AC coil

Yes - until either the upstream fuse blows or the coil overheats. The AC coil will be wound in a coarser wire than the DC and will pass a lot more current than the DC one when it is connected to a DC source.

Far better to replace the AC coil with a DC one before energising it.

Also the core material and the way its made is different for an ac energised coil compared to a dc coil...

#John.

OK, Electroman. Here's a bit of natural stupidity for you. I have a really nice 30V, 30 Amp power supply and a DVM, but no transformer to test it with...

So, what happens when you put DC through a transformer? I know it's not particularly correct, but what happens?

I know!

Then there's a big BANG and I sell you a new one <Splutter>.

When did 24VAC rms become different than 24 VDC?

????

Uhm, when the polarity started alternating???

When it started passing energy through capacitors and transformers?

Yeah, but . . . In ordinary, AC relays which pull a contactor arm down to the top of an armature, the armature has what's called a shaded pole on it, which is virtually a short-circuited turn on the secondary of a transformer thereby causing the primary current to be significantly higher than without the shaded pole through mutual induction. DC of the same voltage does not "see" the shorted turn on the secondary because there is no mutual induction -- e. g. the coil is no longer a transformer. The current in an AC relay coil will actually be a little less in some (depends on the number of turns on the primary coil), and it can be a little more in others, but nevertheless, the currents are close to the same.

In a mercury contactor, there's no shaded pole, and many have built-in rectifiers to create DC. In those cases, the AC current will be less than DC current by about half, so in that case, you're right -- it takes around 10 - 12 VDC to operate a 24 VAC coil. Now, you might say that the coil impedance is a factor, which it is. Inductive reactance of a coil may be higher than the DC resistance, but there are also cases when it's less. Depends on the quality of the magnetic circuit.

Rather than argue about stuff, the best way to check to see if an AC relay coil is O. K. to use with DC is to measure the AC current and use a DC voltage which gives the same current. If heat dissipation from a resistor or zener diode is a concern, 'cause 24 VDC is all that's available, then replace the danged relay with a DC operated one.

Shoulda gone to the trouble to say this earlier . . .

To be fair ...

I only learned the detailed difference in AC and DC relay coils due to a previous thread on CR4... can't remember who to credit, but I was greatly pleased to be thusly enlightened!

that was me, thanks.

Well I did hook the 24VAC coil up and got hot fast, so I unhooked it.

I finally got a contactor w/ a 24VDC coil and used it.

Yesterday I needed to fix the machine asap. so that was the only contactor available in town. Then today I got the correct contactor from the OEM.

Thanks for all your advice everybody!

Gee it seems the first responder was correct after all, even before all the self appointed "experts" weighed in. Lets hear it for PWSlack...

If you're talking about me, then gee, I didn't self-appoint myself as an expert, but I do know a thing or two about electromagnetic coils.

Let's do give PWSlack credit for giving a sound answer, but if you're not going to add anything to the discussion, the least you could do is to keep your self-righteous comments to yourself.

If the coil is only to be energized for very short periods of time (pulsing on and off), it can get you out of a pinch.

It won't last very long though.

http://64.233.169.104/search?q=cache:8gwIoSvWIAQJ:www.ascovalvenet.com/pdf/LiteratureRequest/NextGen_WhitePaper.pdf+AC+and+DC+Coil+differences&hl=en&ct=clnk&cd=11&gl=us&client=firefox-a

I don't know, Why you ask us this question?

Because of nobody tries to use an AC coil for DC or opposite after saw AC and DC coil.

Certainly, It can be used but It can't function properly.

You can try to do it, use contact relay 24 VAC and power supply 24VDC.

Best regard.

See also:Relay <http://globalspec.ip09.com/rd/9z1zjh924ietefi92ob5iq8k06g0jj4c874a3h64uqo>

Post #14

Regards