Please explain 12V system to me--how to keep battery charged while using accessories?

The OP hasn't responded to whether the car was in "P" or "N" (question by Elektroingenieur in Post #4). The answer to that could solve the problem if the car was in "N".

 

I don't believe the OP said the 12V when down while in READY mode. He said, "One morning, when we'd used the Prius to charge the battery several days in a row... as well as lazing in the car with the AC on during hot parts of the day... the car briefly flashed "12V low" and would not start." This could be interpreted as the car would not start after sitting overnight in OFF. He also says they had been using the 12V system to charge his CPAP battery as well as running the AC, and maybe had not been in READY long enough to fully restore the 12V before shutting off overnight.

 

not sure about ben 4, but get 3, both the overhead light, if you turned it on manually.

 

I haven't tried them all, but the boot (trunk?) light turned off on mine after about 20-30 mins.

 

Details like this would have helped. Most likely operator error. BTDT

 

Yes to both. From the New Car Features:

• The battery sensor (battery state sensor assembly) installed on the negative (-) auxiliary battery terminal calculates the current, voltage, battery temperature, SOC (battery charging percentage) and SOH (battery degradation percentage) and sends these signals to the hybrid vehicle control ECU via LIN communication.
• To detect the current, a shunt resistor installed inside the battery sensor (battery state sensor assembly) is used to convert and calculate the voltage generated in the shunt resistor due to the battery charge and discharge current.
• The auxiliary battery temperature is calculated from the resistance value of the thermistor built in the battery sensor (battery state sensor assembly).

 

Aha, that is new for Gen 4. So, Gen 4 enthusiasts installing inverters or other added loads would be well advised to be sure the tap is taken downstream of the battery state sensor assembly.

-Chap

 

On mine, all the interior lights go off 30 mins after switching off and locking the car, even if switched to the permanent on position. Don't ask me how I know

 

I just looked again at the excerpt @Elektroingenieur posted, and saw that it says the battery state sensor assembly lives in the battery negative cable. So, any added load ought to be properly counted, as long as its ground return is to any body ground point, just not directly back to the battery − terminal.

-Chap

 

That’s right. Here’s an annotated photo of the auxiliary (12-volt) battery on my 2016 Prius and some of the nearby connections:



The sensor assembly is bolted to the negative terminal on the battery, and it has a threaded stud (labeled Engine Wire Connection in the photo) to which the No. 3 Engine Wire harness is attached. As @ChapmanF notes, an added load could be connected there or to any ground point, but not directly to the battery terminal, since a direct connection would bypass the current sensor.

As seen in the photo, the No. 3 Engine Wire harness is connected to ground points DA and DF, but according to the Electrical Wiring Diagram (available by subscription to techinfo.toyota.com), within the harness, one wire from the battery is connected to ground point DA and another is connected to ground point DC, not shown. Connector C19 provides the sensor assembly with power and a LIN bus connection to the Hybrid Vehicle Control ECU.

The Electrical Wiring Diagram divides the 12-volt battery and charging system among several System Circuit and Inner Circuit diagrams, which can be a bit tricky to follow, so I put together an unofficial schematic showing how it all goes together:


The fusible link block assembly has the main fuses for the 12-volt electrical system. Here are two annotated photos of one I bought as a spare (part number 82620-47090, price ¥2,360):


The fusible links are not individually replaceable; if one blows, the entire assembly must be replaced.

 

Bugs bug me! I love camping in my Prius! It is my home away from home.

Posted via the PriusChat mobile app.

 

I remember soon after we got our 2010, walking through a parking lot, a chilly morning, on the way to my morning train commute, seeing cabbies "hibernating" in their idling Prius cabs, steam coming out of the exhausts.

 

Made my day!

Posted via the PriusChat mobile app.

 

Along the lines of dead battery needing to be recharged...is it safe to charge the 12v with an automatic charger or battery minder while the evse is plugged in and charging?? Or should I recharge the 12v only when the evse is disconnected. I have a ctek, batteryminder, and regular charger with auto mode.

 

I don't think I'd put a charger on the 12V while the EVSE is plugged in, especially while the traction battery is charging. Beside, when the EVSE is powering the car's traction battery charger, it's also topping off the 12V battery. I haven't measured the voltage on my Prime yet, but I've read here that it doesn't charge the 12V as strongly as the PiP did. But it is charging both batteries.

Back to the original subject, I had something happen one time (so far) with the Prime that might be related to the question about the 12V running down. I shut down the car, got out and closed the door, and it beeped at me. The MID said "Accessory." As far as I knew, it was off. But I got back in, made it ready and shut it off. No more beep. I have read that, if you're running a power window as you shut off the car, it will go to accessory mode rather than off. But I wasn't running any windows or anything else. Very odd, but perhaps that was the cause of the OP's trouble.

 

I didn't see any cautions against this, looking in the Owner's Manual, page 587.