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.
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.
Hul Tytus <ht@panix.com> writes:
David - are the "close coil, open coil" relays the type that are opened by >>a pulse on one coil and closed by a pulse on the other?
Yes....
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.
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.
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.
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?
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?
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?
David Lesher wrote on 10/19/2017 2:04 AM:
legg <legg@nospam.magma.ca> writes:
Anyone seen such?
http://gencontrol.co.uk/3-pole--9a-95a--nc1-type-.html
NO not NC main contacts.
Now I'm confused. Above you said if control power drops the relay contacts >should close. Here you say they should be NO. Those two things are not >compatible.
Do you have room for three separate relays each with a single NC
contact ?
rickman <gnuarm@gmail.com> writes:
David Lesher wrote on 10/19/2017 2:04 AM:
legg <legg@nospam.magma.ca> writes:
Anyone seen such?
http://gencontrol.co.uk/3-pole--9a-95a--nc1-type-.html
NO not NC main contacts.
Now I'm confused. Above you said if control power drops the relay contacts >> should close. Here you say they should be NO. Those two things are not
compatible.
I meant your suggestion was NFG because it is NO; I need NC.
About the only power control circuits I can think of ......
Do you have room for three separate relays each with a single NC
contact ?
legg <legg@nospam.magma.ca> writes:
About the only power control circuits I can think of ......
I hope you're not unhappy to learn that there are situations you
didn't think of, and are unlikely to, especially given I've only
given one tiny part of a bigger picture to you.
On Thu, 26 Oct 2017 05:00:03 +0000 (UTC), David Lesher
<wb8foz@panix.com> wrote:
legg <legg@nospam.magma.ca> writes:
About the only power control circuits I can think of ......
I hope you're not unhappy to learn that there are situations you
didn't think of, and are unlikely to, especially given I've only
given one tiny part of a bigger picture to you.
It would be a pleasure to be enlightened, should you deign to do so.
It would be a pleasure to be enlightened, should you deign to do so.
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