Gunfighter1950

Saw an article on a Corvette Tech Talk channel that claimed, in Modern Cars (not only corvettes) that the alternator doesn't (repeat) doesn't charge the battery. Rather it only maintains the battery at it's current state of charge. If your battery is only half charged then the alternator will keep it there. If it's fully charged it will keep it there as well.
I don't quite understand that concept and if it's true does the theory apply to our older vehicles as well? What year do cars become Modern is another question?
Maybe some of you have heard this and would like to comment.

ChrisBlair

How would it maintain if no charge was provided

jim lockwood

The statement I've highlighted is your tip off that who ever made that silly claim has no clue what he (or she) is talking about!

Duck916

Logically speaking, if the charging system only maintained whatever charge the battery is at, the battery would eventually go flat. Putting it very simply, each time you start the car, you are pulling a little charge out, right? If the charging system doesn't replace that small discharge, then eventually you'd get to zero (or where the battery wouldn't start the car, at least).

I will say that modern cars seem to have pretty sophisticated charging systems that minimize the charging action to avoid overcharging the battery and to reduce unnecessary drag in the search for every iota of fuel economy. But a modern system will bring a discharged battery back to full in the normal course of things. I see this all the time in my newer cars that sometimes sit for a month at a time.

SJW

Whoever authored that nonsense needs to find a new career.

Live well,

SJW

4 Speed Dave

Geez wiz I guess I wasted my money when I ordered my Duramax truck with 2 alternators.

Gunfighter1950

Your comments only go to prove the segment is incorrect at best. The thing that bothered me was they didn't define what was a modern car. Would my 64 be considered Modern? Not by today's C8 but certainly compared to the 53 C1. Crazy the comments floating around out there. Thanks for the input.

jim lockwood

It doesn't matter what's modern or not modern. That claim about "maintaining" is fundamentally wrong for generators, alternators,.... regardless of age.

67:72

Absolutely and it doesn't make any sense when doing voltage tests at the battery. If the charging system only maintained, then why are the tests deemed good if the idle voltage is 13.8v-14.4v? The alternator would have to monitor the battery voltage and only match it to maintain its current state of charge.

apahl

I think the original article misstated the issue. The alternator does indeed charge the battery when it is below a certain voltage. However, when the vehicle is being operated in a mode where the battery is fully charged and there is little load being placed on the battery, the alternator reduces the voltage to around 12.2 volts ( give or take) . I have seen this many times in my 2010 Camaro. When it first ocurred, I thought the alternator was going bad. But atter the next start it was charging 14.5 again. Driving a considerable distance with no accesories allows the battery to be fully charged and the ECM keeps it there until the next load is sensed . If the battery IS fully charged AND there is almost NO load you don't need 14.5 volts to be put into the battery.

leif.anderson93

Read Jim's post #2 in this current thread...it will explain "why" on your modern car.

https://www.corvetteforum.com/forums...diagnosis.html

dplotkin

Right. Jim is right. Of course he's right, he is an EE. So what I write below is subject to his correction or edification.

It is true that modern cars have sophisticated charging regimens not found on our relics. I've seen it for myself on my 2019 Corvette GS. The alternators in our new cars no longer sport voltage regulators built in but use the engine ECM to control current to the alternator field instead of said regulator. The ECM decides when to best charge and at what rate, based on the best use of engine power and to enhance economy. Measuring voltage across the battery in a new car may result in head scratching readings.

The 10DN, by way of example but also true of Chrysler, Motorola & MotorCraft alternators will produce about 18 volts at full RPM. The external regulators used with these are designed to hold alternator voltage at around 13.8 to 14.2 volts by mechanical interruption or electronic clamping of the field circuit. Unlike a generator which needs current regulation too the alternator is constructed such that it self limits current output and cannot be overdrawn. But it can and will overcharge if its output is allowed to exceed 14.5 volts for lengths of running time.

Remember that charging voltage and rate experienced with a properly operating regulator will vary according to ambient temperature, state of battery charge and condition, engine RPM & alternator pully diameter. As such, don't look for a magic voltage on an old car, it could be anywhere between 13.8 & 14.2 volts. And on new cars don't look for old car voltages. You may see 12.6, you may see 14 and anything in-between completely at the discretion of the ECM.

Dan

Avispa

This discussion reminds me of making a fuss over the difference between "true" power steering and "power assisted" steering.

dplotkin

There is a difference. The alternator discussion is technical. A power steering debate between power and power assist is one of semantics. All power steering requires a driver to steer before any assist takes place and is to my knowledge not debatable.

One can argue that a power box is better than a power ram and control valve, but both are power assisted steering and that aspect is again, not debatable.

Dan

jim lockwood

Ya know, Dan, you may have just put an idea for a winter project in my head.

There are really cheap single-chip computers (search for Arduino Nano) which have analog I/O and which are well capable of driving power FETs. I'm starting to visualize a "smart" Voltage regulator for generator systems using a Nano as the brains.....

SJW

We're gonna need to see a build thread on that project, Jim.

Live well,

SJW

GordonR

The short version is currently modern alternator charging systems use pulse width modulation inputs directly based on a manufacture computer strategy's and various bus systems. The bus systems employ communications with several modules to deliver their intel . There is also can be a redundant (backup) mode for some charging systems when communications fail the alternator can utilize an on board internal regulator to maintain the vehicles electrical needs until the systems can be restored too. .

dplotkin

Someone with your brain did just that, a few members are around who have them if you do a forum search. Mr. Fink was among them.
Needless to say, if you came up with a good design for a generator regulator that would replace the 85+ year old mechanical three element regulator (cut-out/voltage/current) you would have not just the best thing since sliced bread but the bagel and cream cheese of the (really) old car hobby.

Dan

jim lockwood

Well, stay tuned. The idea hasn't totally infested my brain cells yet. I may still be able to talk myself out of doing it.

Trouble is that I've done so many Arduino projects that I can immediately imagine how such a smart regulator should work.

Doggonnit, Dan!!!!

reno stallion

I have one