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

[NeverDie]

I did the experiment of charging one of the green Chinese cheapo capacitors for 3 days at 2.7v, and then I removed it from the circuit and measured its voltage after 3 days with no charging and no load at all. It came out at 2.54v. So, I guess I would deem that use-able.

[alexsh1]

@NeverDie I suppose you broke it in. Try to do a few more cycles (charge / discharge) and see if self discharge improves

[gohan]

It should get a little better after some cycles

[alexsh1]

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

I went ahead and made the switch on the node that I'm experimenting with: I'm now using a LTC3235D 3.3v passthrough boost converter. I switch it on when the node wakes up, do various measurements, then switch it off before transmitting the results if the supercap voltage is above threshold. Everything working smoothly.

I think I may next try putting a buck converter on the solar panel so I can get more juice out of it when its voltage is above 3.3v. I'll be trying this one:
https://www.openhardware.io/view/276/33v-Buck-Boost-DC-DC-Converter
because it's the only one I have on hand. If it seems to help, then I'll look for something more on-point (and less expensive!).

How does LTC3235D compare to BQ25570?
BQ25570 has got buck converter with Vout from 3.3V down to 2V (Vbat is from 5.1 down to 2V), which is just enough to run nrf24l01+ with AVR.

[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