Chevy Bolt EV Forum banner

1 - 20 of 30 Posts

·
Registered
Joined
·
41 Posts
Discussion Starter #1
Why does the car need the 12V battery to start since there is no engine to crank and turn over? Can't it start up by using power from motive battery bank as a backup in case the 12V isn't working?
 

·
Registered
Joined
·
1,496 Posts
There are many electrical reasons (on which I will leave to others to expand), but safety is prime. Think of the 12V as the “sentry doorman” of the HV battery. It opens and closes the door to the electrons. In an accident, first responders cut the 12V cable (marked yellow) which effectively isolates the high voltage juice. They do not cut the orange cables.

While the HV battery does “recharge” the 12v, others have pointed that not needing many “cold cranking amps” to turn a starter motor allows crud to accumulate on the plates of the 12V. This keeps the 12V from charging to the max. Many, including myself, bought a low cost trickle charger which I use once monthly overnight to keep my 12V smiling and performing like it is new.
 

·
Registered
Joined
·
293 Posts
I would say that most EVs have a relay inside the sealed battery pack that cuts off all High Voltage (HV) to the outside when the car is off. The relay is only closed (sending power to the outside world) when the computer says so, and the computer is powered by the 12V battery. Of course, the car can switch on the HV to charge the 12V, but it does this on a schedule basis (like every few days) rather than whenever the 12V battery is low.

So.....if you leave some 12V load on with the car parked, you CAN pull down the 12V, and the car will not 'start'. In that case, you can just 'jump' the 12V just like any car, and it will start up (and proceed to charge the 12V from the HV). This takes a lot less power than a normal jump (since you are just booting the CPU, etc). So the smallest/cheapest portable jump starter or flimsiest jumper cables would do the trick.
 

·
Registered
Joined
·
979 Posts
The compact ICE car that I traded-in for Bolt surprised me when it's 12V battery gave up the ghost after 4 years. One cold winter day about 2 miles after starting out from the house, the car went into kinda "safe" mode where it would sputter along only a few miles per hour. Battery voltage looked fine but it failed the load test.

I'll replace the Bolt's 12V battery in 3 or 3-1/2 years. To wait for it to fail IMO is not a good strategy since that 12V is so important in the Bolt.
 

·
Registered
Joined
·
3,777 Posts
The OP brings up a good point.

As Frank pointed out above, EVs disconnect the high voltage battery for safety reasons when it isn't being used. It does this by default whenever 12v power is shut down to the contactors (relay). If the 12v battery loses charge, it no longer has enough power to close the contactors which connect the traction battery to the various circuits, including the 12v battery power supply.

This got me to thinking that the car could include a momentary switch that one could press to connect the high voltage battery just long enough to charge the 12v battery. It would be like jump starting your own vehicle. A minute or 2 of this should give the 12v battery enough juice to close the contactors, which then would activate the 12v charging circuit and top off the weak battery.
 

·
Registered
Joined
·
1,496 Posts
The compact ICE car that I traded-in for Bolt surprised me when it's 12V battery gave up the ghost after 4 years. One cold winter day about 2 miles after starting out from the house, the car went into kinda "safe" mode where it would sputter along only a few miles per hour. Battery voltage looked fine but it failed the load test.

I'll replace the Bolt's 12V battery in 3 or 3-1/2 years. To wait for it to fail IMO is not a good strategy since that 12V is so important in the Bolt.

A very reasonable strategy. Since I charge it monthly (and am hoping for a > 60 month life) could I simply check the voltage every few months and a few days after the trickle charge? Would it give me a "failure to hold a charge" indication before a sudden episode of total failure? {Hate to buy a new battery if I can still (safely) get 18-24 months out of the old one.}
 

·
Registered
Joined
·
979 Posts
A very reasonable strategy. Since I charge it monthly (and am hoping for a > 60 month life) could I simply check the voltage every few months and a few days after the trickle charge? Would it give me a "failure to hold a charge" indication before a sudden episode of total failure? {Hate to buy a new battery if I can still (safely) get 18-24 months out of the old one.}
I just now looked under Bolt's hood (been quite a while!) and noticed the 12V is an AGM type. Thinking again about this AGM in the Bolt`s underhood environment. Versus my prior ICE conventional battery in it's underhood environment, maybe my ultra-conservative replacement timing plan should be 4 to 4 1/2 years. Believe AGM may last a year or so longer than lead acid conventional. I'm shooting from the hip on this based on some prior experience with AGM's versus conventionals as starting batteries in marine environment.

