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Discussion Starter · #1 ·
Car starts fine and runs ok, but when I drive it with a battery voltage readout (plugged into the RH 12 v accessory port below the HVAC controls) the voltage reading RANDOMLY drops from 14.4V/14.2V range to 12.82V/12.58V range .

The battery is the Hyundai OEM that tested show 475 CCA from the 550 CCA rating.
The car has 81K miles on it and the battery is 5.5 years old.

I realize the alternator has the valeo clutch on it but I never saw the voltage drop down to 12.58V when driving.

When the car was tested at an auto parts place at idle and the lights/high beam and AC was turned on the battery voltage dropped down from 14.2V to 12.82V and it stayed there.

I am thinking that the voltage regulator is erratic in the alternator, or worn brushes and that is the problem and/or the Valeo clutch. !

Anyone have any experience with this issue on their vehicle ?
 

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12.82VDC indicates the alternator is putting out, but the speed is too low. If you turn the fan speed to 3 or 4th position the engine should speed up a few hundred rpm and the voltage should come up.

FYI, nominal fully charged 12VDC car battery is 12.6VDC, or 2.1VDC per cell X6.
 

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I think you will find it's fine. Modern ECU controlled alternators will vary the output voltage relative to the load. AUTOSPARK will come on board and give a good explanation of how they work.
 

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They do last longer but yea it might just drop dead sooner than later. The only thing is the concern over the alternator voltage but nothing is actually wrong with the car. Common AUTOSPARK we need a technical explanation.
 

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5 1/2 year old battery - you're living on the edge.
FYI, my Hyundai battery lasted 12 years before it needed replacement. So I must have gone right over the edge into the abyss.

charlescrown said:
The only thing is the concern over the alternator voltage but nothing is actually wrong with the car. Common AUTOSPARK we need a technical explanation.
I've not had to do any work on a Hyundai smart charging system yet, but generally with these systems the engine PCM will switch the charging system off during periods of high engine load (hard acceleration) and switch it back on when engine load is reduced (over run). Obviously, the control logic is a bit more complicated than that but the point is I wouldn't be surprised to see the voltage swing the OP mentions in his opening post from a smart charging system. If the PCM is commanding the charging system off, your voltmeter will display the voltage of the battery. If it commands it on, your meter will show the alternator output voltage.

BTW, my missus used to always complain about the blower motor in her Mazda constantly changing speed as she drove. When I checked it I found that the blower would slow down significantly when you accelerated then would speed up when you lifted your foot off the gas. Nothing wrong with the blower, just the smart charging system doing it's thing. I'm sure I've seen a few folk mention the blower speed symptoms of the smart charging system on the forums here too.
 

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Discussion Starter · #8 ·
5 1/2 year old battery - you're living on the edge.

Replace it and retest.
I agree !

I put in a New Interstate MT47H5 650 CCA battery.
It is the same size as the Hyundai OEM battery but with 100 more CCA.
I charged up the battery and ran with
INNOVA 3721 Battery and Charging System Monitor



[ame]https://www.amazon.com/INNOVA-3721-Battery-Charging-Monitor/dp/B000EVWDU0/ref=pd_sim_263_3?_encoding=UTF8&pd_rd_i=B000EVWDU0&pd_rd_r=FXBKGCMZWH491S0GE629&pd_rd_w=pTbeV&pd_rd_wg=5YYk6&psc=1&refRID=FXBKGCMZWH491S0GE629&dpID=4105fQmT1vL&preST=_SY300_QL70_&dpSrc=detail[/ame]

in the 12v accessory port (cigarette lighter for us older folks).

Battery voltage remained between 13.12 - 13.78 driving at 50 - 60 mph.
When I coasted (no foot on gas) and/or slowed down to make a turn the alternator charging kicked in and the Innova 3721 read 14.02 - 14.50 volts.

There is a Valeo Pulley alternator clutch that engages and disengages at certain rpm for the alternator to charge or not charge your battery.
There is no engine pcm involved with this Valeo Pulley alternator clutch.
It is strictally mechanical spring that functions off of rpm.

The shop where I purchased the battery rebuilds starters, alternator and generators.
They showed me the Valeo Pulley and gave me the explanation.

I inquired what it would cost to rebuild my generator if I ever had to have it done in the future:
To rebuild and replace the following parts:
Valeo Pulley $73.81
Voltage Rectifier $16.67
Brushes $11.08
Bearings $8.00
Labor $13.44
Total $120

or I could buy a new Valeo OEM (Hyundai) alternator for $140
 

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There is a Valeo Pulley alternator clutch that engages and disengages at certain rpm for the alternator to charge or not charge your battery..
I don't know what your battery supplier told you but your valeo pulley is actually an Overrunning Alternator Decoupler (OAD). It's purpose is to isolate the alternator's inertia from the drive belt, not to control the alternator output. Alternator output is controlled by the engine PCM.
 

