Looking for switching circuit from AC source

[Trail Maven]

Can anyone point me to a schematic and parts list to build a simple, rugged circuit that can sense a 4-15 VAC source, without putting much drain on the source, and then provide a switch closure, which can handle 12 VDC to trigger a standard 15 amp car relay?

So when the 4-15 VAC is present the switch will close and energize the relay coil using a separate existing 12VDC supply
When 4-15 VAC is removed the switch will open

This will be used on a Motorcycle so it needs to be durable. It will also be in a possibly wet environment and perhaps hot too. I figure I can pot it in epoxy to improve longevity.

Thanks for any help you can provide. I am capable at soldering circuits, but not designing them or apparently finding them. I have found lots of other sample circuits but not this one. Perhaps I just don't know the proper terminology. :|

 

[siongboon]

Hi,

What application is the relay switching for?

Best Regards,
Siong Boon

MODERATOR - SIGNATURE LINKS ARE NOT ALLOWED

 

[Trail Maven]

The relay will control a DC cooling fan that draws about 5 amps

The purpose of the whole circuit is for the fan to turn off when the engine on the bike is off. Right now if the bike is hot the fan runs after the engine is turned off and kills the small starter battery

 

[siongboon]

Hi Maven,

Do you mean you want the fan to turn on only when the
trottle of the bike is pull, and off when the trottle is at rest.?
And the fan should turn off when the bike is turn off?

Sincerely,
Siong Boon

 

[Trail Maven]

The fan should run only when the engine is running
If the engine is off (no AC voltage) then the fan will not run off the battery

 

[karesz]

Hi,
Why do you not take a signal from your start/ignition switch?
At this point you have the 12V battery continous on if your things is started...
K.

 

[siongboon]

Hi,

I think what is needed.
The AC signal should go through a diode bridge & capacitor configuration,
converting the AC signal to DC signal.
It is the same as the circuit that convert our 230Vac to Vdc.
4 diodes and a capacitor would be enough.
I believe 1A diode should be enough.
You have to try it out.

This DC signal can then be used to turn on a transistor.
The transistor can then be used to switch on your DC fan.

You might like to refer to the website on
using a transistor to switch on the fan.
The section on transistor.

**broken link removed**

Best Regards,
Siong Boon