OT: "An Alternator is a Battery Maintainer, -NOT a Battery Charger."

[BRENT in 10-uh-C]

This comment in the title was recently told to me by a battery salesman. I have thought and thought about this, -and even looked online where I have read the same comment multiple times.

So help me understand what I don't understand about (t)his comment. So if a battery in a Model-A is at 100% capacity ( i.e.: fully charged ), and the engine starts after a prolonged cranking, let's hypothetically say that the battery is now at 90% capacity ( -or 90% of fully-charged ). If an alternator is only a 'maintainer', then is it reasonable to assume that the best that can be expected is the battery will remain at 90%? Then the next time the engine is started, the battery charge may drop to 85%, ...and so on until the voltage has dropped to a point the battery cannot turn the starter motor.

So if the point about an alternator is only a maintainer and not a charger, how is it that a battery can go so long without needing to be placed on a dedicated 'battery charger' to return it to 100%??

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[Bill G]

Then taking this one step further, a generator would also be a maintainer and not a charger? I wonder what the difference in the definition between a maintainer and a charger is. The alternator certainly does recharge the battery once the car is started or drained for some other reason, for instance leaving the lights on with the car not running.

[Big hammer]

Battery salesman, that's enough said. I took a battery back for warranty the salesman popped the caps off a maintenance free battery and said who's been adding water? Not me I said, he said he would replace it but no warranty on the new battery, haven't been back to that store!

[Bob C]

My take on the statement is if say your battery is dead and you jump start it and
let the alternator charge it back up this is hard on the alternator.

[40 Deluxe]

The first thing to keep in mind is that you were talking to a battery "salesman". They seldom understand the technical aspects of their product, but will say whatever it takes to make a sale! If they can impress you with meaningless gobbledygook, all the better. So if "an alternator is a battery maintainer...", that means that it maintains the battery at 100% charge. To do so, it has to recharge the battery after startup (or after accessory use), as you say. Thus, it is also a "battery charger".
It would interesting to ask this salesman to explain the difference!

[Jack Shaft]

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Cant tell you how many dead batteries Ive jumped and allowed the alternator to recharge.

[CC-Mo]

So it's safe to say a generator will keep a new battery equally charged as a car with an alternator?

[Russ/40]

A true battery maintainer performs functions other than charging to maintain bat health. Example would be the shocking of plates as in a desulfate mode or process. Anything else is a bat charger.

[alexiskai]

Originally Posted by Bob C

My take on the statement is if say your battery is dead and you jump start it and
let the alternator charge it back up this is hard on the alternator.

This is the correct take. The quote at the top is best understood in the context of charging a completely dead battery. This is a not-uncommon situation in modern cars: battery is dead, somebody gives you a jump start, you go on with your life, relying on the alternator to bring the battery from 0-100%. As the argument goes, this purportedly causes the alternator to overheat, because modern alternators can put out much higher amperage than those of decades past. With higher amperage comes higher heat that the alternator has to dissipate. If it can't dissipate it (for example if you're idling the car to charge the battery), the alternator can overheat and be damaged or die.

I don't have direct experience of how widespread this is, but it is something that alternator repair shops often say.
https://ademaelectric.com/troubleshooting-alternators

[40 Deluxe]

Originally Posted by CC-Mo

So it's safe to say a generator will keep a new battery equally charged as a car with an alternator?

That would be YES! Generators did so for years. But alternators are an improvement for several reasons:

1. They charge at idle speed, while a generator doesn't. Thus headlights dim noticeably at idle with a generator and the battery will gradually run down if you are just puttering around town with the lights, radio and heater on.
2. Alternators usually last longer. There is a rear bearing instead of a bushing, and the brushes only carry a small load.

3. Less electrical "noise" with an alternator which makes electronic gadgets happy. In a generator, current is generated in the armature and transferred through the brushes. Look in at the brushes at night with the headlights on at a fast idle and see the fire fly as the current arcs across the brushes! Generator brushes carry 30-40 amps, while an alternator's brushes only carry 2 to 3 amps (whatever the field current is). An alternator can be described as an inside-out generator. Current is generated in the case windings instead of the armature, and the field windings are in the rotor (armature in a generator).

[Jordan]

If I heard that, I would understand it in the sense that an alternator "maintains" a battery at a full charge with proper use, where as a generator is a "charging" system. It will continue to charge the battery even if it is at full capacity, therefor overcharging the system.

My 2 cents. But I also wasn't there to hear his comment in context.

[40 Deluxe]

Originally Posted by Jordan

If I heard that, I would understand it in the sense that an alternator "maintains" a battery at a full charge with proper use, where as a generator is a "charging" system. It will continue to charge the battery even if it is at full capacity, therefor overcharging the system.

My 2 cents. But I also wasn't there to hear his comment in context.

You may be thinking of pre-1940 Ford generators with a third brush and a cut-out instead of a voltage regulator. However, a properly functioning voltage regulator controls the generator charging voltage, so the system will not be overcharged. The generator is regulated to approximately 7.2 volts in a 6 volt system and 14.4 in a 12 volt system.

