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philosopherBoi
Phoenix
Joined: Aug 07, 2008
Age: 20
Posts: 1019
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 Posted: Sun Oct 05, 2008 9:57 am Post subject: Capacitors |
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How long can a capacitor store energy for?
Also how much energy is lost of an extended period of time lets say a week?
Is it true that capacitors store energy faster than batteries? |
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x_amount_of_words
Velociraptor
Joined: May 30, 2007
Age: 16
Posts: 484
Location: South Carolina, US
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| Posted: Sun Oct 05, 2008 3:24 pm Post subject: |
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Google may be better for this question.
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Keeno
Phoenix
Joined: Mar 09, 2006
Posts: 1033
Location: Edinburgh, Scotland
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| Posted: Sun Oct 05, 2008 3:58 pm Post subject: |
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Oh, wow. I had a very, very brief special interest in capacitors at one point.
This was just because I went on one of those 3-day work placements that we had in high school, in 3rd year I think (age 14). They put me in a local electronics factory, and in the capacitors section.
I'm surprised that as brief the special interest was, that it came about at all, because I didn't enjoy the placement. |
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pakled
"Bless his Heart"
Joined: Nov 13, 2007
Age: 51
Posts: 3044
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| Posted: Sun Oct 05, 2008 10:18 pm Post subject: |
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long enough. Back in the day, I fixed the occaisional Macintosh (the original), and there was a megohm resistor attached to the monitor (under the nipple on the back). You had to 'unzap' it with a special probe, or it would keel you daid. the power was stored in a capacitor.
It would depend on the brand, capacity (no pun intended), and the overall design of the circuit. i'd make sure you ground things, etc. I'm not an electrician, but I bet there's an EE or just general house wirer floatin' around here. |
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twoshots
Honorary Vertebrate
Joined: Nov 27, 2007
Posts: 2115
Location: NJ
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| Posted: Sun Oct 05, 2008 11:29 pm Post subject: |
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Not very long at all when they're plugged in backwards and given way too much juice...
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Vanilla_Slice
Tufted Titmouse
Joined: Oct 04, 2008
Age: 50
Posts: 27
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| Posted: Mon Oct 06, 2008 4:22 pm Post subject: |
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Good job I know a bit about electronics:
How long can a capacitor store energy for?
This depends on leakage across the terminals and through the dielectric but the larger the value the longer it will hold a charge. Some standard capacitors can store energy for a week or two and the 'super capacitors' can hold a charge for months.
Also how much energy is lost of an extended period of time lets say a week?
See above. This depends on component value and the type of dielectric.
Is it true that capacitors store energy faster than batteries?
Yes, provided you charge them from a low impedence source.
VS |
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Prof_Pretorius
troubled Soul
Joined: Aug 21, 2006
Age: 50
Posts: 4915
Location: Hiding in the attic of the Arkham Library
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| Posted: Mon Oct 06, 2008 8:14 pm Post subject: |
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I've wondered why someone doesn't use large ones in an electric car?
Say the size of a dinner plate, in series. That would give you some quick acceleration, wouldn't it?
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hiker7
Butterfly
Joined: Jul 19, 2008
Age: 48
Posts: 12
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| Posted: Mon Oct 06, 2008 8:44 pm Post subject: |
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Larger electrolytics tend to lose their charge quicker, typically hours to a few days. Some oil capacitors, high voltage types can hold their charge for months, in fact, they can get additional charge from the static in the air. That's why they are usually stored with their terminals shorted together. The discharge rate depends on leakage resistance, call it R. If the capacitance in farads is C, the time constant, where it loses about 63% of its voltage, is Tau. Tau = R * C in seconds. Leakage resistance is usually in the megohms to gigohms. A 10,000uF electrolytic may have resistance as low as a meg, and would discharge in about 3 hours as Tau = 1E+06 ohm * .o1 Farad.
If there is a high voltage capacitor laying around. especially one over a hundred volts, be careful, assume its charged before touching the terminals! You may be in for quite a shock otherwise. |
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ValMikeSmith
Velociraptor
Joined: May 19, 2008
Posts: 488
Location: Stranger in a strange land
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| Posted: Tue Oct 07, 2008 5:11 am Post subject: |
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Many capacitors, especially some of the ones in radios
can charge up and discharge millions of times in a second. |
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Fogman
Econo-class Iconoclast
Joined: Jun 20, 2005
Age: 41
Posts: 2054
Location: SC, USA
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| Posted: Tue Oct 07, 2008 8:40 am Post subject: |
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I have a bunch of tube guitar amps, and it is generally considered that the electrolytic filter caps in the PSU on these take about a week to lose their charge, though it is also recommended that if one has not manually discharged the caps in them prior to a week, it is considered good safety practice to manually discharge them anyways due to the risk of severe shock or even death. -- Filter Caps in a lot of guitar amps store between 400-750 VDC.
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