# 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
69 views

### 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?...
137 views

### 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 ...
71 views

### 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 ...
63 views

### 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 ) ...
1 vote
97 views

### 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 ...
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....
439 views

### 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 ...
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&...
796 views

### 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 ...
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 = ...
1 vote
116 views

### 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 ...
45 views

### 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 ...
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 ...
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). ...
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 ...
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 ...
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 ...
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 ...
422 views

### 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 ...
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
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 ...
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?
3k views

### 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 ...
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 ...
118 views

### 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 ...
82 views

### 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 ...
### "Equivalent resistance" of diode as $V/I$ used to evaluate an approximation
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 ...