i want to add to my "heated" accessories switches so they go off with the car and do not come back on with the car unless re-activated manually, like the cruise control. i want to put it on my rear defrost, heated mirror and seats.

 

i'm sure i'll need a relay but i need one that will keep the switch on only as long as it has power, then default to off.

 

what kind of relay? hard to do? safe to do? what do you call it? what parts would you need?

 

another option might be to add a timer to the circuit, on for 5 minutes or what ever.

 

thanks,

john

Edited March 19, 200917 yr by johnceggleston

One approach is to use a ''latching relay circuit''. A standard relay of the correct coil voltage and contacts rated to handle the accessory current will work. A momentary-contact ''trigger'' switch applies power to the relay coil. Once the relay is energized, its contacts parallel the trigger switch so that when the trigger switch is released, power is still applied to the coil. A ''reset'' switch is needed if you want to turn the load off without killing main power.

 

Figure 3 of http://www.eleinmec.com/article.asp?24 shows the basic concept. However, that circuit (which uses a single-pole relay) requires that the trigger switch momentarily handle the load current each time it's used. A lighter-duty triggering switch is sufficient if a double-pole relay is used instead. The first set of contacts would be wired as shown in figure 3, but the second set would only apply power to the load -- that way, the trigger switch only has to handle the relay coil's current.

it sounds like a fair amount of work since i'm not too familiar, but it they come "pre packaged" i can probably handle it.

 

thanks.