Second or Duel Battery
03-25-2010, 02:52 PM
#11
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Join Date: 12-24-2008
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Posts: 717
VERY Interesting
Charging System Operation
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Charge Mode
• Fuel Economy Mode
• Voltage Reduction Mode
• Start-up Mode
• Windshield Deice Mode
• Battery Sulfation Mode
The engine control module (ECM) controls the generator through the generator L-terminal control circuit. The signal is a 5-volt 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. The following table shows the commanded duty cycle and output voltage of the generator:
Commanded Duty Cycle*Generator Output Voltage
10% * 11 V
20% * 11.56 V
30% * 12.12 V
40% * 12.68 V
50% * 13.25 V
60% * 13.81 V
70% * 14.37 V
80% * 14.94 V
90% * 15.5 V
The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 12-volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.
Charge Mode
The BCM will enter Charge Mode when ever one of the following conditions are met:
• The interpreted fuel rate is greater than 21 g/s and the throttle position is greater than 90 percent.
• The headlamps are ON, low or high beam.
• The wipers are ON for more than 8 seconds.
• The electric cooling fans are on high speed.
• The rear defogger is ON.
Once one of these conditions are met, the generator battery control module will set the targeted generator output voltage to 13.4 volts and then ramp that voltage up to 14.5 volts at a rate of 50 mV per second.
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Charge Mode
• Fuel Economy Mode
• Voltage Reduction Mode
• Start-up Mode
• Windshield Deice Mode
• Battery Sulfation Mode
The engine control module (ECM) controls the generator through the generator L-terminal control circuit. The signal is a 5-volt 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. The following table shows the commanded duty cycle and output voltage of the generator:
Commanded Duty Cycle*Generator Output Voltage
10% * 11 V
20% * 11.56 V
30% * 12.12 V
40% * 12.68 V
50% * 13.25 V
60% * 13.81 V
70% * 14.37 V
80% * 14.94 V
90% * 15.5 V
The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 12-volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.
Charge Mode
The BCM will enter Charge Mode when ever one of the following conditions are met:
• The interpreted fuel rate is greater than 21 g/s and the throttle position is greater than 90 percent.
• The headlamps are ON, low or high beam.
• The wipers are ON for more than 8 seconds.
• The electric cooling fans are on high speed.
• The rear defogger is ON.
Once one of these conditions are met, the generator battery control module will set the targeted generator output voltage to 13.4 volts and then ramp that voltage up to 14.5 volts at a rate of 50 mV per second.
I think "Etherion"(by the way, please update your profile) needs to tell us more; like the vehicle year, history, etc. Also what he is using to measure and EXACTLY where. AND what ground is being used for reference - this whole "problem" could be as simple/complicated as a bad ground.
I just read over my 2009 FSM and the write up that ChevyMgr pasted from his technical literature is correct. The ECM sends a PWM signal to the Generator to control what voltage it puts out. Not something most of us have the capability to measure.
03-25-2010, 08:36 PM
#13
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Join Date: 12-24-2008
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Posts: 717
Not to take ChevyMgr's thunder away, but many of the posts he does are "pastes" from his dealer technical publications that he so nicely shares with us. The paper version of the FSM is not as good.
03-25-2010, 08:44 PM
#14
Join Date: 07-04-2008
Location: Maryville TN
Posts: 7
More info from Etherion
2008 HHR 2.4 using a digital multimeter, fairly reliable as I have 6 or more of the same model and have check each against a reference. Measure engine compartment voltage at post on left of fuse box and ground at strut labeled "ground". Battery measured at battery posts and also checking at body ground where negative battery cable bolts to chasis. Sorry for lack of info earlier.
03-25-2010, 10:06 PM
#15
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Join Date: 01-13-2008
Location: Washington State, where it rains
Posts: 4,708
I would have to say because the battery is the end recipient that it recieves the "leftover voltage" that all the control modules and accessories don't bleed off,,,thats why you have various voltages thruout load cycles..this way the alt is only putting out whats necessary to maintain vehicle life , if it were operating at full tilt 100% of the time it would be wasting eng power, even though with a voltage regulator there is no taper off, its either charging or not...no in between. Remember, your battery does not sustain your car, the alt does, battery is just for starting and power during eng off operations( not like the old days were the batt was actually supplimental power under heavy loads)so now they worked it out to vary the alt output to cover all load conditions while still maintaining battery voltage without the spikes or overcharging, if your battery is fully charged and not under load,,,it should read 12.75 or there abouts reguardless of what the vehicle load is...........how close am I ? I was just guessing.....
