Thread: Powering Headunit off Aux Battery

you can buy a special relay that locks on and holds power if you trigger with a momentary switch to a device until that device is turned off then it releases the power. if you wired one of those inplace to feed power to the accessories trigger on the radio and just hit a momentary switch you could power on the head unit, then when turned off it would release the relay and the unit would operate on accessories as normal.
let me go find the relay you need. i think its called a latch relay.

Or you could buy a head unit which will run without the key by pressing on!

Hook the main power lead to the Aux battery and the "trigger" for ignition to the original trigger wire...

Originally Posted by Tombie2

Or you could buy a head unit which will run without the key by pressing on!

Hook the main power lead to the Aux battery and the "trigger" for ignition to the original trigger wire...

if you are going to do that, just plug the trigger wire from accessories into 12v constant power and then any head unit will turn on without the ignition thats probly an easier solution.

Originally Posted by Rosscoe68

if you are going to do that, just plug the trigger wire from accessories into 12v constant power and then any head unit will turn on without the ignition

Except they wont turn off and will flatten the battery!!!!

The operate without key decks turn off after 60 minutes

hmm, that sounds nifty, might be a good option for my caravan.

Why??? If you have dual batteries and a smart switch, even if you flatten your main battery, it will switch to the Aux for starting and then change back and charge the main. Seems a bit pointless to me.....

But if you really feel the need, just use a DPDT changeover relay, as you need this to switch the power in the headunit and can only do this based on which battery you want to use. Use one pole for the trigger and one pole for the main feed and wire the accessories to the relay coil (pin 86)

The main battery feed will wire to the pole that closes on relay activation and the trigger wire connects to the same wire that activates the relay from accessories wire in the ignition switch.

The aux battery main feed goes to the other side of the switch that makes contact when the relay isnt powered and the trigger wire feed is taken directly from the battery via the other pole on the relay so it activates when key is off and disconnects and allows the relay power to takeover when ignition is turned on, that way you dont have linked power between the two batteries, or, use a manual toggle switch connected to the battery
But I wouldnt bother i fI had a smart switch......