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LED Flasher?
I'd like to build a flashing LED strobe for my recumbent bike. Are
there any kits or How-To books I might use? I would like to use several led's mounted on the flag whip with power source and as much components as possible on the frame. Most of what I find are way too big and/or expensive. I have minimal electronics experience but can follow directions and have built some kit radios and similar stuff. |
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Re: The need to know!
Doug Hale
Yes Jim, You've got it.
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Charge(voltage) and Electric field are to a capacitor what Current and Magnitic field are to an inductor. Doug Hale Jim Purcell wrote: Why is as important as What. When If I know a collection of facts but do not |
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Re: vacuum and charge
Doug Hale
Ah ha, finally the source of confusion.
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The charge IS in the plates, the field IS in the dielectric. The charge and the field ARE NOT the same thing. An electric field exists between two opposite charges. Doug Hale manifold wrote: Try this link too. |
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Re: The need to know!
G Ramasubramani
开云体育Jim,
?
??? Liked your mail. Charge is
stored on the plates and the energy in the gap between the plates. This energy
results from the field between the positive and negative charges on the plates.
The dielectric helps in keeping the charge apart. The maximum amount of charge
that can be kept apart depends on the dielectric. In case the amount exceeds
this level, then the dielectric breaks down and the capacitor gets discharged
real fast. The dielectric also helps in chanellising the field between the
plates - this results in different capacitances for different dielectrics if the
area of the plates and the distance between them remains the same.
?
Rama
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Re: vacuum and charge
Ok, here is part of it. This is the part that I remembered about
permitivity and permeability related to the speed of light. Check out this link: 1 ----------- _________ C = / / uo * eo \/ Nothing goes faster than the speed of light in a vacuum so at least we now have the relationship between a constant and another variable. So now I have to answer this question: o Can we have a a situation where the permittity decreases while the permeability increases? still looking... --- In Electronics_101@y..., "manifold" <manifold_1@y...> wrote: No I can't. That one slipped out from memory and not anattributable reference. I will try and find support and you can try and find a < />solidstate/dielect.htmcapacitor. |
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Re: capacitor discharge practices
Jim Purcell
sallehuddin,
U just, connect a resistor parallel to the chargedIt needn't even be a low value. The reason for not just discharging it by shorting the leads is that short circuit current can damage the capacitor, not usually an amount that you will notice but a little. This might be more true of 'lytics. It's a bit like the static on cmos, probably won't kill it but might shorten it's life. Jim |
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The need to know!
Jim Purcell
Why is as important as What. When If I know a collection of facts but do not
understand why they are so, I have no principles that I can apply in order to apprehend other facts. So when struggling to understand something I may appear to be arguing, as in stating that the other person is wrong. While I have been known to do that some times, usually what I'm doing is trying to get my mind around the facts. That I never took college level physics may explain my difficulties, then again maybe not since I don't know to what extent the issue of 'where a charge is stored in a capacitor, might be answered by college level physics, at least as much of it as an EE might take. As a technician I have often had to just accept some premise, not having the knowledge to question them or to verify them for that matter. And being pragmatic I see no problem with that as long is it doesn't interfere with what I may be trying to do. For example, who care which convention is used, current of electron flow as long as we can follow the function of a circuit. Likewise knowing whether a capacitors charge is stored, the plates or the dielectric won't help me understand why the capacitor seems to allow current to flow right through it. In fact I can operate as current does flow though the capacitor and when working with them in actual circuits we assume a capacitor to be an AC short circuit, albeit a frequency sensitive one. All of this leads me to quote from Nigel Cook, DC-AC Second Edition, 1993. In chapter 11, under the summary on capacitance he actually states that the 'charges on the plates produce an electric field...' Sound like he's saying that the charge is stored on the plates. The last sentence in the paragraph states... 'The energy in a capacitor is actually stored in the electric field within the dielectric.' Sounds like it's stored in the dielectric. Now some interpretation which I would be allowed if I were a student reading this book, but which could be mistaken. Nothing new, I've been wrong before and I plan to be wrong again before I go to that great capacitor in the sky to be fully charged for eternity. :-) I think both views may be wrong. The energy is stored in the electrostatic field, not on the plates, not in the dielectric. That certainly would explain why vacuum capacitors can work. It also agrees with my notion that a conductor can't really store a charge. Oh, and this also agrees with the idea that energy is stored in the magnetic field in an inductor, which always seemed strange to me. Am I right, is one of the other view right? I really don't give a poop. But I have an explanation that will satisfy me until someone comes up with a better one. And I feel that I understand capacitors better now. Maybe I'll take one out to dinner some time. Jim |
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Re: Light Activated Alarm
angtengchat
开云体育----- Original Message -----
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Re: newbie inquiry
angtengchat
<<If in doubt use the gloves. :-).
