Dc and Ac operated relays. What is the difference between 12volt Dc, 24 volt Dc and 120 volt Ac operated relays?

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EdO135 months ago
PaulR12711 months ago

DC relays

DC relays consist of wire wound on a bobbin, which is placed over a ferromagnetic core. A hinged contact assembly is positioned over the core .When current is applied to the coil, flux is induced in the ferromagnetic core, causing the contacts to close.

AC relays

AC relays are manufactured similar to their DC counterparts. If AC current is applied to a DC relay, the relay will pulse at the frequency of the AC current. To overcome this problem, the core is equipped with a shading ring on one-half of the core (Photo 2). The shading ring acts like a shorted secondary winding in a transformer, causing the flux in that half of the core to be 90° out of phase with the flux in the other half. The result is that the flux in the core never falls to zero, allowing the relay to energize the contacts.

The voltages you list are what the coil operates from. You need to apply that voltage to the coil to get it to actuate. If you apply 12VDC to the 24VDC coil, it may not actuate. If you apply 24V to the 12V coil, it may burn it out.

The relay contacts are generally isolated from the coil contacts. So if you need the use the relay to switch a voltage different from that required from the coil, you can generally do that, as long as the voltage and current you are applying to the switch contacts doesn't exceed the ratings of the part. For example, your relay may have a coil that needs 12V DC, but the switched contacts may be rated for 125 AC and some maximum current.
LeShane (author)  LargeMouthBass5 years ago
To LMB I realize that the relays basicly work the same, My intrest is in what differences in the coil windings are present to allow for DC or AC operation of the relay. At this point I am not really interested in hoe the switched contacts work. Do AC coils have nore wire or less wire than an DC relay coils? Are any devices; diodes, resistors used in the coils to make them AC orDC coils?

Is it all just a certain wire wrap count that does the determining as to whether a relay runs on 12v , 24v, or 120vAC ? I thank you all for your informative answers . I love this website! LeShane
Careful with an AC coil that there is never anyway that stops it closing - they can burn out like that.
iceng5 years ago
Same contacts Say DPDT and attach a 12VDC Coil or replace it with a
24VDC coil later you can remove the DC coil and install a 120VAC coil.

All three relays work identically except they need a different coil voltage drive.

Dr.Bill5 years ago
You got it-