Relay question. Safe to use 12V DC on a relay designed for AC?

Factual Questions
1

I went to an electrics shop and asked for a 12V relay. When I got home I realized it was a 12V AC 50Hz relay :smack:

However, I tested it with 12V DC and it works. My concern is that it might burn out. I want this relay to turn on some emergency lights when the alarm siren goes off. So it is going to actually work very rarely and not for more than 3-4 minutes each time.

EDIT: The relay is similar to this one: http://www.abb.com/product/seitp329/6f6b0113b07b5c69c1256d8e003ffd1d.aspx?country=00&tabKey=2&cid=9AAC100111&gid=ABB.BBCGHE3211102R1005

2

Really, you should exchange it. I don’t know from the spec sheet if that is a true AC coil, or a rectifier powered DC coil. If it was a DC coil, it should be fine, if it is AC, it will overheat every time it is energized.

3

Thanks. I got a DC relay today but I was curious so I used a multimeter on the old one and it turns out it draws more than 1 Amp when connected to 12VDC.

For comparison, the DC relay I got today draws just 0.06 Amps

4

A true AC coil depends mostly on inductive reactance to limit current, while a DC coil depends only on resistance. This allows AC coils to run a bit cooler. More so, even, because when the relay armature pulls in, the air gap in the magnetic structure reduces to near zero, which greatly increases the inductance. So you get a current spike when the relay energizes, and a lower holding current when it pulls in.