I have read here on BITOG that on modern automobiles, upon starting, the ecm will command the alternator to deliver 14+ volts until the battery returns to about 80% charge. After that the ecm will manage the alternator to supply enough voltage to run the car and support any accessory loads. Is this understanding correct? If so, is the time honored "20 mile blast up the interstate and back" method of charging up a battery obsolete ? Seems like no matter how you drive, the ecm will only allow the approximate 80% charge. The only way to top off a battery to 100% would be to use a charger or tender. What you say BITOGGERS ?
Battery charging
- Thread starter JunkdrawerDog
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I first noticed this on a 2005 Cobalt bought new (now at 312K miles). No voltmeter so bought a digital guage for acc port. Wasn't having any problems/issues other than cell phone charging was sometimes quick and other times almost none. Volts can get up to high 14's briefly, but can also settle to as low as 12.2 under certain conditions. After some research I learned alternator output was controlled by ecm, using a strategy to increase fuel economy (go figure). Part of the discussion I stumbled onto had more to do with effect on battery life. Battery life in this car has averaged 4-5 years so not stellar but prob. avg.
Now we have start/stop technology, direct gas injection (which has allowed higher compression) but can create its own set of problems, thinner oil spec, pwm of fuel pump and probably more things in the quest for higher CAFE.
Now we have start/stop technology, direct gas injection (which has allowed higher compression) but can create its own set of problems, thinner oil spec, pwm of fuel pump and probably more things in the quest for higher CAFE.
Every car is different, but yes, they are trying to get every bit of gas mileage out of the cars now, so alternators seem to turn off and turn back on again.
What's "pwm of fuel pump"? Thanks
Guessing here but I think PWM "cycles" the fuel pump, alternator etc. Sort of a different approach to variable speed - apparently the motors/electrical components like PWM better? Above my pay grade. PWM eliminated the fuel return line on some (if not all) vehicles, allowing the pump to provide only what fuel is needed. Probably a tad more effieient.
Originally Posted by 379KITTY
Guessing here but I think PWM "cycles" the fuel pump, alternator etc. Sort of a different approach to variable speed - apparently the motors/electrical components like PWM better? Above my pay grade. PWM eliminated the fuel return line on some (if not all) vehicles, allowing the pump to provide only what fuel is needed. Probably a tad more effieient.
Yes - But often at a pretty high frequency.
Imagine if you were Superman, and you could turn the light switch on the wall "on and off" 10,000 times a second.
The (incandescent) bulb would see full voltage, bulb only for a split second. If the length of the pulses of "voltage applied" are low compared to the pulses of "no voltage", the bulb would glow dim. If the pulses of "power on" were longer than the pulses of "power off", the bulb would be brighter.
It's the same with the variable speed fuel pumps.
Older EFI pumps ran at the full car's power of 13.8 - 14.2 volts (or whatever), and a regulator controlled fuel pressure.
Now, a PWM module controls the fuel pressure by controlling the speed of the pump motor instead. Little pulse of power for slow speed, bigger/longer pulses of power for high speed (to adjust fuel pressure)
Guessing here but I think PWM "cycles" the fuel pump, alternator etc. Sort of a different approach to variable speed - apparently the motors/electrical components like PWM better? Above my pay grade. PWM eliminated the fuel return line on some (if not all) vehicles, allowing the pump to provide only what fuel is needed. Probably a tad more effieient.
Yes - But often at a pretty high frequency.
Imagine if you were Superman, and you could turn the light switch on the wall "on and off" 10,000 times a second.
The (incandescent) bulb would see full voltage, bulb only for a split second. If the length of the pulses of "voltage applied" are low compared to the pulses of "no voltage", the bulb would glow dim. If the pulses of "power on" were longer than the pulses of "power off", the bulb would be brighter.
It's the same with the variable speed fuel pumps.
Older EFI pumps ran at the full car's power of 13.8 - 14.2 volts (or whatever), and a regulator controlled fuel pressure.
