Do Alternators Maintain Full Battery Charge?

[SubLGT]

According to battery university.com, the answer is usually "no". That is certainly in line with my own experience.

"............Sulfation occurs when a lead acid battery is deprived of a full charge. This is common with starter batteries in cars driven in the city with load-hungry accessories. A motor in idle or at low speed cannot charge the battery sufficiently.
........Lead acid must periodically be charged 14–16 hours to attain full saturation."
http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it

"..............The correct setting of the charge voltage is critical and ranges from 2.30 to 2.45V per cell. Setting the voltage threshold is a compromise, and battery experts refer to this as “dancing on the head of a needle.” On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate; on the other hand, an over-saturated condition causes grid corrosion on the positive plate and induces gassing.
To make “dancing on the head of a needle” more difficult, the battery voltage shifts with temperature. Warmer surroundings require slightly lower voltage thresholds and a cold ambient prefers a higher level. Chargers exposed to temperature fluctuations should include temperature sensors to adjust the charge voltage for optimum charge efficiency. If this is not possible, it is better to choose a lower voltage for safety reasons.................."
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

 

[supton]

I've heard of that too, and that you shouldn't ask an alternator to charge up the battery. I've put batteries into a couple of vehicles over the years, brand new / off the shelf, and been thankful that they've had enough charge to start initially. I'll just drive them for half-hour or more, then forget about it.

Whether or not the altenator takes it all the way to 100% charge or not, knock on wood, only times I have issues is with high milage altenators or batteries around the 7 year mark. That includes one or two full deep discharges which usually require a jump. Knocking on more wood, the Jetta altenator is fine after 274k/9 years. I'm guessing that uncharged capacity is just riding along for the ride; seems doubtful that it is "costing" me anything as I rarely sit in the car with the radio on and the engine off.

 

[eljefino]

Since my GM charging system gets to 14.8-15.2 volts on a cold morning, and my batteries last 6+ years, I can say yes, mine do.

 

[Clevy]

I've only killed 1 battery in my lifetime that couldn't be charged back up to power the vehicle again.
Mind you my vehicles aren't very high tech either and the only reason I killed the one I did was because of 3 subs and 3 amps

 

[SubLGT]

Keep in mind that a fully charged lead acid battery is generally defined as one that has an open circuit voltage of approximately 12.65V @80 degF. And of course there are also specifications for specific gravity. From what I have read, both those specs can vary a little, depending on specific plate chemistry.

Just because your battery has started your car the last 4 winters, or lasted 5 years, does not mean it is being maintained at full charge by the vehicle alternator. Measurement of the State Of Charge is the only way to determine that.

 

[HerrStig]

Originally Posted By: SubLGT
According to battery university.com, the answer is usually "no". That is certainly in line with my own experience.

"............Sulfation occurs when a lead acid battery is deprived of a full charge. This is common with starter batteries in cars driven in the city with load-hungry accessories. A motor in idle or at low speed cannot charge the battery sufficiently.
........Lead acid must periodically be charged 14–16 hours to attain full saturation."
http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it

"..............The correct setting of the charge voltage is critical and ranges from 2.30 to 2.45V per cell. Setting the voltage threshold is a compromise, and battery experts refer to this as “dancing on the head of a needle.” On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate; on the other hand, an over-saturated condition causes grid corrosion on the positive plate and induces gassing.
To make “dancing on the head of a needle” more difficult, the battery voltage shifts with temperature. Warmer surroundings require slightly lower voltage thresholds and a cold ambient prefers a higher level. Chargers exposed to temperature fluctuations should include temperature sensors to adjust the charge voltage for optimum charge efficiency. If this is not possible, it is better to choose a lower voltage for safety reasons.................."
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
I guess that's why mine only last 7 or eight years. Perhaps alternators and their associated drive pullys are still undesized on modern cars? Maybe they will get it "right when regulators improve.

 

[supton]

Sure. But does it matter? I'm pretty sure anything over 5 years is considered a "good" lifespan, regional allowances required.

Or are you saying I'd get 10 years if I plugged the battery in nightly to ensure full charge?

 

[440Magnum]

Car battery charging systems are actually pretty sophisticated when it comes to correctly maintaining the battery's charge. Even the very first electronic voltage regulators (Chrysler, circa 1970) had temperature compensation that would maintain the battery at the correct voltage for a full charge at the ambient temp. Its even better today since most vehicles have a sensor that measures temp AT the battery, rather than at the voltage regulator like the first Mopar electronic modules did. There is absolutely NO reason to charge the battery externally to the vehicle these days unless you do nothing but short-tripping that never fully tops the battery, OR you run the battery dead.

