Correct Battery Voltages, Revisited

[wizechatmgr]

Alternator and starter cable resistances and bad grounds also affect charging capacity. I once asked the question of a Master Volvo mechanic I trust. He answered anything above 13.5V is good. The bigger issue is giving the car time to recharge after a start. My wife had an 99 Audi A4 that regularly would get starting issues in the winter. She started the car and ran it about 2-3km to the station and back in the winter. Naturally, all the charge drawing items were on. Lights, heated mirrors, rear screen, heater at full blast, heated seats on. It was hardly surprising at -30C it would struggle after about a week of these runs. That was when I first bought a trickle charger over here.

Neil.

Hi there Neil,

Well I think a trickle charger is a really good idea for these cars, maybe many types of cars.

I hate to say this because I don't want to dissuade anyone from taking advice from known good people, but there are some differences between a "master mechanic" and an electrical engineer.
A master mechanic will have good knowledge of vehicle operations and some knowledge of electrical systems. An electrical engineer will have good knowledge of electrical systems and some knowledge of vehicle operations depending on his or her specialty.
An electrical engineer who specializes in battery charging systems and related would be the person to ask. Perhaps a battery manufacturer who is not afraid to tell the truth about the batteries it makes.

I guess we do have to be careful who we ask because different people have different experiences and they would provide information based on those experiences, not necessarily on scientific fact. Then again as i was saying before, it's hard to tell sometimes what is actually working right and what is actually working just OK or just because of certain habits that favor a system that is not even working correctly. That is, a system that is not working right may seem to be working right just because of the habits of the owner and their opinion of the system function.

I can tell you one thing is absolutely certain. If you don't drive much, 14.0 volts is not enough. I've proved this with two vehicles now. That is however assuming that batteries are still made well.
With the Hyundai I had to bring the battery into the house to charge about once every three months, and that charge voltage was also 14.0 volts, and the battery was not even a year old yet. With the Volvo I had to install a solar panel charger with enough power to charge the battery effectively every time the sun was shining.
I also suspect that many owners out there right now have batteries in their cars right now that are not fully charged. They may be 50 percent, 60 percent, 70 percent, etc., but i suspect they are not all the way to 100 percent or near that. This can still work because in many cases the car will still start up and it will seem like everything is normal. This is probably why so many batteries fail in winter and not in the warmer months.

The conclusion therefore I would have to say is if something works for you then I guess you can stick to it. I had to investigate because I am an infrequent driver who sees the battery voltage drifting down farther and farther over time unless I charge it with another method or drive all over the country (ha ha).

One person who has a mechanic friend said that this friend said that "you have to drive the car". I thought that was sort of funny because who wants to drive their car for the sole purpose of charging the battery. What, I am supposed to drive around the block 100 times just to charge the battery ... I don't think so (ha ha).

We also come to the idea of just starting the car every now and then to keep the battery charged. This would mean staying in the driveway with the engine running.
The problem here is you have to keep it running long enough to properly charge the battery, and I don't think 14.0 volts will do this well enough either.

I also think that maybe the in-car battery drain is enough to cause a problem too, even though it is a small drain current. I say this because I can keep a battery for a Volvo inside my house for three months and it still measures above 12 volts. That would not happen if it was installed in the Volvo. Maybe even a 5ma current draw is enough to drain the battery down significantly over several days.

I'll be looking into this more and more as time goes on. If I can find anything else out about this I'll yell.

Oh BTW, I asked another seasoned mechanic who has been around for at least 25 years before he sold his station recently. I needed a jump one day (no surprise there) and he came over and I told him I think the battery is not being charged enough because the charge voltage is too low. He replied that "you don't want to cook the battery".
While that's true, if you only go on short runs you wont cook the battery, but he did not take my drive habits into account. Yes, you don't want to cook the battery, but you also don't want it to go dead and not start the car (ha ha).

If you were an EE, you'd know that a persistent draw on a SLA will drain it as will it's own internal resistance regardless of how well the charging system works if the car isn't allowed to charge it for a sufficient duration after being nearly depleted - this doesn't even include small parasitic draws such as memory circuits for radios, ECUs, etc. Deep discharges often damage a regular SLA car battery - this is why deep cycle batteries are built differently. A 5% variance in the EE world is negligible and is likely not even a pass/fail on the space program for most things. Most resistors are 5 to 10% - and usually such is the design spec as a result. Is your multimeter calibrated? I have a feeling it hasn't been recently. That could account for the variance you're seeing as well.

