its connected so is there a chance it wont even reach 6 volts once it's connected to the supercapacitor?
Regarding zener diodes isnt there a correlation between minimum forward voltage drop and higher current leakage occurring as a result and this could be bad with the super capacitor sending current back to the solar panel? Thats why i chose the smart bypass diode it minimizes forward voltage drop and leakage current.
I'm concerned about forward voltage drop and loss in power efficiency especially in low light conditions.
Of course there's a chance it won't, but there's a good chance it will. So why take that chance? Protect your supercap against over-voltage! Good engineering doesn't rely on hope.
I think you've misunderstood. I believe @jremington meant connect the zener across the supercap (or panel) so it conducts excess current should the voltage from the panel get too close to the supercap limit.
You might also want to consider a buck/boost converter between the panel and the supercap, so that the panel could charge the supercap even when its output voltage is lower than the supercap voltage.
HOWEVER, and this is important: you need to be very careful. Any such converter must be comfortable handling slowly changing input voltages all the way down to 0V. The ones I've tested are not: if the input voltage to the converter goes below the specified minimum, the converter goes into a "locked up" state whereby it puts an almost dead short across the input. If the source can generate enough current it will then blow up the converter. In any case, the only way to exit from the locked up state is to disconnect and reconnect the supply, ensuring it is above the specified minimum.
It might be worth looking for a converter that behaves nicely when the input voltage is below the specified minimum - it will allow you to extract energy from the panel even in low lighting conditions.
Haha okay it's a good point. Won't take the chance.
I was anticipating with a dark night and some moon light
I could get a few milliamps at a low voltage from the solar panel hence the reason for a higher voltage 6V solar panel for a 3.3V device.
I was going to use a buck boost converter to power the Nano 33 IoT with a 3.3V input.
Here is what I was considering (actually on order), it has a minimum 0.5V input and maxes out at 1.2 Amps. It also automatically steps up the voltage, but maxes out at 5.5V input.
The size of that solar panel (post#1) doesn't seem to match a 5F super capacitor.
Did you calculate how long a 5F cap lasts with just the idle current of a boost converter?
I needed 400F to light up a 3volt/10mA LED with boost converter for a whole winter night.
And don't be tempted to order 500F Samwha caps from ebay. They are all crap.
Leo..
I didn't calculate that, I was trying to maximize the amount of Farads I could get at a certain voltage (closest to solar panel voltage) at a good price point.
I wanted to actually have it deep sleep and wake up periodically and send values to the IoT cloud.
Similar to Nick Gammon's example. Solar powered Arduino
However, what I did calculate is how long I can theoretically keep things powered on based on a certain current consumption amount and capacitor varying voltage in a 24 hour time period. It's a rough draft of calculations based on Nick's calculations on his site.
I still need to figure out the latter half of it because I'm trying to make my circuit setup a bit different.
Here is a screen shot, and I've attached it for reference in case any one wants to use it (crossing fingers that the forum now allows .ods libreoffice file extensions - guess not so I zipped it):
Just to clarify with respect to the spreadsheet, I'm not sure if based on capacitor tolerance the nominal voltage varies too
i.e. at + 30% tolerance, is my voltage rating now 7.8 volts or is it still the nominal 6 volts?
at -10% tolerance, is my voltage rating now 5.4 volts or is it still the nominal 6 volts?
That's awesome!!
Not too well versed on the electrical schematics and still learning, but based on the pdf
"Continuous Cathode Current Range 100 ma"
Is this the maximum amount of current I can draw from the solar panel to the capacitor?
This is what I was planning on doing prior to the post above,
I modified Nick's setup and
I didn't want to limit the current going to my diode so I took out the resistor.
Still not clear as to why the Zener diode was used versus just the latter diode only (other than for dropping the voltage to a safe usable range with the right combination of diodes?)
I was considering this schottky diode, but it's 700 mV @ 2A (Vf)
So if my solar panel is at 6.6V on full bright day it drops to 5.9V, but only if it's drawing 2A,
based on the chart it seems it's a lower Vf if the current consumption is lower.
Is that correct?
As a side note I'm reading elsewhere on the forum and other sites that a Schottky diode is a better option for the solar panel, but am still figuring out why.
Yes, a '431/2' can be used for that, with the cathode connected to the panel, and the voltage divider for the reference connected to the supercap, with a Schottky diode between panel and cap.
Not all 431/2 references are created equal though. Some consume 400uA cathode current.
Problem is that that large panel generates more current than the reference alone can consume.
Again, did you calculate for the idle current of a boost converter.
That alone will drain a 5F cap fast.
Leo..
or the step up voltage regulator from Pololu ( I'm limited to 0.5V min input through 5.5V max input, it has 1 mA typ. no-load quiescent current) plus I can shut it down if the power source (capacitor) goes to a certain voltage. (<100 μA typical quiescent current with SHDN = LOW) Pololu 3.3V Step-Up Voltage Regulator U1V11F3
+Planning on deep sleeping and periodic on times for gathering data
Will the things that data is gathered from be powered down during the CPU sleep time? If not, the data gathers will consume power while the CPU sleeps.
Yes that is correct, I will have to figure out how to put them to deep sleep as well.
NEO 6M GPS module will be the biggest power consumer and it's a bit dated.
Right now I can power all of them via the Nano 33 IoT I believe when I'm connected via the USB port. So if I can do this with the 3.3 V out pin too, and it goes into deep sleep then I would assume the other devices will be asleep as well?
they will be
NEO 6M GPS module,
ADPS-9960 color detection/gesture sensing module
BME680 humidity, temperature, barometer, and VOC sensor
