Bob McC
Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON
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 Posted: Sun Dec 22, 2013 10:01 am Post subject: Any know is there a typical failure mode for Solid State Rel |
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Jeffrey;
I have not used the DC relays which you’ve linked to, but at work we have used the AC version of this particular brand of relay for controlling heating elements for approximately 25 years. Their biggest enemy, as with a lot of electronics, is heat. Because we do not implement large heat sinks to cool these relays ($cost$) we oversize them by approx 4X to ensure no heating issues and typically see less than .1% failures. (we do bolt them to steel enclosures, so they have some heat sinking) I have no statistics on the relative age or loads on the failed units. When the failures do occur they are almost always failure to close (in other words fail open) I have had one and only one fail closed however, so it would appear both failure modes are possible. We have also experimented with sizing them to approx 2X load current and have seen the five year failure rates rise, in this group, to approx 5%. As a result we returned to using the 50 amp models for greater reliability of our product. (loads are in the 3 to 14 amp range) While this anecdotal information may or may not apply to the DC versions of Crydom’s product we’re quite satisfied with the AC versions performance. I should also mention that the equipment we manufacture typically employing these relays runs 24/7 and these relays are controlled via a temperature controller cycling on/off up to as much as 50 cycles per minute, so we give them a good workout although we lightly load them.
Bob McC
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Jeffrey Skiba
Sent: Sunday, December 22, 2013 11:27 AM
To: aeroelectric-list(at)matronics.com
Subject: Any know is there a typical faliure mode for Soild State Relays
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 !
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Bob McC
Falco #908
(just starting) |
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