What car charging systems do NOT do well is to recharge a deeply discharged battery. Car charging systems have to also run the vehicle electronics, and that causes the charging system to have to recharge a deeply discharged battery too fast. If it trickle charged the battery, the car bus voltage would drop too low. Batteries can take that kind of fast charge at few times in their life, but its better to trickle charge a deeply dead battery. Sometimes you just can't do that and have to let the car jam it full fast. The price is shorter battery life.

 

[MolaKule]

Quote:
that you shouldn't ask an alternator to charge up the battery


Huh? Where is the battery going to get its charge if not from the alternator?

 

[JHZR2]

No vehicle that Ive ever put a charger on has had te charger accept the battery at 100% and go straight to float. They do charge much faster, as you would expect, than a battery that has self discharged a bit.

The right way to charge a battery is to do constant current to a set voltage, then constant voltage until the current is below some value related to the capacity of the battery. Alternators are obviously not that smart, and thus do not get as optimal a charge in terms of the materials and electrochemistry.

Some of the issues is that the alternator voltage may have some temperature compensation, but insufficient for the underhood temperatures, the float voltages arent optimal, and a true, complete charge is not given. An alternator roughly gives a CV charge only.

 

[wrcsixeight]

Whatever the charging source, it takes a long time to squeeze in every last electron into a battery at which point the battery can be considered truly 100% fully charged whereas a voltage reading can indicate a full charge anywhere above 90%, and most automatic chargers really stop at 93 to 97%. That last 3 to 7% can take another 12 hours on float, or it might require equalization (intentional overcharge) voltages for several hours to bring all the cells back up to their maximum specific gravity.

Many people think/act that if the battery starts the engine, then it is fully charged, or that the alternator will quickly and fully charge it if it was depleted, which is just not true, but like the pennzoil sludge myth, it will never die, and for most, if the engine starts with the key turn, who cares if it is at 100%?

I regularly ask My alternator to recharge 2 rather large deep cycle batteries over an upgraded charging circuit, and these can max out the alternator and V belt at 90+ amps for a few minutes before tapering, and the batteries hold a higher voltage the next night after what I call an alternator quenching, compared to if 200 watts of solar alone recharged them back up to 100% by itself.

My engine battery sees nothing but the engine computer memory overnight, and my engine starts within 1 second of cranking. This particular battery is approaching 6 years old, and was cycled nightly the first 2 years of its life. The alternator amps after starting indicate that right after starting the amps are right around 30, and within 30 seconds are below 12, and within a minute are below 5. When I turn the switch to bring in the depleted deep cycle batteries, the engine note changes as the alternator goes from producing single digits to at least 64 amps.

My vehicle will allow the alternator to produce max amps at a given RPM until 14.5 volts is reached and held for a certain amount of time before reverting to 13.7. Once 14.5 is reached the amount of amps required to hold 14.5 tapers fairly rapidly as the batteries recharge.

It will revert to 13.7 well before the deep cycle batteries are even close to 80%, and as little as 12 amps is required to hold 13.7, while 40+amps was required to hold 14.5.

So in my case despite having the alternator and circuit capacity to feed the batteries As dictated by Crown, the manufacturer of my DC batteries, the Voltage regulator inside my engine computer prematurely decides that 13.7 is safer, and adequate, and if it was recharging or maintaining just the engine battery, perhaps it would be.

Recharging of Lead Acid batteries can be taken to ridiculous levels if one is seeking ultimate lifespan, but for most, the battery just gets replaced every few years and is never even considered until it quits.

 

[cat843]

I think the alternator will get it close enough assuming its giving enough time. If your starting the car in the winter and drive 1/4 mile to a store and back, at nightime on slow roads, your alternator will not have enough time to recharge the battery. Cars seem to get the longest lifespan from a flooded battery. Boats and lawn tractors never get the number of years a car does.

 

[440Magnum]

Originally Posted By: wrcsixeight


Recharging of Lead Acid batteries can be taken to ridiculous levels if one is seeking ultimate lifespan,


This^^^^. you can go WAY beyond a sane cost/benefit ratio if you treat your car battery with the same care as, for example, the old deep-ocean submersibles when they used Pb-acid batteries. When the battery costs about as much as the rest of the vehicle and is supposed to LAST as long as the vehicle, its worth it to have a whole crew just to maintain its state of charge.

 

[punisher]

Originally Posted By: MolaKule


Huh? Where is the battery going to get its charge if not from the alternator?


Well, I think it might be referring to an alternator charging up a totally dead battery, like after a jump start? Dead battery with your AC blower on and some other draws can get real close to full fielding an alternator.

I remember those old Ford alternators. You could shake them and hear the solder balls rattling around in there.

 

[jrustles]

Yes, they do!

Originally Posted By: SubLGT
Keep in mind that a fully charged lead acid battery is generally defined as one that has an open circuit voltage of approximately 12.65V @80 degF. And of course there are also specifications for specific gravity. From what I have read, both those specs can vary a little, depending on specific plate chemistry.

