# Questions tagged [current]

Flow of electric charge - typically movement of charge carriers, such as electrons. Measured in amperes (A).

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### Peak current of inrush limiting inductor?

I have this tricky question and I can't wrap my head around it. There is this inductor to limit the inrush current that will be charging up a capacitor. I'm questioning the design of it, but I don't ...
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### Are smartphone cells actually charged with 9V using QC and other techniques or does the smartphone always step down the voltage?

I'm having this disagreement with a good friend of mine regarding charging voltage of the cells inside modern smartphones when quick charge, USB PPS and other techniques are used. Let's take as an ...
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### Off-grid computing

I am designing the electrical system for a school bus to tiny home conversion (skoolie, by jargon.) The current iteration is entirely solar powered, somewhere around 2640 W in panels, and likely 1000 ...
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### Current transformer wire issues

I would greatly appreciate some advice regarding twisted pair conductors for a current transformer. So, according to the manufacturer, whose equipment I am installing, I need to connect 10 AWG, ...
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### What prevents old (low current) USB cables from catching fire if used to Quick Charge modern devices (at high-current)?

Let's say I have A very old Micro-USB cable. It's USB 2.0 and rated for a max current of 5V, 0.5A (2.5W). A modern, power-thirsty, quick-charging tablet that charges over micro-USB at a max of 100W. ...
1 vote
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### Graphing modes of BJT

Suppose we have this Ic vs Vce graph of a BJT transistor I have been taught this graph is applicable for this BJT transistor configuration. simulate this circuit – Schematic created using ...
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### Calculating the reading on ammeter $A_1$: why am I incorrect?

I have the following circuit: The voltmeter $V_1$ measures the voltage drop across the $9.00 \ \Omega$ resistor and has a reading of $4.50 \ \text{V}$. I am trying to calculate the reading on ...
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1 vote
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### What's the difference between Maximum working current and upper limit of instantaneous current?

I am seeking to protect a Mabuchi RS-380-SH4535 motor + battery system using a BMS. The battery is a single cell 18650 LiIon. The motor has a stall current of 15 A at maximum battery voltage. My ...
103 views

### Vending machine motor: simple DC motor with microswitch, one revolution

Long story short, I'm currently trying to understand and control a DC motor with connected microswitch, which gives back one-revolution feedback (don't know how). I tried connecting INA219 current ...
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1 vote
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### How do I compute the power consumption of an audio amplifier?

I intend to use this audio amplifier in my project : PAM8019 It has two analog inputs : left channel and right channel. It has two analog ouputs, which are the amplified inputs. Let's say I follow the ...
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### Normal Switch and LAN9353

I am reading about the different types of LAN Switches. And I came across the LAN9353 device - Link I want to understand the difference between a normal Gigabit Ethernet 3 port switch and this LAN9353 ...
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### External Interrupt Peripheral Microcontroller

I'm using this ATSAME53N20A-AU microcontroller - Link I'd like to know what does the EIC and EXTINT peripherals would do? So, I went through the Appnotes - EXTINT and EIC I just want to know whether ...
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### How can a reed switch be used for high current applications?

I am planning to use a reed switch as a power switch in my underwater robotics project. The switch will be placed between the LiPo battery (16.8V, 20.8Ah) and the load. The load mainly consists of two ...
1k views

### How to stop current from passing through a transistor?

I have this circuit. When sw1 is open the LED should be off. The thing is, some current passes through the transistor even though it's off making the LED light up dimly. Is there a way to fix this, ...
1 vote
37 views

### What are relationship between cable properties and electrical properties?

I was prototyping esp32-cam (microcontroller aka MCU) on breadboard, I saw brownout error message on serial monitor everytime I initialize WiFi then it keeps restarting. After I google for 24 hours ...
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### Current in a induction dc motor

SO I am building an induction dc motor and using a battery that supplies 12V and 7.0Ah. The wire I am using is a 0.8mm enamel copper wire and I am trying to find how much current was drawn from the ...
1 vote
193 views

