Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.components > #6219

Re: Contactors/Relays

Cross-posted to 2 groups.

Show all headers | View raw

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?

-- 

Rick C

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

Back to sci.electronics.components | Previous | Next — Previous in thread | Next in thread | Find similar

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

csiph-web