AC & DC Relays / Solenoid


Thread Starter


What is the difference in the construction of AC & DC Operated Relays ?

any information is welcome



Michael Griffin

AC operated relays have a lower coil resistance than DC operated relays. In AC operation, the coil current is limited by inductive reactance, while with DC operation, only resistance is present. The practical result is a 24VAC coil will over-heat in 24VDC operation.
AC coils will also normally include a "shading coil" (typically a single turn made from a stamping). This acts to delay the collapse of the magnetic field during zero crossing of the coil supply, helping to prevent relay chatter. This feature is not necessary in DC coils.

Michael Griffin
London, Ont. Canada

Leon Rosario

Coils of AC and DC relays are designed to suite the incoming supply voltage. For example, the coil rating of an AC relay takes into account the impedance of the coil and not just the resistance like in DC ones.

AC relays also require shading of the coil to maintain sufficient magnetic flux.

I presume that you are interested in knowing if you can drive AC relays form DC or vice - versa. If so, you will find the following website useful. It also describes the workings for both types……which is really too long to post here.

See: "": .

Leon Rosario
Rockwell Automation
[email protected]
The number of turn. A DC coil has more turns then a AC coil. It takes about 28 - 30 VAC to operate a 24 VDC coil.
Magnetic Core
In smallar relays the magnetic core is the same solid iron core to save manufaturing cost. In AC coils to prevent the chattering effect of the electromagnet, a shaded copper plate is added in the armature.As the current passes through the zero and the magnetic field about to die, the lagging current from the shading produces a small magnetism to keep the armature in place.

The dc coil current is equal to suplly DC voltage divided by coil resistance in ohms. For the ac coil since the impedance of the ralay ac coil is about five times to that of it's dc resistance, it approximately supply voltage divided by (6 x dc resistance of the coil) A ac 24 v relay if wrongly connected to dc 24 v, the coil will burn out.

If a dc 24v relay wrongly connected to ac 24 v will not work and won't be damaged.If you supply 120v ac to the dc 24v relay, the relay will work but chatter much and contacts will heat up fas if loaded.

Best is that you open up a relay regards.
As such there does not seem to be any difference since the operational principles i.e attraction towards magnetisation due to current... but the difference may be only in the rating of the coil which gets the AC/DC power.