### If two devices both require 12V 2A power can I use a 12V 4A power supply to power them both?

The question title says it all really: I have two devices that both require a 12V 2A power supply, so I'm assuming that I can I just use a single 12V 4A power supply to power them both? I'm also ...
55 views

### I don't get the formula RIN = beta * RE

There is a formula in Malvino's book (page 210 of the 6th edition) which states that the input base resistance of a transistor is beta times the emitter resistance. To quote: "When seen from the ...
47 views

### Pin Buffer Types

I'm going through the datasheet of this PHY Transceiver LAN8742A On table 2.2, it is mentioned as buffer types. I see a row called as O12, which stands for Output 12mA sink or Output 12mA source. My ...
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### Modeling three phase load for EV charger

When designing a power system to supply EV charging stations, are the stations modeled as delta loads or wye loads? Slightly off topic but is it standard practice to assume that three phase loads are ...
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100 views

### Resistance measured individually vs measured on PCB

I always wanted to ask this question. Suppose I have a 1kohm resistor. I measure its resistance by connection a multimeter to both of its terminals (when it is not connected to any part of a circuit.) ...
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### Is it possible to increase the current of an Arduino Nano 3V3 pin without altering the voltage?

I am trying to use an ESP8266 with an Arduino Nano but I see that the NANO can not enough current for supplying ESP8266 from 3V3 pin. I think it is limited from the faactory. If I use the 3V3 pin RX ...
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### How can I best reduce the current drawn by a PCB heatbed?

I have a noob question about fairly basic circuit design (I think). I am building an incubator for making Tempeh at home, and want to use an old PCB heatbed I have lying around as the heating element. ...
34 views

### Same part devices supporting different temperature ranges

I just had this question. We often come across microcontrollers having the same internal peripherals and supporting the same functions but supporting different temperature ranges. Can you tell me how ...
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### Why is the input current for a forward converter negative for a short time? [closed]

We have made some lab excercises with a forward converter and I was wondering why the input current of a forward converter is negative for a short time. Screenshot of oscilloscope can be seen below, ...
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### Is voltage important for calculating PCB trace width? If not, why?

As per the IPC 2221A the formula for calculating PCB trace width follow the process given below; First, the area is calculated: Area[mils²] = (Current[Amps]/(k*(Temp_Rise[°C])b))^(1/c) Then, the width ...
1 vote
125 views

### Get more current

I would like the ESP-WROOM-32 to supply more current than a single pin provides. For example, about 100mA. I have seen in its datasheet that the current a pin supplies when it is HIGH is 40mA. If I ...
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### If there are multiple holes and one electron wants to release then how can i know which hole will trap that electron? [closed]

I saw a tutorial about concept of holes that says : This trap and release is slower than the moving of electrons on its own. According to that image there is just one hole that replaces its position ...
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### Understanding Spec sheet of IC

I'm having trouble understanding the spec sheet of this shift register. What I want to do is to connect a (generic red one, I don't have any specs) LED which will approximately use 15-35 mA to the IC. ...
32 views

### Servo problem (batteries?)

I've bought some of these servos. I'm trying to control them with an Arduino Uno. Currently I'm only trying to control one. It's connected to 4 AA alkaline batteries (Duracell plus), with a common ...
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### How can I control a firework igniter (e-match) with Arduino?

