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Searching for an unusual relay

Discussion in 'Electronic Design' started by Robert, Mar 9, 2009.

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  1. Robert

    Robert Guest

    Hello everyone,

    Once again, a scavenger hunt is at the top of the list. As an employee,
    some decisions are handed to me.

    In times long past, I have seen relays whose coil was wound with fewer
    turns and heavier wire. The coil, wired in series with a load, pulls the
    contacts when the current is above some level. What is such a relay
    called? Does anyone still make such things?

    Have a good day,
    Robert H.
     
  2. delo

    delo Guest

    try "amperometric relay"

    bye
    delo
     
  3. current relay
    yes. Industrial suppliers have them, e.g., McMaster-Carr, MSC. Maybe
    electronics suppliers.

    Bob
     
  4. JeffM

    JeffM Guest

    AC or DC?
    Would a COTS item be OK?
    http://groups.google.com/group/sci....000-watts+zz-zz+*-adjustment-range-is-limited
    http://groups.google.com/group/sci....+current-operated-switch+qq-qq+current.relays
    http://groups.google.com/group/sci....ints-for-each-set-of-contacts+Neilsen-Kuljian
     
  5. Carling calls it 'Shunt Trip' although they may not use it as a current
    trip, just a voltage trip.

    Cheers
     
  6. Robert

    Robert Guest

    AC

    COTS ( Common Off The Shelf ) would be wonderful.

    Looked at the URLs.

    URL 1 Smart Power Strip

    Several outlets are switched on and off with the current drawn from a control outlet.



    URL 2 Current operated switch


    Digikey 582-1020-ND $24 and a $30 SSR would get me there.
    There is a problem with the ambient temperature of 70 or 80 C that has been handed to me
    and most solid state devices. That is why the current driven relay came to mind.



    James Sweet typed: "You can get current relays from HVAC surplus type places, they're
    just a relay wound with a heavy wire designed to carry the load current, the relay
    closes when current flows through the coil. I think I paid $2 for the one I bought,
    you could probably rewind the stator of an AC relay with some #12 enameled wire in a pinch too."

    This is the kind of thing I remembered.

    URL 3 Current Operated Switch The URL mentioned is not in working order.



    Thanks for the leads. The hunt continues.

    Robert H.
     
  7. Eeyore

    Eeyore Guest

    I always thought it was 'commercial off the shelf' but maybe that's just the military etc or another usage has been found for the term embodying the same concept ?

    Graham
     
  8. Robert

    Robert Guest

    Common was just what came to mind. Commercial would also fit.

    Wikipedia says it is commercial.
    http://en.wikipedia.org/wiki/Commercial_off-the-shelf

    It is good when others keep me honest.

    Robert H.
     
  9. Robert

    Robert Guest

    Some off topic thoughts:

    I am not shure what to make of your style. Twice you have posted a list of
    URLs and twice I have looked at them. They seam to be getting a bit off
    topic. Your last post seams to ask for more information to use in
    "crafting a response". Please allow me to help you clarify your response
    crafting. I did ask the question I intended to ask. I am also aware that
    the thecnology has moved forward and that the electromechanical device
    asked about is no longer current. If you have something on topic to put
    forward, please do so. I am shure you will post anything you chose to.
    You would be wist not to expect me to follow every URL you choose to post.

    Back on topic:

    The electromechanical I asked about would provide a 1-device solution.

    Happy posting,
    Robert H.
     
  10. JeffM

    JeffM Guest

    For a moment at the start of the thread,
    I thought you were the Robert H who designs chips.
    You couldn't be farther away from his skill set.

    The point of my last series of links was:
    YOU are not the first clueless person to post to an engineering group.
    The *first* step in a technical undertaking is
    WRITE A SPECIFICATION.

    This link was the the one you should have investigated
    --and still should:
    http://google.com/search?q=intitle:...olerance+OR+tolerances+-dimension+-0471618928

    How do you expect to us to help you find something
    when you have only given the most VAGUE idea of what you want?

    If there was a point you SHOULD have gleaned from my links,
    that was the part that said
    **put.numbers.on.as.many.things.as.possible**.
    I had to drag out of you whether it was even AC or DC.

    Here are some specs that are still unstated:

    Volts on the coil / actuating circuit?
    Actuating level of current in the coil / actuating circuit?
    Dropout current? (Hysteresis)
    Maximum current in the coil / actuating circuit? (if different)

    Maximum current to the load?
    Volts on the load?
    What is the level of isolation needed
    between the actuation side and the load side?
    What is the nature of the load? (Is it inductive?)
    How fast does the thing have to respond?

    NOW go back to my links and see if you can make sense of them.
    ....and?
     
