Relay Help - 8.5 VDC

[shockfire]

Hi all,

I'm currently setting up a house alarm system. I have an external bellbox that requires 12 volts DC to "trigger" it's speaker. However, my alarm control panel outputs 8.5 volts as it's trigger output.

I have attempted to use a 12v relay, but the 8.5v is not enough to trigger it. Looking online, it seems that 12v relays require 9-15 volts. Alternatively, a 6v relay requires 4.8-7.2 volts.

I couldn't find any information on a relay that could be switched at 8.5 volts.

Does anyone know of a solution?

Thanks very much,
Shockfire.

 

[electronicsuk]

Use a 6v relay with a resistor of suitable resistance and wattage in series with the coil. If you already have a 6v relay and you can find out either the resistance across the coil or you know the current consumption, we can help you choose a suitable resistor!

 

[RF Lighting]

Buy a compatible panel / bell box

 

[redpis]

Sounds unusal that the bell trigger won't fire the external sounder, I've never had to resort to an intermediate relay, are the settings right?? SAB or SCB etc

If it is the only way you have, try a transistorised relay such as this for example:


http://www.actmeters.com/120L-Transistorised-Relay.php

 

[shockfire]

Use a 6v relay with a resistor of suitable resistance and wattage in series with the coil. If you already have a 6v relay and you can find out either the resistance across the coil or you know the current consumption, we can help you choose a suitable resistor!

Thanks for your fast reply! I don't think I've got a 6v relay hanging about, but will certainly have a look through my electrical-bits drawer tomorrow.

Buy a compatible panel / bell box

Yeah in an ideal world, reason i'm resorting to this is because i'm doing it on the cheap. Got a very cheap panel, and the bellbox was left on the side of the house by the previous owner...

Sounds unusal that the bell trigger won't fire the external sounder, I've never had to resort to an intermediate relay, are the settings right?? SAB or SCB etc

If it is the only way you have, try a transistorised relay such as this for example:


http://www.actmeters.com/120L-Transistorised-Relay.php[/QUOTE]

Ah that looks fairly cool, will have a look into these.

Thanks for your help!
Shockfire.

 

[ericmark]

Use optical isolator. LED powers photo transistor all in one chip.
However one questions the use of non standard alarm parts I would not think insurance would accept the use of non type tested items.

 

[electronicsuk]

Use optical isolator. LED powers photo transistor all in one chip.
However one questions the use of non standard alarm parts I would not think insurance would accept the use of non type tested items.

The output on an optoisolator, even the open-collector type, usually has a pretty low current rating. I'd be a little uncertain about this arrangement for direct connection to a bell box. Sure, it could be made to work with a few extra components, but then it becomes more work than a relay!

 

[ericmark]

The point is what ever is used it would be non standard and the system would not be NACOS approved alarm. So most insurance companies will not accept it. Alarms don't stop burglars they just satisfy tick boxes on insurance forms. So if it does not satisfy tick box then rather pointless.

One problem with bells is the time they can sound is strictly limited by law and to use unmatched units could result in fines if the sounder did not stop within the time permitted.