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jayber

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I've had this uncertainty going through my head and it has to do with relays.  I recall somebody saying something to the affect that said RS uses 'junk' components.....and then there's been this talk about relay life and such.  I'm just wondering what people are using out there for a reliable relay, if there is such a thing?  If it matters, I'm currently using 6V. I did have trouble with one All Electronics relay one time where it worked at first and then stopped working, but I am not sure what caused it.  I have been using RS relays ever since because I didn't want it to happen again.....and because the RS relays were recommended on the How-To page(s).  Anybody have anything to offer or do I continue to lose sleep at nite??  LOL
 



gizz

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I've used about 20 RS relays for the homebrews, testing boards, and the 3 time redesigned videocam. I lose no sleep because if they start to fail I will just replace the Relay. All things tend to wear out over time although I haven't heard many if any complaints about the relay's going bad yet.
 

Archilochus

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Hi jayber,
RS does tend to sell lower quality components, but I wouldn't go so far as to call them "junk".  The RS relays should last for somewhere around 200,000,000 operations or more.  The problem is that with the RS sensor #49-425 people have been sometimes driving their relays with an audio frequency signal at the speaker wires - thus the "singing relays", and at a serious over-voltage condition - 9 volts instead of the rated 5 volts.  Now assuming a lower quality relay from RS, these stresses could easily destroy the relay after a two or three months of use.

I could find no specs from RS concerning the duty cycle rating for their various relays.  It could well be that the relays are only intended for "momentary" use - and that keeping them "on" for a minute or two at a time might be over-heating them.

RS will fill their stocks with whatever parts are available and cheap.  Some of us might get a high quality relay one day, and others get an "El-cheapo" the next day - even though they have the same RS part number.  So resulting relay life could vary wildly.

If you keep all circuits within specifications for the lowest possible quality of parts you might end up with, your circuit should last a long time.

See the thread "the little relay that couldn't" concerning early failure of relays.

http://www.jesseshuntingpage.com/cgi-bin/i...1&topic=148

For peace of mind - order your parts from a catalog that gives manufacturer information regarding duty cycle, operational life, and allowable supply voltage.
Try
http://www.mouser.com
or
http://www.digikey.com

Archilochus
 

jayber

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I'm using MS20's with a single 3-6V relay connected to pin 3 of the second stage of the timer so hopefully I don't have any problems....at least for a long time <crossing fingers>.

My apologies for the use of the word 'junk'.  It's just the way the post I was referring to sounded.

And thanks for input....I'll look into the other sources!!!
 

gizz

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Arch - Thanks for the link, I must've not seen it the first time. Anyways, by your reply I'm assuming you suspect the problem is with the RS sensor more so than the Relay? I'm using the MS20 PIR so if that is the case then I'm safe?
I don't recall seeing anything about duty cycle on the 9V 275-005a relay but on the 275-248 it is listed as 100,000 cycles (Electrical at rated voltage) and 10,000,000 cycles Mechanical (no load). I've used the 9V with a 12V power source to the coils so I'm assuming that I'll get less than what they are rated at? 1000 rolls of 24Exp film would be say about 25000 cycles given testing and misfires etc... Still way under the rating. Do you think this is a fair assumption?
I sure don't want to start ripping them apart after 10 or 20 rolls of film. Guess time will tell.
 

Archilochus

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Hi gizz,
I've never used the MS-20, so I'm not sure what its specs are - but I'd guess you're OK.  The relay problems when using the 49-425 sensor looks to be a combination of high frequency and over-voltage.

Didn't realize the 275-248 had such (relatively) low operational life expectancy.  My Siemans relay data book lists operational life for many of their small relays at around 500,000,000 to 1,000,000,000 cycles!  Guess that's why their relays cost so much.

Many relays are rated for up to 50% over-voltage, some up to 275% (with reduced operational life).  By driving your 9V relay with 12V you're only looking at 33% over rated voltage - so it should be within tolerance.  Lifetime might be reduced some - just a guess - maybe 10 - 15%.  You could add in a series resistor at the relay coil (maybe 10 to 47 ohms) to reduce current through the coil- extending the life a bit.  You'd have to experiment with resistor values to make sure the relay will operate under all expected conditions.  I have a circuit (not a camera) that uses a 9V relay with a 12V battery.  I put a series resistor on the coil (47 ohms) and the circuit has been working fine for about 4 years of constant use.

By the way...Where did you locate the data for the RS relay?  I could find no specs for the parts.

Archilochus
 

gizz

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Arch - Thanks for the reply. I found the info on the back of the RS relay packaging. Seems it's on some of the boxes and not the others. I seem to remember seeing it on one of the 9V boxes also but I don't have the packaging anymore. That's a good tip on adding the resistor at the coil but since my cams are all tightly put together I think I'll chance it for now. I doubt I'll ever put more than a 100 rolls through a cam and as such should probably not have any problems unless of course a component just goes "bad".
 

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