A while back I'd asked for advice on getting emergency stop switches going in the shop. Based on the advice from this group, I ordered these combo switches and normally closed contactor blocks, model E22JLB2N8B:
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then ran that over doorbell wire to a 24V transformer I picked up at my local electrical supply store, run off a 110V line from my primary subpanel ("Subpanel A"). I then ran a 30A line to a safety switch, from there to an Eaton 30A contactor, and hooked the doorbell line to the 24V hookup on the contactor. Finally, I hooked the output from the contactor to a new subpanel ("Subpanel B") and turned it all on.
Anyway, thankfully, after all that, it worked. :D
But, one question - the contactor hums. LOUDLY. It's only when the 24V is on; I can turn off the safety switch, but not hit an estop switch, and it'll hum. Is it supposed to do that?
It had ocurred to me that I could get a switch which would control both the relay and the transformer, and cut power to both at the same time. Perhaps that's what he's talking about. However, the relay humming while I'm not around isn't much of a concern to me. It's distracting while I am there, but I can learn to live with it, if it's inevitable.
I'm more wondering whether the relay *should* be making that noise, if they all do that, or if mine's doing it because it's about to burst into flames, or something.
I was at least smart enough not to wire the transformer off of subpanel B :)
When I first saw the title... I had visions of 4 people, around a track, each running then humming a verse into the ear of the next guy...and so on... But I resisted expressing that vision in public.
Perhaps it was. My point though was that, from his statement, he either knows why this is happening or believes he does and he could have supplied that information for you and other interested parties (like me). He chose not to contribute so you have to wonder why he participated at all.
I thought at first he was a simple troll but he actually seems quite a helful guy in other current threads here.
If you're supplying constant hold-down voltage - the way you wired it - it will hum.
Had I wired it, I would have had the safety switch control my pull - down current (NO) to a spring-loaded solenoid which would break the current to the shop. This would allow multiple paralleled panic switches, but would require a reset after a panic stop.
I wasn't helpful to him because I didn't know the answer to his question (I was as interested as he to learn). You, on the other hand, did know but chose not to help initially.
I'll leave it to others to judge which is worse.
As always, I think that kind of name-calling says more about you than me ... but again, others can judge. But anyway: *plonk*
Sorry I simply answered your question the first time. I'm prone to do that. Some give elaborate answers to their own questions instead, some just blast in with ad-hominem accusations, for reasons unknown.
Can't take credit for the solution. It's the way every wood shop I've ever worked in is wired.
Too bad, it will be your loss ... George and I aren't exactly enamored with each other, but plonking him is the epitome of cutting off your nose to spite your face, because you will learn something from his posts. So get pissed if you must, we all do, but don't cut off your nose ....
What is the current draw for the solenoid coil? Could it be that your wire size (#26?) is too small to hold the current and that you are possibly experiencing too much voltage drop to hold the coil?
I think my complaint with it is that the failure mode is that, when you hit "stop," it wouldn't stop, since everything has to be intact in order to signal for a stop. But with what I have, the failure mode (an open in the wiring) is that nothing would work until it was fixed.
The downside is the hum. But, if the hum isn't detrimental and doesn't signal something Bad Wrong (i.e., if the contactor is supposed to sound like that when it's engaged, and is designed to be engaged and hum for hundreds of hours at a time), then it's really no worse than the flourescents and I can live with it.
Thanks for the thought. I'm running 20 gauge wire, and, for my test setup, my single estop switch is about three feet away.
Also, to be clear, the coil seems to be *holding*, it just hums while it's doing so and I want to make sure it's OK that it does so (and/or learn if there's some way to make it not hum that I don't know).
The relay is a Cutler-Hammer C25DND330T. You can get formal specs here:
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idea if that seller is any good, they were the first Google hit that had what I wanted. It's a 3 pole because that's all my local electrical supply place had; I'm just not hooking up the third pole. It's listed on that page as:
Coil Voltage Rating: 24 Volts AC
The doorbell tranformer is definitely 24 V AC output.
Everything's within spec - either this is normal for this setup (George's opinion, I believe) or something's wrong. I suppose it's also possible this setup is not just inadvisable, but Wrong.
Converting to _DC_ power (a whole $10, or so) could make for a signficant noise reduction. NOTE: 'AC' coil relays _will_ work just fine on DC power (the 'other way around' can be problematic :)
visit your neighborhood Radio Shack.
Look for a "bridge rectifier", rated for "at least" 24V -- 50V ones are fairly common -- at a couple of amps.
Also a capacitor. rated at _at_least_ 50V, and at least 200 microfarad ("uf").
The bridge rectifier should be a 'little black box', with a lead at each corner. one will be marked "+", the one opposite it will be marked "-", and the other two will either be not labelled, or will have a sort-of "~". Those last two are the AC input, connect one to each wire from the transformer.
Connect the capacitor across the other two leads. making sure that the "+" side of the capaitor is connected to the "+" output from the rectifier, and "-" to "-". Then run connect the existing wiring to the switch/relay to the "+" and "-", as well.
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