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Your alternator is working fine. That's how the smart alternator on these hyundai's work. They go up to higher voltages and ramp down to lower voltages when necessary. I purchased a voltimeter that plugs in to my DC outlet a few years back and the voltage differences you describe on your first post are exactly what I've always observed with that little unit. The system is designed to save gas and increase the life of your battery.
 

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The battery is the Hyundai OEM that tested show 475 CCA from the 550 CCA rating.
The car has 81K miles on it and the battery is 5.5 years old.

From that test result your battery is still in very good condition.
 

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Discussion Starter · #12 ·
Charlescrown,

What I was concerned with was the 12.58V voltage reading I got when driving at 60 mph, which meant I was running on battery voltage only.
The plug in meter had 3 led lights, green, yellow, and red.
During the 12.58 voltage reading the red light stayed on, the the battery icon was flashing constantly.

Since I got the interstate battery installed, the meter is not showing the red led light , nor reading 12.58V or flashing the battery icon.

From what I have observed from the meter, the oem Hyundai battery was borderline, sometimes reading good, but when I had been driving
a distance like an hour or so, and the engine hot, 75F ambient temperature, I interpreted that the battery was breaking down internally.

I am curious what were the low battery voltage readings that you have observed on your vehicle, on hot days, with the engine hot ??

Thank you in advance for your input !
 

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Yea your right with 12.58 it's draining the battery but could it be possible there is a voltage drop with the circuit your measuring it from? I have seen cigi lighters having a 1 volt drop. The best test for a battery is a load test. It's an old test but it's real. I assume you used a newer electronic battery tester which I have used many times and don't have much faith in. When cruising along you should be getting around 14 volts or a little higher but I have had very little experience with the newer alternators other than seeing them being replaced at great cost when the mechanic didn't understand how they worked.
 

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once again, your alternator and battery are/were working fine!!!!!!!!!!! I see 12.6 or 12.7 volts on my voltimeter all the time. It drops that low when the car no longer needs to charge the battery. it's purposefully draining just a little bit of your battery to prolong its life, too much overcharge is bad for Lead acid batteries. It will read that low when it's hot or cold, doesn't matter. When I replaced a bad battery a year ago, i left the voltimeter in just to see when the smart alternator would kick in again, it took 2-3 days if I remember correctly, so you will probably see the same thing tomorrow that you observed earlier...
 

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Discussion Starter · #15 ·
CyprusCorner,

I checked into what you said about voltage drop across the cigaratte lighter and measured a .39 Volt drop from I measured at the battery.

With the new battery I am getting readings as low as 12.41 V at the cigarette lighter.
So 12.41 V + .39 V = 12.80 V at the battery.

I found to get this 12.41 V reading (which is not all the time ) that the fan speed switch position has to be in the number 2 position.
If I move the fan speed switch to position 3 the additional electrical load puts the cigarette lighter voltage reading up into the 14 plus voltage reading.

I still believe my old battery was borderline weak, because every test I had done at several auto parts places always said I needed to charge the battery.
I had been having the old OEM battery checked for the last 2 years in the spring and fall and it always passed the auto parts place test with flying colors !

This was a learning experience as how the EGT alternator voltage changes from the previous alternators I had in the past vehicles.

Thank you for your input.
 

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If I remember correctly, here's what I typically observe:

There's three settings i typically see it run
12.7ish (can drop to this when accelerating)
14.1ish (always in this mode when headlights are on, or PWN fan controller set to max/3 or 4 fan setting in your case)
and 14.6ish (will go this high for a few seconds after starting the car, and when braking)

The car will typically stay at either 14.1 or 12.7 volts most of the time if any of the above conditions are not present.
 

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Discussion Starter · #18 ·
Good point, but I was always present when the test was done and got a printout from the battery/charging electronic tester showing the battery history over time that I kept in the glove compartment.

This way with the data collected every spring and fall (I live in the snowbelt), I would not hopefully be caught unaware.

I at this point believe the electronic tester is accurate, and that the software/firmware in the tester is not programmed to give a negative result so that the store can sell more batteries - (which makes a good conspiracy theory, thou) !
 

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Most basic battery testers aren't very reliable either if they're only testing CCA. you will replace batteries likely much more often and earlier if you rely on those tests from shops.

BU-905a: Testing Starter Batteries in Vehicles ? Battery University

The most reliable way to know whether or not a battery will fail is to turn the ignition ;-)

I always run my batteries till the end, and keep jumper cables in my trunk for that time when it does fail. I live in a city, so there's always someone around who i can jump from if necessary.
 

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As I said I have used a few brands of electronic testers and find you can get different reading by testing the same battery a few times. The best and true test is a load test where you dial up a genuine load of the rated CCA (and others like AH etc) and hold it for 10 seconds and read the battery terminal voltage. It's the real muscle test.
 
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