Looking for a capacitor that can withstand a certain RMS current

Discussion in 'The Projects Forum' started by Obanion, Dec 31, 2009.

  1. Obanion

    Thread Starter New Member

    Nov 26, 2009
    24
    0
    Hi guys,

    I'm trying to find a reasonably priced 22uF capacitor that can handle at least 640 mA (RMS) current. I'd be looking for a rating of 100V or higher. This is my first time really dealing with capacitors that have some pretty tight specifics, so I'm not too sure. This capacitor is for the coupling capacitor of a SEPIC converter. I looked at electrolytics first, but it seems that these guys can't take large ripple currents very well; nowhere near the minimum that I require.

    Ceramics seem like the next best route, but they're very expensive! I've temporarily settled on 3 of these guys:
    http://ca.mouser.com/ProductDetail/AVX/SK051E685ZAA/?qs=VXdo/Jq4YRQKVrDwhYLrjg==

    Is this reasonable? I wasn't able to find any information on RMS current capabilities. It seems rather expensive too, but I don't mind spending the money if it's what I really need.

    Just wondering if you had any suggestions on the capacitor selection. I was also wondering if there is a "rule of thumb" for the current handling capabilities of the average ceramic cap.

    Thanks
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    I suspect that I don't understand your question because I've never seen a cap with a current rating. :confused:
     
  3. Obanion

    Thread Starter New Member

    Nov 26, 2009
    24
    0
    I've found a few of the Nichion caps with a specific Arms rating.

    e.g.

    http://products.nichicon.co.jp/en/pdf/XJA043/e-pj.pdf

    I, too, have not been able to find ceramic caps with Arms ratings. Guess it's because most ceramics are probably for low-power applications where the current isn't really going to be a problem.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    You might also consider pulse grade polypropylene film capacitors ...

    An example of this type is found here.

    http://www.filmcapacitor-st.com/cust_EnergyStorage.htm

    There are bound to be many suppliers of this type although I've no idea of cost and availability.

    If you can't obtain the 22uF value you need you could consider paralleling two or three caps of lower value to give the required equivalent.

    What is your operating frequency?
     
  5. Obanion

    Thread Starter New Member

    Nov 26, 2009
    24
    0
    Thanks. Those polypropylene caps seem like the best candidate for the job. I think I
    might go with them. My operating frequency is 100 kHz

    Thanks.
     
  6. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Well I have now, and I should have suspected it with the proliferation of switching power supplies and high current pulse circuits. Unfortunately we don't have an embarrassment smiley.
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    So I don't remain ignorant on this subject, do these caps bare special markings?
     
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