Now, a PWM module controls the fuel pressure by controlling the speed of the pump motor instead. Little pulse of power for slow speed, bigger/longer pulses of power for high speed (to adjust fuel pressure)
So, is flying up the freeway and back no longer going to charge a low battery? Sounds like 80% charge is all the system will give you. Maybe I should buy a solar powered tender.
Linctex good explanation.
I think optimum battery life is non-important to OEM's as it doesn't play a role in CAFE equation.
I think optimum battery life is non-important to OEM's as it doesn't play a role in CAFE equation.
A Lead acid car battery discharged below 80% state of charge, can potentially be quickly brought back upto 80% state of charge range, if the alternator's voltage regultor is seeking and then holding the 77f battery's voltage in the mid 14v range. Cold batteries require higher voltages, hot batteries require lesser voltages
Getting the 80% battery to 100% state of charge however, takes no less than 3.5 more hours and only if the still relatively healthy battery is held in the mid 14v range for that entire 3.5 hours . Higher voltages will not significantly reduce that time, but lower voltages will significantly increase the time it takes for a healthy 80% charged battery to reach 100% state of charge.
A less than healthy battery might never reach 100% state of charge, even if held at 13.6v for days on end.
An 80% charged battery will have NO issues starting the engine, a healthy 30% charged battery will have no issues starting the engine unless both battery and engine are super cold. It seems people think that if the engine starts the battery is fully charged or nearly so, but this is very much false.
A modern fuel injected vehicle that starts easily and quickly, whose voltage regulator seeks mid 14 volts, can return into the battery the energy used to start the engine, in about one minute. But if the battery was at 80.225% charged when the engine was started, it will only be charged back to 80.225% charged again, a minute later, if the voltage regulator is seekig mid 14 volts, and the alternator has no other huge loads on it like a winch or blower motor on high and headlights which will suck up 40 amps or so of the alternator's available output, in which cas it ould not be able to bring the battery to 14.5ish volts anyway.
There is no getting around the 3.5 hours to get a lead acid battery from 80% charged to 100% charged. The closer to 100% charged the battery is, the slower it charges. Voltages ( electrical pressure) over 14.8v on a 77f battery become increasingly abusive to it. it will bubble very fiercly and shed positive plate material at a much higher rate, and will only charge slightly faster. AGM batteries might vent at voltages over 15. AGm venting is not instant death of the AGM but it is best avoided.
A less than healthy battery will take longer than 3.5 hours to reach full charge from 80% charged in the mid 14v range.
An AGm battery can likely charge faster from 50 to 85% charged compared to a regulr flooded starting batterym but the 85% to 100% recharge times are not reduced and AGM batteries if deeply cycled really want to be returned to 100% state of charge to retain their capacity. AGM$ price does not make them super batteries by any means, they are kind of petulant princesses when not treated well, and treating them well means returning them to full charge quickly when well depleted and keeping them at high states of charge all other times.
A lead acid battery Always wants to be at 100% state of charge, and No, vehicle charging systems are not good at returning a discharged battery to this state, and yes many newer vehicles intentionally keep the battery in the 80% charged range via voltage manipulation, as a discharged battery can accept a lot more amperage than a battery coser to fully charged, and each 25 amps an alternator is said to produce, requires 1HP from the engine due to losses through the diodes and belt drive.
Each newer vehicle will be quite different in terms of its voltage regulation, and proper battery charging is ALL about the voltage regulation, and time. Manufacturers care more about meeting fuel economy standards than they do about battery life, even though a battery that needs to be replaced much more often, likely uses more energy and wastes more resources than that which is saved by keeping it intentionally undercharged.
Maintenance minded car owners, wanting maximum battery longevity, will return the battery to a true 100% state of charge often by using a plug in charger, or perhaps a solar panel of high enough wattage and a solar controller capable of holding a high enough voltage for long enough to accomplish the true full charge. Any charging is better than no charging, but 100% charged is twice as good as getting only back to 98% charged.
