AC vs. DC

Techman

The "ice cube" relay in an Argo control has 24vdc printed  on the relay coil and a Taco control has 24vac printed  on the relay coil. What is what? They are physically identical.

Jean-David Beyer

Difference between AC and DC relay coils.

Back when I designed such stuff, there was a difference between an AC relay coil and a DC relay coil. The DC one may have had more turns of wire on it, or finer wire because it had only resistance to block the flow of current, where the AC one had its inductive reactance as well. But usually the coils in non-sealed units had tape over them so you could not see that. The givaway was that the AC relay tended to have a D-shaped copper shorted turn around half of the steel armature through the center of the coil, at the end where the moving steel piece with the contact(s) are. This may be hard to see in ice-cube style relays.

Tim McElwain

Simple answer

a lot of the plug in "Ice Cube" relays are DC voltage, the 24 VAC applied to the relay is converted to DC through rectification built in to the board. The older relays all had 24 volt AC coils in them  Omron is one of the companies that makes a lot of the "Ice Cube" field replaceable relays. I find by the way that replacement is usually more likely at an electrical supply house than one of the heating supply houses.

Techman

I'm not sure,

but,are you telling me the relays are not electrically interchangable. ? The coils are covered w/ tape.

Mike Kusiak_2

Not interchangeable

No, they are not interchangeable. Although they may look identical, as JDB points out, the AC and DC relay coil windings are not the same. You can confirm this by measuring each relay coil with an ohmmeter. The AC relay coil should read a lower resistance than the DC coll.