Low Voltage Cutoff Switch to Prevent Battery Drain
 

I didn't see any thread for this mod, so I thought I'd post. To prevent my GPS from draining my HHR's battery on those occasions I forget to unplug it from the always-hot 12v power outlet, I spliced a low voltage cutoff switch into an outlet splitter. The switch is set to cut power when the voltage drops below 12.1v, and restore power at 12.8v. Functionally, this means power flows only when the engine is running, and for a short time after the engine is shut off. I added a second splitter so that I can have at least one outlet that is always hot. The circuit is rated at 30A, which exceeds the outlet's capacity of 20A. Yes, that is a fake Tupperware tub substituting as a project box; it tucks out of sight behind the radio stack console, so looks aren't really important. I paid about $20 for the circuit from a US reseller, but it can be ordered for less from China if you are patient.

Also shown is a photo of a modified setup, fully installed. The upper bank of outlets are voltage switched, and the lower bank are always powered unless I manually shut it off with the power button above the voltage meter.

Cool little project. Do you have links for the switch and splitter you used?

Oh, and welcome to the forum.

Cool idea for sure. But are you positive that the outlet does not shut off once the RAP (retained accessory power) times out? I know mine does turn off when the RAP times out and shuts off. I know this because I have tapped into my outlet for a charger for my phone and it shuts off after 20 minutes.

The power outlet is not supposed to be on the RAP. Maybe some years? Maybe if you have a cigarette lighter with the smoker package?

I think the reason is for jump starting.

12.1V is a 60% discharged battery.

https://cimg5.ibsrv.net/gimg/www.che...6716a6cfd2.png


This is the schematic for 2007

https://cimg4.ibsrv.net/gimg/www.che...b68f9751d4.png

Two of splitters I used are quite old; I had them sitting around. The splitter with the voltage indicator and the on/off button was from Amazon. The low voltage cutoff switch came from ebay, but I paid more than I needed to because I didn't want to wait for slow shipping from China. There are several alternative designs and ratings; 30A is overkill, but I like overkill.


http://www.ebay.com/itm/Electronics-...53.m2749.l2649

I can't say for certain, but if I leave the GPS on, it will still be on hours later. Mine is a 2009 2LT without the smokers package. I've only owned it for a month, so I've still plenty to learn.

Very true; I have been using the on/off switch each time I get out of the car, but sometimes I forget. For these occasions, 12.1v is enough to start the car. I wasn't comfortable rewiring the outlet to switched power, and felt this was a decent compromise.

Thanks for the schematic and the table!

My 2008 2LT does have the smokers package and it does shut off after a short time, I used it for the cell phone charge and it did not finish charging so I know what happened.

I have a 2011 LT and I believe mine stays on. I have left my GPS plugged in and it charges will the car is off.

I am not surprised, some of the small changes between year models that do not show up in the owners manual.:nuts:

My 2008 and 2011 both stayed on. I think it is another difference between a cig lighter and a 12V power outlet.

I put a priority start protector on the my car. If I leave something on or just don't drive the car for a long time I can just get in and start it. Never had a dead battery since I installed it. :thumb: