Relay Throw Question

The contacts may have been oxidized. By operating the relay a few times, you may have "scrubbed" the contacts clean, by the normal wiping action.

Another possibility could be that some soft object was stuck in between the pole and the armature and was loosened by operating the relay a few times.

It still may be wise to remove the cover and clean the relay contacts.

Tom

Thank you very much!

Somehow the relay is a sealed one and so I cannot easily remove the cover.

Is it true that if my load is a bit inductive (e.g. cos theta = 0.9), then without a load snubber (R-C), the relay contacts may have higher oxidation/weld possibility? How do I know when I should add a snubber?

Thanks. Billy

Are you sure that the 12V power supply is working properly and is able to supply enough current to drive the relay coil?

Personally, I don't agree with Tom's suggestion that the contacts may have been oxidized: if that were the case, the NC contacts would have opened, even if the NO contacts didn't close. From your post I *think* you're saying that the NC contacts stayed closed. And anyway, I've never heard of oxidized contacts changing the sound of a relay.

But Tom's suggestion of some soft obstruction (or perhaps a small piece of grit in the works somewhere) is very plausible. That's probably where I'd bet my money. And if it's a sealed relay, I wonder if that piece of material is still inside, waiting to cause problems again in the future.

Sounds like your relay was stuck open and then broke free. Could be stuck NC contacts or an armature cocked due to physical abuse. Tom

Walter Harley =E5=AF=AB=E9=81=93=EF=BC=9A

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Yes Yes.. the NC still stays NC... can other be any possibilities? The

Somehow from around 50 relays I have, few of them really have this kind of "random stuck". The phenomenon sometimes occurred and somehow I "activated" it again then the problem went away. But maybe of course it will occur again in the future, I don't know.

Any other possibilities? Thanks! Billy

Sorry, what does "stuck open" mean? In my case the NC stays NC and the NO stays NO, somehow it sounds like the relay throws but bounced back (but the 12V was still applied there!)

Thanks. BIlly

How long had it sat without operating before this happened? There could be some kind of lube grease on the armature that gets gummy with time, and you loosened it up. Or if they're like that out of the box, it could be crappy manufacturing. :-)

But it definitely sounds mechanical in nature.

Good Luck! Rich

It means that. :-)

Cheers! Rich

It means, that the contacts have been fused together.

If it is mechanical... then what can I do about it? Actually is it common to drive a 12V relay with, say, 15V to ensure proper driving?

Thanks. Billy

Then, to avoid the same problem occuring again, should I add R-C snubber to the relay, especially when I use it with inductive loads?

Thanks. Billy

if a used relay possibly the NC contacts were welded. and exercising it unstuck them.

Bye. Jasen

No. A 12V relay should be operated, ideally, by 12V. If you look at the datasheets for some relays you'll see that they are specified in terms of a number of voltages, including a max rated voltage (more than this will fry the coil), and a minimum pull-in voltage (it takes at least this much to make the relay turn on). A 12V relay might have, say, 9V pull-in and be rated for up to 18V maximum. There's also a drop-out voltage; as long as you maintain the coil voltage above the dropout voltage, after the relay is energized, it will stay energized. The dropout voltage is usually a bit less than the pull-in voltage.

If you've got 50 relays that claim to be 12V relays, and a handful of those are not reliably activated by 12V, then what you have is a defective batch of relays. If you purchased these from a manufacturer or legitimate distributor, you should be contacting their technical support for guaranteed-good replacements. If you purchased them from a surplus supplier, or over eBay or some such... well, now you know why you got such a good deal on them.

Yes, but this is a different issue than your original question. I had the impression that the relay was just stuck, not fused.

Thanks, Rich

No. Relays generally will operate below their rated voltage. It is not usual to overdrive them to ensure they transfer. What you want to do is ensure that the path from the supply to the relay coil does not reduce the current below what the relay needs.

As far as old relays that may be sticking mechanically, you can rig up a 555 with a driver transistor to "exercise" them. Set the timer for something like 1 second on, one second off. Let the circuit operate the relay for a few hours. That may help to overcome mechanical binding.

The transistor is not absolutely mandatory, as many relays can be driven directly by the 555, but it's worth adding. The diode is mandatory.

Ed

Thank you... then I will keep the 12V. Let me try to find more information from my supplier.

Thanks. Billy

How do I determine which situation I have now?

Thanks. Billy

I have no idea, other than to open the relay and look at it. Is it really "sealed", or is it one of those ones with the plastic case that you need two little screwdrivers to get off?

Thanks, Rich