CHARGING VOLTAGE QUESTION

[CFD244]

Hi Folks

What are the ramifications of running, lets say, a 15 volt charging system output in a post 1970 system (electronic)?

Thanks FABO

 

[halifaxhops]

Why?

 

[toolmanmike]

A fully charged automotive battery is 12.6-12.8 volts. No need to have a 16 volt alternator output. It will just cause issues.

 

[CFD244]

Why?

Inquiring minds want to know

 

[toolmanmike]

Inquiring minds want to know.

I had a bad ground on a newly installed electronic regulator and it over charged, 16-17 volt range, boiled the battery, burned out my amp gauge and burned out the headlamps as soon as I turned them on. Lucky it didn't cause a wiring fire.

 

[Murray]

Over heating, stressing electrics, leading to fire or unit failure.

 

[CFD244]

We're talking 14.9v to 15v not 16 to 17.

 

[toolmanmike]

We're talking 14.9v to 15v not 16 to 17.

On a system that was designed to operate on basically 12 volts.

 

[halifaxhops]

Think most fsm go up to 15.3VDC for charging at 1200 rpm no load.

 

[toolmanmike]

Think most fsm go up to 15.3VDC for charging at 1200 rpm no load.

Here is a voltage regulator settings chart in my 64 manual.

 

[67Dart273]

With the system warm, the battery charged, and a lead acid battery, the default is 13.8--14.2. You cannot change chemistry. The system does not run 12V and neither does it run 15V. Some new systems may "boost" to 15-15.5 briefly to boost the system, but if you run a lead acid battery at that routinely, AKA road trips, you WILL shorten life, and boil out acid

Long term maintenance "float" voltage is a bit lower, and varies whether liquid or gel, etc. I am referring to maintainers, and stuff like radio sites with backups which need long term trouble free no maintenance backups. For lead acid this is about 13.5---13.8V

It does not matter if you are talking about a small lead acid battery in a backup exit sign, an auto battery, or a WWII submarine, battery chemistry is battery chemistry.

 

[Mattax]

Here is a voltage regulator settings chart in my 64 manual.

View attachment 1716462857

Similar although slightly higher for the later regulator

Its important to note this is not voltage at the battery. This a test whether the regulator is doing its job based on the voltage it 'sees'. The voltmeter is connected from the junction at the ballast resistor to ground.

The factory considered up to 0.7 Volt difference from the alternator to the battery acceptable with 20 amps flowing from the alternator and about 15 amps through the dash ammeter to the battery.

When I look at the voltage on the automatic charger, the maintaining voltage is usually around 14 Volt.

 

[toolmanmike]

Similar although slightly higher for the later regulator
View attachment 1716462883
Its important to note this is not voltage at the battery. This a test whether the regulator is doing its job based on the voltage it 'sees'. The voltmeter is connected from the junction at the ballast resistor to ground.

The factory considered up to 0.7 Volt difference from the alternator to the battery acceptable with 20 amps flowing from the alternator and about 15 amps through the dash ammeter to the battery.

View attachment 1716462885

When I look at the voltage on the automatic charger, the maintaining voltage is usually around 14 Volt.

What year was that just curious? Electronic regulator by chance?

 

[Mattax]

What year was that just curious? Electronic regulator by chance?

Yes. 1973. Transistorized regulator and the new squareback alternator.

Looking again the spec for 140*F is exactly the same.

 

[67Dart273]

Actually a little bit of drop on the charging line is not terrible so long as we are not heating something up. If there is drop on the charge line, the only thing that happens is, that the regulator will read low and ramp up the difference

The single biggest problem with either early or late regulators, aside from the weakness in the ammeter circuit, is that the share the power terminal with the ignition terminal. So far as I know, all OEM GM, other than "one wire," and same with Ford, have a dedicated sense wire. This wire, since it is ONLY used for sense, carries no current, which means it should be able to truly and accurately sense battery voltage.

On a side note, I once had a beater 62 FJ-40 Landcruiser, which had a 360, then 340, then 318 over the years, and after buying a Warn 8K winch, I scored one of the large frame Chrysler 100+A units. I bought a 100A SW ammeter, and it would BURY that thing using the winch or catching the batteries back up afterwards. I don't remember, anymore, what gauge, I think no6. I'm fairly sure it was not 4

 

[Bewy]

I doubt 14.9 - 15v will cause a problem...but no higher.

 

[Mattax]

Hi Folks

What are the ramifications of running, lets say, a 15 volt charging system output in a post 1970 system (electronic)?

Thanks FABO

Inquiring minds want to know

The higher the voltage, the more current a device will draw.

Ever notice the headlights are brighter with the engine running, then the engine off?
The battery at best provides power at 12.8 Volts.
The alternator supplies at 14.0 Volts more or less.

The higher the voltage the more current will run though the bulb. And the brighter it will light up.
Give something too much voltage, and it will burn out.

Why?
Power = Voltage x Current.
Voltage is potential energy (like pressure), Current is moving electrons (flow).
Voltage = Current x Resistance. But we can rewrite that knowing resistance in a bulb or a motor is fixed, and we control the voltage.
Voltage divided by Resistance = Current.

V/R = Current
How does that relate to your question?
Increase voltage = more current
and
More current and more voltage equal more power.

As excessive current tries to get through resistance, heat will be generated.
@toolmanmike listed examples of what happens when system voltage gets too high.

Batteries can be cooked by too much current even at 14.2 Volts.
Here is an example:
This battery was too low to start the vehicle.
Connected to a battery charger, the recharge was adjusted to 14.2 Volts.

Alls good, right?

WRONG!

That's 35 AMPS.

Even though the charger's cables can easily handle 35 amps, its bad for the battery.
If not reduced it will boil down the acid and can do other permanent damage.
If this was in a car, 35 amps continuous will also damage the charging circuit connections and possibly the alternator.

Imagine if we charged this battery at 15 Volts and didn't have an ammeter.
We're just going to have to imagine that because because I wanted to recharge the battery, not cook it!

This is why ammeters are on the battery circuit. Everything else if supplied with X voltage, it will draw a known amount of current. But with a battery, the current draw also varies with its state of charge.

 

[67Dart273]

They say there are no stupid questions, but this one borders on that conclusion. Don't reinvent the wheel. The lead acid battery was established one hell of a long time ago. The operating parameters are established by CHEMISTRY. Wishing something different does not make it so.

 

[CFD244]

They say there are no stupid questions, but this one borders on that conclusion

I must say, Del, that you are one of the most respected electrical authorities on this site. I read most of your responses with great interest when electrical questions are put forth on FABO. Your diagnostic and procedural advice is second to none.

I've got pretty thick skin, and am surprised that you would consider a person's attempt at learning "bordering on stupid".

Please continue to provide stellar advice. I always look forward to following along.

 

[nutz]

14.6 was the max number i was taught years ago over that will bake your battery 13.6 is opitmun

 

[MadScientistMat]

Some battery manufacturers recommend a charging voltage around 15.3 volts in freezing weather. You don't want to run that high once the battery is warmed up.

 

[nutz]

Thats why most newer cars have computer charging systems