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flat plate capacitor?

Discussion in 'General Electronics Discussion' started by gary, Jan 27, 2010.

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  1. gary

    gary

    3
    0
    Jan 27, 2010
    Main question:
    where can I get flat plate capacitors.?? :eek:
    and secondly, do they come as "electrolytic", "mylar", elc.??

    I need it for a project; a flat (planar) type capacitor, 2200 micofarad, 10 volt. Help.

    thanks,
    gary
     
    Last edited: Jan 27, 2010
  2. Mitchekj

    Mitchekj

    288
    0
    Jan 24, 2010
    Digikey.com or mouser.com should have any cap you need.
    If memory serves, caps that large are usually only found as aluminum or tantalum. You may be able to find a surface mount aluminum with those specs. Is that what you mean by flat? Even so, it will be in a can type package most likely.
     
  3. gary

    gary

    3
    0
    Jan 27, 2010

    Thanks Mitch
    but what is a surface mount?
    What I need is sometimes called a "planar" type....I think it is simply flat parallel plates.

    Gary
    p.s. what do you mean "can type" package?
    Sorry for being so electronically challenged.
     
  4. Mitchekj

    Mitchekj

    288
    0
    Jan 24, 2010
    Hmm. Not sure what exactly they mean by "flat planar type"... are they referring to the plates inside of the cap? Those are flat and planar... if they are referring to a special type of cap called a "planar cap" then I don't believe I've ever seen them.

    Surface mount is just a different way of mounting components to a PCB. (No leads, just solder pads.) Through hole is the common method used for breadboarding, proto boards, etc. Those are the leaded components that go through the board.

    A can type package: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=565-2081-2-ND Not important, I thought you were looking for a surface mount device. :)

    My best guess is you'd need something like this: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P13115-ND

    Again, I'm pretty sure something as large as 2200uF will only be found in an aluminum or tantalum type.

    Sorry if that's not what you needed, maybe someone who knows more about "planar caps" can confirm. A google search for planar capacitors yielded some arrays, but they don't go anywhere near 2200uF.
     
  5. gary

    gary

    3
    0
    Jan 27, 2010
    Thanks agin Mitch; what you told me is very helpful. I am learning something.
    I just found out that there is 'another' version of the schematic which uses a "lower" valued flat plate capacitor, namely, 0.22 microfarad. I guess a electrolytic can be made at that value?? Doesn't electrolytic simply mean the type of material??
    Would that be more common? and more reasonable?...

    More importantly, I guess I don't understand what the difference in value represents operationally.

    So let me explain somewhat the usage. This flat (planar) cap is being used as a "detector" in a circuit (whcih I cannot tell you at this point)....Just suffice it to say, it is suppose to "pick up" a very weak signal from the surrounding environment that impinges upon it.

    So, in that usage, what effect does a v. high capacitance mean verses a LOW capacitance. Does high capacitance simply mean it ALLOWS a greater build up of charge. And if so, does higher Cap mean easier or harder detection of a very weak signal in your opinion.

    Thx,
    Gary

    PS. also, one other question to help eliminate my stupidity:
    What does the voltage rating represent? THe maximum value ? OR does it represent the amount of voltage that must be matched (by the circuit resistance etc.) at the point crossing the capacitor.??
     
    Last edited: Jan 27, 2010
  6. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Voltage rating = maximum continuous voltage.
    Electrolytic capacitor; consists of two etched and oxidized aluminum foils separated by paper and wound tightly into a roll, then moistened with a conductive electrolyte and put into a can and sealed with a rubber bung. The aluminum oxide layer is the insulator, and being very thin it makes the capacitance high.
    A constant current of 1A put into a capacitor of 1F will make the voltage across it rise with 1V/second.
    You can find the formulas on the net for energy [Joules] and charge [Coloumbs] stored in a capacitor.
    There's no such thing made as a flat or planar electrolytic capacitor. You'd have to make it yourself. And for what reason? How can anyone tell you what type or value is best for detecting some mystical signal? What big secret are you going to try to detect? Gravity waves? Go ahead and use any big 'lytic, that's what have been used before.
     
  7. Mitchekj

    Mitchekj

    288
    0
    Jan 24, 2010
    Learning is half the fun. :)

    Electrolytic refers to the type of liquid inside of the cap that acts as a plate. Aluminum Electrolytic, Aluminum... I was referring to the same thing, sorry to confuse you.
    With the 0.22uF, that's usually a really small value for those types of cap. May be able to fin them though.

    You can also look at ceramic, disk caps, etc. That's probably what you'd want to use.

    I'm not certain how they're using caps as detectors... but if it's on the input line in series, it's most likely being used as a coupler. Basically only allowing certain frequencies (or ranges) to pass into the circuit. If the circuit is trying to pick up specific signals at very low levels, then I can see them using something like that to filter out any unwanted 'noise.'

    The impedance (capacitive reactance - basically a resistance) of the cap is based on the capacitance (the amount of farads) and the frequency of the signal. The size of the cap (referring to farads) when comparing high versus low will all depend on the frequency of the signal, and what you're trying to block or pass.

    When used as bulk storage caps (as in switch mode power supplies) the cap comes into an energy storage role. This is not what your circuit is using them as, so far as I can tell.

    The voltage rating on the cap is telling you how much voltage you can put across it without damaging it. A general rule of thumb is to rate your cap at twice the voltage it will see. For instance, if my cap will have 5 volts across it, I will source a 10V rated cap.
     
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