I have an always-on accessory in my lighter socket. But it keeps killing my battery if I don't run it every day. I was hoping I could use a simple circuit that would only work when the lighter is over 12V (meaning it 14V because the alternator is on)

I think I would just need a transistor and a resistor?

Many thanks!
PS. I tried to search for this, but I didn't even have a good idea what to google.

 

Depending on your car, you may be able to program the outlet to be keyed instead of battery-direct. My minivan offers that option.

Just about anything else you want to do to the vehicle will qualify as an automotive modification - a topic forbidden by the Terms of Service here.

I'm not sure how the mods will feel about it, but I think altering your ACCESSORY to auto-off on low voltage should be an OK topic. We had a low-battery auto-off thread here recently. Search a bit and you should find it very useful.

 

I just tried a TIP 120 circuit. Too much Vbe drop. This will have to be done with a relay (if you can't just "tell the car" to make it a "run only" outlet).

Zener, resistor, transistor as a switch, relay coil.

 

What load are you drawing (amps) from the cig lighter?

 

It varies, it is a dash cam, but supports a charging port for phones, which draws 1600ma when there is a phone plugged in, not including the dash cam.

Why I want this is so I don't have to modify my car at all. I want to put the circuit inline - actually in the line to the dash cam - and let the acc port work as it currently does, when I need to charge my phone in the car. So TOS should not be a problem, as this would go on the dash cam wire.

 

Can you confirm what the lighter socket voltage actually is when the engine is running?

 

Can you confirm what the lighter socket voltage actually is when the engine is running?

My prediction:

Engine running, > 14V
Engine stopped, < 13V

 

Can you confirm what the lighter socket voltage actually is when the engine is running?

My prediction:

Engine running, > 14V
Engine stopped, < 13V

I have a circuit on my other computer using a TL431 driving a PFET as a high-side switch which would do this. I can post it later today...