As the title says, I'm looking to light one firework igniter with an Arduino Uno but I'm a bit of a noob to electronics. From the little I could find online, it looks like I'd need to use a relay? But ...
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### Are vehicle electrical components powered from the negative side?

still trying to get my head around electron flow as opposed to conventional current regarding automotive electrical circuits. There seems to be a ton of conflicting information/advice out there so I'm ...
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### Zener diode Zener breakdown modelling

The IV curve of a Zener diode inside the Zener breakdown region looks like the IV curve of its forward bias operation. Is there a formula which can give the IV relationship in the Zener breakdown? The ...
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### How to input range of current values in LT Spice

Firstly, I'm a beginner at LT Spice. I wanted to learn how could you input a range of values for current. For example, let's say, I want my waveform to oscillate from 10uA to 10mA in the circuit below ...
55 views

### Is this ('RV style' 16amp) -> (2 x 13amp) mains socket adapter dangerous? (2 x 13 being far more than 16)

The 2 sockets are 13 amp rated, and whatever is plugged in would be fused with anything up to a 13amp fuse. The blue 'RV' style wire/plug is 16amp rated. If either plug were to run over 13 amps they ...
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### Why can't current change instantaneously in a given inductor?

I know the mathematical reason behind this. Given the inductor I-V characteristic we know that: I understand mathematically that a function which is differentiable must be continuous, but what is the ...
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### Current measurements - shunt switching

I have been designing a current measuring device, and since it requires high wide-range accuracy, I decided to use two shunt resistors of different sizes. The schematic is shown below: The design ...
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### 240V Mains - Current draw and when to use Solder vs Welding

No specific application, just for interest - I opened up a multiplug/multiboard and noticed that all the contacts for welded (i.e. no solder). I was just wondering if this had anything to do with ...
606 views

### 0 current in a circuit using tunnel diode

Suppose we have a diode with negative differential resistance of -40 ohm in the region of 0.3-0.5 V and we put it in parallel with a 40 ohm resistor: simulate this circuit – Schematic created ...
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### Help Solve a Circuit Using Mesh Current Analysis

I'm Trying To Solve This Circuit Using Mesh Current Analysis But I'm getting that the currents are unsolvable (Matrix is wrong ) . Question : Find The Power of Each Source in : $$\Downarrow$$My ...
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### Odd results from mesh current analysis in a circuit with a diode

I have this circuit: simulate this circuit – Schematic created using CircuitLab The reverse saturation current of the diode is 10^-6 A. I use mesh current analysis to find the current inside ...
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1 vote
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### How to control/remove "quiescent current" of UniversalOpamp2

In the circuit below, I get a quiescent current (entering positive supply and leaving negative supply of the op amp) of about 497 µA, while the load current is only 5 µA. I am aware that this ...
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### Switching step-down voltage regulator gives lower output-current than input current

I'm currently trying to build a photovolatik cell -> DC Converter -> Battery-management-System. In the early stages of the build I was trying to use the adjustable voltage regulator alongside of ...
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### Circuit shorting creates less resistance

Using only intuition, without mathematics, why can't the total resistance in the circuit of the 1st image be less than the total resistance in the 2nd image? The 2nd circuit gives more path options ...
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### ESP32 sourcing 20 times 5 mA?

I want to drive 20 optotriacs (MOC3063, each requiring 5 mA from the control side for the diodes in the optos). I want a 3.3 V ESP32 nodemcu board (wifi enabled as acces point) to control them. These ...
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### Measuring the diode current

R1=15kΩ R2=40kΩ R3=40kΩ E=4V VI--> -8V<VI<8V. In this circuit, diodes D1 and D2 are the same model 1N4007 diodes. (Is=7.02767E-09, VJ=0.7) When I assume that D1 is on and D2 diode is off, ...
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### How does a variable frequency drive reduce the energy consumption of a motor?

If the relationship between frequency and current is inversed as answered in this question, how does reducing the supply frequency reduce the energy consumption of a motor?
1 vote
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### Double loop, double voltage source circuit analysis problem, with three unknown voltages/currents, using Kirchhoff's laws and Ohm's law [Post #2]

I recently asked this question: Find the currents and voltages in the circuit shown in Fig. 2.28. Answer: $v_1 = 6 \ \text{V}$, $v_2 = 4 \ \text{V}$, $v_3 = 10 \ \text{V}$, \\$i_1 = 3 \ \text{A}...
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