Second or Duel Battery
02-13-2009, 01:43 PM
#1
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Join Date: 12-24-2008
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Second or Duel Battery
I’m going to add a second battery to my 2009 HHR LS 2.2L non-Panel with Auto Trans. I apologize in advance for the length of this post.
The spare battery will only be connected to the vehicle via a continuous duty starter solenoid during the time the Fuel Pump is activated. This will allow the vehicle to charge the batteries and to disconnect the spare battery from the circuit when the engine is not running, thus allowing me to have at least one fully charged battery when I leave the radio or some other accessory on too long. I’ve read elsewhere on this forum of other peoples problems with trying to run the accessories for too long on the factory battery. Actually I’ve had this problem with every vehicle I’ve had in the last 15 years – so it’s not vehicle specific, it may be user specific.
I’ve done this modification to several other vehicles with no ill effects and many benefits.
What is different with this vehicle from others I have owned is the presence of a current sensor on the Ground wire between the battery and the body ground. My theory is this sensor is used by the vehicle computer to monitor the discharging and charging of the stock battery. There is room for a new wire to fit inside the current sensor and this seems like the best bet, but I like to understand what I am doing and the functioning of the vehicle’s systems. So does anyone know exactly what this current sensor’s function is? This vehicle does not have an Amp Meter on the Instrument Panel to display the current readings.
There is one other quandary I will have to solve and that is where to tap into the Fuel Pump power. I would prefer to do this in the rear of the vehicle as there is less wire to string and the fuel tank is in the back close to the battery. At this time I am assuming several things, one is that the fuel pump is in the fuel tank and that the wires to the fuel pump runs within the vehicle, then penetrates the body and enters the top of the fuel tank with the fuel level sensor wire. I have had the rear seats out of this vehicle before and noticed various wire bundles running through out the vehicle so I feel this is a good first guess assumption. Does anyone have an educated response as to where this penetration occurs and the color markings of the wire that powers the fuel pump? My plan is to tap into this wire to directly power the starter solenoid OR if the solenoid coil load is too great for the fuel pump circuit I will add a second relay powering the solenoid from the battery.
Notes of possible interest:
An auxiliary switch is needed to activate the starter solenoid to connect the spare battery into the power system when the main battery is dead. I’ve not made a decision on its location yet. On other vehicles I’ve put this switch on the dash, but then this was a bit easier with the battery in the engine compartment.
In the engine compartment there is both a Fuel Pump Relay(19) and a 15 Amp Fuel Pump Fuse(13). The fuel pump power could be accessed here. I just don’t want to run a wire all the way to this relay location.
I do not want to use one of those expensive Battery Isolators/Combiners with the running of wires to the ignition/alternator circuits. I like simple discrete components that can be easily troubleshot in the field.
Also, I don’t know what function the 50 amp fuse at the battery serves. Any ideas? If it were a main fuse for the whole vehicle, minus the starter, I would imagine it would be sized larger than the 60 Amp Electric Power Steering(EPS) fuse. This fuse is mentioned in the owners manual only as to location(next to the battery) with no description as to its function. This vehicle does not have the optional Rear Power Plug.
I again apologize for the length of this post.
The spare battery will only be connected to the vehicle via a continuous duty starter solenoid during the time the Fuel Pump is activated. This will allow the vehicle to charge the batteries and to disconnect the spare battery from the circuit when the engine is not running, thus allowing me to have at least one fully charged battery when I leave the radio or some other accessory on too long. I’ve read elsewhere on this forum of other peoples problems with trying to run the accessories for too long on the factory battery. Actually I’ve had this problem with every vehicle I’ve had in the last 15 years – so it’s not vehicle specific, it may be user specific.
I’ve done this modification to several other vehicles with no ill effects and many benefits.
