Stop/Start model railway module

Discussion in 'The Projects Forum' started by Tatman, Sep 13, 2013.

  1. Tatman

    Thread Starter New Member

    Sep 13, 2013
    5
    1
    Hi All

    Sorry in advance if the questions below have been answered elsewhere

    I bought some logic delay circuit boards on ebay whic said they could be used to control the power to a model railway and thus I could use them to stop the train at the station by use of read switches. and then after a selected time period start the train again having changed the signals automatically in the mean time.

    However when I came to set it all up there seemed to be no power to the line at all from the module. When checked with the trusty multi-meter it turns out that the module does not provide enough current to drive the model train (approx 500mA needed)

    I know that I need to put a relay between the module output and the power to the line but don't have a clue what relay I need other than a SPST normally closed relay

    The input (switching i presume) details are 2 to 3v @ approx 1mA which will then allow power to the line of 5 to 12v @ max of 500mA

    BTW live in the uk so if anybody can tell me what i need to buy of ebay or Maplins I would be most grateful

    Thanx in Advance

    Steve
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    Do you have an ebay link?
    You may just need to add a power transistor?
    Max.
     
  3. Tatman

    Thread Starter New Member

    Sep 13, 2013
    5
    1
  4. Tatman

    Thread Starter New Member

    Sep 13, 2013
    5
    1
    Must admit I have not a clue about the use of transistors
     
  5. Tatman

    Thread Starter New Member

    Sep 13, 2013
    5
    1
    Just taken Transisitors 101. I think if I use a 2N3906 PNP general purpose amplifier transisitor with a 5v supply, R1 of 1K Ohm connected to the collector and R2 of 10K Ohms between the collector and supply. I should be a happy bunny with a more stable and enduring solution. Thanks for the Tip :)
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The 2N3906 is only rated for 200mA collector current (maximum) - but a more realistic maximum design current is half of that, or 100mA - when the base is supplied 1/10th of the desired collector current. You say you just have a few mA available, so that's not going to cut it.

    Here's a datasheet for the 2N3906:
    http://www.fairchildsemi.com/ds/2N/2N3906.pdf
    Have a look at Page 4, Figure 2. Collector-Emitter Saturation Voltage vs.
    Collector Current.

    You haven't made it clear just how MUCH current is available, and at what VOLTAGE when that much current is flowing out of the "relay".

    In the Ebay listing, it appears that the time-delay "relay" was meant to just control LED lighting, as in aspect signals, crossing signals and the like. LEDs might generate sufficient light with just a couple of mA current flowing through them. You obviously need far more than that.
     
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