03-26-2010, 10:41 AM
#16
Join Date: 07-04-2008
Location: Maryville TN
Posts: 7
A little more info, maybe
Thanks for taking the time "Woody" to comment. I understand your points. On several occasions I have had to jump start the car and when a charger is connected at the engine compartment I get 14 or so volts at the posts, measured at the posts not from the charger clamps so I know the connection is good. If I go back to the battery the voltage is just 12.x that would indicate that the battery is disconnected from the engine area. No matter how long I keep the charger on the battery will never charge. If I take the charger to the battery then it charges fine. I understand that under heavy charge the battery will tend to pull the voltage down but after the battery is charged the voltage will rise. When the car is running I may or may not get parity between the engine posts and the battery. Short of taking a lot of time to do a tear down and a physical trace of the wiring, I am at this time convinced that there is something between the battery and the alternator (other than the 50a fuse). Sincere thanks for your contribution.
03-26-2010, 04:08 PM
#17
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Join Date: 12-24-2008
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There are two battery cables leaving the battery:
*One goes directly to the front right corner of the engine compartment fuse box. According to the FSM it is a direct wire run with no fuse whatsoever. Be careful, there is what appears to be a second battery cable connected to the rear right corner of the engine compartment fuse box; this is actually the power that feeds the EPS.
*The second smaller cable leaving the battery goes through the 50 AMP fuse and connects to the BCM connector with the exposed wiring. Ignore this cable it is not used for charging or starting of the vehicle. It is one of three power supplies to the BCM.
The main battery cable to the engine compartment fuse box is long compared to a regular vehicle so it will have an atypical IR loss. So you do definitely have something between the engine compartment and the battery - the cable! Any connections are also suspect. Even if they look good have you cleaned the connections with a wire brush? Sounds simple, but a common problem through out automotive history.
Are you the only owner of this vehicle? Is this the original battery? Has this vehicle been flooded? What does the corrosion look like, etc. This is what I mean by “history”. The original battery will have a tube coming off the topside and going through the floor of the battery/tire compartment.
Beyond this, try somebody else’s battery charger.
*One goes directly to the front right corner of the engine compartment fuse box. According to the FSM it is a direct wire run with no fuse whatsoever. Be careful, there is what appears to be a second battery cable connected to the rear right corner of the engine compartment fuse box; this is actually the power that feeds the EPS.
*The second smaller cable leaving the battery goes through the 50 AMP fuse and connects to the BCM connector with the exposed wiring. Ignore this cable it is not used for charging or starting of the vehicle. It is one of three power supplies to the BCM.
The main battery cable to the engine compartment fuse box is long compared to a regular vehicle so it will have an atypical IR loss. So you do definitely have something between the engine compartment and the battery - the cable! Any connections are also suspect. Even if they look good have you cleaned the connections with a wire brush? Sounds simple, but a common problem through out automotive history.
Are you the only owner of this vehicle? Is this the original battery? Has this vehicle been flooded? What does the corrosion look like, etc. This is what I mean by “history”. The original battery will have a tube coming off the topside and going through the floor of the battery/tire compartment.
Beyond this, try somebody else’s battery charger.
03-26-2010, 11:20 PM
#18
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Join Date: 01-13-2008
Location: Washington State, where it rains
Posts: 4,708
Like a diode....is it possible this is normal and when jumping it directs all power to starting and 'after' starting then it allows the batt to charge off the alt on a different circuit.....this way there is no batt spike and damage from overpowering in boost mode...so the only way to charge the batt is thru direct connection.....seperated maybe as in relays.. this is probably going left field ..
Ive read where many peeps jump started off these terminals but not heard anybody trying to charge off them....I myself have always gone direct to batt post, no loss of power this way and eliminates bad grounds if there was a draining problem so troubleshooting can be made.
Ive read where many peeps jump started off these terminals but not heard anybody trying to charge off them....I myself have always gone direct to batt post, no loss of power this way and eliminates bad grounds if there was a draining problem so troubleshooting can be made.
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