You could try a different battery technology instead of standard SLA, I'd suggest an AGM personally with the largest group size possible that fits in your car. Also note that ambient temperature has a huge effect upon both the battery and the charging system. A battery in freezing weather may show as depleted, when warmed up, the same battery most likely will not show that state using voltage alone. This is why measuring battery voltage to determine state of charge fully is generally a fool's errand, as you can have a battery that shows 12.85v but cannot sustain even 500mA of load. This is why generally the accepted methodology includes a load test for the battery. You could also have a bad cell with the others over-charging.

What group size battery do you currently have installed? Which alternator - 120A? What is the current battery condition from a commercial battery tester?

I've not driven both my cars for upwards of 6 weeks and had no issues starting them. You have something going on with either the battery, the wiring, a parasitic load, or the alternator - assuming this isn't a case of simply not driving the car often enough or long enough.

[MrAl]

Agreeing with abscate. This is just due to different manufactures cars / systems. 13.9 - 14.1 is normal, for these cars.

Hello,

Well 'normal' doesn't necessarily mean 'good'.

Took my temperature today, and it was......normal. Hmm. Guess now I have something else to worry about.

Hi,

That's an interesting comparison, human body temperature vs car battery voltage.
I don't think the human body temperature has a tolerance of 5 percent though (hee hee).
It does point out the difference between something that is highly controlled and something that is not as controlled.

While I am replying to your post, let me interject a little more info here to show my thoughts on this more clearly.

Every battery has internal resistance, and that means they have two basic voltages: one is internal, and the other is external. When we measure the battery voltage during the charging phase, we are seeing the external voltage. The external voltage will always be higher than the internal voltage.
For the most basic battery model, these two voltages work along with the internal resistance, and that sets the particular charge current with a given applied external voltage. For simplicity, I'll call the internal voltage Vin and the external voltage Vex. The internal resistance I'll just call Rs which stands for the 'series' resistance (hence the 's').

The internal voltage Vin is there before we start to charge the battery, and it is fairly constant even when we start to charge the battery. That is because the equivalent capacitance of the battery is very, very large. That means it takes a somewhat long time to raise that voltage during the charge process. This is also the voltage we measure when the battery is not being charged nor drained of any current (no current flowing in or out of the battery).
The external voltage, when not charging or draining the battery, is the same as the internal voltage, so we measure the internal voltage at the terminals when the battery is not being charged nor drained.

When we apply an external voltage that is higher than the internal voltage, current begins to flow into the battery and that means it is being charged. Since the internal voltage Vin is constant and the external voltage Vex is what we are applying and we can easily measure that at the battery terminals, we can calculate the charge current, if we knew the internal series resistance Rs. We don't usually know that, but we can still use theory to figure out what happens as soon as we connect a charger or start the car which runs the alternator which charges the battery, and we can measure Vex like that in the same way as if we connected a charger. Most importantly, we can look at what happens with the current level during charge.

Now let's assume a value for the internal series resistance Rs. I'll assume a rather high value for now, but it really doesn't matter because we are just looking for behavior not actual numbers from a real life battery. We can always address the real life battery after we get a feel for what is happening during the charge phase, and also mention some variations if needed. I'll assume it is 0.100 Ohms for now, just because that is a fairly easy number to work with and it is low enough to see some results that we might see with some battery somewhere. We can vary this later too.

Now if Vin=12.000v and Vex=12.000v, the current will be:
i=(Vex-Vin)/Rs=(12-12)/0.1
which of course is zero because Vin=Vex.
If we raise Vex by 0.1 volts, it is now 12.100 volts. The internal voltage is still 12.000 volts.
Note the use of three decimal digits to the right of the decimal point. That's because we want to understand what happens even with small changes in the applied voltage Vex.
Ok, so we now have the current:
i=(12.100-12.000)/0.100
which of course comes out to 1 ampere.
Now let's raise Vex to 12.200 volts, the current is now:
i=(12.200-12.000)/0.100
which is now 2 amperes.
Let's go higher now, with Vex=13.000 volts.
i=(13.000-12.000)/0.100
and now we see 10 amperes of charge current.
If we go to 14 volts, we see current:
i=14.000-12.000)/0.100
and this comes out to 20 amperes.
That would be considered very good for any car I believe. But what if the internal resistance goes up to 0.200 Ohms.
Suddenly we see this current:
i=(14.000-12.000)/0.200
and this is just 10 amperes. That's not enough to charge the battery unless we have a decent time to charge the battery, which may be as long as an hour. That's a decently long drive.
But let's now raise that external voltage again, to 15.000 volts. Now the current is:
i=(15.000-12.000)/0.200
and so this comes out to 15 amperes. Not a huge increase for this simple example, but if it took an hour to charge at 10 amps, it will now take 40 minutes to charge at 15 amperes. This means we saved 20 minutes of charge time.
So we can see how the charge time gets lower for higher applied Vex.

