Solar-to-Lithium Ion Capacitor (LIC) charger

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gmlou007
 
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Solar-to-Lithium Ion Capacitor (LIC) charger

Post by gmlou007 »

Is Adafruit currently considering creating a Solar-to-Lithium Ion Capacitor (LIC) charger/power supply (solar harvesting), including circuitry to prevent the LIC from being discharged below 2.2V?

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barshatriplee
 
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Re: Solar-to-Lithium Ion Capacitor (LIC) charger

Post by barshatriplee »

I think it will be a good addition to the line of Adafruit products.

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adafruit_support_mike
 
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Re: Solar-to-Lithium Ion Capacitor (LIC) charger

Post by adafruit_support_mike »

We don't have any plans for such a thing, but I'll mention it to our products team.

Fair warning: supercapacitors are still niche application devices for power storage. A typical SIC has a nominal operating voltage of 3.8V, putting its stored energy at about 7.2J per Farad of capacitance. That translates to a little more than 0.5mAh per Farad.

That puts a 450F device like the TPLC-3R8 (which holds about 3250J: (450F*3.8V^2)/2):

https://www.digikey.com/en/products/det ... 0/12417604

at about 70% the storage capacity of a 350mAh LiPo (~4660J: 3.7V*350mAh*3.6J/mAh*V):

https://www.adafruit.com/product/2750

and well below 2xAA cells (~23,760J: 3V*2200mAh*3.6J/mAh*V).


A supercap's major advantage is its lifespan: the TPLC-3R8 is rated for 500,000 charge/discharge cycles.. enough to last a thousand years recharging once a day. In more practical terms it would be used in a sealed device that never needs to be opened, but is limited to an energy budget a little below 10mAh.

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gmlou007
 
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Re: Solar-to-Lithium Ion Capacitor (LIC) charger

Post by gmlou007 »

Thanks for your feedback. I have now run two tests using a 250F LIC with a Gemmo M0 and a 7-NeoPixel Jewel, programmed using CircuitPython.

With test #1 I had one of the seven NeoPixels continuously alternating between red, blue and green at brightness=.3. The starting LIC voltage was 3.78v. Current throughout the test remained around 14mA. The single NeoPixel continued alternating between red, blue and green until the voltage dropped to about 2.99v, after 6.5 hours. It appears that the Gemmo M0 controller decided that the voltage was too low to continue because although the NeoPixel stopped alternating between red, blue and green, i.e. it continued displaying one of the colors until I terminated the test (after +-7 hours).

With test #2 I had all seven of the Jewel's NeoPixels running the rainbow_cycle code (shown below) at brightness=.3.

def rainbow_cycle(wait):
for j in range(255):
for i in range(7):
rc_index = (i * 256 // 7) + j * 5
pixels = colorwheel(rc_index & 255)
pixels.show()
time.sleep(wait)

The starting LIC voltage was 3.79v. Current throughout the test remained around 28mA. All 7 NeoPixels performed as expected (continuously changing rainbow colors) until the LIC voltage dropped to about 2.99v, after 2.5 hours. Again, it appears that the Gemmo M0 controller decided that the voltage was too low to continue because although the NeoPixels stopped changing colors, it continued displaying all of the NeoPixels at the last color each of them was set to when the controller stopped, until I terminated the test (after +-2.75 hours).

Based on these test - and considering that I'm using a 250F LIC (as opposed to 450F) - I believe that creating a LIC charger for use with wearables would be a worthwhile exercise. Thanks again for your response :)

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gmlou007
 
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Re: Solar-to-Lithium Ion Capacitor (LIC) charger

Post by gmlou007 »

FYI, regarding test #2 that I discussed previously - i.e. were all 7 NeoPixels of a Jewel continuously changed rainbow colors for 2.5 hours, until the LIC voltage dropped to about 2.99v - although the NeoPixels stopped changing colors because the Gemma M0 stopped the process, all 7 NeoPixels of the Jewel continued displaying the last color each of them was set to (when the controller stopped) for a further 2 hours until the LIC voltage reached 2.5V, at which point I switched the circuit off. Evidently an LIC voltage should not be dropped below 2.2V.

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gmlou007
 
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Re: Solar-to-Lithium Ion Capacitor (LIC) charger

Post by gmlou007 »

I have run another 250F Lithium Ion Capacitor (LIC) test, based on the https://learn.adafruit.com/neopixel-nov ... t/overview project (using the 'Adafruit 5x5 NeoPixel Grid BFF Add-On for QT Py and Xiao' and 'Adafruit QT Py RP2040'). The voltage and current at the LIC at the start of the test were 3.7V and 35mA respectively. The 5x5 NeoPixel matrix continued cycling through the display of hearts and scrolling texts as expected until I stopped the test at 4 hours, at which point the voltage and current were 2.5V and 27mA respectively.

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