Contactor coil: 50 Hz vs. 60 Hz

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IME relays pull in at in the region of half rated voltage, and dc ratings are typically about half the voltage of the ac rating, which gives an idea of how much current is determined by L and how much by R. Running your relay on 220v 60Hz it will work fine. Contact closing speed will be slightly slower. Margin will be reduced, but its only being reduced from enormous to slightly less enormous, so its a non- issue except in very unusual situations. The vibration tolerance of the contacts will be little affected in practice; if your environment is harsh enough to shake the relay contact open, then you've got bigger worries than contacts crackling.

If instead you meant you would use it on 110v 60Hz, then dont. But you could use diodes to get a higher dc voltage and use that.

NT

When relays have dual ratings for ac and dc, its normal for the dc voltage rating to be half the ac voltage rating.

I really dont agree. I do know the basics about relays, and one normally finds that pull-in occurs at around 50% rated voltage. The OP is welcome to test theirs to see if it behaves the usual way.

I dont know why you think I've forgotten it. What's relevant here is inductance in the closed position.

true with all relays under all ac conditions. Theyre designed to work that way.

No, its exactly how theyre designed to operate.

Where's the conjecture? I get the feeling you could do with bringing your skills up to speed on relays.

That would work.

You're not saying where you got those figures from. Typically dc rating is half ac rating.

The effect of the relay's inductance, when run off a BR, is simply to smooth the current flow somewhat. Mean current remains much the same. So we're looking for 120v rms, which is what the BR would deliver.

and overheat the relay by increasing its rms dc voltage to above 120v.

NT

yup

yes. I guess in theory both matter, one determines closing behaviour, the other ensures the relay doesnt overheat. In practice though the margins are very large, and its normal to simply fix holding current to suit the relay, and not worry about closing current, which will be so close as to make no real world difference in all but exceptional circumstances. But yes, we can consider both if need be.

I'd like to see you find one single electromechanical relay that wont work for.

This 2:1 ratio normally is good for relays, and the OP can check his to see if it conforms to that. If it does, the thing will always work when subject to this formula.

FWIW, when ac is applied you get puling force plus vibration. With dc there is no vibration component when its closed, so less holding current is needed. How much less I've really no idea.

Some relays are fast movers capable of 100s of Hz, some are slow. Ac relays can always work on dc, but dc ones often dont work ok on ac.

Re ripple: If the relay is designed to run on ac 50 or 60Hz, its designed and rated to live with the current and force variations that go along with that, 100-120 times a second. Running it on rectified mains will only serve to reduce the current variations through the cycle, it wont cause the relay any issues.

Re rms voltage: With my 2:1 figures, rectified 120v is spot on. With your 174v figure, 120v is well within the 50% margin. Of course for some uses that margin would need to be confirmed by testing before production, and reconfirmed if a new relay type is used. Or as you say, a cap could be added. Or for off brand consumer goods, in it goes, relays are good for it.

RMS can be applied to any and every waveform, dc included. Its very relevant when working with rectified ac, semismoothed or unsmoothed.

With the same current it wont, with higher curren ti will. IIRC you proposed using 174v rms, that would be ok on your specific relay, but not a universal solution.

NT

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We know that. I also know from observation of various mfr specs that ac relays are normally happy on half the voltage at dc. The relays I've seen the dual ratings on havent been significantly different to others.

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Yup just means yes, it indicates agreement. Nothing else.

The coil v/i margins, the difference between what works and the nominal voltage rating

a design question for the relay manufacturer perhaps, its a non-issue for us

One seldom need worry about the must open rating. The must close and wont overheat points are what counts in 99.9% of applications.

I'm saying it already taken into account in teh design of the relay, its an ac relay. All we need do is give it enough current, but not too much.

ent

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I'm talking about what relays actually do in the real world. Reality and mfr specs often dont match.

I have to say that is false. Its fairly normal engineering practice to use parts outside of mfr's specs so long as their effectiveness in such conditions is verified, they can reasonably be counted on to continue to operate satisfactorily, and so long as the level of reliability that gives is sufficient for the app. And in this case the OP has good motivation to do so.

On delay specs are seldom critical. If they are then of course you'll hit the coil with full rated v - or as I used to do at times, much higher for a small fraction of a second to get it switching faster.

Bounce specs, again whether its ok depends on the app, and effect on lifetime depends on whats being switched, and what lifetime is in fact required of the part.

e,

Its not bogus at all. If you really want to settle this, take a pile of random relays and test what v they actually do close at. Then we can discuss why what you find and what the mfr says are different.

You're stuck on mfr spec when the situation is that the OP is strongly motivated to use the part outside of its mfr spec. Engineers do that.

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fwliw I said use diodes, you came back with a FW BR. I dont think it matters.

Your proposd BR+C delivers the right i for one specific relay. For some relays it will fry them.

NT

Snipped a lot of repetitious, self serving nonsense.

ow

If you want to go get some specs of other relays, you can. This is starting to get silly.

