next topic »

[on:]

Is it possible to use very large capacitors (super capacitors) as a power supply for small projects?  I know that capacitors are used to store charge, and can be utilized to slowly release their charge, but I don't get how .

This is the capacitor I had in mind:

http://www.cutedigi.com/product_info.php?cPath=260_272&products_id=4294&osCsid=ea443abf8844416c173225c297850c57

I had no immediate plans, but that's a pretty good deal for a large capacitor (1F!), and I thought I might as well get it if it could be used to power something small.

I was thinking something along the lines of using a solar cell to put in charge, and then it would continue to work without the sun during the night.  I chose capacitors because of all the problems with overcharging batteries (and I'm no expert), so I don't want things to explode..

Thanks!

[Reply #1 on:]

I chose capacitors because of all the problems with overcharging batteries (and I'm no expert), so I don't want things to explode..

overcharging a cap will make it explode just as quick, if not quicker, its not a way out of making a proper charging circuit

[Reply #2 on:]

Not really possible to use 'super caps' as a power supply for anything but very very small current loads. One big disadvantage is that as you draw current from a cap it's output voltage decreases linearly rather then a near constant voltage as a battery supplies. If you can estimate the current load you have in mind then one can do some math and see if it's possible.

Super caps as a power source have very limited applications. I've seen them used to supply standby voltage for volatile SRAM type memory chips, and stand-by power for real time clocks, etc but other then that they are really limited.

Lefty

[Reply #3 on:]

Alright, well, like I said, I'm no expert .

Thanks for the responses.  I'm seeing that it really wouldn't be practical.

I did not know that the voltage drops, the real reason it wouldn't work for me .

Thanks for the help!

[Reply #4 on:]

Mouser has specs (PDF) on these on their site.

That particular cap is supposed to supply 1.5mA for half an hour.  Good for keeping your real-time clock chip running while you change batteries,  but not even good enough to maintain it during some power outages.

I suspect that they might be good for dramatically upstaging this guy,  if you can borrow a high-speed camera,  though   ;D

Ran

[Reply #5 on:]

overcharging a cap will make it explode just as quick

But a "correct" charging circuit for a capacitor is trivial; a simple constant voltage source (which you probably already have) will do fine in most cases.

In general, even the most modern supercaps have very low energy density compared with batteries.  For 1.5mA at 3V<v<5V for 30 minutes requires about 1.8F, according to one of the vendors' spreadsheets:
http://www.cooperbussmann.com/otherFiles/eeca4652-2ec7-4a1b-9a19-ffa15e4b8694.xls

[Reply #6 on:]

new ones are a different story

http://en.wikipedia.org/wiki/Electric_double-layer_capacitor
http://www.maxwell.com/ultracapacitors/products/index.asp

[Reply #7 on:]

Some reading material for you:

http://en.wikipedia.org/wiki/Solar_Engine


This is a very common method to charge with a solar cell for long periods and then utilize it later on.

Just remember that it is not a battery so 4 hours charge will not give you 4 hours run.  Some of our bots charge for about 5-6 seconds then use that entire energy store in about .25 seconds.

Check out the BEAM robotics crowd.  They do projects like this fairly routinely.
http://en.wikipedia.org/wiki/BEAM_robotics


(One application:
http://www.solarbotics.com/products/k_pp/)

[Reply #8 on:]

Ive been looking at Supercaps too, I found one thats 55F but I think I need to refresh myself on the electronics side as Im having to look stuff up a lot. But there are supercap flashlights you can get and Ive seen a few mods to use them when you look. evilmadscientist had a comp and I think there was one guy who had a single led going for months.

[Reply #9 on:]

What about this?

http://hackaday.com/2005/12/06/supercap-9v-battery/

I understand these wouldnt work too long such as this...

http://www.popsci.com.au/diy/article/2008-02/make-instant-charge-screwdriver

But that seems to be under a bit of load, would an ardiuno and a few other not so heavy use components (umm like say switches, leds, maybe sd card reader?) last a bit longer? If you had say an hour or two of use for example for a 60 second recharge that would be pretty cool depending on the project you made.

[Reply #10 on:]

What about this?

http://hackaday.com/2005/12/06/supercap-9v-battery/

I understand these wouldnt work too long such as this...

http://www.popsci.com.au/diy/article/2008-02/make-instant-charge-screwdriver

But that seems to be under a bit of load, would an ardiuno and a few other not so heavy use components (umm like say switches, leds, maybe sd card reader?) last a bit longer? If you had say an hour or two of use for example for a 60 second recharge that would be pretty cool depending on the project you made.

Indeed.  Thanks for the link. Like others said though, the voltage drops pretty quickly with Caps, but the use of the booster could help .

Too bad the link from Hackaday to the instructions, etc. is broken .

[Reply #11 on:]

Yee of little faith...

http://www.scribd.com/doc/17684600/SuperCap-Battery

I was kinda thinking just the supercap to a 5v booster/regulator (maybe the pololu one - http://www.littlebirdelectronics.com/products/pololu-5v-boost-regulator-ncp1402 or maybe http://www.littlebirdelectronics.com/products/pololu-adjustable-boost-regulator-2-5-9-5v). USB to recharge....

Im building a sort of all purpose handheld tool. I could live with recharging as long as I get a little use, 5 minutes wouldnt be acceptable but say 2 hours or even 4 would be. I think I can fit 1 or 2 55F supercaps with the space im trying to keep to (smaller the better as youd expect but i can make some allowances).