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 Posted: Apr 22, 2009 - 01:30 PM |
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Joined: Jul 02, 2005
Posts: 5921
Location: Melbourne, Australia
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Hi folks,
It looks like I may be in the running for a new design project to add a capability to an existing facility at a major semiconductor fab house in Asia. An existing commercial ESD testing product controls the access turnstile or doors via a changeover (Form C) relay. My project will copy this "drive" approach but implement the additional testing and logic sequence before opening the turnstile or door.
The question is ... should I even consider mounting the relay in a socket. Most of the suitably rated units have only a 100,000 or 200,000 electrical operations spec. This facility would hit that mark easily in 9 months with the size of its workforce and all those lunch and work breaks. I don't know what relay the ESD tester uses, but I should equal or exceed its MTBF and certainly ease the repair time ... hence the socket consideration.
Any thoughts, recommendations for long life relays?
Cheers,
Ross |
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Ross McKenzie
ValuSoft
Melbourne Australia
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Posted: Apr 22, 2009 - 01:45 PM |
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Joined: Apr 06, 2008
Posts: 415
Location: Singapore
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I assume you've done the appropriate snubbing on the contact-side? That should help increase life a bit, that and reducing switching currents.
I've seen several relays mounted on sockets, but they have a nasty habit of coming loose from the mechanical vibrations, but I'd doubt solder would do any better.
I'd recommend a cautious approach either way. Will the relays be properly mounted?
Also, is a solid state alternative not possible? |
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Posted: Apr 22, 2009 - 02:01 PM |
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Joined: Jul 27, 2001
Posts: 7429
Location: St. Leonards-on-Sea (UK)
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I worked for Rank-Xerox many years ago. All Xerox copiers at that time used lots of relays, and they were all socketed.
Leon |
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Leon Heller
G1HSM
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Posted: Apr 22, 2009 - 02:02 PM |
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Joined: Jul 02, 2005
Posts: 5921
Location: Melbourne, Australia
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Thanks Timgoh0,
Yes snubbing in place.
Some relay cradles have wire clips to prevent vibration effects and that is what I would use anyway. I am not doing the installation, so they would be freighted and I would want them to survive that final vibration test program.
Having trouble getting information about the doors and turnstile interface, so am unaware of any polarity issues. A relay solves that.
Thanks,
Ross |
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Ross McKenzie
ValuSoft
Melbourne Australia
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Posted: Apr 22, 2009 - 03:47 PM |
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Joined: Oct 20, 2005
Posts: 257
Location: Colorado
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On all the equipment I have ever seen, if it was expected to have any type of lifetime, the relays were socketed. In fact, one of my early jobs was to 're-form' relays and clean the contacts. 
Just make sure the sockets are high quality. |
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Posted: Apr 25, 2009 - 04:07 PM |
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Joined: Nov 03, 2006
Posts: 1120
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| You could just lay the sockets for the relays in line, and use a board- or case-screwable plastic bracket to go on top of them to secure the relays in the sockets. In the case of a replacement, just unscrew/unclip/pop the bracket, change relay, resecure bracket. |
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Posted: Apr 25, 2009 - 04:24 PM |
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Joined: Feb 19, 2001
Posts: 25881
Location: Wisconsin USA
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[full disclosure: bit-pusher's blog...] Are you switching AC or DC? Inductive or resistive loads?
I'm getting at addressing the electrical life by making it easier on the relay, with proper snubbing and zero-crossing. It >>will<< make a difference versus just tossing a relay at the situation.
Also consider SSR especially if the currents are relatively low. For low currents an SSR setup won't cost much more and should give virtually unlimited life.
Higher-current SSRs are usually more expensive than the relay. But consider the "life" cost of the socket, spare parts, downtime, ... and maybe it ends up "cheaper".
Just very general.
Lee |
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Posted: Apr 25, 2009 - 11:31 PM |
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Joined: Mar 28, 2001
Posts: 20323
Location: Sydney, Australia (Gum trees, Koalas and Kangaroos, No Edelweiss)
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We used about 8,000 relays in the SOH (Sydney Opera House) for signalling and intercommunications, all socketed, mostly PCB mounted.
My goodness that was more almost 40 years ago!! |
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John Samperi
Ampertronics Pty. Ltd.
www.ampertronics.com.au
* Electronic Design * Custom Products * Contract Assembly
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Posted: Apr 26, 2009 - 03:30 AM |
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Joined: Apr 06, 2008
Posts: 415
Location: Singapore
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I'd like to see a picture of that, and possibly a total power consumption when all of them energize at the same time. 
js wrote:
We used about 8,000 relays in the SOH (Sydney Opera House) for signalling and intercommunications, all socketed, mostly PCB mounted.
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Posted: Apr 26, 2009 - 05:04 AM |
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Joined: Mar 28, 2001
Posts: 20323
Location: Sydney, Australia (Gum trees, Koalas and Kangaroos, No Edelweiss)
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Quote:
I'd like to see a picture of that,
So would I. The design engineer was a friend but unfortunately he died about 4 years ago. I should try and get copies from his family, he had lots of them, in B&W of course. |
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John Samperi
Ampertronics Pty. Ltd.
www.ampertronics.com.au
* Electronic Design * Custom Products * Contract Assembly
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Posted: Apr 26, 2009 - 05:55 AM |
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Joined: Aug 08, 2008
Posts: 192
Location: Minnesota
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Just a thought. A lot of vehicles have socketed relays these days. My last 2 had 8 or so each. None of the relays were retained. I've got to believe that the vibration/ temps in those environments is pretty awful.
What I'm getting at is that sockets can be pretty reliable.
ford2go(hj) |
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Posted: Apr 26, 2009 - 09:50 AM |
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Joined: Jun 11, 2004
Posts: 2422
Location: Vilanova (Barcelona)
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I'm working with electronics test equipment that uses hundreds of relays, switching at low Hz. Low currents and voltages, but all of them socketed.
I have absolutely no doubt for turnstyle doors: socket your relays, and use snubbers. They tend to turn on/off motors, although they are usually switched off by some internal mechanical system when it reaches the position.
In a previous life I worked for a thermostat compay. Cheap thermostats tend to have short lives, about one year, due the relay wearout. Given the low price, it was cheaper to replace the whole thermostat than try to fix or change the relay, even if they were socketed. Of course, they weren't, since the business are to sell thermostats, not relays. |
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Guillem.
"Common sense is the least common of the senses" Anonymous.
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Posted: Apr 26, 2009 - 02:29 PM |
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Joined: Jun 21, 2002
Posts: 679
Location: Canberra, Australia
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| I've had a state machine using din-rail mounted, socketed relays controlling lights in a theatre running for about 25 years. 240V AC coils and they all control each other. The only problem was when a filament bulb blew and tripped the breaker for its set of lights, I was called in because the electrician didn't know what to do. 1/2 hour in, click, 1/2 hour home! |
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Posted: Apr 29, 2009 - 04:51 AM |
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Joined: Jul 02, 2005
Posts: 5921
Location: Melbourne, Australia
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Thanks everyone.
Have been away for 4 days.
Lee, I don't really know the nature of the load. The customer is reluctant to say too much during the tendering process. (Weird I know). I am hoping that the present relay closure simply drives other electronics to start and control the turnstile motor; but do not know the specifics.
John, I too would like to see a photo of your opera house efforts.
Have been told that a recommendation is possible today. Fingers crossed.
Cheers,
Ross |
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Ross McKenzie
ValuSoft
Melbourne Australia
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