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Most reliable relay? — Parallax Forums

Most reliable relay?

ArchiverArchiver Posts: 46,084
edited 2003-01-01 22:23 in General Discussion
Hi All,

I am working on a temperature minder/ backup heater/ overheat over-ride/ for
my aquarium. In normal operation, the Stamp will monitor the temp and
override the heater if required, or turn on the backup heater. In case of
the Stamp failing, I want to have the heater revert to it's independent
operation. So my plan is to have a relay held or latched closed by the
Stamp, then if the Stamp dies, the relay will open and allow the heater to
resume independent operation. So my question is, what is the most rock solid
reliable relay I can use? Assuming the Stamp doesn't fail, the relay will be
in continuous operation for years, and of course with an aquarium,
relaibility is paramount.

Thanks!

Jonathan

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2002-12-28 15:32
    Jonathan, take a look at Digikey 255-1002. This is a 12V realy, DPDT, that
    will plug into an 8-pin DIP. I have been using them for my model train under
    very severe conditions, and have had no problems. Contacts are rated at 1
    amp, but with them wired in parallel it will handle 2 amps.

    By sever service I mean this - when I start one of my trains up, the relay
    will pulse at 20ms intervals for over a thousand times. This happens
    everytime I start or stop the train. Relay sounds like a buzzer!!



    Sid Weaver
    W4EKQ
    Port Richey, FL


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2002-12-28 17:11
    Jonathan,

    I don't think I'd worry yourself too much about this aspect of your
    project. As long as you pick out a relay that has contacts rated
    above the amount of amps you will switch with it, you should be
    fine. The most common relay failure I have seen is an open coil, in
    which case the relay will not pick up at all. Second would be that
    the relay picks up but the contacts do not close due to some
    obstruction, such as dirt. It's possible that you could
    actually 'weld' the contacts closed if you try to switch excessive
    amounts of current. I have seen this only on very large relays such
    as those used for industrial crane control. In that application you
    are switching very high amounts of current for hundreds (if not
    thousands) of iterations in an 8 hour period. Your relays also have
    some amount of spring tension on the contacts which force them
    apart. The tension is set so that the closing coil can overcome the
    spring tension and close the contacts, but enough that the contacts
    are pushed apart quickly when the coil drops out.

    Ron


    --- In basicstamps@yahoogroups.com, "Jonathan Peakall"
    <jpeakall@m...> wrote:
    > Hi All,
    >
    > I am working on a temperature minder/ backup heater/ overheat over-
    ride/ for
    > my aquarium. In normal operation, the Stamp will monitor the temp
    and
    > override the heater if required, or turn on the backup heater. In
    case of
    > the Stamp failing, I want to have the heater revert to it's
    independent
    > operation. So my plan is to have a relay held or latched closed by
    the
    > Stamp, then if the Stamp dies, the relay will open and allow the
    heater to
    > resume independent operation. So my question is, what is the most
    rock solid
    > reliable relay I can use? Assuming the Stamp doesn't fail, the
    relay will be
    > in continuous operation for years, and of course with an aquarium,
    > relaibility is paramount.
    >
    > Thanks!
    >
    > Jonathan
  • ArchiverArchiver Posts: 46,084
    edited 2002-12-29 00:18
    most reliable relay ?

    any name brand unit. get one that is low coil wattage so you are not
    heating it up too much, power it for the proper voltage and current
    rating.

    Life of coils is measured in number of closures, not life of coil, so
    your infrequent coil closure is not going to effect the life.

    The relay Sid listed is small, very unobtrusive and has a closure
    rating of like a million closures. Hard to beat that.

    Also, the minature unit will have a low power drain meaning low
    heat. also good for longer life.

    Dave





    --- In basicstamps@yahoogroups.com, "Jonathan Peakall"
    <jpeakall@m...> wrote:
    > Hi All,
    >
    > I am working on a temperature minder/ backup heater/ overheat over-
    ride/ for
    > my aquarium. In normal operation, the Stamp will monitor the temp
    and
    > override the heater if required, or turn on the backup heater. In
    case of
    > the Stamp failing, I want to have the heater revert to it's
    independent
    > operation. So my plan is to have a relay held or latched closed by
    the
    > Stamp, then if the Stamp dies, the relay will open and allow the
    heater to
    > resume independent operation. So my question is, what is the most
    rock solid
    > reliable relay I can use? Assuming the Stamp doesn't fail, the
    relay will be
    > in continuous operation for years, and of course with an aquarium,
    > relaibility is paramount.
    >
    > Thanks!
    >
    > Jonathan
  • ArchiverArchiver Posts: 46,084
    edited 2003-01-01 22:23
    There is no guarantee that the relay will drop should the Stamp fail.
    It is very likely that the Stamp may get "glitched" and your program
    stops executing while the relay is still picked.
    At the very least you should consider adding a "I'm alive" indicator
    such as a slowly blinking LED under software control. If the LED
    stops blinking you will know that your program has stopped. I would
    also suggest adding several buttons which will initiate failure
    events so that you can verify from time to time that all will go as
    planned.

    Hal
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