Reports of any specific battery's longevity, good or bad, are entirely meaningless without knowing the battery's average state of charge, and its average temperature. PLease read that sentence again and keep it in mind when the inevitable battery threads start and people start claiming one battery lasts longer than another, in their experience. A battery kept at an average 92% charged will greatly outlive one kept at an average of 82% charged. The vehicle's voltage regulator, and how the vehicle is used can easily account for higher variances in average state of charge than this.
Defects aside, the worst constructed LEAD ACID car battery kept at a very high average state of charge will outlast, by a large margin, the most expensive 'best' lead acid battery, wet or AGm or GEl, kept chronically undercharged.
The label on the battery does not denote any resistance to chronic undercharging.
The label 'might' indicate some ability to be returned to some usable level of capacity if a prolonged intentional overcharge is performed in an attempt to revive it, once it is shown to be weak.
Getting the 80% battery to 100% state of charge however, takes no less than 3.5 more hours and only if the still relatively healthy battery is held in the mid 14v range for that entire 3.5 hours . Higher voltages will not significantly reduce that time, but lower voltages will significantly increase the time it takes for a healthy 80% charged battery to reach 100% state of charge.
A less than healthy battery might never reach 100% state of charge, even if held at 13.6v for days on end.
An 80% charged battery will have NO issues starting the engine, a healthy 30% charged battery will have no issues starting the engine unless both battery and engine are super cold. It seems people think that if the engine starts the battery is fully charged or nearly so, but this is very much false.
A modern fuel injected vehicle that starts easily and quickly, whose voltage regulator seeks mid 14 volts, can return into the battery the energy used to start the engine, in about one minute. But if the battery was at 80.225% charged when the engine was started, it will only be charged back to 80.225% charged again, a minute later, if the voltage regulator is seekig mid 14 volts, and the alternator has no other huge loads on it like a winch or blower motor on high and headlights which will suck up 40 amps or so of the alternator's available output, in which cas it ould not be able to bring the battery to 14.5ish volts anyway.
There is no getting around the 3.5 hours to get a lead acid battery from 80% charged to 100% charged. The closer to 100% charged the battery is, the slower it charges. Voltages ( electrical pressure) over 14.8v on a 77f battery become increasingly abusive to it. it will bubble very fiercly and shed positive plate material at a much higher rate, and will only charge slightly faster. AGM batteries might vent at voltages over 15. AGm venting is not instant death of the AGM but it is best avoided.
A less than healthy battery will take longer than 3.5 hours to reach full charge from 80% charged in the mid 14v range.
An AGm battery can likely charge faster from 50 to 85% charged compared to a regulr flooded starting batterym but the 85% to 100% recharge times are not reduced and AGM batteries if deeply cycled really want to be returned to 100% state of charge to retain their capacity. AGM$ price does not make them super batteries by any means, they are kind of petulant princesses when not treated well, and treating them well means returning them to full charge quickly when well depleted and keeping them at high states of charge all other times.
A lead acid battery Always wants to be at 100% state of charge, and No, vehicle charging systems are not good at returning a discharged battery to this state, and yes many newer vehicles intentionally keep the battery in the 80% charged range via voltage manipulation, as a discharged battery can accept a lot more amperage than a battery coser to fully charged, and each 25 amps an alternator is said to produce, requires 1HP from the engine due to losses through the diodes and belt drive.
Each newer vehicle will be quite different in terms of its voltage regulation, and proper battery charging is ALL about the voltage regulation, and time. Manufacturers care more about meeting fuel economy standards than they do about battery life, even though a battery that needs to be replaced much more often, likely uses more energy and wastes more resources than that which is saved by keeping it intentionally undercharged.
Maintenance minded car owners, wanting maximum battery longevity, will return the battery to a true 100% state of charge often by using a plug in charger, or perhaps a solar panel of high enough wattage and a solar controller capable of holding a high enough voltage for long enough to accomplish the true full charge. Any charging is better than no charging, but 100% charged is twice as good as getting only back to 98% charged.
