110v AC to 24v DC relay for emer. lighting

[bczoom]

I need a relay (or something) that will trip if the AC power goes out which will then kick on the emergency lights (24v DC that are powered via battery).

Can someone give me an idea of what to get or search for? My searches aren't coming up with the right things.

 

[Jim_S]

if you want instant transfer you can use a relay with a 110vac coil and normally closed contacts. when the coil is energized the contacts are open. When the 110 goes away, the relay de-energizes and the contacts close to turn on the 24 volt system.

If you want a delay they make relays with a delay built in or you can build an electronic delay.

Jim

there are thousands of relays that would work, many different manufacturers and form factors.

here's an example, look at the s86/s87 series
http://www.mouser.com/catalog/625/1340.pdf

an example of a time delay relay, top of the page, the CB series.(a little on the expensive side)
http://www.mouser.com/catalog/625/1339.pdf

you should mount the relay in an enclosure and make sure you fuse the 110 line feeding the relay coil.

 

[bczoom]

Thanks Jim,

I've printed the info on the S86/S87.

When you say a time delay, do I assume correctly that wouldn't be appropriate for an emergency lighting system as you would want the lights to come on immediately?

you should mount the relay in an enclosure and make sure you fuse the 110 line feeding the relay coil.

Can you elaborate on putting a fuse in there? It's current configuration is the relay is on a breaker in the 110V box.

 

[Jim_S]

When you say a time delay, do I assume correctly that wouldn't be appropriate for an emergency lighting system as you would want the lights to come on immediately?.

If your power just drops upon failure you don't need a delay. If it stutters off and on the relay will drop in and out causing the emergency lights to flash. If you have a delay of a few seconds you will be in the dark for the delay period but it will stay on when it does come up.

An example is the power failure start relay on an automatic transfer panel for a generator. It doesn't kick in immediately it waits for a pre-programmed delay time to make sure the power is really off.

In this case it doesn't make a difference, either way would get you light in the long run.

Can you elaborate on putting a fuse in there? It's current configuration is the relay is on a breaker in the 110V box.

If there is a failure in the relay coil such as an partial short the coil could overheat and catch fire while only drawing a few amps. A 15 or 20 amp breaker would never know anything was wrong.

The relay is energized 24x7, already hot. It's wise to use a good brand in these cases too. P & B makes good stuff.

Jim