During battery charging how much is the voltage at its terminal?

[jak9]

hello friends,
Suppose my car battery current voltage is 10V and the alternator is charging my battery during the car run so if the voltage arriving at battery terminal is 13V then what value of voltage i should consider in my equivalent circuit of battery?
my equivalent circuit consists of a resistance in series with parallel combination of a capacitor and resistance. For this circuit i have the values of voltage and current generated by the alternator. So to calculate the total impedance of the circuit should i directly divide voltage(alternator) by current(alternator) or it would be something else?
The reason i am confused is because the battery current voltage is 10V and at time t=1s the alternator voltage is 13V and current is 35A. Then to calculate total impedance of the battery should i divide 10/35 or 13/35 or i should consider both the voltages that is 10V and 13V?
please help
thanks

 

[jak9]

impedance of a total circuit?

hello friends,
i am calculating total impedance of a car battery. To achieve this i have an equivalent circuit which consists of a resistance(r1) in series with parallel combination of capacitor and resistance(r2). The input to this circuit is varying dc voltage because of ripples and corresponding varying current, capacitor value and resistance r2 value which is a charge transfer resistance and is also a varying quantity. So first thing i have to do is to calculate total impedance of the circuit. So if i divide V/I will it give total impedance or it should be something like V=Vdc+Vaccos(2*pi*f*t) and divide by I=Idc+...?
please help me in getting this
thanks

 

[vk6kro]

The current into a battery is limited by the regulator circuit in a car, so it isn't that simple.


However, you can regard a car battery as a voltage source in series with a resistor. The voltage source increases in voltage when the battery charges up.

So the alternator produces DC which flows into the battery.

The voltage across the series resistance is the alternator voltage MINUS the battery voltage.

So, if you had 35 amps flowing and 3 volts difference between the alternator and battery voltages, the resistance must be E / I, ie ( 13 V - 10 V ) / 35 amps or 0.085 ohms.

You can see that if the battery voltage equals the charging voltage then the charging current will drop to zero.

 

[jak9]

thanks i got your point...actually now i want to calculate the total internal impedance of a battery and i think its not the right way to divide directly the battery voltage by its current because the battery measured voltage is not a pure dc it has some ac components also so i heard of something like regulating the voltage by its ripple component that is V=Vdc + Vaccos(2*pi*f*t) but i don't know how to apply can u correct my equation for calculation of total impedance.
The thing is when i plot this voltage and current signal their is no phase difference but the signals are having a lot of ripples so how to calculate the total internal impedance from the voltage and current values?
thanks

 

[berkeman]

hello friends,
i am calculating total impedance of a car battery. To achieve this i have an equivalent circuit which consists of a resistance(r1) in series with parallel combination of capacitor and resistance(r2). The input to this circuit is varying dc voltage because of ripples and corresponding varying current, capacitor value and resistance r2 value which is a charge transfer resistance and is also a varying quantity. So first thing i have to do is to calculate total impedance of the circuit. So if i divide V/I will it give total impedance or it should be something like V=Vdc+Vaccos(2*pi*f*t) and divide by I=Idc+...?
please help me in getting this
thanks

Why are you modelling it as something more than an ideal voltage source and a series resistance? Are you trying to take the model to a more accurate level for the real car battery?

And AFAIK, there are no voltage ripples caused by the car battery. Are you trying to model the more complex source impedance of the chemical reactions in the car battery?

What level course is this for? What other resources have you looked into to see what other models have been done for car batteries?

 

[berkeman]

(BTW, I merged your two similar threads here in EE)

 

[vk6kro]

The output of a car alternator is rectified DC pulses at some multiple of the engine speed, depending on pulley sizes.

So, the battery will not charge while this voltage is lower than the battery voltage and it will charge when this voltage is greater than the battery voltage.

When the battery voltage is low, there will be a current flowing for a large portion of each cycle, and when it is high, there will be a current flowing for a smaller portion of each cycle.

