I need a mechanical relay that when 12 vdc is applied it sends out a single shot, 12vdc signal to ring a fire bell with a coil.
I'd like this signal to be adjustable from every 1 second to 5 seconds.
I'm going to use it on my 52' trailer for a backup alarm.
Might someone out there know of such a heavy duty relay?
Thank you in advance.
Michael

 

Heavy Duty Relay is a pretty broad term. The 12 volts is simple enough but no mention of the back up alarm current? We choose a relay based on coil voltage and the current (AC or DC) the contacts can handle or switch. In the interest of keeping things simple I would be looking at automotive type relays which can handle 20 ~ 30 amps. My guess is that you plan to drive the relay from backup lights? Anyway if an automotive relay can handle your desired current load for your backup alarm that would be my choice. They are common and inexpensive.

Ron

 

If you really want to use that bell as an alarm then you will need a circuit to pulse the relay, which could be done by a 555 timer IC and a transistor driver to the relay coil.
Are you up to building a small circuit?

 

The relay portion is easy, that isthestandard5 terminal cube relay with 30 amp contacts. But unless you like building projects with small parts, and then figuring a way to package them that will survive in a vehicle, I suggest a commercially available timer. That would be connected to start when powered, and after the delay time operate the relay, while the relay normally closed contact opens, which removes power from the timer so that it resets and starts timing again, to operate the relay again.It may require a capacitor across the relay coil to keep it engages long enough for the bell to bang and the timer to reset.

 

I would suggest a generic "Turn-Signal-Flasher", available at any Auto-Parts-Store.

They are designed for a fairly heavy-Load of around ~10-Amps.

We still don't know how many Amps the Bell requires to operate.
What is the DC-Resistance of the Bell's Coil ?
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I

I would suggest a generic "Turn-Signal-Flasher", available at any Auto-Parts-Store.

They are designed for a fairly heavy-Load of around ~10-Amps.

We still don't know how many Amps the Bell requires to operate.
What is the DC-Resistance of the Bell's Coil ?
.
.
.

vote for the turn signal flasher plus a relay. I have a similar bell from a battery security system and it draws about one amp. It also includes an interrupting contact so it sounds a continuing alarm, not a single chime. It may actually work very well using an older turn signal flasher directly. But it might give a few rings each time. A series power resistor might be needed to reduce heating.