  11. Robert

    Robert Guest

    Good morning,

    Most of the overload relays I looked at are thermal. When heated a set of
    contacts open. This works fine for shutting down when aced with a
    sustained overload. I needed contacts that opened when the current, or
    heating, fell too low. Compared to the usual power power levels for such
    devices, mine are quite low. I deeded to switch at less than an amp.

    Fortunately, those in control have backed away from 80 C ambient. I am
    back into a temperatur range that can be met with commonly available items.
    An electronic current sensor, a relay to handle the load, and a momentary
    switch to get things started.

    Having explained the application many times, I may not have done so here.
    Unfocused conversations and corispondance eats up a lot of time. A small
    motor with internal, automatically resetting, thermal protection has been
    used for a long time. The hazard of having it restart is now understood.
    A field installable way of requiring operator intervention for a restart is
    needed. When a requirement of 80 C ambient was added, an electromechanical
    device came to mind. While they may have been common at one time, that
    time has past.

    I offer my thanks to those who offered thoughts and information on this
    subject. While ranking the responses is inappropriate, the term
    amperometric does stand out.

    A good day to all,
    Robert H.
     
  12. Ross Herbert

    Ross Herbert Guest

    ::
    :<snip>
    :> About the only thing still available that is close is what is called
    :> an overload relay. The coil is typically in series with the load
    :> device and is supposed to pull in when that device is overloaded. As
    :> for meeting the rest of your design criteria, i have not a clue.
    :
    :Good morning,
    :
    :Most of the overload relays I looked at are thermal. When heated a set of
    :contacts open. This works fine for shutting down when aced with a
    :sustained overload. I needed contacts that opened when the current, or
    :heating, fell too low. Compared to the usual power power levels for such
    :devices, mine are quite low. I deeded to switch at less than an amp.
    :
    :Fortunately, those in control have backed away from 80 C ambient. I am
    :back into a temperatur range that can be met with commonly available items.
    :An electronic current sensor, a relay to handle the load, and a momentary
    :switch to get things started.
    :
    :Having explained the application many times, I may not have done so here.
    :Unfocused conversations and corispondance eats up a lot of time. A small
    :motor with internal, automatically resetting, thermal protection has been
    :used for a long time. The hazard of having it restart is now understood.
    :A field installable way of requiring operator intervention for a restart is
    :needed. When a requirement of 80 C ambient was added, an electromechanical
    :device came to mind. While they may have been common at one time, that
    :time has past.
    :
    :I offer my thanks to those who offered thoughts and information on this
    :subject. While ranking the responses is inappropriate, the term
    :amperometric does stand out.
    :
    :A good day to all,
    :Robert H.


    It sounds to me as if you are looking for a standard motor overload protector
    which has both overcurrentand thermal overload tripping. I am certain that these
    devices do not automatically reset once tripped - you have to manually press a
    button to restart.
    eg. http://web5.automationdirect.com/static/specs/centsablestarters.pdf
     
  13. Robert

    Robert Guest

    The motor being used is not being changed or modified. It is a small AC
    motor. It has internal over temp that automatically resets. It is the
    automatic restarting that is the problem. A way of externally preventing
    the restart is needed.

    The item you pointed out looks like it trips with overloads and over
    current. I need to trip in response to the motor shutting down from the
    internal protection opening up.

    Fortunately those who imposed the 80 C ambient rating have yeilded.
    Specification by a comitee that has only a single member familar with the
    technology can be a challenge.

    Thanks,
    Robert H.
     
  14. Ross Herbert

    Ross Herbert Guest

    ::
    :>:Most of the overload relays I looked at are thermal. When heated a
    :>:set of contacts open. This works fine for shutting down when aced
    :>:with a sustained overload. I needed contacts that opened when the
    :>:current, or heating, fell too low. Compared to the usual power power
    :>:levels for such devices, mine are quite low. I deeded to switch at
    :>:less than an amp.
    :>:
    :>:Fortunately, those in control have backed away from 80 C ambient. I
    :>:am back into a temperatur range that can be met with commonly
    :>:available items. An electronic current sensor, a relay to handle the
    :>:load, and a momentary switch to get things started.
    :>:
    :>:Having explained the application many times, I may not have done so
    :>:here. Unfocused conversations and corispondance eats up a lot of
    :>:time. A small motor with internal, automatically resetting, thermal
    :>:protection has been used for a long time. The hazard of having it
    :>:restart is now understood. A field installable way of requiring
    :>:eek:perator intervention for a restart is needed. When a requirement of
    :>:80 C ambient was added, an electromechanical device came to mind.
    :>:While they may have been common at one time, that time has past.
    :>:
    :>:I offer my thanks to those who offered thoughts and information on
    :>:this subject. While ranking the responses is inappropriate, the term
    :>:amperometric does stand out.
    :>:
    :>:A good day to all,
    :>:Robert H.
    :>
    :>
    :> It sounds to me as if you are looking for a standard motor overload
    :> protector which has both overcurrentand thermal overload tripping. I
    :> am certain that these devices do not automatically reset once tripped
    :> - you have to manually press a button to restart.
    :> eg.
    :> http://web5.automationdirect.com/static/specs/centsablestarters.pdf
    :>
    :
    :The motor being used is not being changed or modified. It is a small AC
    :motor. It has internal over temp that automatically resets. It is the
    :automatic restarting that is the problem. A way of externally preventing
    :the restart is needed.
    :
    :The item you pointed out looks like it trips with overloads and over
    :current. I need to trip in response to the motor shutting down from the
    :internal protection opening up.
    :
    :Fortunately those who imposed the 80 C ambient rating have yeilded.
    :Specification by a comitee that has only a single member familar with the
    :technology can be a challenge.
    :
    :Thanks,
    :Robert H.
    :


