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#4594405 - 12/04/17 08:18 PM Sonata strange battery charging behavior
Nick1994 Offline


Registered: 02/19/13
Posts: 10108
Loc: Phoenix, AZ
I've always noticed that while braking/coasting my hvac fan blows a little harder than it does at idle. Didn't think much of it all year but I have a volt meter thing that plugs into the 12v outlet so I plugged it in.

While driving down the road with any amount of throttle, the voltage is in the low 12's, sometimes dips into the 11's. When coasting to a light or in traffic, or when braking, the voltage shoots up into the 14V range. At idle it goes back down into the 12's. I've also observed that with the headlights on my voltage goes up.

I put in a new battery in October, I don't have any issues. It starts fine and everything works. I was as just curious about this behavior. I left the volt meter in the 12V outlet for a week and glanced at it every now and then, same results. It's almost like a hybrid!

I'm guessing this is new car technology or something? About a month ago I hooked up my Solar Prologix PL2310 charger and it said it was 100%. When I go back to the car but don't start it, the voltage is around 12.7V.

I have 3 videos below. #1 is driving on the freeway. Sometimes with my foot on the gas, sometimes coasting. Voltage up when coasting, voltage down when accelerating. #2 is starting the car at a light. Voltage at startup is always above 14V. I then took off from the light and stopped at the next one shortly. I then revved the car in neutral. #3 is in a parking garage with me turning the headlights on and off. voltage up with lights on. voltage down with lights off.





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2015 Hyundai Sonata 2.4L 79k PU 5w30 & OEM
2000 Toyota Camry 2.2L 228k M1 AFE 0w30 & Wix
1996 Jeep Cherokee 4.0L 146k M1 HM 10w40 & Fram Ultra

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#4594417 - 12/04/17 08:33 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
eljefino Offline


Registered: 06/15/03
Posts: 32635
Loc: ME
I suspect your suspicions are accurate.

BMW has a car that only charges when braking, and the dealer gives complimentary batteries b/c to recode the computer to charge more would be an EPA/ MPG violation.

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#4594431 - 12/04/17 08:39 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
KneeGrinder Offline


Registered: 11/28/17
Posts: 221
Loc: North of you Idaho
Is the Sonata a Hybrid?

It's almost like a hybrid!

I guess not! lol! I would take it to the dealer since you should have hyundai's 100,000 mile warranty. The voltage should be much more stable, and much more around 14.0 to 14.3 almost all the time.


Edited by KneeGrinder (12/04/17 08:46 PM)
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06 Accord Hybrid 131k PUP 5w20 wix
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#4594432 - 12/04/17 08:40 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
Check for poor connections at the alternator. (And or Battery, but if it was replaced most likely not here)

Meter the thick wire on the alternator to the battery ground and see if you have 14 volts at idle. Then try just the battery posts. If the voltage is higher at the back of the alternator referenced to ground than it is at the battery you have a bad connection.

You could also have a faulty voltage regulator in the alternator that functions normally when the alternator spins faster but fails to do it's job when it spins slower because internal resistances change. I have seen this before.

What's it like with every possible accessory running at idle / 2,000 rpm?



Edited by StevieC (12/04/17 08:40 PM)
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#4594440 - 12/04/17 08:49 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
JHZR2 Offline



Registered: 12/14/02
Posts: 41780
Loc: New Jersey
Must be a "smart" alternator. BMW has done it for a few years, adding more charge under no throttle/braking, and less to reduce load under normal use. Some cars even have a gauge showing it.

My hybrid has a DC voltage of 12 and change under normal use, goes up to 14+ with headlights on, and IIRC other stuff. Never noticed a change in the fans though. Different controls/electronics though. The hybrid voltage is controlled by a power converter, as the 12V battery is charged via a dc-dc converter from the HV hybrid battery.

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#4594443 - 12/04/17 08:50 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
KneeGrinder Offline


Registered: 11/28/17
Posts: 221
Loc: North of you Idaho
More than likely the alternator has a faulty voltage regulator, maybe it was smuggled across the boarder from the north...j/k
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00 F350 133k Delvac 1300 15w40 wix

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#4594459 - 12/04/17 09:20 PM Re: Sonata strange battery charging behavior [Re: KneeGrinder]
Thax Offline


Registered: 11/07/10
Posts: 786
Loc: VA
Most likely have a faulty alternator. Charging voltage should be between 13v-14.5v depending on load ,rpm and ambient temps.
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#4594464 - 12/04/17 09:30 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
Rand Offline


Registered: 08/20/03
Posts: 12641
Loc: NE,Ohio
Its hyundai's smart alternator strategy.

