What type of relay to use?

[ibroussard]

I want to use this data logger (which I have already purchased) to record start/stop times for my standby generator. In the generator ATS, I have a wire connected to one of the gen's "hot lug" and another to the neutral bus. I have 120vac present at the two wires during weekly exercise cycles and when running on generator power.

I wanted to use a regular enclosed relay like this one, but the guy at Grainger said it would oxidize quickly and fail because there won't be any current going thru the load side of the relay, since the data logger senses resistance (open or closed).

So are there relay types or other devices that will better handle what I have? For an idea of the duty cycle it will be in, under normal conditions, the generator runs once for 15 minutes per week for its exercise cycle. Power outages can range from minutes to days (hurricane country).

Thanks,
Ira

[Bill190]

I've never heard of anything like that!

Oxidize?

Basically any mechanical relay I have had anything to do with has been VERY reliable. Especially relays which are sealed and do not allow outside dust/dirt to enter.

It is a royal pain to search for the right relay on the internet, let alone a specific type. I would say go with that and don't worry about it.

[ibpooks]

Your relay looks just fine. The oxidation comment makes no sense to me; metal lasts longer when there is no current running through it.

[Bud9051]

Well,,,,yes contacts will oxidize, but like Bill said, I don't think it will bother you here. Switch designs that worry about dry contact (no current) usually have a sliding function to be self cleaning. Although your relay is intended to handle a current load, it should do just fine dry. I like the relay, did Graingers give you a price on it.
Bud

[ibroussard]

Originally Posted by ibpooks

Your relay looks just fine. The oxidation comment makes no sense to me; metal lasts longer when there is no current running through it.

The guy at Grainger said that when current is present on the load side, a momentary arc created during open/close will "clean" the contact surfaces. That is also the reason why there are different contact surface metals/alloys. I did some more research and it sounds like he is right, although it still may not be a concern for me. He recommended either a reed relay (the contacts are in a tube filled with an inert gas) or a mercury wetted relay (doesn't have oxidation problems). However, I haven't been able to find one that is enclosed and pre-wired like the one in the link above.

Since it's not a critical circuit (I'm only monitoring the gen startup/shutdown times), I will probably take my chances with one from Grainger.

Thanks,
Ira

[Bill190]

Hummm... That is interesting! Again ya learn something every day!

I will say that all the relays I have ever worked with would have had arcing, so maybe that is why I never had any trouble?

I have worked with sealed reed switches and reed switch relays and they are the absolute best, but good luck finding one as you said.

Perhaps a solid state relay? But would there be a lot of heat in this area? I don't think these like heat very much...

[ibroussard]

Originally Posted by Bud9051

I like the relay, did Graingers give you a price on it.
Bud

The one I linked to in my first post is $25. I'm considering this one at $35 because it has an override switch. The only problem is that I can't tell if the override switch forces the contacts to stay open even if power to the coil is present, or if it forces the contact closed even if there is no power to the coil. Forcing the contacts closed would be good for testing (simulating a "gen on" state) so I wouldn't have to start the gen to test the relay and logger/software.

[Bill190]

Ok folks....

You have heard of "Boy's Life".

You may have heard of "Nun's Life"...

And now we have.... (Drum roll)....

Relay Contact Life!

http://relays.tycoelectronics.com/ap...fs/13c3236.pdf