I looked around but couldn't find anything regarding this. The question is... when a relay goes bad (say the coil burns out) does it rest normally at 30/87a, or 30/87? I would guess 30/87a since that's where it normally rests, but wanted to see if anyone knew for sure. I all my years I can't remember ever seeing a bad relay.
You can't say for sure, because it depends on how it fails.
If the coil fails the relay will always rest at 87A based on the principle of how a relay works (the coil provides the magnetic field to pull the relay in). If there is no magnetic field, there is no switch.
However, relays also have springs that can break, that would prevent them from returning reliably to the NC position.
Finally, the contacts can wear. If you are switching a high load over an extended period of time, espcecially a load with a high in-rush current the contacts will arc each time they switch. This arcing will eventually cause the contacts to quit connecting. It can also weld the contacts in a particular state (the high current state). This occurs when the contacts spark and the spark mechanically bonds the contactor to the output pin, and the bond is stronger then the spring. Usually, a swift blow to the relay will free the contacts and you can get a few more uses out of it before it fails all together.
In my experiance, the contacts fail 99 out of 100 times when a relay fails. Because of this, it is simply impossible to predict the state the relay will fail in.
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Kevin Pierson
KPierson wrote:
the contacts can wear.
Is there any data on how long these are rated for? For example, a on/off switch is rated for a certain amount of cycles, what would a relay (
a good one like Bosch) be rated for? I've never seen a relay go bad, even old (
over 5 years) relays still seem to work good, so I'm guessing the number of cycles has to be fairly high.
Anywhere from 100,000 to 10,000,000 cycles I would guess, based on the quality of the relay.
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Kevin Pierson