Same thing on the 2010 accent only even more so on newer models.

They fully load the alternator in coasting.. and not so much at other times..

I think its asinine to save .2mpg but it is what it is.

nothing to see here operating as engineered and intended.
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#4594483 - 12/04/17 09:57 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
Tman220 Offline


Registered: 09/20/16
Posts: 144
Loc: MN
This is a charging strategy that is used for extra mpg's. Lots of cars have this feature and the reason you don't hear of it is because it works much better than BMW's (too aggressive) approach which kills batteries.

There is nothing wrong with your car, alternator, or voltage regulator. My 2012 regal uses a similar strategy, as well as my (gasp!) 2004 Civic.

Sleep well it's normal.
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#4594484 - 12/04/17 10:00 PM Re: Sonata strange battery charging behavior [Re: Rand]
Colt45ws Offline


Registered: 08/15/06
Posts: 9640
Loc: Central Washington
Originally Posted By: Rand
Its hyundai's smart alternator strategy.

Same thing on the 2010 accent only even more so on newer models.

They fully load the alternator in coasting.. and not so much at other times..

I think its asinine to save .2mpg but it is what it is.

nothing to see here operating as engineered and intended.

Agree.
This is the new norm. And I think thats why the long pro-rated battery warranties disappeared. But thats my pet conspiracy theory.
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2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
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#4594503 - 12/04/17 10:30 PM Re: Sonata strange battery charging behavior [Re: Nick1994]
dogememe Offline


Registered: 04/15/17
Posts: 605
Loc: SF BAY AREA, CA
totally normal. "smart charging" has been common since the early 2000s in many vehicles. When you are accelerating it reduces alternator load... I think some newer cars disable AC compressor under heavy acceleration too?


Edited by dogememe (12/04/17 10:32 PM)
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2007 Ford Crown Vic P71 4.6 ~124K Miles, SynPower 5W-30, Royal Purple.
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1997 Chevy Suburban 5.7 ~214K Miles, O'Reilly FSHM, MicroGard.

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#4594558 - 12/05/17 01:21 AM Re: Sonata strange battery charging behavior [Re: dogememe]
rubberchicken Offline


Registered: 07/07/08
Posts: 399
Loc: Maryland USA
I had a 1985 Camaro that would disable the a/c compressor under hard acceleration, so that in itself is not a new feature.

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#4594582 - 12/05/17 02:50 AM Re: Sonata strange battery charging behavior [Re: Nick1994]
Kibitoshin Offline


Registered: 04/19/16
Posts: 693
Loc: Kaiōshinkai
A lot of newer cars will also have a current sensing ring on one of the battery leads to measure current draw. The amount of amps leaving/entering the battery also determines the alternator duty cycle. On GM's turning on the headlights disables the smart charging mode.

Ammeter coil on negative cable that measures amp draw on a 2016 GMC Sierra.


Someone will diag this as a bad alternator when misinterpreting this data:


Edited by Kibitoshin (12/05/17 02:51 AM)
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#4594688 - 12/05/17 07:31 AM Re: Sonata strange battery charging behavior [Re: Nick1994]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
My Dodge Journey has a clutch on the pulley but the voltage regulator keeps the voltage the same regardless of acceleration, deceleration and idling. That's really weird if that is what it is. Haven't seen that before. (Smart Alternator Charging)



Edited by StevieC (12/05/17 07:32 AM)
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'15 Dodge Journey - 90,000 KM's - SSO 5w20
'06 Hyundai Santa Fe - 535,000km - SSO 0w30 (R.I.P)

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#4594809 - 12/05/17 09:46 AM Re: Sonata strange battery charging behavior [Re: Rand]
JTK Offline


Registered: 08/14/03
Posts: 10580
Loc: Buffalo, NY
Like Rand said above, it's the technology built into the charging system by Hyundai to maximize fuel economy causing this. Pretty rare to have an alternator or charging system issue with a 2015.
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