# Questions tagged [internal-resistance]

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### Battery terminal voltage and internal resistance

I read somewhere that a battery reaches the end of its useful life because of an increase in its internal resistance rather than a decrease in its open-circuit terminal voltage. Is it correct?
1 vote
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### Are the AC resistances in the hybrid pi model and the T model of BJT the same?

I have been wondering if the AC resistances in the two models of BJT circuit mean the same thing, that is $$r_{c} = r_{c'}$$ $$r_{b} = r_{b'}$$ $$r_{ex} = r_{e'}$$ If they are different, please ...
1 vote
64 views

### Does effective internal resistance of batteries depend on their size? If so how?

It was asked to us by our professor- Consider the AA and AAA batteries, what do we think will happen to the internal resistance, will it increase or decrease or can we actually tell something about it?...
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### Internal Resistance of Battery

I might be in the wrong place but I want to try and get a decently credible answer. I have just bought a brand new 12v AGM car battery. The voltage drop in the battery when a load is applied appears ...
4k views

### Why does my 120V 40W lightbulb only have 26 ohms across it?

I thought that if the voltage source is 120V and the lightbulb is 40W then the current would be 1/3 of an ampere meaning that the resistance of the lightbulb would be 360 ohms. But when I checked it ...
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### Internal resistance measurement algorithm using DC method

I have a circuit that allows me to add a load to a battery and measure the voltage, current and temperature of the battery. I am trying to derive what is the best method for measuring the internal ...
• 1,463
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### Deducing the equation of the circuit which is composed of batteries in parallel and the external resistor

We assume that the $n$ batteries have been connected in parallel, and the external resistor connecting the endpoints(terminals) of the parallel part. $n:=$ number of the batteries. $r_i:=$ith ...
157 views

### BJT Constant Current Driver

I'm currently working on this circuit and I ran into 2 questions that I'm not sure I understood them correctly ( I have U1 = 15V , URE = 2 V , β = 180 , UCE = 5V and a constant current I = 2mA ) ...
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1 vote
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### Why does a string of LEDs (Christmas lights) behave differently with battery compared to same voltage power source?

I have a string of Christmas lights (mini LEDs wired in parallel.) My LEDs were too dim, so I took it apart. I found they are powered by a single 1.2V NiCd same shape/size as 1.5V AA battery. The ...
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61 views

### Battery internal resistance calculation

I am trying to figure out a simple, DC based way of approximating the internal resistance of the battery. I am familiar with the concept of instantaneous measurement, like here: https://retrotechlab....
• 1,463
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### internal resistance of inductor effect

I'm trying to analyze an RL Circuit . I saw this equation for voltage drop over an inductor: V = L * di/dt But what about internal resistance of the inductor ? I ...
1 vote
206 views

### Measurement of internal resistance of a battery

I found two circuits online of almost same approach to measure internal resistance of a battery. Both the methods excite the battery at 50Hz using a square wave and AC voltage drop is measured across ...
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2k views

### Does a battery's ability to supply high current mainly depend on its internal resistance?

I was posed the question of whether or not you would be able to start a car with 8 small 1.5V batteries in series (thereby creating the required 12V most cars run on). I immediately answered "no&...
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### How to calculate voltage drop with internal resistance and load values

Is there a way to calculate voltage drop with internal resistance and load values in the equation? Or is it somehow connected to ohms law? If so, how is it done? I have this test circuit below to ...
121 views

### Is the process of adding new parallel (matching) cells into an already built battery pack safe?

I just built a 5p13s 18650 li-on battery pack with a bms. I realized after the build I add more of the same cells (all new), so I could have built a 7p13s instead. Is it possible, after setting the ...
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1k views

### Series internal resistance of Power Supply

I have this power supply - GPC-3030D There are 3 independent channels. 2x (30V/3A) and 1x (5V/3A) To find the internal resistance of the voltage source channels, its just 30V/3A = 10Ohms and 5V/3A = ...
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1 vote
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### Measuring battery resistance