Reports of any specific battery's longevity, good or bad, are entirely meaningless without knowing the battery's average state of charge, and its average temperature. PLease read that sentence again and keep it in mind when the inevitable battery threads start and people start claiming one battery lasts longer than another, in their experience. A battery kept at an average 92% charged will greatly outlive one kept at an average of 82% charged. The vehicle's voltage regulator, and how the vehicle is used can easily account for higher variances in average state of charge than this.
Defects aside, the worst constructed LEAD ACID car battery kept at a very high average state of charge will outlast, by a large margin, the most expensive 'best' lead acid battery, wet or AGm or GEl, kept chronically undercharged.
The label on the battery does not denote any resistance to chronic undercharging.
The label 'might' indicate some ability to be returned to some usable level of capacity if a prolonged intentional overcharge is performed in an attempt to revive it, once it is shown to be weak.
Originally Posted by wrcsixeight
An 80% charged battery will have NO issues starting the engine, a healthy 30% charged battery will have no issues starting the engine unless both battery and engine are super cold. It seems people think that if the engine starts the battery is fully charged or nearly so, but this is very much false.
Very informative post! When October comes around here, and the weather gets rapidly colder, one definitely gets the feel for one's battery's health in a hurry.
My dad always believed in periodically putting a battery on at least an automatic charger of the day overnight.
An 80% charged battery will have NO issues starting the engine, a healthy 30% charged battery will have no issues starting the engine unless both battery and engine are super cold. It seems people think that if the engine starts the battery is fully charged or nearly so, but this is very much false.
Very informative post! When October comes around here, and the weather gets rapidly colder, one definitely gets the feel for one's battery's health in a hurry.
My dad always believed in periodically putting a battery on at least an automatic charger of the day overnight.
Originally Posted by wrcsixeight
A Lead acid car battery discharged below 80% state of charge, can potentially be quickly brought back upto 80% state of charge range, if the alternator's voltage regultor is seeking and then holding the 77f battery's voltage in the mid 14v range. Cold batteries require higher voltages, hot batteries require lesser voltages
Getting the 80% battery to 100% state of charge however, takes no less than 3.5 more hours and only if the still relatively healthy battery is held in the mid 14v range for that entire 3.5 hours . Higher voltages will not significantly reduce that time, but lower voltages will significantly increase the time it takes for a healthy 80% charged battery to reach 100% state of charge.
A less than healthy battery might never reach 100% state of charge, even if held at 13.6v for days on end.
An 80% charged battery will have NO issues starting the engine, a healthy 30% charged battery will have no issues starting the engine unless both battery and engine are super cold. It seems people think that if the engine starts the battery is fully charged or nearly so, but this is very much false.
A modern fuel injected vehicle that starts easily and quickly, whose voltage regulator seeks mid 14 volts, can return into the battery the energy used to start the engine, in about one minute. But if the battery was at 80.225% charged when the engine was started, it will only be charged back to 80.225% charged again, a minute later, if the voltage regulator is seekig mid 14 volts, and the alternator has no other huge loads on it like a winch or blower motor on high and headlights which will suck up 40 amps or so of the alternator's available output, in which cas it ould not be able to bring the battery to 14.5ish volts anyway.
There is no getting around the 3.5 hours to get a lead acid battery from 80% charged to 100% charged. The closer to 100% charged the battery is, the slower it charges. Voltages ( electrical pressure) over 14.8v on a 77f battery become increasingly abusive to it. it will bubble very fiercly and shed positive plate material at a much higher rate, and will only charge slightly faster. AGM batteries might vent at voltages over 15. AGm venting is not instant death of the AGM but it is best avoided.
A less than healthy battery will take longer than 3.5 hours to reach full charge from 80% charged in the mid 14v range.
An AGm battery can likely charge faster from 50 to 85% charged compared to a regulr flooded starting batterym but the 85% to 100% recharge times are not reduced and AGM batteries if deeply cycled really want to be returned to 100% state of charge to retain their capacity. AGM$ price does not make them super batteries by any means, they are kind of petulant princesses when not treated well, and treating them well means returning them to full charge quickly when well depleted and keeping them at high states of charge all other times.