[CC-Mo]

Originally Posted by 40 Deluxe

That would be YES! Generators did so for years. But alternators are an improvement for several reasons:

1. They charge at idle speed, while a generator doesn't. Thus headlights dim noticeably at idle with a generator and the battery will gradually run down if you are just puttering around town with the lights, radio and heater on.
2. Alternators usually last longer. There is a rear bearing instead of a bushing, and the brushes only carry a small load.

3. Less electrical "noise" with an alternator which makes electronic gadgets happy. In a generator, current is generated in the armature and transferred through the brushes. Look in at the brushes at night with the headlights on at a fast idle and see the fire fly as the current arcs across the brushes! Generator brushes carry 30-40 amps, while an alternator's brushes only carry 2 to 3 amps (whatever the field current is). An alternator can be described as an inside-out generator. Current is generated in the case windings instead of the armature, and the field windings are in the rotor (armature in a generator).

Thanks for that info. My lights indeed dim as I'm stopping the car to open the garage doors, also noticed it while pulling in the garage in the dark.
I thought I may have grounding issues to chase down but now maybe I just didn't know what normal looked like!

[Patrick L.]

The same with an alternator. An alternator is basically an AC generator. The diode bridge changes the AC to DC. Without regulation of either generator or alternator output the battery can be overcharged.
One difference is that a generator will charge on a dead battery where an alternator will not. A generator is or can act as a motor. An alternator can't and needs electricity supplied to it to be able to charge.
That doesn't do anything for the OP though does it. Isn't a battery 'maintainer' also a charger ? Every one I've had or known of is. A maintainer charges at a low rate and then somehow is able to remain connected and add a bit of charge only when needed. Thats my take on this anyway. Tell if I'm wrong and convince me differently.

[Kurt in NJ]

I left the key on --- for 3 months, so totally dead battery, no voltage at all, put my 3 amp trickle charger on the car, hand cranked it to start, took off charger, drove to show 40 minutes, battery up enough to start car then, drove home parked car-- never charged battery otherwise, got 6 more years out of battery

Another experiment-- I have a diode cutout, good pull with hand crank made 4 volts, enough to start car

[eagle]

All voltage regulators on alternators are not created equal. Some maintain the battery voltage at 13.8, some at 14.2. Foreign cars, especially from 20 years ago, ran lower voltage on the regulator. They would maintain a battery that was never allowed to run dead, but a dead battery should be charged more than that to return them to deep capacity. It's estimated that each time you deep discharge a lead acid battery, you are going to lose at least 10% capacity. If the battery sits dead for a long period you can lose 50% or more. Its a good idea to put a trickle charger on a battery that's been dead, leave it on for 24 hours+.

[rotorwrench]

It all just sounds like semantics to me. By the original meaning of the words, the alternator charging system does both since the definitions are not that far apart. The alternator will give the battery charge which is technically maintaining the battery for use.

"Maintainer" implies that something is being maintained. Since many modern batteries can not be serviced externally, the only way to maintain them is to use them regularly so that the can both give energy and receive energy to keep the internal plates in good serviceable condition. The old wet cell batteries can be maintained by adding water when low and checking them for state of charge with a hydrometer now and then. Those actions make the operator or mechanic the maintainer of the wet cell lead acid batteries. The AGM batteries need the electronic charger/discharger units to maintain them if they set too long. All batteries like to be used regularly to make them last better.

Most manufacturer's will only honor one warranty exchange. Not too many will do better than that but if it's a good product, it won't need any warranty.

[30 Closed Cab PU]

My definitions, I am sure I will be corrected if there is disagreement.



Trickle charger (sometimes referred to incorrectly as a maintainer) - usually lower current maxim outputs, typically 1 1/2 amp max, charges slightly even when battery is fully charged. Typically the current is low enough so electrolyte boiling-outgassing does not occur.



Maintainer (also referenced as a Smart Charger)- typically lower current max charging. Have additional features as mentioned above, plus have the "float" feature that monitors battery charge and turns off charging when fully charged, and turns on again when battery drops below a set charge level.


Charger - Higher current charging capabilities, does not have the "Smart" features. These have to be manually monitored to avoid overcharging/boiling-outgassing of the electrolyte.

[rotorwrench]

Most of the old chargers would lower the current output as the battery charged up. These were smart enough for me. I also use a 3-amp steady state charger for 12-volt cycle batteries but a person shouldn't charge longer than recommended by the battery manufacturer to top one off.

The generator or alternator is an integral part of a vehicles electrical system. The original 3-brush units were just constant output generators unless someone puts one of the little regulators on them like John Regan's unit. With those things installed they will gradually reduce current output as the battery charges but still ramp up the current when the lights come on. The alternators hardly have to work at all since there function is automatic. They top the battery up quickly then wait for a high current draw from accessories or lights.

As one of their tasks in the system, they all charge the battery to maintain full charge. It's as simple as that. Salesmen will come up with all sorts of excuses if their product has problems.

[Jack Shaft]

Running an alternator at regulated full load occasionally doesn't drastically reduce its life.That being said,all electrical components perform well and have a long life when all components work as the should..starters draw correctly,batteries deep cycle and recover correctly,alternators maintain the system.