Today's Message Index:
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1. 01:12 PM - Re: Relays (Robert L. Nuckolls, III)
2. 07:15 PM - Re: Relays (user9253)
3. 08:06 PM - Re: Re: Relays (Robert L. Nuckolls, III)
Message 1
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Here's some additional materials that go toward
understanding 'contact science' . . . whether
you're talking about switches or relays. Relays
are just remotely operated switches. The
CONTACTS share the same physics.
http://tinyurl.com/nda9su5
Here's a couple of documents produced by one of the
'granddaddies' of switch and relay business
http://tinyurl.com/ngnjglx
http://tinyurl.com/nenvxrx
Bob . . .
Bob . . .
Message 2
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Quote from the Tyco paper,
> Some relay users connect a diode across the inductive load to prevent counter-voltage
from reaching the contacts. . . . While this is an acceptable method
of protecting the contacts, it does result in lengthened hold-up time of the inductive
load.
So Bob, this does not contradict the results of your lab experiments (If I remember
your posts correctly.) that demonstrate that arc suppression diodes delay
opening of relay contacts, but do not cause the contacts to open slower once
they start opening. A hold-up delay of less than one second is of no consequence
in most amateur built aircraft.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=440026#440026
Message 3
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At 21:13 2015-03-29, you wrote:
>
>Quote from the Tyco paper,
> > Some relay users connect a diode across the inductive load to
> prevent counter-voltage from reaching the contacts. . . . While
> this is an acceptable method of protecting the contacts, it does
> result in lengthened hold-up time of the inductive load.
>
>So Bob, this does not contradict the results of your lab experiments
>(If I remember your posts correctly.) that demonstrate that arc
>suppression diodes delay opening of relay contacts, but do not cause
>the contacts to open slower once they start opening. A hold-up
>delay of less than one second is of no consequence in most amateur
>built aircraft.
Good eye!!!! There was a lengthy discussion here
on the list some years ago. About that same time,
I was deeply immersed in some failure studies of
relays on the roll trim system on the Beechjet.
Even the folks who supplied the relays couldn't
figure out what was going on . . . and it took
me several years of sifting the reports and doing
the science to identify and demonstrate
the root cause.
Here's 'the meat' of a report I crafted for RAC.
http://tinyurl.com/pstsggm
Turns out that primary stresser for causing very
lightly loaded contacts to stick was an effect not
discussed or warned against in any relay applications
document I could find.
Some years earlier, I was able to explore and confirm
that the form of coil suppression on a relay had
very little effect on the contact spreading velocity
once the relay started to open. Diodes have
a PROFOUND effect on drop out delay . . . but that
forcing function has almost no effect on spreading
velocity . . . hence tendency to arc. Once the armature
comes off the electro-magnet pole-piece, the AIR GAP
produced therein weakens the magnetic force far
more rapidly than the diode can retard it's decay.
http://tinyurl.com/qgkgo88
It's tar-bucket stepped into by many
authors in the 'relay arts'. A document
from Tyco was often cited here on the list where
one ASSUMED that because the diode retards
drop-out response . . . if just logically followed
that the contacts must spread more slowly as well.
http://tinyurl.com/ndc6cvl
Now, if we were using relays in systems wire TIMING
was critical . . . the extended drop-out delay
might cause other problems . . . but not reduced
contact life due to aggravated arcing.
Bob . . .
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