In addition to voltage checks (after it's sat for at least 12 hours or so) I think a check of terminal cleanliness and after a few years a load test check during cold weather will be worthwhile activities.
 

·
Registered
Joined
·
1,291 Posts
The OP brings up a good point.

As Frank pointed out above, EVs disconnect the high voltage battery for safety reasons when it isn't being used. It does this by default whenever 12v power is shut down to the contactors (relay). If the 12v battery loses charge, it no longer has enough power to close the contactors which connect the traction battery to the various circuits, including the 12v battery power supply.

This got me to thinking that the car could include a momentary switch that one could press to connect the high voltage battery just long enough to charge the 12v battery. It would be like jump starting your own vehicle. A minute or 2 of this should give the 12v battery enough juice to close the contactors, which then would activate the 12v charging circuit and top off the weak battery.
Once again, the EV-1 was ahead of the curve:
Interesting that the GM EV-1 had a little button under the dash on the passenger side that would shunt some traction-pack electrons to the auxiliary battery to "self-jumpstart" if the aux battery was dead.

That was in 1997. *sigh*
 

·
Registered
Joined
·
3,777 Posts
I just now looked under Bolt's hood (been quite a while!) and noticed the 12V is an AGM type. Thinking again about this AGM in the Bolt`s underhood environment. Versus my prior ICE conventional battery in it's underhood environment, maybe my ultra-conservative replacement timing plan should be 4 to 4 1/2 years. Believe AGM may last a year or so longer than lead acid conventional. I'm shooting from the hip on this based on some prior experience with AGM's versus conventionals as starting batteries in marine environment.

In addition to voltage checks (after it's sat for at least 12 hours or so) I think a check of terminal cleanliness and after a few years a load test check during cold weather will be worthwhile activities.
Lead acid battery longevity has more to do with keeping them charged up than number of years in service. Running it dead just once will permanently damage it.

That said, why pre-preemptively replace a working battery when you could just buy a $30 jump pack and keep it in your glove box? It only takes a couple hundred watts to start the Bolt, so any jump pack would do the job. It comes in handy for charging dead phones too.



 

·
Registered
Joined
·
1,766 Posts
The Hyundai Ioniq has done away with the 12V lead-acid battery. The U.S. version of the car has a small portion of the Li-Ion battery pack reserved for "12V uses". If it is ever too low, there is a button in the car to "jump start" (use the main traction battery to charge the "12V" part of the pack).

I trickle-charge my 12V lead-acid batteries (including AGM) regularly (maybe twice a month) in order to make sure that it is fully charged. I expect my current crop of 12V batteries to last 8 years or more.
 

·
Registered
Joined
·
507 Posts
You definitely need a reliable 12V. At 8 months mine began to act up. While sitting it would randomly drop under 10 V and require a jump start. Left me stranded several times. Three trips to the dealer. On the second trip, they discovered that the charging system went into "service mode", which doesn't charge 12 V system, when it was in drive. By then the battery had a bad cell that would randomly short out. Fremont Chevrolet refused to replace the battery, because it passed their Chevy approved tester. On the third visit in month 11, it failed their test, I got a new battery and works great now. In gory detail this is covered in any earlier thread called 12 V battery trouble.

Bottom line, without a good 12 V battery, the Bolt is a Dolt.
 

·
Registered
Joined
·
1,569 Posts
To answer the OP’s question:

No, it won’t start.
 

·
Registered
Joined
·
185 Posts
Lead acid battery longevity has more to do with keeping them charged up than number of years in service. Running it dead just once will permanently damage it.

That said, why pre-preemptively replace a working battery when you could just buy a $30 jump pack and keep it in your glove box? It only takes a couple hundred watts to start the Bolt, so any jump pack would do the job. It comes in handy for charging dead phones too.



http://www.amazon.com/FlyHi-Portable-Powerful-Charging-Flashlight/dp/B01LX6J2HG/ref=pd_sbs_263_12?_encoding=UTF8&pd_rd_i=B01LX6J2HG&pd_rd_r=DADQDW7BHRA5TWJ5FBAJ&pd_rd_w=H34el&pd_rd_wg=oygXg&psc=1&refRID=DADQDW7BHRA5TWJ5FBAJ
I second this. Bolt was dead with a dead 12v. I was lucky there's another car in garage to 'jump' it.

http://www.mychevybolt.com/forum/viewtopic.php?t=7415
 

·
Registered
Joined
·
574 Posts
Most 12V batteries have a rated life. Most new cars come with a 4 year battery. What is the rated life of the 12V battery in the Bolt? In my experience, these expected life ratings are quite accurate, even here in the San Francisco Bay Area, where frosts are rare and the highs rarely exceed 100 degrees F. When your 12V battery reaches it's predicted end-of-life, it's best to simply replace it: don't try to get any more life out of it.

