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two capacitors in series = double the uF? :S I need help to make this fun circuit!:P

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  • two capacitors in series = double the uF? :S I need help to make this fun circuit!:P

    Im a little confused.

    Im trying to make a relay turn on (once it gets power) and stay on for 3 seconds then shut off.

    I got it working with a 4700uF capacitor but it didnt last for long and stopped working...

    I went to buy some resistors and all I could find were 22K resistors, so i put two in parallel to get 11K for the circuit on the12volt.com ( http://www.the12volt.com/relays/page5.asp#ctm )

    But the circuit only works once or twice, and only for about 1/2 a second, i tihnk the resistors are not what I need...

    Is there a way to get a longer connection (possibly 2.5 seconds) with the stuff I have?

    I have 3 - 4700uF capacitors, 2 - 680uF, 1 - 47uF, and a few resistors @ 22K, about 5 @ 1K


    Thanks for any help, its greatly apprechiated!

  • #2
    Capacitors add in parallel. If you put two in series you would get less capacitance. Hooking them up in parallel you will simply add the capacitances.

    I've never dealt with relays, but in general a delay with that set up will be on the order of the product of the resistance and capacitance (RxC). Increasing R or C will increase the delay. Try more caps in parallel, or remove one of your parallel resistors.
    MII-12000 / Ampie / Lilliput 7" / BU-355 / PicoPSU / uSDC
    Currently: Enjoying the setup, but always contemplating my next move...

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    • #3
      Originally posted by rsd212
      Capacitors add in parallel. If you put two in series you would get less capacitance. Hooking them up in parallel you will simply add the capacitances.

      I've never dealt with relays, but in general a delay with that set up will be on the order of the product of the resistance and capacitance (RxC). Increasing R or C will increase the delay. Try more caps in parallel, or remove one of your parallel resistors.
      Thanks for your help. Ill try that in a hour when i go back in the garage.

      I heard that if theres too much resistance the cap will be rendered almost useless, is this true?

      I had tried the caps in series but not in parallel..

      Thanks for your help

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      • #4
        ok so i tried putting the capacitors in parallel, it worked, i was able to get about 1 second, im going to look around for some more capacitors to see if i can get something going here...

        Only problem is it works once, and only works again once the caps have lost their charge...

        Any ideas on what could be causing this?

        Also, i tried w/ and w/o the two reisistors in parallel and it didnt change anything...

        Any ideas?

        Thanks

        Comment


        • #5
          Increasing the capacitance will cause it to take longer to discharge, thus longer before you can re-trigger. You could try less resistance (more current discharging from the caps), but like I said, would probably decrease delay. You may just need a more sophisticated circuit, a transistor circuit triggered by the momentary 12V that will cause the caps to discharge through a low resistance when the relay is off. If you cant get anything to work, I can sketch something, but again, I've never actually *used* a relay before, just going off electronics knowledge.
          MII-12000 / Ampie / Lilliput 7" / BU-355 / PicoPSU / uSDC
          Currently: Enjoying the setup, but always contemplating my next move...

          Comment


          • #6
            I have attached a diagram with a simple timer circuit. You might wanna make that capacitor a variable one to be able to set the time the relay stays on. R1 is the charging resistor, R2 and R3 are discharge resistors but bear in mind that R2 also "steals" some current from the line when charging capacitor so it does influence the duration of the charge. Although you can calculate the time necessary for the capacitor to charge (time in seconds = resistance in ohms x capacitance in farads) it's better if you try them practically; it might get you there faster.
            Hope this helps.
            Attached Files
            Why drink and drive when you can smoke and fly ?

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            • #7
              Thanks for your reply kronos

              I tried but that didnt work.

              I went in the house and found some 100ohm resisitors, i wired 3 up in series and put it between the caps in parallel, everything works now, i put everything on a piece of MDF and hot glued it. now when ever i put power to the inverter it turns on by itself!

              thanks a lot everyone!!!

              (its now 5:15 AM, i work soon )

              Take care ppl

              Comment


              • #8
                this is what the 555 timer is used for... it is REALLY cheap and REALLY easy to use, the diagram is on the back of the box... there are TONS of examples all over the web... you will be able to dial in EXACTLY the time you are looking for...
                EPIA SP13000, 512 DDR400, Seagate 300GB, Belkin PCI 802.11g w/external antenna, Holux GM-210 GPS, XM Direct w/ serial, Dlink FM, Opus 120 p\s, Rockford P4004 amp, Xenarc 7" VGA touchscreen custom mounted in double din spot -- see pics and write up here!!

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