Just because your battery has started your car the last 4 winters, or lasted 5 years, does not mean it is being maintained at full charge by the vehicle alternator. Measurement of the State Of Charge is the only way to determine that.


Never forget that "full charge" is a constantly declining parameter in the lead acid battery, either due to disintegration or sulfation plate loss. High frequency/voltage chargers can cause wearing batteries to mimick a good initial open circuit voltage. However, immediately putting that battery into a car, starting it, and handing it over to the alternator's regulator, will yield a more realistic open circuit voltage after a while. The alternator is capable of supplying high amperages, much much higher than that of the Ctek, but nominal voltages, unlike the CTEK which can provide upwards of 4x cell voltage and uses a pulse frequency to inhibit plate sulfation.

In a nutshell, the smart charger is able to saturate the battery beyond it's wear limits, and the alternator, using nominal voltage only, is only able to bring it up to it's actual capacity.

 

[jrustles]

Originally Posted By: punisher
Originally Posted By: MolaKule


Huh? Where is the battery going to get its charge if not from the alternator?


Well, I think it might be referring to an alternator charging up a totally dead battery, like after a jump start? Dead battery with your AC blower on and some other draws can get real close to full fielding an alternator.

I remember those old Ford alternators. You could shake them and hear the solder balls rattling around in there.


It's no problem for the alternator.
They can safely provide as many amps as their rating suggest and those ratings are based on a given RPM. The idea is, whether charging the battery or powering your lights and fans, the alternator will have no problem. BUT if the loads begin to exceed the alternator's power output at a given RPM, like everything on while idling in gear, then the voltage regulator and rectifiers begin to heat up and their lives will be shortened. As batteries charge and discharge, their internal resistance changes correspondingly. This determines how much current the battery will accept at a nominal voltage, not the alternator. As a note, the "equilibrium" of that resistance chart will slide higher as the battery ages.

 

[jrustles]

Originally Posted By: SubLGT

........Lead acid must periodically be charged 14–16 hours to attain full saturation."
http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it

Sorry, forgot to address the actual topic

There is only 'one stage' of charging on automotive electrical systems, and that's at one voltage (ie system voltage does not change in relation to battery charge). There is no specialized charging system in cars as described in the article. Each and every time a vehicle is started off of it's battery, it does not require "14-16 hours" to recover! On a bench, you can get a battery "fully saturated" by trickling for many hours, but to not much benefit on a starting battery. Starting batteries also reach full saturation much faster than deep-cycle batteries because they have much thinner plates/more plates and more plate-electrolyte surface area. So as long as your alternator generates more current than the actual demand, your battery will be recharged in short order.

 

[eljefino]

Originally Posted By: jrustles

Sorry, forgot to address the actual topic

There is only 'one stage' of charging on automotive electrical systems, and that's at one voltage (ie system voltage does not change in relation to battery charge).


With a temperature compensated alternator there may be a minute where it hasn't yet "gotten the memo" that the battery has warmed up. This slight boost may either get it to 100% charge (past the float point) or may help desulfate.

Probably varies from car to car and is probably by design on some and completely by accident on others.

 

[jaj]

Originally Posted By: jrustles
Sorry, forgot to address the actual topic

There is only 'one stage' of charging on automotive electrical systems, and that's at one voltage (ie system voltage does not change in relation to battery charge). There is no specialized charging system in cars as described in the article. Each and every time a vehicle is started off of it's battery, it does not require "14-16 hours" to recover! On a bench, you can get a battery "fully saturated" by trickling for many hours, but to not much benefit on a starting battery. Starting batteries also reach full saturation much faster than deep-cycle batteries because they have much thinner plates/more plates and more plate-electrolyte surface area. So as long as your alternator generates more current than the actual demand, your battery will be recharged in short order.


Well, that may have been true at one time, but modern cars have controllable alternators and a complex alternator management routine built into the ECU. It controls of the alternator output voltage and charging strategy, with particular attention to making sure that there's the correct voltage for the fuel pump (in particular) at heavy loads.

 

[JHZR2]

Originally Posted By: 440Magnum
Originally Posted By: wrcsixeight


Recharging of Lead Acid batteries can be taken to ridiculous levels if one is seeking ultimate lifespan,


This^^^^. you can go WAY beyond a sane cost/benefit ratio if you treat your car battery with the same care as, for example, the old deep-ocean submersibles when they used Pb-acid batteries. When the battery costs about as much as the rest of the vehicle and is supposed to LAST as long as the vehicle, its worth it to have a whole crew just to maintain its state of charge.



For something that is known to offgas hydrogen, have a locally acidic environment, release acid and corrode its conductors, undergo thermal runaway, freeze and crack at low states of charge, etc., Id say that something with a little bit of capability to optimize the charge is a good thing. One doesnt have to be measuring the SG of each cell necessarily...