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sticky relay help

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bythor

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Hi, another newbie with probably a stupid question but fingers crossed.....
I'm trying to switch on a horn. A remote button is pressed, activates an rf transmitter, the receiver then activates a relay and the horn sounds. The rf side works fine, but if I connect the horn it continues to sound when the button is released. If I use a bulb or buzzer etc it works perfectly - eg relay goes off when the remote button is released. The horn is 12VDC, drawing about 7A. The relay is rated at 20A. Relay coil is 12V too (separate supply to horn). Can any one suggest why this happens only with the horn and not a buzzer, and how to overcome it?
 
The horn has vibrating contacts that may be generating interference into you receiver. Try moving the receiver farther from the horn. Putting a 0.1µF capacitor directly across the horn terminals and/or connecting a car generator hash filter in series with the horn may also help.
 
Yes, it's a noise suppressor such as this.
 
You need to power the electronics with a separate battery. If this works, you need to look at separating the two supplies as much as possible.
 
Thanks Colin, separate supplies are already in use for the electronics and the horn. Separating them spacially is not possible, as the receiver is in the same box as the horn relay.
I'll try the cap across the horn tomorrow, if there are any other suggestions I'd be grateful.
 
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