Useful info on 12V car batteries:

https://auto.howstuffworks.com/under-the-hood/vehicle-maintenance/often-replace-car-battery.htm
 

·
Registered
Joined
·
3,777 Posts
When your 12V battery reaches it's predicted end-of-life, it's best to simply replace it: don't try to get any more life out of it.
Why not simply measure it to confidently get more life out of it? Perhaps replacing relatively inexpensive things is trivial to those who can afford a new Bolt, but I don't replace things when there is likely a lot of life left. For example, I regularly get 8 years or more from a 12v battery. Life has very little to do with years of service, and very much to do with how it has been used and maintained.
 

·
Registered
Joined
·
108 Posts
Hello everyone and thanks for all your educational and sometimes entertaining posts. This site is phenomenal.

Background:
I'm storing the Bolt for 5 weeks and was wondering what process I should follow.

Owners manual says bring the high voltage battery down to 2-3 bars and trickle charge the 12v battery.
Then I discovered this from electricrevs.com, interpreting the service manual:

12V battery maintenance mode
Many drivers are familiar with having a “dead” 12V battery either due to accidentally leaving a light on after turning off a car or having the lead acid battery self-discharge after sitting unused for several weeks. In order to reduce the need for jump starts, the Bolt EV has a 12V battery charging maintenance strategy.

If the car is plugged in but not charging, it will wake up and check the status of the 12V battery every 6 hours. If the 12V battery is low the car will begin charging it for up to 2 to 3 hours.

If the car is not plugged but has been turned on within the last 30 days, it will wake up every 3 days to check the 12V battery and if the main battery is at least 40 percent full it will begin charging the 12V battery for 45 to 90 minutes


Note: xj12 discusses this in a post elsewhere on this site.
 

·
Registered
Joined
·
989 Posts
Hello everyone and thanks for all your educational and sometimes entertaining posts. This site is phenomenal.

Background:
I'm storing the Bolt for 5 weeks and was wondering what process I should follow.

Owners manual says bring the high voltage battery down to 2-3 bars and trickle charge the 12v battery.
Then I discovered this from electricrevs.com, interpreting the service manual:

12V battery maintenance mode
Many drivers are familiar with having a “dead” 12V battery either due to accidentally leaving a light on after turning off a car or having the lead acid battery self-discharge after sitting unused for several weeks. In order to reduce the need for jump starts, the Bolt EV has a 12V battery charging maintenance strategy.

If the car is plugged in but not charging, it will wake up and check the status of the 12V battery every 6 hours. If the 12V battery is low the car will begin charging it for up to 2 to 3 hours.

If the car is not plugged but has been turned on within the last 30 days, it will wake up every 3 days to check the 12V battery and if the main battery is at least 40 percent full it will begin charging the 12V battery for 45 to 90 minutes


Note: xj12 discusses this in a post elsewhere on this site.
I posted this a while back...... Enjoy!



Charging System Description and Operation
12 V Battery The following information is for the 12 V battery only.
For information about charging the high voltage drive motor batteries, refer to Drive Motor Battery System Description.
Charging System Operation The purpose of the charging system is to maintain the battery charge and vehicle loads. The main difference between a conventional generator charging system and this system is that the generator has been replaced by the 14V Power Module. The 14V Power Module provides the power to charge the battery from the high voltage system. There are 7 modes of operation and they include:
Battery Sulfation Mode
Normal Mode
Fuel Economy Mode
Headlamp Mode
Voltage Reduction Mode
Battery Maintenance Mode
Plant Assembly Mode