What is different with this vehicle from others I have owned is the presence of a current sensor on the Ground wire between the battery and the body ground. My theory is this sensor is used by the vehicle computer to monitor the discharging and charging of the stock battery. There is room for a new wire to fit inside the current sensor and this seems like the best bet, but I like to understand what I am doing and the functioning of the vehicle’s systems. So does anyone know exactly what this current sensor’s function is? This vehicle does not have an Amp Meter on the Instrument Panel to display the current readings.
There is one other quandary I will have to solve and that is where to tap into the Fuel Pump power. I would prefer to do this in the rear of the vehicle as there is less wire to string and the fuel tank is in the back close to the battery. At this time I am assuming several things, one is that the fuel pump is in the fuel tank and that the wires to the fuel pump runs within the vehicle, then penetrates the body and enters the top of the fuel tank with the fuel level sensor wire. I have had the rear seats out of this vehicle before and noticed various wire bundles running through out the vehicle so I feel this is a good first guess assumption. Does anyone have an educated response as to where this penetration occurs and the color markings of the wire that powers the fuel pump? My plan is to tap into this wire to directly power the starter solenoid OR if the solenoid coil load is too great for the fuel pump circuit I will add a second relay powering the solenoid from the battery.
Notes of possible interest:
An auxiliary switch is needed to activate the starter solenoid to connect the spare battery into the power system when the main battery is dead. I’ve not made a decision on its location yet. On other vehicles I’ve put this switch on the dash, but then this was a bit easier with the battery in the engine compartment.
In the engine compartment there is both a Fuel Pump Relay(19) and a 15 Amp Fuel Pump Fuse(13). The fuel pump power could be accessed here. I just don’t want to run a wire all the way to this relay location.
I do not want to use one of those expensive Battery Isolators/Combiners with the running of wires to the ignition/alternator circuits. I like simple discrete components that can be easily troubleshot in the field.
Also, I don’t know what function the 50 amp fuse at the battery serves. Any ideas? If it were a main fuse for the whole vehicle, minus the starter, I would imagine it would be sized larger than the 60 Amp Electric Power Steering(EPS) fuse. This fuse is mentioned in the owners manual only as to location(next to the battery) with no description as to its function. This vehicle does not have the optional Rear Power Plug.
I again apologize for the length of this post.
Last edited by Sno White; 02-13-2009 at 02:08 PM. Reason: clarity
02-13-2009, 01:50 PM
#2
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Join Date: 11-23-2007
Location: Texas
Posts: 8,210
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-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 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-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.
02-13-2009, 04:14 PM
#5
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Join Date: 12-24-2008
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Posts: 717
50 Amp Battery Fuse
ChevyMgr,
Do you mean the 50 Amp fuse near the battery feeds the Engine Compartment Fuse Box only OR does it also feed the Floor Console Fuse Box? Either way it brings up the question, “What is Chevy doing using a 50 amp fuse to protect another device(EPS) that has a 60 amp fuse protecting it?” Master fuses, it was my understanding were always of a higher value than the downstream power distribution.
Looks like I am going to have to splurge on the 2009’s wiring diagrams. Are they only available from Helm? Or are they available for the 2009 yet? The last time I purchased Chevy wiring diagrams was for a 1991 2500K - absolutely great diagrams, much better than the F.O.R.D. I most recently had.
Do you mean the 50 Amp fuse near the battery feeds the Engine Compartment Fuse Box only OR does it also feed the Floor Console Fuse Box? Either way it brings up the question, “What is Chevy doing using a 50 amp fuse to protect another device(EPS) that has a 60 amp fuse protecting it?” Master fuses, it was my understanding were always of a higher value than the downstream power distribution.
Looks like I am going to have to splurge on the 2009’s wiring diagrams. Are they only available from Helm? Or are they available for the 2009 yet? The last time I purchased Chevy wiring diagrams was for a 1991 2500K - absolutely great diagrams, much better than the F.O.R.D. I most recently had.
