How the 12 volt battery works on the Volt

[silverton38]

I asked Chevrolet specifically for an answer to these questions and they sent it to Volt Engineering and this is the reply. They knew that it would be posted.

I would agree that the 12 volt battery should be charged with the car but it is not. It is charged while the car is operational. Since the generator starter uses the main battery; I do not think they should even have a 12 volt battery (personal belief).


Regardless; we all need to know how this battery works so that we can manage it. It would be fun boosting an electric car

[WopOnTour]

I asked Chevrolet specifically for an answer to these questions and they sent it to Volt Engineering and this is the reply. They knew that it would be posted.

I would agree that the 12 volt battery should be charged with the car but it is not. It is charged while the car is operational. Since the generator starter uses the main battery; I do not think they should even have a 12 volt battery (personal belief).


Regardless; we all need to know how this battery works so that we can manage it. It would be fun boosting an electric car

Again, I repeat. This is incorrect.
Either they were simply mistaken OR you are interpreting/transposing their response incorrectly.

Don't believe me or want to prove me wrong? No problem
Try this.
Put even a basic $10 Radio Shack voltmeter across your + and - battery posts. (to access them lift off the small square black plastic covers in your rear hatch storage area)
Then once you have a reading (say ~12-13V) then plug in your Volt and read/record the voltmeter again a few seconds after the green LED comes ON steady.It will increase above your initial reading to indicate charging is taking place.

There is very good reasons why we still require a 12V battery. Yes, the lithium ion battery is used to start the ICE once the initial charge is depleted but that will only occur once you achieve the minimum speed for CS. Up until that point the car had been operating electrically and it is the 12V management system that permits the high-voltage an electrical pathway to the traction motor.

As a new volt owner and member I suggest you start by reading up in the FAQs in the Newcomers forum on this site for more information.

Welcome to gm-volt.com

HTH
WOT

[vdiv]

So while the propulsion 380 V battery is being charged, the auxiliary 12 V battery is also being charged. What happens when the propulsion battery is fully charged and the car remains plugged in? Can the auxiliary battery in this case be completely discharged or is the charge on it also being maintained? Do we need to carry jumper cables/jumper batteries in the Volt if we leave it plugged in at say the airport for a month?

[DonC]

Do we need to carry jumper cables/jumper batteries in the Volt if we leave it plugged in at say the airport for a month?

It's going to be like any car. If you're comfortable leaving your ICE the Volt isn't going to be that different, though it has a lot of electronics which can be potential drains. I always carry jumpter cables. Scott's little charger is a good idea. WOT suggested a mod where you apply clips in case the BCM is dead.

Maybe WOT or someone else can help me out? I'm wondering why the manual says to jump to the front connectors. Most times it would be more convenient to jump from the back since in parking lots you usually pull in head first and there may not be a space available next to you. Perhaps using the front connectors protects the accessories since there is a lower amp fuse or something? Anyway carrying the Wagan battery booster and using the rear connectors would seem to be a piece of cake.

[mikeg3]

If the 12V battery is dead you can't easily open the trunk.

You can open the front door and then the hood mechanically. Once 12V is applied to the jumper terminals, you can immediately start the car and then the main battery though the DC-DC converter starts supplying 12V to the car and also charging the 12V battery.

My question, which others have also asked above, is whether or not the 12V battery is being charged by the On Board Charge Module or the DC-DC converter when the vehicle is off, the 110V/240V charger is plugged in, and the main battery is at maximum charge. This would explain how a plugged in Volt can go dead.

[volt3939]

If the 12V battery is dead you can't easily open the trunk.

You can open the front door and then the hood mechanically. Once 12V is applied to the jumper terminals, you can immediately start the car and then the main battery though the DC-DC converter starts supplying 12V to the car and also charging the 12V battery.

My question, which others have also asked above, is whether or not the 12V battery is being charged by the On Board Charge Module or the DC-DC converter when the vehicle is off, the 110V/240V charger is plugged in, and the main battery is at maximum charge. This would explain how a plugged in Volt can go dead.

Good point about the trunk.

Your question has already been answered:

...

