relays can you keep the power on?

Hi This may seem a stupid question. Most of the circuits I've seen with relays puts a brief (momentary) current through the coil. I was wondering what happens with if you keep a constant current through the coil for a long time? Except the switch being on can it damage the coil or overheat it? thanks

A Bosch/Now Tyco relay is a constant duty device.  No harm will come to the relay even if it is energized for weeks on end.  It will however run down a cars battery if left energized without having the motor running.  It will take a day or 2, but it will go dead.

hi Thanks for the reply. I'm using a 12v relay (JQX-115f - not sure of the manufacturer) and a omron DPDT latch relay. I can do a circuit so that it only sends a pulse but would mean a whole lot more work. The circuit will only be on when the cars on so no risk of battery discharging. Do you think it would be ok to keep the coil charged in these relays? thanks

With the accent on "THINK". What are you trying to achieve, can't you use just the latching relay?

Relays do handle constant on - unless not "continuously" rated as with some LARGE relays used for starter motors, winches etc. Many relays in both industry and automotive use are permanentaly on as long as the equipment or vehicle is on. They are only off under certain circumstances (eg, the is an alarm, or the fan is needed, etc). Those relays can last 20 years or longer.