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nuckolls.bob(at)aeroelect
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 Posted: Sun Dec 22, 2013 1:38 pm Post subject: Any know is there a typical faliure mode for Soild State R |
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At 10:27 AM 12/22/2013, you wrote:
Any know is there a typical failure mode for Solid State Relays?
Like do they typically fail OPEN ??? or do they Typical fail CLOSED (just
like sometimes of a typical mechanical relay that the points weld together
or the spring fails ?)
I am considering using solid state relays to replace mechanical relays but
do not know if the ssr has a failure mode worse than them.
I have attached one relay I found thus far to possibly replace a hydraulic
motor contactor for a landing gear pump.
Thanks in advance and HAPPY HOLIDAYS !
They can fail in ANY mode. I.e. stuck closed or stuck open.
It depends on the stress that might have precipitated the
failure. Were I considering such a device for use in a
TC aircraft, the litany of deliberations goes something
like this:
1. How many ways can this part fail?
2. How will each failure affect system operation?
3. How will I know it failed?
4. Is the failure pre-flight detectable?
5. Is failure of this part, in any failure mode, likely to create
a hazard to flight?
6. Will failure of this part be likely to overtax my piloting
skills for comfortably terminating the flight?
Come of the gate ASSUMING the part will fail in
every conceivable way . . . how do the answers
to the above questions affect the way you use the
part and how you react to the failure.
Rule #1 Things Break
Rule #2 Systems shall be designed so that when things
break, no immediate hazard is created.
Rule #3 Things needed for comfortable termination of
flight require backup or special considerations
to insure operation and availability.
Rule #4 Upgrading the quality or reliability of a part
shall be because you are tired of replacing it
or want some new feature, not because it damned
near got you killed.
Suggest you review this short piece on FMEA. The FMEA worka
around the problem of not knowing the whether or not the
part has established reliability numbers. Assume that it
will fail, rework the design or craft a plan-b so you can
be pleasantly surprised when it never fails but have a
comfortable response if it does.
This philosophy for systems design is spelled out in
more detail here
http://tinyurl.com/ljl9qe6
http://tinyurl.com/lfkm2fl
As a final note, be aware that your hydraulic pump
motor is probably a permanent magnet variety with
hefty inrush current. Make sure the device you pick
can stand 500-1000 amp inrush for a few milliseconds . . .
i.e. "rated" for motor or large incandescent lamp
control.
Bob . . . [quote][b]
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Sun Dec 22, 2013 6:08 pm Post subject: Re: Any know is there a typical faliure mode for Soild Sta |
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There is arguably no "typical" failure mode for anything at all.
If there were, the engineers would be happy to see it because it would be an easy fix.
A failure can be "typical" if a device is being misused. "Hey, the device typically fails if being misused!" I'll bet there are a million engineering stories there.
Note: I have sold many SSRs, and I sometimes get "complaints" from customers who think that the apparent SSR no load output voltage when the relay is OFF indicates some flaw. Hmmmmmm....Well...there is always an no-load output voltage on every switch or relay...ON or OFF. But an SSR won't pass more than a microamp or so when OFF. So it won't light an LED. It is DEFINED as OFF for all practical purposes.
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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nuckolls.bob(at)aeroelect
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| Posted: Mon Dec 23, 2013 7:38 am Post subject: Any know is there a typical faliure mode for Soild State R |
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At 08:08 PM 12/22/2013, you wrote:
| Quote: |
There is arguably no "typical" failure mode for anything at all.
If there were, the engineers would be happy to see it because it
would be an easy fix.
A failure can be "typical" if a device is being misused. "Hey, the
device typically fails if being misused!" I'll bet there are a
million engineering stories there.
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PRECISELY!!!! Further, it's an incomplete
analysis for all the concerns if one does not
also consider installation generated failures.
Screw fell out, wire pulled out of terminal,
fault in the controlling circuitry, etc. etc.
Doing an FMEA seems like a daunting task but
it gets easier if you ignore all the detail
reasons WHY it might fail and concentrate
on HOW if fails: (1) doesn't close on command
or (2) closed without command. The WHY is
irrelevant.
Take those two conditions and run
them through the failure detection
and response tree. What are your options
for dealing with either of those two
failures in flight . . . and can the failure
'hide' . . . is it pre-flight detectable
such that you don't take off with an already
failed component.
The SAFE airplane is one that produces
benign and/or predictably managed failures.
If parts on airplanes never failed, FBOs
would be out of business.
Your prime directive as the one and only
flight safety manager for your project is
to design for failure tolerance.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Mon Dec 23, 2013 9:41 am Post subject: Any know is there a typical faliure mode for Soild State R |
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At 11:02 AM 12/23/2013, you wrote:
| Quote: | On Dec 22, 2013, at 10:51 PM, Jeff Luckey <jluckey(at)pacbell.net (jluckey(at)pacbell.net)> wrote:
| Quote: | | they sure are pricey - $130 ea. (at) Mouser, ouch! |
eBay is your friend. A search for "SSR 100A" returns 91 hits, including appropriate heatsinks, starting at ~$9 delivered.
This presumes the words "China" and "Hong Kong" don't scare you. For solid state devices like these, I wouldn't lose any sleep. |
Yes . . . but take care that you get a DC/DC
device . . . they LOOK just like the DC/AC.
[img]cid:7.1.0.9.0.20131223113822.02165410(at)aeroelectric.com.0[/img]
Note the 5-60vdc rating on the output terminals
of this one.
I've ordered one of these to ponder and
perhaps bash on a bit . . .
http://tinyurl.com/l73b6lf
Bob . . .
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jluckey(at)pacbell.net
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| Posted: Mon Dec 23, 2013 10:08 am Post subject: Any know is there a typical faliure mode for Soild State R |
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what are the power dissipation stats on these devices? I didn't see any data on this in the EBay link...
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Monday, December 23, 2013 9:40 AM
Subject: Re: Any know is there a typical faliure mode for Soild State Relays
At 11:02 AM 12/23/2013, you wrote:
| Quote: | On Dec 22, 2013, at 10:51 PM, Jeff Luckey <jluckey(at)pacbell.net (jluckey(at)pacbell.net)> wrote:
| Quote: | | they sure are pricey - $130 ea. (at) Mouser, ouch! |
eBay is your friend. A search for "SSR 100A" returns 91 hits, including appropriate heatsinks, starting at ~$9 delivered.
This presumes the words "China" and "Hong Kong" don't scare you. For solid state devices like these, I wouldn't lose any sleep. |
Yes . . . but take care that you get a DC/DC
device . . . they LOOK just like the DC/AC.
[img]cid:1.1547562507(at)web184902.mail.gq1.yahoo.com[/img]
Note the 5-60vdc rating on the output terminals
of this one.
I've ordered one of these to ponder and
perhaps bash on a bit . . .
http://tinyurl.com/l73b6lf
Bob . . .
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edpav8r(at)yahoo.com
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| Posted: Mon Dec 23, 2013 10:32 am Post subject: Any know is there a typical faliure mode for Soild State R |
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Good catch!
Eric
do not archive
On Dec 23, 2013, at 10:40 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:
| Quote: | Yes . . . but take care that you get a DC/DC device . . . they LOOK just like the DC/AC.
|
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Jane_03
Joined: 24 Dec 2013
Posts: 2
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| Posted: Wed Dec 25, 2013 9:32 pm Post subject: Re: Any know is there a typical faliure mode for Soild Sta |
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nice post!
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