Battery switch activation via security system?

[patrickt]

Originally Posted by mkassab

So, my question to those that understand electronics…. Do you believe the 200mA negative output from the security system will work OK to supply the ground to the reply switch to activate it and therefore offer a good ground to the battery switch to cause it to active?

Mark, you're planning on buying a simple automotive relay and using that relay to provide the ground to that nice Painless solenoid, correct? You can find relays that will draw under 200mA. If you know that your automotive voltage can be as high as, say, 14.8 volts, and you've only got 200mA to play with, then the resistance across the coil of the relay must be 74 ohms or greater. If you click on this page: http://www.allelectronics.com/make-a...-Relays/1.html you'll see two automotive relays. One with a resistance above your cut-off, and one below. So, in theory, the 88 ohm relay would work. There's not a whole lot of margin for error though, and the intial draw from the coil will spike above your 200mA number -- who knows if that will take its toll on the Viper. Plus, if that little relay "blinks" because of either a current overload, or just a blip from the Viper, then you're disonnecting your batter while the car is running. Not good. Personally, I'd hide a switch somewhere that only you knew about instead of using the relay being fed from the Viper.