# Battery circuit current flow when charging

• shonuff
In summary: The current that's used to crank the vehicle is the current that is used to power the alternator, not the battery. In summary, the current flow of a battery charging system is a series opposing circuit.
shonuff
I would like to know when a alternator is charging a battery is the current flow a series opposing circuit......?

Welcome to PF.

I can see why you think that might be the case, but it is probably not a good model.
Since the circuit is closed, the battery and alternator are really in parallel, not series.

Yes they are connected in parallel but my question was about the current flow.....The alternator current will be flowing in a (say.a) CW rotation. The. Battery current will be flowing CCW.....So until the alternator exceeds battery voltage is it a series opposing circuit ?

The alternator and battery are connected in parallel.
There are loads in parallel with the alternator and the battery.

Now, if we ignore those loads and consider only the alternator and battery.
Where does the "voltage opposed" difference voltage appear ?
Where is the load that limits the circulating charge current ?

The load is the internal resistance of the battery. Which cannot be measured directly but can be calculated ....Battery internal resistance acts
like a variable resistor.R1 & R2 represents the internal resistance of a 2 battery hookup
E1 sub as a alternator then delete R2 . The diagram is the best I can do until I get more familiar with posting

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shonuff said:
The load is the internal resistance of the battery.
If the internal resistance is modelled as an external lump, then only the charging circuit and battery are in a series opposed circuit.
shonuff said:
Battery internal resistance acts a variable resistor.
Don't forget that the alternator produces 3PH AC, which is then rectified to DC. The charge regulator limits the maximum alternator current, and regulates the battery voltage. The battery is then clearly in parallel with the charging system.

Perhaps the following image will help? Assuming the vehicle systems are connected to the chassis for ground, then the battery is in parallel with a great many things, including the alternator.
shonuff said:
Yes they are connected in parallel but my question was about the current flow.....The alternator current will be flowing in a (say.a) CW rotation. The. Battery current will be flowing CCW.....So until the alternator exceeds battery voltage is it a series opposing circuit ?
If you want to treat the leg with the battery as being in series with a power source you certainly can, as long as you don't care about what's happening elsewhere in the circuit, such as when you're just looking at when the battery is charging. You don't have to model the rest of the circuit if it isn't important for whatever you're doing.

I'd simply recognize that the alternator applies a voltage to the battery terminals. If this voltage exceeds the battery voltage then current flows into the positive terminal and the battery charges. Whether you draw this out on a piece of paper as a simplified series circuit or a parallel circuit is up to you.

So I suppose the answer is no, the current doesn't flow like a series opposing circuit. But you can sometimes treat it as if it does.

shonuff said:
I would like to know when a alternator is charging a battery is the current flow a series opposing circuit......?
Yes, when we charge a battery we force charge into it against its own EMF (or voltage) by connecting + on the charger to + on the battery. So you can say they are series opposing. By contrast, when we connect two batteries in series we connect + to -, so they are series aiding. Internal resistance is usually treated as negligible for lead acid batteries and charging curent will be controlled by the charger.

Lead acid internal battery resistance is very important. If the resistance becomes low then the battery will become overcharged and start to use excessive water....Giving you short battery life over time..

Once the current that is used to crank the vehicle it must be replaced.A good battery replacement current will
be some where close to 200 milliamps once it becomes fully charged..just enough current flow to maintain the battery .
That's the reason batteries are load tested.....Load testing a battery is a test to determine if the internal resistance is within specs .....Could be just a under charged condition if it fails.or the resistance is to low. creating excessive return current ....

shonuff said:
Lead acid internal battery resistance is very important. If the resistance becomes low then the battery will become overcharged and start to use excessive water....Giving you short battery life over time..
It is not the internal resistance of a lead-acid battery that limits the charge current, it is the voltage regulator that controls the alternator. Gas is produced and water consumed, only if the regulated voltage is set too high.

shonuff said:
Once the current that is used to crank the vehicle it must be replaced.A good battery replacement current will be some where close to 200 milliamps once it becomes fully charged.. just enough current flow to maintain the battery.
The float current will be determined by the battery type and size. 200 mA will take some batteries overvoltage, with the production of heat and explosive gases. During float charging, there must be overvoltage detection, and maybe also freeze detection.

shonuff said:
That's the reason batteries are load tested.
The internal resistance of a lead-acid battery increases gradually as the battery ages. At some point, usually when it is cold, the CCA will be insufficient, limited by the internal resistance. The battery must then be replaced.

Hi
Baluncore said:
It is not the internal resistance of a lead-acid battery that limits the charge current, it is the voltage regulator that controls the alternator. Gas is produced and water consumed, only if the regulated voltage is set too high. The float current will be determined by the battery type and size. 200 mA will take some batteries overvoltage, with the production of heat and explosive gases. During float charging, there must be overvoltage detection, and maybe also freeze detection.The internal resistance of a lead-acid battery increases gradually as the battery ages. At some point, usually when it is cold, the CCA will be insufficient, limited by the internal resistance. The battery must then be replaced.

