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Re: Contactors/Relays

Cross-posted to 2 groups.

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legg wrote on 10/19/2017 11:02 PM:
> On Thu, 19 Oct 2017 18:48:50 -0400, rickman <gnuarm@gmail.com> wrote:
>
>> legg wrote on 10/19/2017 3:02 PM:
>>> On Thu, 19 Oct 2017 06:11:58 +0000 (UTC), David Lesher
>>> <wb8foz@panix.com> wrote:
>>>
>>>> legg <legg@nospam.magma.ca> writes:
>>>>
>>>>
>>>>> This 'fail closed' issue may be a misconception. What mode of failure
>>>>> are you anticipating this to cover?
>>>>
>>>> Nope, it's what's needed....
>>>> Control power drops, relay contacts close.
>>>
>>> Where does control power come from?
>>> I'd expect use a power fail signal to do it's business during a
>>> hold-up time period.
>>>
>>> If there is only control power, then there's nothing to control, so
>>> the normal state, in that condition, should be your 'fail-safe'
>>> default.
>>
>> Are you suggesting the relay needs to be powered from the contacts and it
>> needs to *remember* the state it was last in when control power fails?
>> Seems simpler to just power the coil from the control side and use a NC
>> relay.  No small part of the use of relays comes from the isolation.
>> Powering the relay from the load side means you have to start all over again
>> with an isolation barrier.
>
> There's no memory involved. This is the designer's decision. If it is
> important that the contacts be in a certain configuration under
> certain conditions, then it's the designer's responsibility to provide
> circuitry that's smart enough to enforce it.
>
> Intentionally configuring a lower power electronic control circuit
> that can't function, always, when the higher-powered controlled
> electrical quantity is present doesn't make sense.

So all designed equipment has to be 100% reliable?  How about since the 
requirement is to have the contacts closed when the controlling circuitry 
isn't powered to be implemented by a relay with normally closed contacts?

I don't get what your problem with this is.  The controlling system will be 
built to run from whatever power is deemed appropriate.  Your assertion that 
it *must* be powered by the load is without basis.  You are aware that the 
controlling circuit might be doing other things.  YOU seem to be unaware 
that there may be a larger system involved.

-- 

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

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Thread

Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-14 18:16 +0000
  Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-14 15:38 -0400
    Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-18 22:32 +0000
      Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-18 23:11 -0400
        Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-19 06:11 +0000
          Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-19 15:02 -0400
            Re: Contactors/Relays rickman <gnuarm@gmail.com> - 2017-10-19 18:48 -0400
              Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-19 23:02 -0400
                Re: Contactors/Relays rickman <gnuarm@gmail.com> - 2017-10-20 00:49 -0400
                Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-20 12:03 -0400
                Re: Contactors/Relays rickman <gnuarm@gmail.com> - 2017-10-20 13:17 -0400
                Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-21 09:52 -0400
                Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-22 06:25 +0000
                Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-26 05:00 +0000
                Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-29 13:23 -0400
                Re: Contactors/Relays Michael A Terrell <mike.terrell@earthlink.net> - 2017-10-30 16:04 -0400
                Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-11-03 06:07 +0000
      Re: Contactors/Relays upsidedown@downunder.com - 2017-10-19 13:00 +0300
        Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-22 06:23 +0000
        Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-26 05:04 +0000
  Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-14 15:52 -0400
    Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-19 06:03 +0000
  Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-14 16:20 -0400
    Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-19 06:04 +0000
      Re: Contactors/Relays rickman <gnuarm@gmail.com> - 2017-10-19 03:49 -0400
        Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-22 06:18 +0000
          Re: Contactors/Relays rickman <gnuarm@gmail.com> - 2017-10-22 03:57 -0400
  Re: Contactors/Relays Hul Tytus <ht@panix.com> - 2017-10-14 21:20 +0000
    Re: Contactors/Relays David Lesher <wb8foz@panix.com> - 2017-10-19 06:07 +0000
      Re: Contactors/Relays legg <legg@nospam.magma.ca> - 2017-10-19 23:11 -0400
  Re: Contactors/Relays John Larkin <jjlarkin@highlandtechnology.com> - 2017-10-14 16:43 -0700
  Re: Contactors/Relays upsidedown@downunder.com - 2017-10-15 10:20 +0300
  Re: Contactors/Relays Neon John <no@never.com> - 2017-10-15 09:49 -0400

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