The actual numbers would be much worse though. Let's look at an internal voltage of 13 volts.
With an applied Vex=14v we see current:
i=(14-13)/0.2=5 amps
with an applied voltage Vex=15v we see current:
i=(15-13)/0.2=10 amps
Now we can see the current actually doubled, which is quite a bit higher. That cuts the charge time in half.

It can be even more drastic than that however. If the internal voltage is more like 13.5 volts then we see a three-fold current increase from 2.5 amps to 7.5 amps. That's a big difference.

This illustrates the importance of how high the external voltage is.
This also may show that the external resistance in the charging system (if not anything else that is) may be the main problem, as mentioned in another post in this thread. That's because it is very doubtful that the internal resistance is really as high as 0.2 Ohms or even 0.1 Ohms. That would limit the engine starting current to a value much lower than what we actually see in real life. If the current really is as low as the 0.2 Ohm example, then there must be some other resistance at play also.
If this is the case, then a measurement on the alternator should show a higher voltage than 14.0 volts when we measure 14.0 volts at the two battery terminals. That test may be easy enough to do with a volt meter provided you can get to the proper terminals on the alternator.
The only other possibility then is that the battery internal resistance went up higher than normal, or the charge acceptance went down (the charge acceptance figure correlates the apparent charge put into the battery vs the actual change in state of charge SOC, and will also change over the life of the battery).  

In any case, it seems clear to me that the higher the charge voltage, the faster the battery charges, period. There's no way around that because there is no physical mechanism that would cause the reverse: for the higher voltage to charge slower. That's never going to happen. What could happen though with a voltage that would be considered too high is the battery could get damaged. That means we do have to have a limit to how high we go as well as how low we go vs drive time.

I hope this helped to shed some light on what i was looking into, and it is mainly because i have had so many problems like this with some of my cars, which i never had with my older model cars (1970, 1964 production years for example).
Either something has changed with the alternators, or something has changed with the batteries, or perhaps the wiring is not as good as with the much older cars. Because of the way the economy affects manufacturing sometimes, I would not doubt it if car batteries are not being made as good as they used to be. It could be that they get damaged more easily.
There may be another answer though, maybe the static drain on the batteries is higher than with the much older cars. They had no real drain to speak of when the engine was not running. These newer cars all have computers and sensors and stuff, although the old 1988 Hyundai did not have that and yet the problem still surfaced with that car too.

Ok, I have to take a rest now ha ha.

 

[abscate]

Average car is driven 12,000 miles a year in the US, that’s 250 miles a week

If you fall under 50 miles a week, you need an external charger to keep your battery at top charge/ best life, unless you are taking a one way 50 mile highway trip

You either hook up a charger and plug in, or you put the battery on a charger once a month and top it off

[Sveedy]

Geez ! Put it back in the holster, Pistol Pete. You're completely missing the point(s).
Is 13.9 - 14.1 volts " normal " for these cars ? Yes.
Is " normal " the same as " good " in this example ? Yes.
As others have stated, your battery voltage is not a problem, unless it's dropping off under load ( starting ), which you would clearly see.

[MrAl]

Geez ! Put it back in the holster, Pistol Pete. You're completely missing the point(s).
Is 13.9 - 14.1 volts " normal " for these cars ? Yes.
Is " normal " the same as " good " in this example ? Yes.
As others have stated, your battery voltage is not a problem, unless it's dropping off under load ( starting ), which you would clearly see.

As Steve has noted, 'normal' is not normal for every driver. If it was normal for every driver, I would not be here right now talking about this. If it was not a problem, then I would have never had a problem. It's that simple.

You'd have to be at least an electrical engineer with a specialty in batteries or related to understand this completely.

You'd also be surprised at what some people think they can get away with when charging batteries of different chemistries. There are people out there that want to charge Li-ion batteries with a lead acid battery charger. Also some people who want to charge Li-ion batteries in series without a charge balancer. The list goes on and on.
Check out what happened in New York with rechargeable batteries for scooters.