Charging System Components 14 V Power Module
The 14V Power Module provides the power to charge the battery from the high voltage system. The ECM provides a pulse width charge request signal (L Terminal) to the 14V Power Module. The 14V Power Module returns a PWM feedback signal (F Terminal) to the ECM. The 14V Power Module reports status and fault modes as a function of duty cycle. The 14V Power Module charges the battery based on the ECM signal.
Drive Motor/Generators
The drive motor/generators are serviceable components located within the transmission housing. When the rotors are spun, an alternating current (AC) is induced into the stator windings. This AC voltage is then sent to the drive motor generator power inverter module (PIM) where it is converted to high voltage direct current (DC) power. The output of the PIM is converted into low voltage electrical power by the accessory DC power converter module 14V Power Module for use by the vehicle's electrical system to maintain electrical loads and battery charge.
Body Control Module (BCM)
The body control module (BCM) is a GMLAN device. It communicates with the engine control module (ECM) and the instrument panel cluster for electrical power management operation. The BCM determines the desired voltage set point and sends the information to the engine control module (ECM) which sends this information to the 14V Power Module. The BCM monitors a battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge.
Battery Current Sensor
The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates a 5 V pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0–100 percent. Normal duty cycle is between 5–95 percent. Between 0–5 percent and 95–100 percent are for diagnostic purposes.
Engine Control Module (ECM)
The ECM receives control decisions based on messages from the BCM as well as the HPCM2
Instrument Panel Cluster
The instrument panel cluster provides a means of customer notification in case of a failure and a voltmeter. There are 2 means of notification, a charge indicator and a driver information center message of SERVICE BATTERY CHARGING SYSTEM.
Hybrid/EV Powertrain Control Module 2 (HPCM2)
The Hybrid/EV Powertrain control module (HPCM2) is a GMLAN device. It communicates with the engine control module (ECM) to control the voltage set point sent to the 14V Power Module during the battery maintenance mode.
Battery Sulfation Mode Battery sulfation mode is used to help maintain the battery life. The charging system will enter a battery sulfation mode which tries to increase the vehicle charging when the charging system voltage is less than 13.2 V for about 30 minutes. Once in this mode, the BCM will set a targeted output voltage between 13.9–15.5 V for about 5 minutes. Following this 5 minutes, the BCM will then determine which mode to enter depending on the system voltage requirements.
Normal Mode The BCM will enter Normal Mode whenever one of the following conditions are met.
The wipers are ON for more than 3 seconds.
GMLAN Climate Control Voltage Boost Mode Request is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
The estimated battery temperature is less than 0°C (32°F).
Vehicle Speed is greater than 145 km/h (90 mph)
Current Sensor Fault Exists
System Voltage was determined to be below 12.56 V
Tow/Haul Mode is enabled
When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9–15.5 V, depending on the battery state of charge and estimated battery temperature.
Fuel Economy Mode The BCM will enter Fuel Economy Mode when the ambient air temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is greater than −8 A but less than 5 A, and the battery state of charge is greater than or equal to 85 percent. Its targeted 14V Power Module set-point voltage is the open circuit voltage of the battery and can be between 12.6–13.2 V. The BCM will exit this mode and enter Normal Mode when any of the conditions described above are present.
Headlamp Mode The BCM will enter Headlamp Mode whenever the high or low beam headlamps are ON. Voltage will be regulated between 13.9–14.5 V.
Voltage Reduction Mode The BCM will enter Voltage Reduction Mode when the calculated battery temperature is above 0°C (32°F) and the calculated battery current is greater than −7 A but less than 1 A. Its targeted 14V Power Module set-point voltage is 12.9–13.2 V. The BCM will exit this mode once the criteria are met for Normal Mode.
Battery Maintenance Mode That battery maintenance mode is designed to ensure the 12V battery has a good state of charge. It accomplishes this by checking the voltage of the 12V battery and providing a charge if needed.
When the vehicle cord is plugged in
The Hybrid/EV Powertrain control module (HPCM2) will check the 12V battery every 6 hours if the ignition is off. If the voltage is below a temperature dependent threshold ranging from 12.1 (cold) to 12.4 (warm)V, the Hybrid/EV Powertrain control module (HPCM2) will send the voltage set point to the engine control module (ECM). The engine control module (ECM) will send this to the 14V Power Module. Battery maintenance mode will charge the battery for 2-3 hours. If the Ignition is ON, the APM will cycle on as needed to maintain the 12V SOC.
When the vehicle cord is not plugged in
The Hybrid/EV Powertrain control module (HPCM2) will check the 12V battery every 4 days (2.5 to 3 days) and if the voltage is below a threshold of 12.0 may activate battery maintenance. If the high voltage battery state of charge is greater than 40% and the propulsion system is not active, Hybrid/EV Powertrain control module (HPCM2) will send the voltage set point to the engine control module (ECM). The engine control module (ECM) will send this to the 14V Power Module. Battery maintenance mode will charge the battery for 45-90 minutes..
Plant Assembly Mode The BCM will increase charging voltage for the first 500 miles of operation in an effort to ensure that the 12 V battery is fully charged when the vehicle is delivered to the customer.
Electrical Power Management Overview The electrical power management system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems. This electrical power management system primarily utilizes existing on-board computer capability to maximize the effectiveness of the charging system, manage the load, improve battery state of charge and life, and minimize the system's impact on fuel economy. The electrical power management system performs 3 functions:
It monitors the battery voltage and estimates the battery condition.
It takes corrective actions by adjusting the regulated voltage.
It performs diagnostics and driver notification.
The battery condition is estimated during Vehicle OFF and during Vehicle in Service Mode. During Vehicle OFF the state of charge of the battery is determined by measuring the open-circuit voltage. The state of charge is a function of the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open circuit voltage when the battery has been at rest for several hours.
The state of charge can be used as a diagnostic tool to tell the customer or the dealer the condition of the battery. During Vehicle ON mode, the algorithm continuously estimates state of charge based on adjusted net amp hours, battery capacity, initial state of charge, and temperature.
While running, the battery degree of discharge is primarily determined by a battery current sensor, which is integrated to obtain net amp hours.
In addition, the electrical power management function is designed to perform regulated voltage control to improve battery state of charge, battery life, and fuel economy. This is accomplished by using knowledge of the battery state of charge and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.
Instrument Panel Cluster Operation Charge Indicator Operation
The instrument panel cluster illuminates the charge indicator and displays a charging system warning message in the driver information center when the one or more of the following occurs:
The engine control module (ECM) detects system voltage less than 11 V or greater than 16 V. The instrument panel cluster receives a GMLAN message from the ECM requesting illumination.
The BCM determines that the system voltage is less than 11 V or greater than 16 V.
The instrument panel cluster receives a GMLAN message from the BCM indicating there is a system voltage range concern.
The instrument panel cluster performs the displays test at the start of each Vehicle ON cycle. The indicator illuminates for approximately 3 seconds.
Vehicle ON, with the engine OFF.
Battery Voltage Gauge Operation
The instrument panel cluster displays the system voltage as received from the BCM over the GMLAN serial data circuit. If there is no communication with the BCM then the gauge will indicate minimum.
This vehicle is equipped with a regulated voltage control system. This will cause the voltmeter to fluctuate between 12–14 V, as opposed to non-regulated systems which usually maintain a more consistent reading of 14 V. This fluctuation with the regulated voltage control system is normal system operation and NO repairs should be attempted.
SERVICE BATTERY CHARGING SYSTEM
The BCM and the ECM will send a GMLAN message to the driver information center for the SERVICE BATTERY CHARGING SYSTEM message to be displayed. It is displayed whenever the charge indicator is commanded ON due to a failure.
 

