Wiring accesory power to modern radio

[Ron67Alpine]

I'm setting up a modern "Alpine" radio. I got ingition power to the radio, but there is no separate ACC power wire. I'm gonna need to splice an ACC wire into the single radio power wire. I know I'm gonna need a diode on the Ig power wire but will I also need a diode on the ACC wire?
Thanks
Ron

 

[RootesRacer]

A far better way to wire in a medium to high power load to a garbage wiring system (IE our old lucas system) is to use the ignition/acc switch output to trigger a relay, and wire the relay straight off the battery lead at the starter solenoid. Output of the relay goes to your radio or other load.

This keeps the load off your fragile wiring and uses the ignition switch to drive a relatively light load (relay coil) rather than the whole load.

 

[Ron67Alpine]

Thanks for the reply, RootesRacer. I guess I should have added a bit more information. I've replaced pretty much all of the original Lucas wiring/electricals, w/ modern stuff, so don't have to worry about the fragilility of the original system. Putting a diode in the power supply line from the Ign power will prevent power from feeding back into the Ign system when using ACC power. My consern is there may be something in the ACC circuit which may be effected by power feeding into it from the Ign system. I can't think what that would be but prefered to be safe, by asking.
Ron

A far better way to wire in a medium to high power load to a garbage wiring system (IE our old lucas system) is to use the ignition/acc switch output to trigger a relay, and wire the relay straight off the battery lead at the starter solenoid. Output of the relay goes to your radio or other load.

This keeps the load off your fragile wiring and uses the ignition switch to drive a relatively light load (relay coil) rather than the whole load.

 

[RootesRacer]

Thanks for the reply, RootesRacer. I guess I should have added a bit more information. I've replaced pretty much all of the original Lucas wiring/electricals, w/ modern stuff, so don't have to worry about the fragilility of the original system. Putting a diode in the power supply line from the Ign power will prevent power from feeding back into the Ign system when using ACC power. My consern is there may be something in the ACC circuit which may be effected by power feeding into it from the Ign system. I can't think what that would be but prefered to be safe, by asking.
Ron

Putting a diode inline to something that consumes any level of power is not a good idea.

Yeah, you prevent backfeed, which would power the ignition when on the acc switch setting, but you loose a diode drop in voltage (~1v), and prevent the radio/load from being able to dump energy back to the battery.

If you take your ign and acc switch outputs, take each one to the anode of a 1N4003 diode, put the cathodes together and use that to drive a relay coil (other side of coil to ground) you then have a solution that gives isolation without the negative consequence and loss of the diode drop.

HTH

 

[Ron67Alpine]

Thanks RR, I appreciate the input.
Ron