Capacitor Discharge unit

Discussion in 'FAQs' started by Xaniel, Jan 3, 2004.

  1. Xaniel

    Xaniel Member

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    Hi there,

    Should a Capacitor discharge unit be dedicated to a single turnout, or can it be used for several turnouts?

    Don0t know if i've explained my slef correctly.

    Thanks in advance.
  2. shamus

    shamus Registered Member

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    Hi,
    One Capacitor discharge unit will handle as many turnouts that you have, will also be powerful enough to throw more than one turnout at a time, if you use a 24volt transformer to power it.
    I use mine to throw three points(Turnouts) together.
    Shamus
    [​IMG]
  3. Xaniel

    Xaniel Member

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    I'm planning to use the M1 Gaugemaster Transformer wich have 2x 16v. AC. Is that enough with a CDU to throw my turnouts?
  4. shamus

    shamus Registered Member

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    Better off using as I stated before, (24volt for the CDU)
    Shamus
    [​IMG]
  5. Xaniel

    Xaniel Member

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    Even if it is to throw only one turnout at each time?
  6. shamus

    shamus Registered Member

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    Yes
    Shamus
    [​IMG]
  7. Lightbender

    Lightbender Member

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    Hello Luis,

    By CDU do you mean you have a box that does this or have you made your own? I ask because it should be powered by a DC source.
  8. 60103

    60103 Pooh Bah

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    Luis:
    I use mine on a power pack or Lionel transformer, which means I use about 14V AC. I find that I sometimes have problems where I'm trying to throw 2 different makes of switch machines, usually new Peco plus an old Hammant and Morgan (really big things). One of them seems to absorb all the current, but a second touch throws the second machine. Two or more of the same isn't a problem.
    Now how do I get 24 volts?
  9. jon-monon

    jon-monon Active Member

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    I think a cheap doorbell transformer will give you 28 VAC, good enough for government work. Or is it 24?
  10. shamus

    shamus Registered Member

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    When you buy a CDU, the makers (Of mine and those I have used in the past) recommend that you use 24volts AC to power it. It is also AC and not DC which is required to throw a point motor such as Peco PL10 or even the old HM (large ones).
    Shamus
    [​IMG]
  11. ezdays

    ezdays Out AZ way

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    OK, I can't contain myself any longer. Just what is the purpose of a CDU and could someone please explain just how it works in an AC circuit? A capacitor stores energy, just like a battery and can only store DC. In order for it to work in an AC enviroment, it would need a rectifier to convert the AC input to DC, then another circuit to convert back to AC to operate the equipment. What's the point? What is being gained here that I don't understand?:confused: :confused: :confused: :confused:
    Don
  12. hawkeye2

    hawkeye2 New Member

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    ezdays,
    You are right concerning capicators, they require DC to charge. In an AC circuit a capicator adds inductance, won't charge and therefore won't discharge. A commercial CDU may well require AC and rectify it to charge the capicators. About 30 years ago I put together a CDU for a friend's RR. It was powered by fixed AC from a power pack rectified. I went to Radio Shack, bought some diodes and a bag of capicators, went home and started soldering. I added capicators till all the switchs I could activate w/ both hands sounded like one big click. Worked fine and cost about $3 then.

    Doug
  13. hawkeye2

    hawkeye2 New Member

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    My train of thought was derailed and I left out the following. Common twin coil switch machines are solenoids (electromganets) and work best w/ DC. They are intended only for momentary use and will burn out if power is applied continuously. A CDU provides a brief burst of DC to activate the switch machine (not to be used w/ motor driven switch machines). The greater the burst of current sent through the coil the faster and more positive its action is. This burst of current helps overcome bad connetions, dirt in the tunout, and inertia of the switch components.

    Doug
  14. ezdays

    ezdays Out AZ way

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    It was my thought that the objective was to get a short, high current spike to operate the solenoids. I am use to relays and solenoids that have coils wound specifically to operate either AC or DC and continously. I can vouch for the senitivity of switch machines. :oops:

    Now, just as a matter of interest, a full wave bridge rectifier (four diodes) will produce a DC output regardless of whether the input to the rectifier is AC or DC. To be sure, one cannot get the polarity reversed even though the input is DC.:rolleyes: :D

    The other thing that concerns me is that the duration of the output is dependent on the load, or the number of switches. I'm sure this must be taken into account by those that use them, but I'm kinda shooting from the hip since I've never heard of these devices used like this until now. So forgive me for asking such basic questions....:)

    Don
  15. shamus

    shamus Registered Member

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    CAPACITOR DISCHARGE UNIT
    For operating heavy duty point motors
    The unit stores up power in capacitors and when a point
    motor is actuated, discharges in one big punch giving the
    point motor a firm and positive switching action. Connected
    to points via switches or probe and studs. Prevents burnt
    out motors.
    Input: 16v to 24v A.C. at a maximum of 2.5 amps
    Recommend Gaugemaster T3.
    Here's a photo of one,from:-
    http://www.gaugemaster.co.uk/access.html

    shamus
    [​IMG]

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  16. ezdays

    ezdays Out AZ way

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    Thank you Paul, it's starting to become clearer. I guess I need to know just what a "point motor" is before I really understand what's going on here. It appears from the picture and description that the CDU is a half-wave rectifier, and regulator and a couple of capacitors and the output is a large shot of DC current.

    What I said about using DC as an input still holds true, just that you need to observe the right polarity in this case. Not that anyone would ever want to, just that it will work if they do.:) The second point I mentioned is that the amount of time the output is present is dependent on the load. Energy is equal to the power (volt-amps) times the time. The higher the load, the higher the current and the shorted the discharge time. So I guess I really would like to know the application, or what a point motor is/does so I know if this is even worth bringing up.

    I'm not trying to turn a simple problem into a complex one, I'm just trying to understand it better.:rolleyes: :rolleyes: I guess I've lived a sheltered and boring life to think this way. Most engineers do...:D :D

    Don
  17. Lightbender

    Lightbender Member

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    Hello Don,

    Simple twin coil point motors will work with either AC or DC because they have the 2 coils at each end of the actuating rod. A single coil motor would be mounted in the centre and would require DC only and would work by reversing power. Nobody makes these.

    I have a few beer can sized caps and built my own CDU with one of them. The unit I made plugs into the wall for 120v AC and provides 12v DC with a fearsome whallop.

    The unit that Shamus showed us with a 16v input would deliver a similar 12v DC but with 24v input it could be as high as 20v DC. A higher voltage is very handy if you are sending over thin wire or great distance
  18. 60103

    60103 Pooh Bah

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    Don, being biligual (Brit + Yank), I can tell you that a "point motor" is also a "switch machine". In Britain turnouts are labelled "points", because that is the bit that most railwaymen are concerned with, the little wiggly bits that change the train's route.
    The CDU gives you a number of features -- large current, short duration and DC output. The DC allows you to cascade switch machines using diodes (diode matrix) to set a route that has a bunch of switches with one motion. Disadvantage is that it takes a bit of time to recharge. Lots of fun if several of you are working from the same CDU.
  19. RailRon

    RailRon Active Member

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    Here's an example of a CDU I built out of almost nothing: 1 capacitor and four diodes for the bridge rectifier.

    It is fed from an old power pack with 15 V AC

    Ron

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  20. RailRon

    RailRon Active Member

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    And here is the complete setup with the control panel at left and the powerpack at right.

    This CDU has power enough to shoot four PECO switch machines at once without any problems.

    Ron