Worth investigating, to me. JF gave a specific relay & numbers. I tried to find a relay to support the idea that an AC/DC relay would be happy with DC voltage about 50% of AC rating. Can you please provide a reference?

Meanwhile, what I did find was an ap note from Tyco entitled "Operating DC Relays from AC and Vice-Versa" .

It does not agree with the DC at ~50% of AC rating idea. It uses the example of a KR series relay coil. Their example uses a 12 volt AC relay fed by DC. The example states that the "DC voltage cannot exceed 9.8 volts", and "should not be lower than 7.35 volts". Thus the DC range would be ~61%(minimum) to ~81% (maximum) of the

Extrapolating, it does agree with the idea of BR+C fed by 120 for the 240 volt relay, insofar as the DC voltage: ~146VDC min to ~194VDC max, which makes the midpoint ~170VDC. That's very close to ~168 from the BR+C

Regarding coil ratings, I've worked with DC relays, and I've worked with AC relays, but I haven't worked with AC/DC coil relays, so I can't speak from experience with them, and I haven't found anything yet specifically dealing with that, other than the link I found to Tyco. So a specific link or links would be most helpful.

Thanks, Ed

You must remember that AC coil relays are wound a little different, its not just induction here. Inter pole windings help keep the AC coil from chattering the armature. I am sure under DC operation, this may effect the calculations.

There are some AC coil relays that do not do this and thus the 50% voltage for DC should come close, but then again, DC R in the coil also plays a role in this.

Jamie

Your post contains nothing specific and does not address my question.

I am looking for a specific link or links that shows a datasheet, ap note, or example of a relay that NT has in mind. Do you have one?

I want specifics, like John Fields posted; the specs that NT said you could get: "If you want to go get some specs of other relays, you can." The specs I have been able to find so far do not demonstrate what NT was talking about, thus my post asking for a reference.

Ed

Don't be anal, they make relays that will do AD/DC because they have a diode imbedded in them. The voltage ratings are the same. The coil is actually of DC type.. They also have relays with shunt diodes built into them, for those you need to insure the polarity is correct and are strictly DC only.

We also deal with solenoids to operate in the same manner..

Scroll down and read about AC coils, I am sure if you're looking for some more detailed information you can find it, but this will explain some of the differences.

Jamie

I don't know how to make it clear enough for you to understand. While I do appreciate your attempt to help, I must say it misses the point.

I want a *specific* link to an *AC/DC* relay of the type *NT* had in mind, or to an ap note or reference that discusses a relay coil that is rated for *both* AC and DC as he indicated.

Do you have a link to what NT was talking about? Here's what he said: "The various ones I've seen that have coil 2 ratings, one for ac one for dc, have consistently had the dc coil rating be half the ac voltage rating."

I _do not_ need generalizations, hand waving and condescending responses. You mentioned a relay that will "do" DC because it has an imbedded (sic) diode and say "The voltage ratings are the same." That is *NOT* what NT said. He talks about the dc coil rating being half the ac rating.

Ed

Is this what you're looking for ?

It explains operating AC coils on DC and AC coils using the internal DIODES for shading rings design.

These are just some examples out there.

I don't know what "NT" had in mind, if this isn't what you're after, than I'll stand down. ;)

Btw. P&B got bought out, in case any one didn't know.

Jamie

Geeeez. I posted that link in my _first_ post in the thread, and you replied to that post. I guess you either didn't read the post properly, or didn't understand it. The ap note does not agree with the DC at ~50% of AC rating idea - details are given in that post.

Yup. To operate an AC relay on DC, (the Tyco ap note says doing so is impractical, but that you can do it in an emergency) you should install a residual and you must lower the voltage below the AC rating. An AC rated coil needs DC in excess of 61% of the ac rating on the minimum side, and less than 82% of the ac rating on the maximum side, per the example given in the ap note.

Ok.

Ed

Sorry, I didn't see that.

No, that wasn't a hack as far as the diodes goes, that is a practical design in a family of relays, We use large contactors with the dual coil and diodes in them. You don't see this from the out side world but they are incased in the encapsulation. Those particular types can have DC going directly to them. It's just the way they are with obvious reasons.

The app note is pointing equivalent power dissipation, as you know relays will pull in at a lower current So I don't see a problem here.

Why don't you put a few AC types on the bench and test them yourself?

I think you'd be surprised in what you find. Lab testing tells a lot about what you can do.

The only problem I have found with this practice of using AC on DC is that some AC units use material that has a high hysteresis and the AC will help keep this down. They do this in cases where they don't use the dual coil system. In DC operation, I've seen it over magnetize the core and cause a little slow release on the contacts. But that may not be such a big deal in most cases.

Have a good day.

Jamie

I have an Essex contactor which was removed from my old A/C outside unit. It has a 24VAC 50/60 Hz coil. I can make some measurements on it if anyone is interested.

John S

If you have IR gun/camera, you should also do some comparisons.

Jamie