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

[NeverDie]

@alexsh1
Well, I'm sure it's easier to solder than the BQ25570. I'm no longer really considering anything that's difficult to solder unless there's just absolutely no alternative.

It looks as though @ceech sells them though already soldered to a breakout board, so maybe he can answer your question.

[NeverDie]

I'm playing around with a coulomb counter, actually a clone of:
https://www.sparkfun.com/products/12052

The only downside to it is that it requires a minimum of 2.7v on the input current that it's measuring, which isn't really ideal for a solar panel that might nonetheless be charging at a lower voltage. It also includes its own current consumption in the measurement, and it appears to be about 75ua. In addition to counting the coulombs, you can also measure the average current between interrupts by doing a little math (which is illustrated in the sample sketche).

So, kinda cool. I changed out the sense resistor from 0.05ohm to 10ohm so that I get more frequent interrupts.

[alexsh1]

I found this interesting fella

https://www.tindie.com/products/closedcube/tps63030-high-efficient-buck-boost-up-to-96/

Anyone tinkered with tps63030?

[gohan]

It's kind of pricey 😧

[ceech]

@alexsh1 I use it. On this board:
http://www.ebay.com/itm/ATmega328p-board-w-NRF24l01-socket-LTC4079-battery-charger-in-Arduino-PRO-form-/331800929918?ssPageName=STRK:MESE:IT

It works.

[NeverDie]

@alexsh1
Is it any better than:
https://www.openhardware.io/view/276/33v-Buck-Boost-DC-DC-Converter
?

[alexsh1]

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

@alexsh1
Is it any better than:
https://www.openhardware.io/view/276/33v-Buck-Boost-DC-DC-Converter
?

Interesting buck-boost converter, but Input voltage is from 1.8v to 5.5v.
I'm looking at the one with a better range of 0.9-5.5V
I need to use two 2.7V super caps in series with a maximum efficiency

[alexsh1]

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

It's kind of pricey 😧

Not cheap, I agree, but ideally I'm looking to use the whole range from 0 to 5.5V in two 2.7V super caps in series. If you have an idea of a good buck-boost converter outputing 3.3V, I'm all ears

[alexsh1]

@ceech no wonder I like your board. These buck-boost converter works really well with a solar panel

[gohan]

I already have one boost buck converter, I only need the supercap charge controller for 2 supercap or use the 5.5v 4F I have

[alexsh1]

@gohan what's the input voltage for your buck-boost converter?

[gohan]

https://m.aliexpress.com/s/item/32757272432.html

[alexsh1]

@gohan I think it looked at it. I liked the range, but I think it is a noisy one. Did you test it with oscilloscope?

[gohan]

Nope, no oscilloscope available 😇

[NeverDie]

@alexsh1 said in How best to find the "best" small solar panel of a particular size?:

Interesting buck-boost converter, but Input voltage is from 1.8v to 5.5v.
I'm looking at the one with a better range of 0.9-5.5V
I need to use two 2.7V super caps in series with a maximum efficiency

According to its datasheet (http://www.ti.com/product/TPS63030), the TPS63030 has exactly the same Input Voltage Range: 1.8 V to 5.5 V

[ceech]

There is a Maxim integrated buck-boost converter, that goes down to 0.7V
http://www.mouser.com/ds/2/256/MAX1584-MAX1585-43040.pdf
It's quite complex though

[alexsh1]

@NeverDie you are correct - TPS63030 has got 1.8-5.5V input voltage.

I wonder if there is a buck-boost converter with lower than 1V lower voltage?

[alexsh1]

@ceech you bet - personally I'd stick to something much more simple

[NeverDie]

@alexsh1 said in How best to find the "best" small solar panel of a particular size?:

@NeverDie you are correct - TPS63030 has got 1.8-5.5V input voltage.

I wonder if there is a buck-boost converter with lower than 1V lower voltage?

You'd probably get the biggest range by combining a separate boost converter with a separate buck converter, rather than using a single integrated buck-boost unit.

[NeverDie]

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

Well, so far the green supercap isn't holding its charge any better. I'll leave it in-circuit for two or three days, though, and see if that improves. It's encouraging that the rate of voltage decrease is decreasing. Some supercaps apparently improve their ability to retain charge if they are forced to hold a charge long enough, though I have no idea why that is. For instance, some capacitor leakage test protocols call for holding a capacitor at its rated voltage for 72 hours before running the leakage test.

Well, try as I might, I just can't recommend these Chinese supercaps. I've held them at rated voltage for days on end, and I've power cycled them too. For whatever reason, they just don't perform as well as the branded supercaps that I've ordered from Digikey. I'll use-up the few I have on some throw-away prototype experiments, and I won't be ordering any more of them. Presently I think the 10F supercap on Digikey for $2 from Illinois Capacitor continues to be the best of the "value" capacitors. For best performance, I've been pleased with the AVX brand of supercaps.

However, if someone finds something better, either by value or by performance, please do post and let me know.