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Time delay assistance

Discussion in 'General Electronics Discussion' started by wutang43, Dec 25, 2013.

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  1. wutang43


    Dec 25, 2013

    I'm new to this forum and to electronics in general so bear with me...

    I'm a civil engineering student working in a lab on campus, and for an experiment that we're running next quarter, we need to create a device that will release charge at a given time interval (say, every 10 seconds or so) for up to 24 hours at a time.

    Now, charging up a 100v, 1000uf capacitor to 10 A using a standard DC power supply, and then touching each end of the capacitor to each end of this copper coil that we had, seemed to provide enough power to drive the experiment that we're trying to run (we're essentially creating an electromagnetic hammer--there's a small piece of iron inside a tube which is wrapped in copper wire, and the iron bounces up and then down when the charge is released from the capacitor into the copper wire).

    So that would be fine, except I need to automate this process so that I can attach a constantly charged capacitor to the copper coil, and have it discharge at a given time interval, and then recharge, discharge, etc for about a day. From reading things online, it appears to me that a programmable time delay relay would do the trick. However, most of the ones I've seen only allow ~16 different on/offs per day.

    So, I was hoping that someone here could recommend some type of device that would allow me to automate this process, or if I'm barking up the wrong tree, then hopefully point me in the right direction. I'm hoping not to spend too much money on this, though the professor I work for has allotted a couple hundred bucks to build this, so anything within that price range would be acceptable.

    Many thanks!
  2. Laplace


    Apr 4, 2010
    I would recommend using a 555 timer driving a high-voltage SPDT power switching relay. More likely the 555 timer output will drive a switching transistor and the transistor will drive the relay coil. One relay throw charges the capacitor, the other throw discharges it. Go with the relay for simplicity. There are high-voltage power MOSFETs that would provide a more elegant solution, and would give years of reliable operation. But you only need this to operate for a day so a relay should last for one day even if you don't properly snub the contact points.

    Now if you were in mechanical instead of civil engineering, I would recommend using a gearmotor driving a cam at one revolution per 10 seconds, and having the cam open & close a set of old style automotive ignition points to switch the capacitor.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    In an application such as this, an IGBT may be better suited as they tend to have a constant voltage drop and opposed to constant current characteristics under high loads.
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