Groups > sci.electronics.components > #6225

Re: Contactors/Relays

From	legg <legg@nospam.magma.ca>
Newsgroups	sci.electronics.design, sci.electronics.components
Subject	Re: Contactors/Relays
Date	2017-10-21 09:52 -0400
Organization	A noiseless patient Spider
Message-ID	<iujmuc5da0t05k9ftcrt02qevh52bglbpc@4ax.com> (permalink)
References	(6 earlier) <osba4k$4n9$1@dont-email.me> <uboiucthlv05ip54ffeno7omeb6pq96j8k@4ax.com> <osbv85$fdm$1@dont-email.me> <kg6kuc1muqr62scvc8opciskc38437homp@4ax.com> <osdb3c$u7d$1@dont-email.me>

Cross-posted to 2 groups.

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On Fri, 20 Oct 2017 13:17:32 -0400, rickman <gnuarm@gmail.com> wrote:

>legg wrote on 10/20/2017 12:03 PM:
>> On Fri, 20 Oct 2017 00:49:08 -0400, rickman <gnuarm@gmail.com> wrote:
>>
>>> 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.
>>
>> This isn't reliability, it's functionality.
>>
>> About the only power control circuits I can think of that could use
>> normally closed power contact is a circuit breaker (fuse function) or
>> motor starter (who's on first function).
>> Both of these are motivated by the controlled source of power or it's
>> physical effect, and the latter isn't really affecting the source, so
>> much as it is signalling the load.
>>
>> For signal level applications, potential damage to the switch itself,
>> or the effects of normal power flow on the switch's ability to
>> function are not usually a consideration.
>>
>> I've worked on the development of an ultrafast multiphase transfer
>> switch, with hybrid semiconductor/mechanical brush contacts, and it's
>> automatic/manual control interface. At a certain power levels, you
>> have to enforce your own 'fail safe' environment. Gravity, leaf
>> springs or permanent magnets just don't cut it.
>>
>> Isn't the apparent rarity of the requested hardware sufficient
>> indication that the OP might be barking up the wrong tree?
>
>Or maybe you just don't understand his application?

Quite likely.....

But then, I didn't get to be where I am today by (insert trumpism
here)!

RL

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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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