Last edited by Sno White; 02-13-2009 at 04:16 PM. Reason: clarity
02-13-2009, 04:50 PM
#6
Founding Member
Join Date: 11-23-2007
Location: Texas
Posts: 8,210
ChevyMgr,
Do you mean the 50 Amp fuse near the battery feeds the Engine Compartment Fuse Box only OR does it also feed the Floor Console Fuse Box? Either way it brings up the question, “What is Chevy doing using a 50 amp fuse to protect another device(EPS) that has a 60 amp fuse protecting it?” Master fuses, it was my understanding were always of a higher value than the downstream power distribution.
Do you mean the 50 Amp fuse near the battery feeds the Engine Compartment Fuse Box only OR does it also feed the Floor Console Fuse Box? Either way it brings up the question, “What is Chevy doing using a 50 amp fuse to protect another device(EPS) that has a 60 amp fuse protecting it?” Master fuses, it was my understanding were always of a higher value than the downstream power distribution.
Looks like I am going to have to splurge on the 2009’s wiring diagrams. Are they only available from Helm? Or are they available for the 2009 yet? The last time I purchased Chevy wiring diagrams was for a 1991 2500K - absolutely great diagrams, much better than the F.O.R.D. I most recently had.
03-25-2010, 11:10 AM
#7
Join Date: 07-04-2008
Location: Maryville TN
Posts: 7
Can Mr. Chevy Current Sensor Question
I have another post on this issue but this thread is very close to the area I need help in. I have noticed that the engine compartment can read 15 or so volts, engine running, but the battery is at 12 or so volts at times but can also be at the same voltage as the engine compartment at other times. That means something is between the alternator and the battery. I assume to limit charging current to the battery. What is the device that is isolating the battery from the alternator? Where is it located? Does the current sensor on the battery ground affect this mystery device? Or am I just going in the wrong direction here? My reasons are that I am having charging problems and the battery is good. Thanks Mr. Chevy and my apologies if I have posted incorrectly.
03-25-2010, 12:11 PM
#8
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Join Date: 12-24-2008
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Posts: 717
My vehicle has ~14.5 VDC everywhere(engine compartment or battery) when the engine is running and ~12.8(battery voltage) everywhere when the engine is not running. The 14.5 VDC is higher than any other vehicle I have had. Your measurement of 15VDC is yet higher and I would suspect a less than accurate voltmeter.
There is nothing between the alternator and the battery except a long run of undersized wire. GM is saving weight.
I have since found out what that 50 AMP fuse next to the battery does, as was my question in the original post. It feeds the BCM connector #3 directly – there are two other 12 VDC feeds from the engine compartment to the BCM as well.
AND of course that larger cable from the battery to the engine compartment fuse box.
The current sensor on the battery ground does just that, it senses a power draw the BCM can keep track of.
There is nothing between the alternator and the battery except a long run of undersized wire. GM is saving weight.
I have since found out what that 50 AMP fuse next to the battery does, as was my question in the original post. It feeds the BCM connector #3 directly – there are two other 12 VDC feeds from the engine compartment to the BCM as well.
AND of course that larger cable from the battery to the engine compartment fuse box.
The current sensor on the battery ground does just that, it senses a power draw the BCM can keep track of.
03-25-2010, 01:07 PM
#9
Founding Member
Join Date: 11-23-2007
Location: Texas
Posts: 8,210
Mr. Chevy??? Oh my!
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.
03-25-2010, 01:31 PM
#10
Join Date: 07-04-2008
Location: Maryville TN
Posts: 7
Thank You Mr. Chevy, However...
If, as Sno White mentioned that there is a direct connection between the battery and the alternator, how can there be only 12.x volts at the battery and 15 volts at the engine compartment when the car is running? I have checked all wiring attachment points, fuses, etc. There is certainly no burning or any evidence of intermittent connections anywhere. Lastly, what would happen if I disconnected the current sensor at the battery ground? Oh, anyone know where I can get a wiring schematic?