A lead acid battery Always wants to be at 100% state of charge, and No, vehicle charging systems are not good at returning a discharged battery to this state, and yes many newer vehicles intentionally keep the battery in the 80% charged range via voltage manipulation, as a discharged battery can accept a lot more amperage than a battery coser to fully charged, and each 25 amps an alternator is said to produce, requires 1HP from the engine due to losses through the diodes and belt drive.
Each newer vehicle will be quite different in terms of its voltage regulation, and proper battery charging is ALL about the voltage regulation, and time. Manufacturers care more about meeting fuel economy standards than they do about battery life, even though a battery that needs to be replaced much more often, likely uses more energy and wastes more resources than that which is saved by keeping it intentionally undercharged.
Maintenance minded car owners, wanting maximum battery longevity, will return the battery to a true 100% state of charge often by using a plug in charger, or perhaps a solar panel of high enough wattage and a solar controller capable of holding a high enough voltage for long enough to accomplish the true full charge. Any charging is better than no charging, but 100% charged is twice as good as getting only back to 98% charged.
Reports of any specific battery's longevity, good or bad, are entirely meaningless without knowing the battery's average state of charge, and its average temperature. PLease read that sentence again and keep it in mind when the inevitable battery threads start and people start claiming one battery lasts longer than another, in their experience. A battery kept at an average 92% charged will greatly outlive one kept at an average of 82% charged. The vehicle's voltage regulator, and how the vehicle is used can easily account for higher variances in average state of charge than this.
Defects aside, the worst constructed LEAD ACID car battery kept at a very high average state of charge will outlast, by a large margin, the most expensive 'best' lead acid battery, wet or AGm or GEl, kept chronically undercharged.
The label on the battery does not denote any resistance to chronic undercharging.
The label 'might' indicate some ability to be returned to some usable level of capacity if a prolonged intentional overcharge is performed in an attempt to revive it, once it is shown to be weak.
You have answered my questions. Thanks!
A Lead acid car battery discharged below 80% state of charge, can potentially be quickly brought back upto 80% state of charge range, if the alternator's voltage regultor is seeking and then holding the 77f battery's voltage in the mid 14v range. Cold batteries require higher voltages, hot batteries require lesser voltages
Getting the 80% battery to 100% state of charge however, takes no less than 3.5 more hours and only if the still relatively healthy battery is held in the mid 14v range for that entire 3.5 hours . Higher voltages will not significantly reduce that time, but lower voltages will significantly increase the time it takes for a healthy 80% charged battery to reach 100% state of charge.
A less than healthy battery might never reach 100% state of charge, even if held at 13.6v for days on end.
An 80% charged battery will have NO issues starting the engine, a healthy 30% charged battery will have no issues starting the engine unless both battery and engine are super cold. It seems people think that if the engine starts the battery is fully charged or nearly so, but this is very much false.
A modern fuel injected vehicle that starts easily and quickly, whose voltage regulator seeks mid 14 volts, can return into the battery the energy used to start the engine, in about one minute. But if the battery was at 80.225% charged when the engine was started, it will only be charged back to 80.225% charged again, a minute later, if the voltage regulator is seekig mid 14 volts, and the alternator has no other huge loads on it like a winch or blower motor on high and headlights which will suck up 40 amps or so of the alternator's available output, in which cas it ould not be able to bring the battery to 14.5ish volts anyway.
There is no getting around the 3.5 hours to get a lead acid battery from 80% charged to 100% charged. The closer to 100% charged the battery is, the slower it charges. Voltages ( electrical pressure) over 14.8v on a 77f battery become increasingly abusive to it. it will bubble very fiercly and shed positive plate material at a much higher rate, and will only charge slightly faster. AGM batteries might vent at voltages over 15. AGm venting is not instant death of the AGM but it is best avoided.
A less than healthy battery will take longer than 3.5 hours to reach full charge from 80% charged in the mid 14v range.
