Supercap - Page 1
Forum section: electronics / beginners

author: TRa757
author_rank: Contributor
timestamp: September 03, 2013, 01:28:41 am
content: Hi all,I have a bunch of Cooper Series HB supercaps rated at 110F @ 2.5V and I am curious what would be the best method to charge them. Back in the TV shop days as a kid we would take a radial 450uF @ 100v and plug them straight into the mains. A short duration for a charge and a long duration for smoke and flames. I want to use these supercaps in a automatic chicken coup door with a solar panel to charge them up during the day.Thanks for any advice and, Crikey, keep up the great blog!Tim

author: c4757p
author_rank: Super Contributor
timestamp: September 03, 2013, 01:39:09 am
content: Quote from: TRa757 on September 03, 2013, 01:28:41 am

author: MacAttak
author_rank: Unknown
timestamp: September 03, 2013, 01:46:20 am
content: I'm pretty sure you weren't plugging a naked capacitor of any type directly into AC mainsYou sure there wasn't a rectifier involved somewhere?

author: TRa757
author_rank: Contributor
timestamp: September 03, 2013, 02:57:51 am
content: Buck naked. But then what would you expect from a 13 year old in the early 70's? We (brother and I) did the same thing with diodes and the assorted carbon resisters.So I found a LTC3625 that looks just the ticket for charging a supercap the right (safe) way. Any other ideas?

author: IanB
author_rank: Super Contributor
timestamp: September 03, 2013, 06:02:17 am
content: Supercapacitors are probably the wrong technology for this application. If you used regular rechargeable NiMH batteries you could charge them up in a manner similar to solar garden lights. It would be much simpler and cheaper.However if you do use supercaps the most important thing is not to exceed their specified voltage. So for a 2.5 V cap any regulated 2.5 V supply will be fine. An easy way to do this with a solar panel would be some kind of over voltage bypass or clamping circuit that feeds current round the capacitor when the voltage exceeds 2.5 V, for example a 2.5 V zener diode.You could probably use the LTC3625, but I think it would be overkill for a one-off circuit.

author: dfmischler
author_rank: Frequent Contributor
timestamp: September 03, 2013, 09:09:28 am
content: Quote from: MacAttak on September 03, 2013, 01:46:20 amSure. Didn't you ever take an AC line cord with alligator clips and a box of old electrolytic caps you pulled out of dead TVs and radios to the back yard because you were out of firecrackers? I did. Great fun when you are 12 or so. Much better than resistors or diodes.

author: Zbig
author_rank: Frequent Contributor
timestamp: September 03, 2013, 11:55:06 am
content: Kids at my elementary school were doing the same and we had 220V. They used to put electolytics directly into the mains socket for a while and then zap the girls with them "for fun" (there were no "lolz" back then). I was a weird kid so I already knew it was not exaclty that great of an idea but, well, for some reason they wouldn't listen to me...

author: MacAttak
author_rank: Unknown
timestamp: September 03, 2013, 04:33:33 pm
content: I must be missing something then. No, I never used them as fireworks. I did some stupid stuff as a kid, but always knew to respect electricity after seeing a squirrel instantly get turned inside out by walking on the wrong part of a pole transformer.A capacitor appears as a short to AC, so the explosions are what I would expect as the electrolyte vaporizes and bursts the can open.But holding a charge? What charge is it going to hold? Maybe if you manage to pull it exactly at the cycle peak?And electrolytics are always polarized, aren't they? Driving a polarized cap in reverse destroys it, does it not?

author: Zbig
author_rank: Frequent Contributor
timestamp: September 03, 2013, 05:17:20 pm
content: Quote from: MacAttak on September 03, 2013, 04:33:33 pmIf it's beefy enough, chances are mains AC won't destroy it immediately and relatively low 50/60Hz frequency won't make it appear as a straight short but I think I vaguely remember a kid actually tripping the breakers this way. And of course there's no chance that AC did any good to those polarized electrolytics but they tended to survive for one or two "pranks". It's not as if those punks were to build a radio with them afterwards, anywayAnd of course you're right the caps (luckily!) were not able to charge fully and the whole thing was a bit of a hit or miss approach, depending on when they managed to pull them out during the AC cycle.

author: G7PSK
author_rank: Super Contributor
timestamp: September 03, 2013, 05:24:23 pm
content: As a 13 year old at school I had an old oil filled HT capacitor from a TV ( a maroon colored cylinder about 5 inches high and two inch diameter with a bras stud top and bottom) it would take a charge just by holding it close to a fluorescent lamp and then give you a nasty shock if you were stupid enough to touch both ends and most of my peers at that time were, trying to prove how tough they were.

author: TRa757
author_rank: Contributor
timestamp: September 03, 2013, 09:25:26 pm
content: We would plug our rather large electrolytic caps into a power strip and either cycle the power switch for a quick charge and just flipped it and ran for the explosions. All this was done, of course, while dad was on service calls. We would also charge up a cap and the toss it to some unsuspecting new employee encouraging the "catch it". The guys that would catch it were usually the ones that spent hours searching for the Areivasack transformer in a tv so they could replace it. Oh to be young again.BTW, that is a reasonable charge current for a 110F 2.5v super cap?I finally found a document that states max charge current is Charge volatage / device impedance. I'll give it a go!

author: nukie
author_rank: Frequent Contributor
timestamp: September 03, 2013, 10:42:05 pm
content: Nothing, if your worried about your powersupply then put a current limiting resistor. Just make sure you don't go over 2.5v

author: edavid
author_rank: Super Contributor
timestamp: September 03, 2013, 11:27:08 pm
content: Quote from: TRa757 on September 03, 2013, 01:28:41 amSince those caps go for $46 each, maybe the thing to do is sell them and use the money to pay a neighbor's child to open the door.

author: ivan747
author_rank: Super Contributor
timestamp: September 04, 2013, 02:32:37 am
content: Quote from: edavid on September 03, 2013, 11:27:08 pmOr buy 5000ft worth of cable, a solenoid and a switch.

author: TRa757
author_rank: Contributor
timestamp: September 04, 2013, 03:33:54 am
content: Yeah, they are pricey units, but the scrap pile is always very good to me at work. I pull these out of storage controllers all the time and have a large pile of them, so no worries about the price.I have a 5V supply charging through a 100ohm resister across a pair in series. They come in a pair with a temp sensor in the bundle. I noticed one went negative (bad) and the other was at .5v so I charged the negative cap from -.2v to +.5 and then started charging the pair to 5v. They were charging fairly quickly but have slowed way down and are at 4.7 volts. I will stop the charging at 5 volts and then see how long the pair will power my chicken door actuator. I have heard they will power an arduino for weeks so fingers crossed!