    Without modification to the motor itself there can be no means by which control
    of an external device or protection method is possible. The only way I cansee
    out of your dilemma is for the external motor protector to have priority over
    the internal temperature overload function of the motor.

    Since the motor temperature is a function of mechanical load and the current
    being drawn by the motor, you can use a motor protector such as the one I
    mentioned and set the overload current (yes, this value is adjustable) to some
    value below that at which causes the motor to exceed its overload temperature.
    That way the external protector will have priority and will trip before the
    motor temperature is reached and then you have manual control via the external
    protector.
     
  15. Ross Herbert

    Ross Herbert Guest

    :On Sun, 15 Mar 2009 07:28:51 GMT, Ross Herbert <>
    :wrote:
    :
    :
    :>Without modification to the motor itself there can be no means by which
    control
    :>of an external device or protection method is possible. The only way I cansee
    :>out of your dilemma is for the external motor protector to have priority over
    :>the internal temperature overload function of the motor.
    :
    :---
    :View in Courier:
    :
    :Like this?
    :
    :.AC>---+------+
    :. | O COM
    :. | |- - - - - - -[COIL]K2
    :. S1| O NO | <-O NO | |
    :. | O START | | |
    :. | | | |
    :. +----------+ | |
    :. | T1 | |
    :. +---P||S---+ |
    :. R||E |
    :. +---I||C------+
    : |
    :. +----|----+
    :. | | |
    :. | O|S2 |
    :. | O| |
    :. | | |
    :. | [MOTOR] |
    :. | | |
    :. +----|----+
    :. |
    :.AC>--------------+
    :
    :If the thermal cutout switch, S2, in the motor assembly is closed, then
    :pressing S1 (a normally-open momentary switch) will connect the motor to
    :the mains through the primary of T1, a current transformer. When that
    :happens the motor will start to turn and a voltage will be induced in
    :the secondary of the transformer which will be placed across the coil of
    :K2, a normally-open relay with an AC coil.
    :
    :When the contacts of K2 close they will be in parallel with the contacts
    :eek:f S1 and will provide a redundant connection of the motor and the
    :transformer to the mains.
    :
    :Therefore, when S1 is released, the connection to the mains will be
    :maintained by the closed K2 contacts.
    :
    :However, should S2 open because of motor overheating, (or any other
    :reason) the current in the coil of K2 will be interrupted, the relay
    :contacts will open, and the connection to the mains for the motor and
    :K2's coil will be broken.
    :
    :Once that happens, the connection to the mains will remain broken even
    :if S2 closes once the motor cools off, pressing S1 being the only way to
    :begin the cycle anew.
    :
    :
    :JF


    Yes John, that's exactly the way I see it. The motor protection current limit is
    dialled up on the external motor starter/protector so that it is below that
    required to heat the motor up to the internal temp setting for S1 to trip.
     
  16. Jasen Betts

    Jasen Betts Guest

    so you want a current relay with windinf in series with contacts, wired in
    series with a 80C thermostat switch, and a push-button across the relay
    contacts.

    or something like that.
     
  17. Robert

    Robert Guest

    The schematic above is functionally what I ended up doing. The idea of
    using a transformer to drive the relay had not crossed my mind. It does
    provide a low impedance that can be placed in series with the motor.

    Fortunately the 80 C ambient rating on the components to be used was
    droped. A prototype was delivered this afternoon. Digikey has a current
    sensor in stock with an AC switch output.
    http://www.digikey.com/scripts/dksearch/dksus.dll?Detail&name=582-1020-ND
    http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR9321
    Power for the relay coil was taken from the incomming power.

    Have a good day,
    Robert
     
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