Alternator Question

[Ozy44]

My voltage readout on my radar detector and my OBDll are reading as far down as 12.3v and as high as 14.2v. When on my way to work with lights on it shows 12.4v until I stop at a light, then climbs to 13.2v. When It's bright enough, I turn off the lights and get a normal reading in the 14v range. My question, is this a sign my alternator is on it's way out? I have a new H8 AGM installed and it is testing good..... I'm at 165k mileage.... No codes or dash lights. Besides the voltage regulator/alternator, is there something else I should be concerned with?

 

[jep604]

Assuming your radar detector is plugged into a cigarette lighter? The alternator is only charging the battery, not the entire electrical system.

 

[joegr]

Assuming your radar detector is plugged into a cigarette lighter? The alternator is only charging the battery, not the entire electrical system.

The voltage at the power port is the same as the battery voltage. The electrical system, the alternator, and the battery are all connected together. There is no isolation.

 

[jep604]

The voltage at the power port is the same as the battery voltage. The electrical system, the alternator, and the battery are all connected together. There is no isolation.

Is this a disagreement? If I check a battery with the engine off and it shows 12 volts via a multimeter and then starting the engine and checking the battery volts and it shows 13.8 to 14.1 volts, are you saying the entire electrical system is producing 14.1 volts or is there a voltage regulating system reducing part power to operating systems?

 

[joegr]

Is this a disagreement? If I check a battery with the engine off and it shows 12 volts via a multimeter and then starting the engine and checking the battery volts and it shows 13.8 to 14.1 volts, are you saying the entire electrical system is producing 14.1 volts or is there a voltage regulating system reducing part power to operating systems?

In that example, I am saying that the entire electrical system is at 14.1 volts. Don't take my word for it, make some measurements. Some circuits may measure slightly lower, but that will be due to slight voltage drop in the wiring to the high current loads.

 

[Ozy44]

Thanks for the great discussion people. Does anyone have an answer to the two questions in my original post? Any input related to the questions would be greatly appreciated.

 

[joegr]

Thanks for the great discussion people. Does anyone have an answer to the two questions in my original post? Any input related to the questions would be greatly appreciated.

For an older car, the answer would be easy (failing alternator), but it's not as simple for more recent cars. I know that mine has some intelligent control for the alternator that causes it to reduce voltage (to stop charging the battery) if the battery has a decent estimated state of charge and the car is not decelerating or idling. I don't know for certain if this is true or not for your year. I will say that 12.3 is lower than I would ever expect it to go because below 12.8 or so it is actually discharging the battery.

 

[Ozy44]

For an older car, the answer would be easy (failing alternator), but it's not as simple for more recent cars. I know that mine has some intelligent control for the alternator that causes it to reduce voltage (to stop charging the battery) if the battery has a decent estimated state of charge and the car is not decelerating or idling. I don't know for certain if this is true or not for your year. I will say that 12.3 is lower than I would ever expect it to go because below 12.8 or so it is actually discharging the battery.

My understanding is that 13.7 to 14.5 ish volts should be the range the regulator maintains at all times when the engine is running.The alternator supplies voltage to all of the electrical systems of the vehicle and also keeps the battery topped off for starting and for when the vehicle is off and you are using accessories. It seems strange that at 12.2 to 12.3 volts while the engine is running, I'm not getting any lights on the instrument cluster. I have a remanufactured Denso alternator on the way from Rock and figured due to mileage, I would be better off just replacing the whole unit rather than just the regulator. I'll let you know on Friday how it turns out.

 

[jep604]

In that example, I am saying that the entire electrical system is at 14.1 volts. Don't take my word for it, make some measurements. Some circuits may measure slightly lower, but that will be due to slight voltage drop in the wiring to the high current loads.

I would think the alternator would charge the battery to 14+ volts and the voltage regulator would "step" things down to those circuits requiring 12+ volts and those little "gremlin" reducers would further step down voltage for accessories. Not sure if that is a question or a statement...?

 

[joegr]

I would think the alternator would charge the battery to 14+ volts and the voltage regulator would "step" things down to those circuits requiring 12+ volts and those little "gremlin" reducers would further step down voltage for accessories. Not sure if that is a question or a statement...?

That's not how it works though. The output of the alternator is regulated by controlling the current to the field windings in the rotor. This way, a large current is controlled with a small current. Trying to regulate the output of the battery would be very inefficient.

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[Gunkk]

My voltage readout on my radar detector and my OBDll are reading as far down as 12.3v and as high as 14.2v. When on my way to work with lights on it shows 12.4v until I stop at a light, then climbs to 13.2v. When It's bright enough, I turn off the lights and get a normal reading in the 14v range. My question, is this a sign my alternator is on it's way out? I have a new H8 AGM installed and it is testing good..... I'm at 165k mileage.... No codes or dash lights. Besides the voltage regulator/alternator, is there something else I should be concerned with?

re: bold highlight: Normally the car voltage will sag a bit (maybe half a volt) at idle due to low RPM (<1000) and high load, not increase. So what you describe seems odd to me. But I can tell you that turning the steering wheel on electric power steering cars at low/zero speed can also show a bit of a sag (dimming the headlights) as the electric PS pump sucks down a lot of current. In my 3 cars, my 2009 showed this behavior more than my two '12s, and when everything in the car was powered on (HVAC, audio, lights) on rare occasions the EPS would drop out and turn to stone for a split second before recovering.

