Charging Voltage?

What voltage is this vehicle supposed to charge at? The gauge seems to fluctuate a lot. I stuck a cigarette lighter gauge in mine, it runs from 12.xx to over 15. Mostly below 13. I realize there is high technology these days, but historically , a vehicle needed to be charging at around 14.2 or 14.3. My last truck, an F-350, didn't have a voltage gauge. I am guessing it's normal. Just wondering what you guys are seeing?

 

Normal. Variable alternator turns down on acceleration and cranks up on braking for more engine braking load. Lights on they hover at 12.9-13.2 volts. All for mpg

 

Interesting. Thanks for the info!

 

I am not sure that is the correct interpretation. DC voltage will vary because the load measured in amps varies unless there is some kind of voltage regulation. With older voltage regulators the object was constant voltage from the alternator, 14.4vdc or somewhere close. We normally rate an alternator’s capability in amps at a specific voltage, 14.4vdc for example, and rpm. Because of that we measure energy in terms of watts which is volts x amps. So a decrease in voltage on acceleration and an increase on deceleration cannot be explained for reasons of fuel economy, since it is directly related to the number of watts needed to run the electrical system not a range of output voltages.

In summary, I don’t know why it varies. Typically an alternator’s unregulated output voltage increases as rpm increases. For the gauge to show a voltage decrease on acceleration is just the opposite.

 

Indeed. I guess what would be really important to know, is at what voltage the alternator is NOT charging?

 

Newer vehicles use deep cycle or flooded batteries. That can run the vehicles electrical system with little input then recharge under a heavier load. We have special chargers in vw to maintain batteries while we update or flash cars. This is the reason we have these systems in vw land and would only imagine the same reason across the board. This is also why the batteries are so much more money to replace. If someone replaces them with a non agm/efb (absorbed glass mat or enhanced flooded battery) it will not last as long because the charging profile will hurt the battery. On acceleration if you lighten the load and use the battery it will take strain off the engine. Then while slowing if you engine brake and fully load the alternator to add load it will replenish the loss of acceleration and save some brake life. If you look at the negative battery terminal there is a shunt on it that measures load out and in to maintain correct levels. The battery chargers don’t do a slow cycle it is a load and a trickle that varies to not sulfate the battery.

 

They precisely control the charge voltage is my guess. My F150’s tune has like 10 target battery voltage tables for different conditions and temperatures.

 

Interesting. Thank you. What is vw?

 

Volkswagen. I've got a couple, and although they've been great cars for myself, they can overly complicate their engineering IMO. For instance, need to replace your battery? No problem.. hope you have your scan tool ready, and purchased the correct battery, as Duke was referring to in his post.

 

Ah, yes of course, thanks. I have never been a fan of those. Some friends have had them over the years. Much less grief with a Corolla in my opinion..

 

Looking at the battery in my Tundra, it has both a CCA rating of 776 amps and an AH rating of 75 at the 20 hour rate. In marine parlance this would be called a dual purpose battery, capable of both starting and deep cycle operations. This kind of makes sense as the battery will have demands of both starting and providing electrical energy during auto start stop operations. As a lead acid chemistry battery one thing they don’t like is sitting partially charged as the result is sulfation over time on the lead plates. The affect of this on battery capacity is more or less reversed by applying a higher voltage for period of time in a process called equalization. When a lead acid battery is fully charged it likes to stay at a float voltage of between 13.4 and 13.6 vdc. So I would expect to see a range of voltages between 13.4 and 15 depending on what’s going on with the battery at a particular time with the engine running. If voltage drops below 13 then that may be because the battery is responding to an instantaneous load from steering for example while the alternator’s voltage regulation circuits adapt to the new load.

I’ll have to watch the volt meter to see if the readings match this theory.

 

Not sure if the new Tundra is the same but my work recently bought a brand new Suburban. It charges at variable rates. I was driving in across Colorado one day and the voltage gauge was at 12v. I was worried alternator was failing. 10 mins later gauge was at 14v.

Long story short it’s a “smart” system that only charges when it needs to. We have put 80k miles on it in 1.5 years with no problem.

I would assume Toyota could be doing something similar.

 

This is what I suspected. Just seems illogical to see it below 14V. Getting old I guess.

 

Oh I was real worried when I first saw it because I was on a highway in the middle of no where. I think later we look in the owners manual and it generically explained the system and the range the voltage gauge should operate in.

 

I suspect this why most vehicles don't have them anymore....

 

yup we have a scanner like at the checkout line at your local grocery store and have to scan old and new batteries to reset the ecu to know it has a new battery and the change the algorithm. Sucks but we have had this style for almost ten years and bmw a few more than us. Sigh

 

Computer controls the charging voltage depending on the state of the battery and probably some other factors.

 

Totally normal. It’s all for mpg and efficiency get used to variable voltage and variable oil
Pressure. Your all good dude

 

Ah this explains a lot I noticed the different "tiers" of charging voltage but wasn't sure exactly what was going on other that it probably related to BMS, but didn't know about the whole breaking thing.