Which brand of gloves would be good ! What must i do to make sure that the gloves is Good / insulated. I am always afraid of electricity. _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at |
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Re: vacuum and charge
No I can't. That one slipped out from memory and not an attributable
reference. I will try and find support and you can try and find a way to refute it! Dang, I'll have to open that physics book yet... --- In Electronics_101@y..., Sunantoro <SUNANTORO@K...> wrote: Mr. Manifold (?)INCREASES the charge stored in a capacitor? I think there must be situationswhere change of dielectric DECREASES it.does not include the value of the permittivity of free space, 8.85 x 10-12farad per meter (F/m). < /> solidstate/dielect.htmcapacitor. Actually, the dielectric always increases the charge stored in acapacitor. |
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Re: vacuum and charge
Sunantoro
Mr. Manifold (?)
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Can you be more specific in stating that dielectric always INCREASES the charge stored in a capacitor? I think there must be situations where change of dielectric DECREASES it. SUNAN -----Original Message-----
From: manifold [SMTP:manifold_1@...] Sent: Tuesday, October 30, 2001 7:28 AM To: Electronics_101@... Subject: [Electronics_101] Re: vacuum and charge Try this link. I think it is a good explaination though it does not include the value of the permittivity of free space, 8.85 x 10-12 farad per meter (F/m). <> solidstate/dielect.htm Yes, the dielectric can increase the charge stored in a capacitor. Actually, the dielectric always increases the charge stored in a capacitor. |
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Re: Capator tester
angtengchat
开云体育<
I have not done this. However a good lead would be
to use the principle of RC constant.
I normally use a simple sanwa multi-meter to check
if a capacitor is still "s".
?
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Re: vacuum and charge
Try this link too.
,,sid9_gci211945,00.html Yes, a vacuum is a dielectric. The dielectric is defined as a "supporter of electrostatic fields". That means, the charge is in the field and the field is in the dielectric and... The charge is in the dielectric. Even if it's a vacuum. Something for nothing, it just doesn't seem right. |
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capacitor discharge practices
I'm reading another basic book to get two points of view plus the little
extras each book kind of offers. All the beginning books warn about cap. discharge, but they don't tell safe methods to discharge them. I would like to hear capacitor discharge practices so I can be safe. |
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Re: newbie inquiry
angtengchat
开云体育
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Re: vacuum and charge
Try this link. I think it is a good explaination though it does not
include the value of the permittivity of free space, 8.85 x 10-12 farad per meter (F/m). solidstate/dielect.htm Yes, the dielectric can increase the charge stored in a capacitor. Actually, the dielectric always increases the charge stored in a capacitor. --- In Electronics_101@y..., Doug Hale <doughale@x> wrote: permittivity of a known asvacuum (or of 'free space'.) It also has an inherent inductance, They arethe permeability of vacuum. These are values you can look up. that mayboth very close to what we find in air at atmospheric pressure. we find inseem. They typically have very small capacitance values, just as betweenair-dielectric capacitors. The air doesn't store the charge in an charge isthe plates and the charge will remain.The air dielectric capacitor is the finest example of why the in the plate, not the dielectric -therefor "the vacuum stores the charge" or that the dielectric is air andsince the air can be blown away, the plate needs to store the charge?charged, one plate has a negative charge and the other plate has a positivedielectric keep the negative charges away from the positive charges?opposing charges on the plates from one another.of air at would below pressures than the one suggested. While a balloon experiment jelly jar.fun, I've done the same thing with a small vacuum pump, my trusty air. One electrode gap inaxis of the Paschen curve plot is the voltage and the other is the curve isthere somewhere (memory fails at times.) It turns out that this for arcfairly linear near atmospheric pressure. The voltage necessary vacuumsinitiation is lowest at a partial vacuum. It rises for very high and for very high pressures.
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Re: newbie inquiry
Keith Messent
IIRC, the dangerous levels are such as would deliver energy of 10 Joules
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along a path through the Heart, i.e. across the Thorax or via Head to Foot. A large capacitance could deliver this! Keith Messent, Skipton, UK ----- Original Message -----
From: Jim Purcell <jpurcell@...> To: <Electronics_101@...> Sent: Monday, 29 October, 2001 05:30 PM Subject: Re: [Electronics_101] Re: newbie inquiry (snipped)You mean you are writing from 'the other side', i.e. you If in doubt use the gloves. :-). If the voltage is less Avoid touching them with both |
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Re: vacuum and charge
Doug Hale
Mark Kinsler wrote:
Vacuum has an inherent dielectric constant, known as the permittivity of a vacuum (or of 'free space'.) It also has an inherent inductance, known as the permeability of vacuum. These are values you can look up. They are both very close to what we find in air at atmospheric pressure.The air dielectric capacitor is the finest example of why the charge is in the plate, not the dielectric - and how do the plates know that the dielectric is a vacuum and therefor "the vacuum stores the charge" or that the dielectric is air and since the air can be blown away, the plate needs to store the charge? It is basic material physics - plates store charge - dielectrics insulate the charges. This leads to another way to explain things. If a capacitor is charged, one plate has a negative charge and the other plate has a positive charge. If the dielectric stored the charge, how does the dielectric keep the negative charges away from the positive charges? That IS the purpose of the dielectric - to insulate the charges opposing charges on the plates from one another. Doug Hale
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