Our cars are not AGM cars. While many folks use them without issue, I do not recommend AGM batteries because the charging systems in our cars are not designed to avoid overcharging AGMs.



12.4v may not be low enough to turn on the "red battery" dash light (charging warning indicator), but it is indeed no bueno. If the car isn't generating 13.5 volts above 1000rpm, then something is indeed wrong.



If your car is not exhibiting any of the above symptoms, and you're still concerned about it, have your mechanic or automotive electrician it out. If you do swap out the alternator, avoid used/reman'd/aftermarket alternators; stick with new OEM. New batteries can go bad too. Had one take a dump on me <90 days once.

 

[Ozy44]

No EPS on my Genesis so no load problems there. I have noticed a load strain with the A/C blower at it's highest setting and when the lights are on. Doing some research, I found that big H8 AGM's need about 13.8v or higher for a proper charge cycle and I'm only getting 12.2-13.1v unless the headlights are off, only then do I get 13.9-14.1v. This morning I pulled the original Denso alternator and removed the rear cover to inspect the brush and regulator assemblies. I noticed a burnt electrical smell as soon as I pulled the cover off and the brushes are worn down to the point that they are, more than likely, barely touching the rotor. In reality, I probably only need to replace the brush assembly and the regulator since the bearings are super smooth, but with 11 years and 165k, I'm opting to replace the alternator. Fedex delivering the alternator today so results soon.

 

[Ozy44]

re: bold highlight: Normally the car voltage will sag a bit (maybe half a volt) at idle due to low RPM (<1000) and high load, not increase. So what you describe seems odd to me. But I can tell you that turning the steering wheel on electric power steering cars at low/zero speed can also show a bit of a sag (dimming the headlights) as the electric PS pump sucks down a lot of current. In my 3 cars, my 2009 showed this behavior more than my two '12s, and when everything in the car was powered on (HVAC, audio, lights) on rare occasions the EPS would drop out and turn to stone for a split second before recovering.

Our cars are not AGM cars. While many folks use them without issue, I do not recommend AGM batteries because the charging systems in our cars are not designed to avoid overcharging AGMs.

View attachment 57439

12.4v may not be low enough to turn on the "red battery" dash light (charging warning indicator), but it is indeed no bueno. If the car isn't generating 13.5 volts above 1000rpm, then something is indeed wrong.

View attachment 57441

If your car is not exhibiting any of the above symptoms, and you're still concerned about it, have your mechanic or automotive electrician it out. If you do swap out the alternator, avoid used/reman'd/aftermarket alternators; stick with new OEM. New batteries can go bad too. Had one take a dump on me <90 days once.

RE: "Our cars are not AGM cars. While many folks use them without issue, I do not recommend AGM batteries because the charging systems in our cars are not designed to avoid overcharging AGMs."

My 2012 had an OEM Hyundai labeled H8 AGM in it when I bought it. Can you please share some more info regarding our cars overcharging AGM's or point me to a post with some valid info on this?

 

[Gunkk]

RE: "Our cars are not AGM cars. While many folks use them without issue, I do not recommend AGM batteries because the charging systems in our cars are not designed to avoid overcharging AGMs."

My 2012 had an OEM Hyundai labeled H8 AGM in it when I bought it. Can you please share some more info regarding our cars overcharging AGM's or point me to a post with some valid info on this?

The TL/DR is:

1) AGMs are more sensitive (vs. flooded cell) to temperature rise and over-voltage conditions during charging, and modern cars designed for AGM batteries have "smart" charging circuits that vary both voltage and current during and after the charge cycle to prevent damage to the battery (similar to any modern portable electronic device with a lithium ion battery, but AGMs are much less sensitive to all of this than Li-ion, but that's another thread).

2) Our cars have "dumb" constant-voltage-constant-current charging systems designed for flooded cell batteries. The dumb CCCV charger doesn't know when the AGM battery is starting to get overcooked and doesn't know to let up, so it keeps right on cookin'. Does it blow up? No. Does it melt? nope. Does it slowly over time accumulate damage and lose capacity (akin to sulfation in a flooded cell)? Yep.

Perhaps the greatest perceived cost/benefit of an AGM battery is double the service life in an engine bay vs. flooded cell. Why pay $150 every 5 years when you can pay $300 for 10 (which for most of us is life of the car). But much of this "life span benefit" is already mitigated by the trunk mount. But that gain from trunk mount thermal stability is versus external sources (i.e. engine bay heat), not internal thermal excursions during charging ... which is where most if not all of the thermal damage will come from in a trunk mount, which most folks don't understand and the AGM guys don't tell you. Their incentive is to sell more high-margin AGM batteries, not talk you out of buying one.