·
Registered
Joined
·
1,931 Posts
Five weeks storage during summer is nothing for the Bolt... give her a 3/4 charge and go on vaca!

She'll be waiting for you when you get back.... no need to do anything special for that short period of time especially since it's not winter.
 

·
Registered
Joined
·
163 Posts
Why does the car need the 12V battery to start since there is no engine to crank and turn over? Can't it start up by using power from motive battery bank as a backup in case the 12V isn't working?
I can now tell you if the car will work without the 12V battery. If you need a 3000 pound brick, then yes, the car will work without the 12v battery. But if you need it for any other purpose, it won't.

In some ways 12v battery is even more important that the main high voltage battery. Without the 12v battery you can't open the trunk, you can't roll the windows up or down, you can't shift from park to neutral (to move the car), and you can't even start a charging session (!). So if the 12v battery is bad, your car is a brick. And if you think that you can just get a jump start - think again. I personally think this is a significant design flaw.
 

·
Registered
Joined
·
2,671 Posts
I can now tell you if the car will work without the 12V battery. If you need a 3000 pound brick, then yes, the car will work without the 12v battery. But if you need it for any other purpose, it won't.

In some ways 12v battery is even more important that the main high voltage battery. Without the 12v battery you can't open the trunk, you can't roll the windows up or down, you can't shift from park to neutral (to move the car), and you can't even start a charging session (!). So if the 12v battery is bad, your car is a brick. And if you think that you can just get a jump start - think again. I personally think this is a significant design flaw.

Why can't you "just get a jump start"? Doing so should be no different than jumping any other vehicle's 12V "starter" battery.
 
1 - 20 of 30 Posts
Top