You could use this change in duty cycle to control the process, although it tends to be self regulating. A reduced duty cycle and a lower difference between charging voltage and battery voltage results in less charging, which is what you want for a fully charged battery.

The input pulses would only have a frequency of about 300 Hz so the inductance and capacitance in the battery would not have any effect.

 

[uart]

my equivalent circuit consists of a resistance in series with parallel combination of a capacitor and resistance.

That's not a good model for a battery.

 

[jak9]

thanks for the replies but i still got my answer about the total impedance. As you said their won't be any ripples but i have already measured continuously the values of current and voltage during the car run and when i plot these two signals i can see some ripples. So if i have to calculate the total impedance then what value of voltage has to be considered?
and this circuit is quite accurate because its a reference of a standard randles circuit which is used to define a battery.
In this circuit the every parameter will change continuously because it is done in real time so the voltage,current, charge transfer resistance and frequency keeps on changing. This model is basically based on electrochemical impedance spectroscopy and it takes cares of all aspects of a battery right from electrical to chemical terms.
If you think its a wrong model then can you correct this?
thanks

 

[jak9]

hi again,well i have attached my circuit for the battery during charging that is it is getting charged by the alternator when the vehicle is moving. The Ubatt and Ibatt are measured at the battery terminals and are assumed to be same as the alternator output excluding the resistance of the alternator. So now in the circuit Ubatt=Uc0+Ibatt*Ri+Voltage across the capacitor/rct. But i am finding it difficult to resolve this circuit maybe i have wrong voltage directions. Can you please check it out.
thanks

 

[berkeman]

hi again,well i have attached my circuit for the battery during charging that is it is getting charged by the alternator when the vehicle is moving. The Ubatt and Ibatt are measured at the battery terminals and are assumed to be same as the alternator output excluding the resistance of the alternator. So now in the circuit Ubatt=Uc0+Ibatt*Ri+Voltage across the capacitor/rct. But i am finding it difficult to resolve this circuit maybe i have wrong voltage directions. Can you please check it out.
thanks

Um, well. I understand now that the "ripples" were coming from the alternator, not from the battery. Ok.

But 186000 Farads as a series capacitance with the voltage source? I definitely do not understand what you are trying to do with your model. How did you arrive at this model?

 

[jak9]

well thanks for the reply...actually this value of capacitor is what i got as a given from manufacturer even i was so confused after looking at this value but they said its a replacement capacitor and its value is very high but how would i can calculate Ri. As you see i have two unknown and basically the voltage across this capacitor and emf is considered as one so i can replace these two with a capacitor. I am doing a simulation in simulink for which i get continuous reading of voltage and current and emf at run time that is during car running. So can you help me in finding Ri or total impedance or voltage drop? please
thanks

 

[berkeman]

well thanks for the reply...actually this value of capacitor is what i got as a given from manufacturer even i was so confused after looking at this value but they said its a replacement capacitor and its value is very high but how would i can calculate Ri. As you see i have two unknown and basically the voltage across this capacitor and emf is considered as one so i can replace these two with a capacitor. I am doing a simulation in simulink for which i get continuous reading of voltage and current and emf at run time that is during car running. So can you help me in finding Ri or total impedance or voltage drop? please
thanks

I have a feelting that the manufacturer was saying that if you needed to replace the lead acid battery with a capacitor, it would take that monster (unreal) capacitance to do it.

I googled SPICE model lead acid battery, and got lots of hits. Here's the hit list:

http://www.google.com/search?source..._enUS301US302&q=spice+model+lead+acit+battery

The first hit on the list is a discussion forum thread with some model info, and the other hits on the list look useful as well. I hope this helps you get farther along toward a realistic, practical model of your system.

 

[jak9]

ok thanks but if i put that capacitor parallel that is in place of emf then what will be the total impedance of the circuit??

 

[berkeman]

ok thanks but if i put that capacitor parallel that is in place of emf then what will be the total impedance of the circuit??

The point is not to use that capacitor at all, or the other one that's 160 Farads or whatever. Please have a look at the SPICE models in the Google hit list.

