Please help me find a relay?

Discussion in 'Model Rail Operations' started by geb, Jul 9, 2008.

  1. geb

    geb New Member

    I'm going crazy. I need an 'impulse latching' relay. That is to say, one that latches (preferably magnetically) and switches states via a SINGLE input.
    Here is an example of exactly what I need..
    except that it is about six times too large for my application.

    Does ANYONE (excuse the shouting, but I'm that frustrated) make a smaller version of this?

    For a variety of reasons, I'd prefer to do this electromechanically. I'd rather not use a dedicated pcb flip flop circuit... cmos, 555 timers, transitor arrays, etc.

    If I'm forced to, I will jerry rig a little push solenoid and a miniature latching pushbutton, but I'd so much rather use a well manufactured unit. Contact rating is unimportant... if it's compact enough, I can use it to trigger an endless assortment of miniature relays available with any contact rating I want.

    I am just ASTOUNDED that I cannot find this animal!!! Can anyone help?

    Thanks so much.
  2. ezdays

    ezdays Out AZ way

    To start with, welcome to the Gauge train forums.

    Secondly, that's a stiff requirment for a latching relay, less than .5" square, I don't know of one on the market, even with a much lower contact rating. I'll check some of my resources and let you know, but I doubt that any relay as small as you're looking for will have a contact rating of over one amp.
  3. geb

    geb New Member

    ezdays thank you for getting back to me.

    I've actually located dozens and dozens of pcb sized latching relays.
    Here is an example.. the third and fifth on the following page.
    .. and contact rating is unimportant.

    All that would be required in that form/size is a miniature latching mechanism (similar to that in a retractable pen or a latching pushswitch) contained within. I've heard that they were actually more commonly available until microcontrollers became so prevalent. Relay manufacturers simply phased them out.

    I'm hoping I can find that one manufacturer who still makes one.
    ... or a more elegant workaround than I've found thusfar on the web.
    ..for example..


    Good lord! This is the simplest answer for electromechanically emulating a push on/off switch? Even with this I'd have to add a fourth relay just to get an isolated dpdt for my 120 legs! Why on earth would anyone have conceived this webpage when (now that they've bulked up to three 3PDT relays) they might just as easily have purchased the tyco version I linked above?
  4. lester perry

    lester perry Active Member

    Now I know very little about electronics stuff. but I have used magnetic latching reed switches for a lot of things. Maybe I am missing something but this seems rather simple.
  5. geb

    geb New Member

    Lester Hi,

    Your mag latching reed switch is incapable of performing the trick I'm looking for. If it is single pole dual throw, it can switch signal x over to y, and x back again to z ad infinitum. It can latch either of those conditions without requiring constant current to hold the armature (the magnet does this trick). So far so good.

    BUT, the relay we've just described cannot use a single source/button/signal on pole x to switch from y to z and back again. Every magnetic (or even mechanical) relay made requires two SEPARATE signals, either reversed polarity (in the case of single coil relays) or an entirely separate signal/input (as is the case with dual coil relays).

    Try to imagine using a single momentary pushbutton to switch a SPDT (or dpdt or 5pdt or whatever) from one side to the other. It cannot be done.
    Or rather it cannot be done without some mechanism either mechanical or circuit driven that performs this trick internally.

    I finally did order the Magnecraft 711 series. It has a circuitboard inside dedicated to switching the polarity of the input each time it is received. Somehow they built it so that it retains its setting regardless of whether the board is powered or not. Interesting trick. Don't know how they did it but I have it in hand finally on my workbench and it indeed works as I want it to. Bonus that with the plastic housing removed it is quite compact enough to suit my needs.

    But I don't blame you for having a difficult time getting your head around this. Apparently this is highly esoteric stuff (or so you'd think from all the blank looks I got while searching for it. My hunch is that if more guys understood this little relay, magnecraft would sell millions of them. The 711 performs a trick that is usually gotten around using much more complicated means.

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