I am trying to measure the resistance of a AA alkaline battery. The circuit I am using is shown in a photo below. I have also attached the values I obtained. Somehow, the values I am getting ...
225 views

### Question about battery internal resistance measurement

I have a 65 mAh thin Li-Po pouch cell. I tried measuring the internal resistance of the same using the foll. steps: (The battery was fully charged before this process) Battery open circuit voltage ...
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### Max power transfer of source with variable internal resistance

I have been reading how to obtain maximum external power from a source using the maximum power transfer theorem. However, it is for a source with a finite internal resistance. Can you have power ...
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1 vote
2k views

### Transistor internal resistance

Does a transistor have an internal resistance, because when I run a circuit simulation in proteus I discovered that bc547 has a collector to emitter resistance of 99ohms... Does that apply to real ...
81 views

### Battery output power calculated from internal resistance - explanation, relation to heat generation and actual power?

On a battery manufacturer specification (https://www.scib.jp/en/product/cell.htm, "High power 10Ah cell") it says: Output power 1800W* (SOC:50%, 10s, 25°C), *This value is calculated from the internal ...
273 views

### Voltage dip at source side during heavy loads due to Internal Resistance

In any application, during initial start-up/load step, there is an high current requirement. Due to this high current requirement, there is a dip in that connected voltage rail. I researched on why ...
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117 views

### Should we include Source and Load Impedance while calculating two port parameters?

While calculating the $Z$, or $Y$ or $h$ parameters of a two port network, should we include the source impedance and load impedance or not? In other words, for finding $Y_{11}$, we short the ...
378 views

### 18650 pack building - is it better to have similar batch or similar capacity?

I'm gonna build battery packs. I have quite a lot of experience with 18650 Li-ion cells, but there's one thing I still don't know. I will buy CCA 100 new cells from seller (for example LGEBHE21865). ...
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63 views

### What is the internal resistance of a LiPo battery determined by?

Given DKNguyen's answer to my last question, I wanted to know what determines the internal resistance of a LiPo battery. Does it have something to do with its inside chemistry? Is it just roughly ...
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793 views

Whenever we load a circuit, there's a drop from the open circuit voltage $v_{oc}$ due to the internal source resistance or Thevenin's resistance$R_{th}$. So we need to have an $R_{load}$ that ...
1 vote
328 views

### Should series connected battery cells have similar internal resistance and to what degree?

I have some Toshiba SCiB cells that I wish to string in 4s configuration. These are Lithium Titanate (LTO) cells. They have a 20Ah capacity and operate safely between 1.5 V and 2.7 V. The cells were ...
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741 views

### Difference between analog signal and battery voltage

I want to find out if using an analogue sensor is feasible in my noisy environment by running some signal integrity tests before I buy it. Because I don`t have the sensor yet, I need to simulate its ...
1 vote
144 views

### Battery Bank total internal resistance

Let's assume you have a battery bank not connected to anything and we are dealing with perfect ideal values. You just want to calculate the total battery internal resistance of your battery bank. To ...
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1k views

### Do rail gun systems require high voltage?

I couldn't justify, as to why most rail-gun examples I found would have high current and high voltage. When the rails & projectile can be designed to have low resistance by varying the volume of ...
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### Internal resistance of LDo

I was trying to measure the internal resistance of an LDO that will produce 2.85V. I used a Digital multimeter to do this, but I got a resistance of 810 Ohm and the LDO can support upto 450 mA. Will ...
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985 views

### Under what circumstances would the large internal input resistance of an actual op amp affect circuit operation?

I was able to find a lot about why the input resistance is high and basically infinite. I understand that the input resistance is high so that it doesn't become a load on the signal. I also know that ...
5k views

### Finding the Internal Resistance of an Ammeter using a shunt

There is this lab procedure to determine the internal resistance of an ammeter which differs from the usual process. In this new procedure, we connect a voltage supply in series with a resistor of ...
1 vote
2k views