 

[jak9]

oh i see, i checked the specifications again and it says that Cdl that is the one which i placed in parallel to the resistance is 0.003*186692. Now the Ubatt=IRi+V(across the parallel rc)??

 

[Studiot]

Is this a theoretical exercise or do you have some end purpose in mind?

If it is academic, have you been instructed to use a particular model?

Most car alternators avoid ripple by being both polyphase and using specially shaped poles. Their no-load tiny ripple output is nothing like sinusoidal.

 

[jak9]

well i have some purpose like i read on internet about batteries internal resistance calculation and i developed a model in simulink which calculates internal resistance of a car battery during cranking phase that is when car is started and also i wrote a algorithm which calculates continuous frequency of a large signal at runtime so now i want to extend more but i am badly stucked at this point of calculating internal resistance during charging phase that is when alternator is charging
please try to check my attached document and only one change is that instead of series emf and capacitor it should be replaced by a parallel capacitor so friend can you help me in extending my thought

 

[Studiot]

I can't see how your model can do anything useful since it is incomplete as the load representing the car wiring is missing. The model also includes a nonexistant capacitor - series or parallel doesn't matter - there is just no such capacitor involved in battery charging.

Unfortunately I don't see how anyone can help since you choose to ignore comments others believe helpful, both here and in another electronics forum.

I don't know if you are a programmer, but your understanding of circuit theory need to improve to make your attempt at this project successful.

 

[jak9]

i do agree that i am weak in circuit theory but my model for internal resistance at cranking phase is working very fine but with charging not going well. Ok atleast tell me how the total impedance of the circuit which i have attached can be calculated is it Ubatt/Ibatt?

 

[jak9]

solving circuit problem

hello friends,
i have attached a image with this post in which i wanted to find the value of Ri. It is a dc circuit but the input voltage and current have some ripples so its not a pure dc. I have also frequency of ripple which can be used further to calculate Xc if in case needed. So with all these inputs how to calculate Ri?
i know by calculating the voltage across each element Ri,C1 and Cb(the voltage Vcb is given) the value of Ri can be calculated. But i am not able to calculate the voltage drop across Ri.
please help
thanks

 

[jak9]

also one thing left out is the input voltage and current signal are not in phase with each other

 

[berkeman]

hello friends,
i have attached a image with this post in which i wanted to find the value of Ri. It is a dc circuit but the input voltage and current have some ripples so its not a pure dc. I have also frequency of ripple which can be used further to calculate Xc if in case needed. So with all these inputs how to calculate Ri?
i know by calculating the voltage across each element Ri,C1 and Cb(the voltage Vcb is given) the value of Ri can be calculated. But i am not able to calculate the voltage drop across Ri.
please help
thanks

Are you familiar with the concept of Phasors? That's the easiest way for you to calculate the input impedance of that circuit:

http://en.wikipedia.org/wiki/Phasors

.

 

[jak9]

you mean without knowing the rct and ri i can calculate all the terms? well i know little bit about phasors like in phase and out of phase for capacitors and all i will try to do but friend could you please help me i know i have to read but still

 

[jak9]

ok from phasor it can evaluated but i am doing it in simulink at real time where the voltage and current signals are changing continuously with respect to time

 

[berkeman]

ok from phasor it can evaluated but i am doing it in simulink at real time where the voltage and current signals are changing continuously with respect to time

But you said you were measuring both the input current and input voltage, correct? Then just do the division to get the Zin as a function of time.

 

[jak9]

ok thanks but i think i should take out the Vb as you said in earlier post either i should consider the Cdl or Cb...so i have to think on it

 

[jak9]

well after going through lots of literature i conclude that during charging of a battery the terminal voltage is bigger than cell emf so the internal resistance of a cell causes the terminal voltage to change because of voltage drop across it so the internal resistance of a cell during charging would be
Ri=Vterminal-Emf/I
and the circuit would consist of only one resistance and a capacitor(electrochemical double layer capacitor) in series
i hope i succeed with this assumption
if you have any views or suggestions about this then please let me know