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Forum Index : Electronics : Warning system drives small siren, how to drive a 240VAC SSR?

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domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 08:18am 03 Oct 2020

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A friend has given me an Arlec Entry Warning Security System, which is used in shops where customers break a beam. A 240VAC plug pack supplies 500mA of 9VDC for the sender and a 20mm dia. siren is driven from it at 9VDC.

The 20m cable and the siren seem to have a resistance of 5MOhm. Using Mr Ohm or A = v / R or A = V/R = 9V/5,000,000 or 1.8uA seems to make the siren work?

My SSR has a control voltage of 3-32VDC and needs a trigger current of 7.5mA at 12V or 90mW and if all my calculations are correct, that means 10mA at 9VDC? I doubt the sender is supplying that much.

I may wish to drive lights or cameras (to be switched on) from that pulse of 9V going to the siren and am happy to do the low-power electronic work to trigger a relay on, which then switches the SSR on with the load and it will need a timer to switch off after a while or the second pulse when the burglar leaves switches everything off again!

Help with a circuit or link, please!

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