How long can I leave ACC power on?

[Sqrly]

Anecdotal evidence and/or actual current measurements, both are welcome.

RE: I sit in line in front of my kids school for 30 minutes everyday to pick him up. It's cooling off here and I no longer need the AC, I'm comfortable with the windows open now.

I want to play my radio for 30 minutes 5 days a week without the vehicle running. I know there's a lot more stuff 'awake' then just the radio when the key is in the ACC position. I don't want to drain my battery down though. The school is only a mile away so there's not a lot of charge time going on.

The radio isn't stock but it probably pulls less current and the volume is set pretty low while I'm sitting in front of a school with the windows open. It's the rest of the systems that are awake when the key is in the acc position that I'm wondering about.

 

[Blckshdw]

I got one of these bluetooth battery monitors, it's pretty handy. You can watch your voltages in real time, and if you feel it's getting lower than you're comfortable with, crank the engine and get a little charge back into it.

Amazon.com

 

[TJBaker57]

A lot will depend on the battery.

I don't know if the following will work for a non_factory radio.

I would guess it depends on the particular radio and possible adapter modules?

I never replace audio systems so I have no knowledge there of.

As an alternative to leaving the key in ACC you 'may' be able to turn the key off and the radio should continue for ten minutes. When the radio turns off, cycle the key again for another ten minutes and so on.

 

[budwich]

you can buy a "digital" voltage display that plugs into your lighter socket. They have a usb output socket also. There about $5. They have some that also provide you with "indoor temp" so you can see why you are "baking"...

As an alternative to cycling the key, you can wire in a double throw, single pole (dtsp) switch. One throw to the "normal powering" of radio (Ie. accessory power). The other direction to "hot at all times" power. Using this method, you don't have to keep "keying on" repeatedly to active the "timed accessory delay relay".... but this method also cuts off any extra "accessory drain" that comes with the accessory position. Of course, the down side, is you could leave the switch, accidently, in the wrong position resulting in the radio being on longer than you wanted and thus draining your battery.

 

[Sqrly]

you can buy a "digital" voltage display that plugs into your lighter socket. They have a usb output socket also. There about $5. They have some that also provide you with "indoor temp" so you can see why you are "baking"...

As an alternative to cycling the key, you can wire in a double throw, single pole (dtsp) switch. One throw to the "normal powering" of radio (Ie. accessory power). The other direction to "hot at all times" power. Using this method, you don't have to keep "keying on" repeatedly to active the "timed accessory delay relay".... but this method also cuts off any extra "accessory drain" that comes with the accessory position. Of course, the down side, is you could leave the switch, accidently, in the wrong position resulting in the radio being on longer than you wanted and thus draining your battery.

That's what I have been doing, "cycling the key" so it's only the RAP power on. I don't know what actual difference that makes but I don't see as much stuff lit up so it makes me feel better.

My vehicle is used primarily for taking kids to school or running errands around town so it only gets driven a few miles at a time. I usually slow charge the battery overnight every few months or after it sits for more then a week during school vacations.

After posting this I remembered we have a nice BT speaker, a Soundcore 2, I'm going to start taking it with me so I can leave the vehicle off when it's not running for the AC or heat. I'm actually watching old Sci-Fi series on my tablet while I wait, I've just been pairing it to use the stereo for better sound.

Note: When I was about 11 I hid a switch like that up under the dash in my fathers truck so I could listen to the radio while we were camping and the parents were away from the campsite. If he ever found it, he never mentioned it.

 

[TJBaker57]

That's what I have been doing, "cycling the key" so it's only the RAP power on. I don't know what actual difference that makes but I don't see as much stuff lit up so it makes me feel better.

My vehicle is used primarily for taking kids to school or running errands around town so it only gets driven a few miles at a time. I usually slow charge the battery overnight every few months or after it sits for more then a week during school vacations.

After posting this I remembered we have a nice BT speaker, a Soundcore 2, I'm going to start taking it with me so I can leave the vehicle off when it's not running for the AC or heat. I'm actually watching old Sci-Fi series on my tablet while I wait, I've just been pairing it to use the stereo for better sound.

Note: When I was about 11 I hid a switch like that up under the dash in my fathers truck so I could listen to the radio while we were camping and the parents were away from the campsite. If he ever found it, he never mentioned it.

I also have a Soundcore, nice little unit.

About radios, I cannot speak about aftermarket but for factory radios there is no keyed power at all. None. "Hot at all times".

So where would a switch be installed??

The factory radio is another module on the serial data bus. It "turns on" and "turns off" in response to a "power moding" serial data message from the BCM which DOES have sensory wires to the ignition switch. A timing function of the BCM keeps the RAP 'power' on.

I know that early models like my 2002 do not even have an RAP relay. It's all done by power moding messages.

 

[Sqrly]

I also have a Soundcore, nice little unit.

About radios, I cannot speak about aftermarket but for factory radios there is no keyed power at all. None. "Hot at all times".

So where would a switch be installed??

The factory radio is another module on the serial data bus. It "turns on" and "turns off" in response to a "power moding" serial data message from the BCM which DOES have sensory wires to the ignition switch. A timing function of the BCM keeps the RAP 'power' on.

I know that early models like my 2002 do not even have an RAP relay. It's all done by power moding messages.

You bring up a good point. When I did it to my father truck as a child vehicles didn't have networks, just 12v relays and not many of those.

In my current vehicle I am using an aftermarket radio and the PAC RP5-GM11.

I suppose one could connect a switched 12v source to the wiring in between the PAC and the stereo using a diode to prevent sending voltage into the PAC or a relay to switch the connection from the output of the pac to the 12v source.

You could probably come up with some way to power a factory unit too but wouldn't you run into issues with the theft deterrent system?

 

[TJBaker57]

You could probably come up with some way to power a factory unit too but wouldn't you run into issues with the theft deterrent system?

The only way to have a factory radio 'turn on' without turning the key is by sending the correct "power moding" message.

However, if you do this the BCM will immediately counter your message with what is sees as the proper 'power mode" based on ignition switch poaition and other 'flags'.

Some modules on the vehicle have their own dedicated wires to the ignition switch. These are failsafes in case the BCM doesn't send the proper 'power mode' message. If these modules see signals from the ignition switch and it disagrees with the BCM message they will operate in a default mode that allows the vehicle to operate.

The factory radio does NOT have this capability as there are NO such failsafe signal wires to the radio.

And yes, the factory radio will lock if the radio does not see matching partial VIN messages broadcast by a BCM during the key-on sequence.

 

[Mooseman]

Adding a switched 12V+ in between the PAC and the HU's switched power wire would work. Don't know if a diode to prevent backfeeding the PAC is really necessary but wouldn't hurt. The caveat would be that you can't forget that switch on or it will kill your battery.

 

[Sqrly]

Adding a switched 12V+ in between the PAC and the HU's switched power wire would work. Don't know if a diode to prevent backfeeding the PAC is really necessary but wouldn't hurt. The caveat would be that you can't forget that switch on or it will kill your battery.

At this point it's all just conjecture, I'm not actually going to modify anything.