A regulator set point determines only the voltage..The loads determine the current output of the regulator set point....You can override the resistance in the voltage drop from the alternator to the battery by using a
wire to the regulator sence terminal if equipped....Many regulators sense the voltage internally ..Many have a sense terminal wire that comes from the battery to over come the voltage drop from alternator to battery.

shonuff said:
A regulator set point determines only the voltage.
That is only with the simplest battery charging regulators.
More complex battery charging regulators taper the current as the battery approaches high limit float voltage, where the current becomes zero.

shonuff said:
You can override the resistance in the voltage drop from the alternator to the battery by using a
wire to the regulator sence terminal if equipped....Many regulators sense the voltage internally ..Many have a sense terminal wire that comes from the battery to over come the voltage drop from alternator to battery.
Anything is possible given more complexity.
The internal resistance of the battery and cables can also be cancelled by introducing variable negative resistance.

I don't understand the real question in this thread. Is it the semantics of aiding versus opposing?

Averagesupernova
anorlunda said:
I don't understand the real question in this thread. Is it the semantics of aiding versus opposing?
The OP seems to be arguing that because the current flows in a circle, through the alternator and then the battery, that the components must be in series, with opposed voltages.
That is reinforced by the fact that, while charging, the alternator current and battery current are equal, suggesting that they must be in series.

If the battery was replaced by a resistor, capacitor, or Zener diode, we would call it a parallel circuit, even though the same current flows through the alternator and the parallel component.

This series vs parallel thing is a bit silly. I'll throw in my 2¢ anyway. Components are in series ONLY if the current through them is always the same. The voltage source is a special case. The current through it is always the same as the current through the entire load, but not individual loads that are in parallel. I will not argue whether it is in series or parallel. Arguing about semantics is only useful if one wants to establish a standard to avoid miscommunication.

Tom.G
Baluncore said:
The OP seems to be arguing that because the current flows in a circle, through the alternator and then the battery, that the components must be in series, with opposed voltages.
That is reinforced by the fact that, while charging, the alternator current and battery current are equal, suggesting that they must be in series.

If the battery was replaced by a resistor, capacitor, or Zener diode, we would call it a parallel circuit, even though the same current flows through the alternator and the parallel component.
Can the circuit be parallel and series-aiding? What about series-parallel?

Can the circuit be parallel and series-aiding? What about series-parallel?
When components are in parallel, they share two terminals.
When components are in series, they share only one terminal.
I cannot see how they can be both parallel and series at the same time.

The "series opposing" concept is an unnecessary distraction, and is not actually useful.
We always add voltage sources in series, some of those voltage sources may be negative.

While the battery is charging, the alternator is the source, and the battery is the load.
Energy is being transmitted from the alternator to the battery.
That is clearly a parallel connection of a source and a load.

Baluncore said:
Anything is possible given more complexity.
The internal resistance of the battery and cables can also be cancelled by introducing variable negative resistance.
shonuff said:
The load is the internal resistance of the battery. Which cannot be measured directly but can be calculated ....Battery internal resistance acts
like a variable resistor.R1 & R2 represents the internal resistance of a 2 battery hookupView attachment 319906E1 sub as a alternator then delete R2 . The diagram is the best I can do until I get more familiar with posting
shonuff said:
I would like to know when a alternator is charging a battery is the current flow a series opposing circuit......?
shonuff said:
The load is the internal resistance of the battery. Which cannot be measured directly but can be calculated ....Battery internal resistance acts
like a variable resistor.R1 & R2 represents the internal resistance of a 2 battery hookupView attachment 319906E1 sub as a alternator then delete R2 . The diagram is the best I can do until I get more familiar with posting

According to Kirchhoff's laws a circuit with multiply voltages....

Series-Aiding and -Opposing Sources

When multiple voltage sources exist in a circuit they can be series-aiding or series opposing.

Sources that cause current to flow in the same direction are series aiding.

Sources that cause current to flow in opposite directions are series opposing. In an opposing circuit the current flow direction is determined by the larger

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shonuff said:
I would like to know when a alternator is charging a battery is the current flow a series opposing circuit......?
Sorry about not being able to understand some of my wording in my posts...My schooling in electronics was over 65 years ago.Which consisted of 1 year in the military then 3 years as a electronic tech..After discharge it was a few years in TV & automotive test equipment repairing ..Then the next 50 some years in automotive electrical repairs.
So I might seem a bit rusty in theory.....

Tom.G

## What is the direction of current flow in a battery circuit when charging?

When charging a battery, the current flows from the positive terminal of the charger to the positive terminal of the battery, through the battery, and out the negative terminal of the battery back to the negative terminal of the charger.

## How does the current flow change as the battery charges?

As the battery charges, the current flow typically decreases. This is because the voltage difference between the charger and the battery decreases as the battery's state of charge increases, leading to a reduction in current according to Ohm's Law.

## What factors affect the current flow during battery charging?

Several factors affect the current flow during battery charging, including the battery's state of charge, the charger’s voltage and current ratings, the internal resistance of the battery, and the temperature of the battery and charger.

## Why is it important to control the current flow when charging a battery?

Controlling the current flow is crucial to prevent overheating, overcharging, and potential damage to the battery. Proper current regulation ensures efficient charging and prolongs the battery's lifespan.

## What happens if the current flow is too high during charging?

If the current flow is too high during charging, it can lead to excessive heat generation, which can cause thermal runaway, battery swelling, leakage, or even explosion. High current can also degrade the battery's internal components, reducing its overall capacity and lifespan.

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