Cheap aliexpress supercapacitors - Page 1
Forum section: electronics / projects

author: BradC
author_rank: Super Contributor
timestamp: February 02, 2025, 08:55:35 am
content: I have a small array of battery powered wireless stuff at home. These are all monitored using a raspberry pi, but being battery powered they tend to boot up with a new address if power is interrupted. Because my monitoring is an awful hack, and I have 6 identical sensors, I tend to hardcode the ID's and have to update them as I replace the batteries.Even the display for my weather station is battery powered, but replacing the batteries means I need to reset the clock and config. Sure, it's only once every 18 months, but still I'm sure we can do better.All these devices use 2 AA batteries so I bought a couple of sets of 0.1F and 0.33F 5.5V supercaps from Aliexpress. Stupidly cheap, no manufacturer data or data sheets. Even if I want to use lithium primary cells, I'm ok for voltage. I've just installed a few in some of the devices, and gee it's nice to be able to replace the batteries without re-configuring anything.I was concerned about leakage and how that might impact battery life. I set up a test rig with my bench power supply and hp3457a to look at leakage. When first charged they tend to leak about 160uA, but after a couple of hours that settles down to ~5-6uA.At $1.30 AUD each, in my hand I really can't complain. Even if the leakage increases over the following years by an order of magnitude I'm still pretty happy with the result for the price. The other advantage is as the alkaline batteries reach end of life the supercap provides more "oomph" for the transmitters, so the signal strength holds up better. I usually get ~9 months once the low battery signal pops up. It'll be interesting to see if this lets me eek out a bit more life.Frankly even if the leakage increases and I have to replace the batteries more frequently, I'm happy to do that as I won't have to reconfigure anything. I avoid and drag out battery replacements as I can't be arsed resetting the config.Edit : A few more hours later and we're down to 1.6uA leakage.

author: bingo600
author_rank: Super Contributor
timestamp: February 02, 2025, 01:41:57 pm
content: Nice ideaHow do you connect to "target" ?Via a resistor or directly on VCC/GND pins ?I have some Lacrosse Temp sensors, that changes ID when i change the battery ....What type did you buy i see V,C & H types here.https://www.aliexpress.com/item/4000868503154.html?Seems more expensive than yours.Any URL ?Can you provide approx sizes of the caps ?/Bingo

author: BradC
author_rank: Super Contributor
timestamp: February 02, 2025, 01:53:14 pm
content: For 0.33F the V caps are 4.6mm thick and 9.8mm diameter.The C caps are 7mm thick and 13.1mm diameter.I searched around until I found them being sold in packs of 5. I bought a V & C in 0.33F and a V in 0.1F. Oddly enough the 0.1 & 0.33F are the same physical size in the V form factor.I bought from here :https://www.aliexpress.com/item/1005003731712022.htmlHuge size difference between the V & C in 0.33F. Not sure why.I just wired them directly in parallel with the battery terminals. I figure alkaline AAs have a relatively high impedance, and these caps seem to have a high enough ESR that I don't imagine running into issues. I did pre-charge the caps before soldering them in.

author: BradC
author_rank: Super Contributor
timestamp: February 04, 2025, 09:46:09 am
content: After 24 hrs at voltage the leakage has dropped below 1uA. I'm pretty happy that isn't going to materially affect battery life. These batteries seem to do between 1 & 3 years depending on the device.