Powering mote 24/7 using only a supercap and solar

[NeverDie]

Am noticing that on Aliexpress you can now get an entire LTC3558 board for about the same price as just the ltc3558 chip on digikey.
https://www.aliexpress.com/item/GY-LTC3588-LTC3588-Energy-Harvester-Breakout-LTC-3588-Energy-Harvest-Collector/32755828984.html?spm=a2g0s.13010208.99999999.277.HJ7HHP

So, for low light energy harvesting, it might be interesting.

[alexsh1]

@neverdie I think the size is a killer for me. I watched Julian's video and also remember this one:

https://www.youtube.com/watch?v=gzaLF5tFf88

Great caps and the price is really good too.

[NeverDie]

@alexsh1 I purchased one of the 700F supercaps after my prior post just to see, and sure enough it has a pretty terrible self-discharge rate: about 0.4-5v per day. With a boost converter, maybe it would be good for powering an LED garden light at night.... Not sure what else it might be good for.

[alexsh1]

@neverdie That's really bad - 0.5V a day. Questionable quality I guess?
I can see that similar capacitor AVX branded is much more expensive:

http://uk.farnell.com/avx/sccy1kb707plble/super-cap-700f-2-7v-weldable-pin/dp/2856928?st=700F

Prices are coming down gradually. I suppose soon enough we may see AVX priced more affordably.

[NeverDie]

Cypress Semiconductor has an interesting energy harvesting chip intended for wireless nodes:
http://www.cypress.com/file/219311/download
The chip looks a little easier to solder than some of them.

[NeverDie]

https://www.openhardware.io/view/620/Supercap-Solar-Charger

[NeverDie]

@neverdie said in Powering mote 24/7 using only a supercap and solar:

I notice Julian Ilett seems to enjoy playing around with these 700F supercapacitors:
https://www.youtube.com/watch?v=B8T9KR3b-RM

Ebay seems to have the lowest price: https://www.ebay.com/itm/1pcs-2-5V-700F-Automobile-Super-Farad-Capacitance-NEW-L85/262714791208?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Anyone here tried them? I'm curious as to their self-discharge rate when they're not being charged.

I charged up this supercap 5 months ago and then set it aside. Checking it now, it still has 0.6v left on it. I thought it would be at zero! So, maybe it really did hold a useful charge for much longer than I thought....(?)

[gohan]

On the cheap supercaps I have they hold the 0.6v, they don't go to zero

[NeverDie]

@gohan said in Powering mote 24/7 using only a supercap and solar:

On the cheap supercaps I have they hold the 0.6v, they don't go to zero

Interesting. So, if we were to put a few high Farad garbage Chinese capacitors in series, using a balance circuit, such that each just holds 0.6v, then I guess we could actually hold a meaningful charge for a very long time? Then, using my new efficient boost converter, we could drain most of the energy out of them:
https://www.openhardware.io/view/628/Efficient-Low-Current-Boost-Converter

[NeverDie]

Apparently the answer is yes:
https://www.youtube.com/watch?v=hQfDqE2AbkI

It also nicely illustrates that what's really needed is charge balancing across supercaps, not merely overcharging protection. Otherwise you are much more limited by the weakest supercap in the series chain of supercaps.

[gohan]

what I meant is that they don't actually go to 0v even if you short them as you will always be able to measure some small voltage. I am no expert but my bet is that that 0.5/0.6v is kind of their bottom line where they don't hold any more useful energy below that.

For balancing there are SAB Mosfets that help to keep all the supercaps on the same voltage, but the reverse charge issue is the same for all series circuits, also LiPo worn out batteries can get to 0V and then getting reverse charged with all the consequent risk of fire.