Q: Does the 12 volt slave off of the home charger if needed?
WOT's A:...

the 12V does actually get an auxiliary charge when OFF and plugged in but only while charging is actively taking place.(i.e. steady "ON" green LED on dash)

However charging current DOES NOT come from the DC-DC converter as it normally would when the car is "ON". Instead it comes from a totally separate 12V charger that is built directly into the on-board charging module. So as long as your car is actually charging the Lithium Ion battery (again, steady green LED) then so too is your 12V battery. This is necessary because there needs to be a certain number of 12V modules and devices electrically participating during charging operations and it doesn't really make sense to draw current FROM the Li-Ion source when our primary goal is to charge it, and since the DC-DC converter is only ON when the car is ON, there is a necessity for this auxiliary 12V charger.
...
WopOnTour

Emphasis mine...

[WopOnTour]

It's going to be like any car. If you're comfortable leaving your ICE the Volt isn't going to be that different, though it has a lot of electronics which can be potential drains. I always carry jumpter cables. Scott's little charger is a good idea. WOT suggested a mod where you apply clips in case the BCM is dead.

Maybe WOT or someone else can help me out? I'm wondering why the manual says to jump to the front connectors. Most times it would be more convenient to jump from the back since in parking lots you usually pull in head first and there may not be a space available next to you. Perhaps using the front connectors protects the accessories since there is a lower amp fuse or something? Anyway carrying the Wagan battery booster and using the rear connectors would seem to be a piece of cake.

As per the owners manual under "jump starting" underhood boost points are to be used for a Volt to accept a boost/jump from another vehicle, but becuase the + boost point IS fuse protected (80A) these points MUST NOT to provide a jump to another vehicle. (in that case connect the cables directly at the 12V battery in the rear of the car)

mikeg3 is correct, one of the primary considerations for this is the fact that the rear hatch area may not be accessible when the 12V battery is dead as the latch release it electrically operated.
However in an emergency the rear hatch CAN be released mehanically from teh inside.(after folding down teh rear seats of course) If you look on the inside edge of the hatch just below the glass, there is a small rectangular plastic cap/plug that can be removed with a small flat-bladed screwdriver or other tool. You then must insert a blade-type screwdriver vertically into the hole to engage the lever and turn counter-clockwise to release the latch. I beleive Rusty may have even posted some pics of the proces, see the Volt FAQs for more info.

and YES, since the 12V battery is being only charged while in the act of charging the Li Ion battery, if charging stops for ANY reason (including having reached a full charge) then 12V charging ceases at that point as well.

WopOnTour

[mikeg3]

I was looking at ChevroletVoltage.com and found an interesting comment. As background, WOT said, and I confirmed by taking a magnifying glass to page 100 of the SAE Volt compendium, that the On Board Charging Module takes power from the 110V or 240V charger and feeds the main battery and separately feeds the 12V battery. But at some point the main battery is full and the On Board Charging Module no longer has a power source. What can happen then to the 12V battery if the car is left on or the car is left plugged in for weeks?

BobGPSr's salesman: "Okay, talked to the resident Volt expert technicians. They had instant answers to your questions. Your 2012 Volt does charge and maintain the 12 volt battery as long as it is plugged in. Apparently GM listened and changed that since the blog posts that you found. ..."

Is this correct? Is the change available for 2011 Volts? What's the technical bulletin number?

silverton38's sources sound both accurate and authoritative, but I don't know. Here is his full thread:
http://www.chevroletvoltage.com/inde...tid=11&id=6271

This would mean that some other module, like the Auxiliary Power Module or the DC-DC voltage step-down converter (same thing?) will trickle charge the 12V battery from the fully charged main battery after the On Board Charging Module is no longer getting power from the external charger.

[Henry_FL]

I went out to my volt, which is fully charged and has a kill-o-watt connected so I can see the power drain.

Turned on the lights headlights for 5 minutes, charger never kicked on as measured by the amp draw using the kill-o-watt, so this is counter to what you posted

[mikeg3]

Henry_FL: The quote said that there was a "change". Perhaps you and I just don't have the change installed.