### Internal Resistances of Capacitors

I have read somewhere on a forum that there are two effective internal resistances of a capacitor in a DC circuit but can't seem to find any further information. From what I read 'parallel resistance' ...
608 views

### Can you calculate internal resistance of battery by shorting it?

Can I measure the current of a battery by shorting the circuit and by ohms-law divide the voltage of the battery by the current measured to get internal resistance?
1k views

### Measuring the Internal Resistance of an Electrolytic Capacitor

I was wondering if its possible to measure internal resistance of a capacitor from a DC circuit using the below formula and method. $\ V=V_0e^{\frac{-t}{\tau}}$ $\ lnV=-1/\tau\ *t + ln V_0$ ...
482 views

### Electrolytic Capacitor Internal Resistance

I'm doing an experiment to investigate the internal resistance of an electrolytic capacitor in a DC circuit. Doing this I am measuring the discharge voltage against time, finding tau and from there ...
1 vote
1k views

### What is the recommended battery chemistry for digital multimeters?

I would like to know if the different internal resistances of different battery chemistry somehow affects the calibration of a digital multi-meter. If so, then what would the optimal battery ...
1 vote
169 views

### Input resistance of a BJT common-emitter amplifer

What's the input resistance of the circuit below? I think it is $R_{in}=R_B || r_\pi$, but I am not sure
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1k views

### Internal Resistance of a Supercapacitor

I am attempting to replace a wall plug power supply with a supercapacitor. From analysing the behaviour of the wall plug I can see that the current drawn is .25A with 800ms spikes of 1.5A (as ...
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2k views

### Under what conditions would using a voltmeter be more accurate than an ammeter to measure current?

Suppose you have a simple circuit with a voltage source V1 connected to a resistor R1, like this: simulate this circuit – Schematic created using CircuitLab You could connect an ammeter in ...
2k views

### How do I measure internal resistence of voltmeter without ammeter?

I know how to do it with ammeter, but how can I find internal resistence without ammeter?
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### Maximum current is drawn from a cell when it is shorted. But, why?

First, I must apologize for the trivial-sounding question. We've only recently started with Current Electricity in class, and our teacher posed this question (well, something similar) to us. For ...
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1 vote
1k views

### What might cause a fluctuating resistance of a generator winding?

Before assembly of a machine that contains a three phase generator I check the resistance between the 3 phases of the generator with an ohmmeter. The generator is kept stationary and the temperature ...
2k views

### JFET - transconductance, gain (μ), and internal resistance at the drain

Here is an assignment: to determine gm, internal resistance at the drain, and maximum gain (μ). Can transconductance gm be found from the formulas and graph? How to determine graphically the internal ...
6k views

### Real output resistance of MOSFET

This question is related to MOSFET. NMOSFET's resistance was till now defined in many different ways, for example as: or which value varies from 1-50k Ohm. And there is also drain-source on-state ...
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### Is the series resistance of an analog ammeter the parallel equivalent of shunt resistor and resistance of galvanometer?

An analog ammeter is made by a galvanometer (with certain $i_{max}$ and resistance $r$), in parallel with a shunt resistor $R_s$ that depends upon the max scale chosen. Nevertheless, when an ...
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### Constant voltage term in model of diode with internal resistance

Ideal diode equation is $$V(I)=\eta V_T \mathrm{log}(\frac{I}{I_s}+1)$$ Model: simulate this circuit – Schematic created using CircuitLab If the diode has an internal resistance $r$, a more ...
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### "Equivalent resistance" of diode as $V/I$ used to evaluate an approximation

Consider the circuit in picture, used to measure the voltage across diode and current flowing through it. simulate this circuit – Schematic created using CircuitLab With this circuit I do ...
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Imagine to model a solar cell as a power supply $V_p$ in series with an internal resistance $R_p$. This solar cell is connected to a variable load resistance $R_{load}$. Suppose that I keep the ...