As I said above, there are plenty of folks out there who are running AGM batteries in their cars without issue. Your money, your car, your choice. That AGM in your ride will probably outlast the car... especially with 165k but who knows. Do like the former owner and go with AGM if helps you sleep well at night. But spending more to get the same or less is not my preferred cup of tea. My personal experience: my 2012 is on its second flooded cell battery. My previous 2012 had 3, and one of those 3 was the one I mentioned that failed in <90 days. Hence, my recommendation. For the long read, go here: Battery University Homepage

Also: free advice is worth every cent. Double on the internet!

 

[Ozy44]

The TL/DR is:

1) AGMs are more sensitive (vs. flooded cell) to temperature rise and over-voltage conditions during charging, and modern cars designed for AGM batteries have "smart" charging circuits that vary both voltage and current during and after the charge cycle to prevent damage to the battery (similar to any modern portable electronic device with a lithium ion battery, but AGMs are much less sensitive to all of this than Li-ion, but that's another thread).

2) Our cars have "dumb" constant-voltage-constant-current charging systems designed for flooded cell batteries. The dumb CCCV charger doesn't know when the AGM battery is starting to get overcooked and doesn't know to let up, so it keeps right on cookin'. Does it blow up? No. Does it melt? nope. Does it slowly over time accumulate damage and lose capacity (akin to sulfation in a flooded cell)? Yep.

Perhaps the greatest perceived cost/benefit of an AGM battery is double the service life in an engine bay vs. flooded cell. Why pay $150 every 5 years when you can pay $300 for 10 (which for most of us is life of the car). But much of this "life span benefit" is already mitigated by the trunk mount. But that gain from trunk mount thermal stability is versus external sources (i.e. engine bay heat), not internal thermal excursions during charging ... which is where most if not all of the thermal damage will come from in a trunk mount, which most folks don't understand and the AGM guys don't tell you. Their incentive is to sell more high-margin AGM batteries, not talk you out of buying one.

As I said above, there are plenty of folks out there who are running AGM batteries in their cars without issue. Your money, your car, your choice. That AGM in your ride will probably outlast the car... especially with 165k but who knows. Do like the former owner and go with AGM if helps you sleep well at night. But spending more to get the same or less is not my preferred cup of tea. My personal experience: my 2012 is on its second flooded cell battery. My previous 2012 had 3, and one of those 3 was the one I mentioned that failed in <90 days. Hence, my recommendation. For the long read, go here: Battery University Homepage

Also: free advice is worth every cent. Double on the internet!

Great info Gunkk. With the way batteries are priced in todays market, the AGM's are getting less expensive as compared to standard lead acid and have a better replacement warranty. Walmart, for example, stocks a standard lead acid H8 Maxx for $159.88 with a 3 year free replacement. They also stock an H8 AGM Platinum for $179.88 with a 4 year free replacement. That's only a $20 difference, so what route would you go?

 

[Gunkk]

20 bucks is 20 bucks

 

[Gunkk]

Welp the battery karma gods saw this thread and "blessed" my car with a dead battery this morning.

Tested it with my tender and it threw a red light. 10.2 volts is all it could support. Presumed cause of death: internal short/failed cell in the Duralast gold with a date code 8/17. I and the former owner got our money out of it. Replaced with a Diehard Silver (flooded cell) at the LAPS. Walmart didn't have the H8 Maxx in stock near me or I'd probably have gone that route because 20 bucks is 20 bucks

Out with the old and in with the new:

 

[jep604]

Welp the battery karma gods saw this thread and "blessed" my car with a dead battery this morning.

Tested it with my tender and it threw a red light. 10.2 volts is all it could support. Presumed cause of death: internal short/failed cell in the Duralast gold with a date code 8/17. I and the former owner got our money out of it. Replaced with a Diehard Silver (flooded cell) at the LAPS. Walmart didn't have the H8 Maxx in stock near me or I'd probably have gone that route because 20 bucks is 20 bucks

Out with the old and in with the new:

Sorry to hear that. I just went out to check mine as it is an H8 Hyundai dealer replaced battery from 12/2017 so I guess mine is close to going out of commission. They didn't even remove the install characters and there is no manufacturer date. Battery connectors are unusual, negative in back has an odd set-up and positive up front has a large plastic box covering it. Never seen a vent tube on a vehicle battery, just helo, airplane and corporate jet batteries.

 

[Charlie1982]

Some car batteries had vent tubes back in the 1990s. (I would hope that any car with a battery in the trunk would have a vent tube, but I suppose that isn’t guaranteed…)

 

[joegr]

Some car batteries had vent tubes back in the 1990s. (I would hope that any car with a battery in the trunk would have a vent tube, but I suppose that isn’t guaranteed…)

GM had some with the battery under the back seat. Those had vent tubes. My Lincolns with the battery in the trunk also had vent tubes. I would expect that all in cabin batteries have vent connections.