An AGm battery can likely charge faster from 50 to 85% charged compared to a regulr flooded starting batterym but the 85% to 100% recharge times are not reduced and AGM batteries if deeply cycled really want to be returned to 100% state of charge to retain their capacity. AGM$ price does not make them super batteries by any means, they are kind of petulant princesses when not treated well, and treating them well means returning them to full charge quickly when well depleted and keeping them at high states of charge all other times.
A lead acid battery Always wants to be at 100% state of charge, and No, vehicle charging systems are not good at returning a discharged battery to this state, and yes many newer vehicles intentionally keep the battery in the 80% charged range via voltage manipulation, as a discharged battery can accept a lot more amperage than a battery coser to fully charged, and each 25 amps an alternator is said to produce, requires 1HP from the engine due to losses through the diodes and belt drive.
Each newer vehicle will be quite different in terms of its voltage regulation, and proper battery charging is ALL about the voltage regulation, and time. Manufacturers care more about meeting fuel economy standards than they do about battery life, even though a battery that needs to be replaced much more often, likely uses more energy and wastes more resources than that which is saved by keeping it intentionally undercharged.
Maintenance minded car owners, wanting maximum battery longevity, will return the battery to a true 100% state of charge often by using a plug in charger, or perhaps a solar panel of high enough wattage and a solar controller capable of holding a high enough voltage for long enough to accomplish the true full charge. Any charging is better than no charging, but 100% charged is twice as good as getting only back to 98% charged.
Reports of any specific battery's longevity, good or bad, are entirely meaningless without knowing the battery's average state of charge, and its average temperature. PLease read that sentence again and keep it in mind when the inevitable battery threads start and people start claiming one battery lasts longer than another, in their experience. A battery kept at an average 92% charged will greatly outlive one kept at an average of 82% charged. The vehicle's voltage regulator, and how the vehicle is used can easily account for higher variances in average state of charge than this.
Defects aside, the worst constructed LEAD ACID car battery kept at a very high average state of charge will outlast, by a large margin, the most expensive 'best' lead acid battery, wet or AGm or GEl, kept chronically undercharged.
The label on the battery does not denote any resistance to chronic undercharging.
The label 'might' indicate some ability to be returned to some usable level of capacity if a prolonged intentional overcharge is performed in an attempt to revive it, once it is shown to be weak.
You have answered my questions. Thanks!
dedicated chargers like Ctek give a start charging voltage of 12.6v, increasing to 14.4v (higher with cold temerature setting) and declining charge current. I doudt car charging system is as sophisticated as this; it will just put out the fixed charge volts until the battery no longer draws any current at which point, excess chard is dumped to earth.
as WRC highlighted, the charging rate/ time varies with the state of the battery.
I would not assume battery full charge recovery over short trips (specially in cold winter days!); so either a mains charger or a drive
as WRC highlighted, the charging rate/ time varies with the state of the battery.
I would not assume battery full charge recovery over short trips (specially in cold winter days!); so either a mains charger or a drive
My car has this smart alternator approach that aims to keep the battery some where below full I charge. I've monitored the charging voltage and seen it rise when the car is on the overrun and then fall when accelerating. What I've also noticed though is that while it never fully charges when the car is in local use, it does get a lot closer to full charge after long motorway use. I tend to charge the battery once a week to top it up, in fact it's on charge now, but I'm doing a long run this weekend and I know that afterwards it will need a much shorter topping up charge if any.
I'm mainly a weekend driver (e-bicycle to work); mostly short trips.
I used to give the car battery an overnight charge every 3 months.
Battery in my last (Toyota) car was going strong at 9 y.o.
For the past 9 months I use a 10W solar panel on the dash.
In bright sun this floats the battery at ~13.2V.
The "smart" regulator in the Tucson stays at 12.6V except for headlights, decel etc.
I used to give the car battery an overnight charge every 3 months.
Battery in my last (Toyota) car was going strong at 9 y.o.
For the past 9 months I use a 10W solar panel on the dash.
In bright sun this floats the battery at ~13.2V.
The "smart" regulator in the Tucson stays at 12.6V except for headlights, decel etc.
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