Questions tagged [current]

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

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2k views

Current capacity of copper wires in vacuum

I’d like to know the current carrying capacity of copper wires in vacuum. The current plan (NPI) calls for sending ~3 amps through the vacuum space of a cryostat. Has anyone done this? Have any ...
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Electrical circuits homework

I am pretty new to circuits analysis and I have the following problem as homework: ig2(t) = 4sin(ωt + π/4), e3(t) = 12sin(ωt + π/4), R1 = 10 Ω, ωL1 = 4 Ω, ωL3 = 3 Ω, 1/(ωC2) = 6 Ω I have to calculate ...
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300 views

How to use MAX7219 with high current LEDs

I am fairly new to electronics. I am using the MAX7219 to control an led matrix and the data sheet for the MAX7219 says that the maximum current each light can get is 40mA, but for my purpose I need ...
3
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1answer
70 views

Measuring integrated current

I want to measure the amount of light striking a photodiode in a specific time window (about 1ms). In this window, we get \$10^6-10^7\$ photons, which get converted into electrons with about 80% ...
3
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1answer
86 views

Problem with high current draw in circuit design

I am working on a project where I've taken an LDC1612evm (inductance to digital converter) and removed the connected micro controller portion to communicate with a TM4C123G LaunchPad via I2C. I have ...
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0answers
207 views

How to distribuite high current in multilayer PCBs

I'm designing a 150Amp controlled rectifier and I'd like to know how to distribute the current using a multilayer design. Currently, I have a 4 layer design containing: Top Layer: 6oz, Vdc+ and Vdc-...
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2answers
332 views

Battery failing. Oscilloscope?

The question is - is there an inexpensive oscilloscope I can use to measure DC voltage and current to see why my battery pack is failing to power a DSLR? In order to take long time lapse photos with ...
3
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1answer
298 views

How do current spikes over limit affect Lithium battery life?

In one of my application, I am using Tadiran Lithium Thionyl Chloride Batteries MODEL TL-5934. In the data sheet , the max pulse current shows 50mA. However, in my application, we have low duty cycle ...
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716 views

Connect speaker directly to Samsung Galaxy S6. Minimum impedance accepted

I want to connect an external (passive) speaker (3W/16 ohm) directly to my Samsung Galaxy S6 using the headphone jack. I want to do this on my bicycle using the smallest space possible. Connecting the ...
2
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0answers
75 views

Shunt current measurement on phase

I measure the current of two phases (directly phase current, not the low side MOSFET current) of a PMSM motor and on some hardwares (2 of 10) I have issues with the phase current measurements. As a ...
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Question about outdated "amplidyne" technology

Can someone please help me understand something better about "amplidyne" technology that was used back in the day. What I know It appears to be a dc motor generator that acts like an ...
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86 views

Beginner trying to resolve transistor issues

I have designed a basic transistor circuit with the EveryCircuit simulator. The idea is that when the switch is open, one LED comes on and when the switch is closed the other LED lights up instead. It ...
2
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2answers
567 views

How do I safely power 2m 144 LED/m WS2812B strip with 5v and 10a?

I am using a 2 meter strip with 144 led/m on a WS2812B led strip. By doing the maths on how much current would be required to power this we get 60mA * 288 = 17.28 amps. However, I am not planning on ...
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0answers
66 views

Multimeter measuring different values on different probe polarities?

I have a UNI-T UT33A+ model multimeter and I'm using it to read current values for my assignments. The weird thing is I get entirely different values when I switch probe positions. For example when I ...
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82 views

Why does my lightbar draw more current when connected to a battery than a power supply

When I measure the current draw of the lights when connected to a car battery, they draw about 2.4A However if I connect the lights to a 12V power supply, they only draw around 0.8A. Even though the ...
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0answers
66 views

Where exactly earth current flows-SMPS/DC-DC and DC-AC

Ashamed to ask this question after having lot of experience in Converter designs. i always heard and learnt from Sr. Mentors that For better EMI performance we need to give path for conducted noise(...
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101 views

Why does my multimeter report a tiny current through a shunted 9-V battery?

Why does my multimeter report a tiny current (microamps, if that) through a shunt resistor (e.g., 1.5 kΩ) or even a short placed across the terminals of a new 9-V battery? The multimeter and all ...
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0answers
27 views

wave form of the diode current of a rectifier circuit and difference between the transformer and the AC source

So I have two questions I hope you would answer it, the first one is about how would the current Id of this circuits be? I mean his waveform. and my second question is these two circuits who are in ...
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0answers
27 views

DS3231M Current Consumption

I have bought a DS3231M Real time clock. From the datasheet, one can see that when the RTC is powered from VCC with 3.63V, the max current I_CCA is 200uA when I2C is active, and I_CCS 130uA when I2C ...
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2answers
260 views

Charging a Phone With a Lower Current-Rated Power Supply

My friend's iphone charger exploded. She was charging an iPad with it. Since the iPhone power supply has a current rating of 1A while the iPad charges with a 2A current, many are blaming her that she ...
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0answers
151 views

LED Matrix creation using resistors & MAX7219

I've been attempting to create my own LED matrix, but now I've plugged it all together I'm getting some unexpected LED's lighting up, it seems some are getting power when they shouldn't (not very ...
2
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2answers
74 views

Switches for current source

simulate this circuit – Schematic created using CircuitLab I1 is an wilson modified current source by 4 pnp transistors. SW1 and SW2 are doubts. When SW1 is open, SW2 must be closed and vice ...
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0answers
92 views

Is there a limit on the current carrying capacity of a wire?

Obviously, for continuous current there is - the melting point. If it is superconducting, the field strength at which it quenches. OTOH if we specify a pulse of arbitrarily short timescale in order to ...
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1answer
368 views

Put RS485 microcontroller and transceiver to sleep and wake it up on incoming data

I have to do a network of devices based on MCU. This network in a RS485 and the device is battery powered. For save the battery I put the MCU into sleep mode and I want to wake the MCU up, when ...
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0answers
178 views

Current derivative in RLC circuit

How to find the current derivative(di/dt) at t = 0+ in the first loop?
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3answers
881 views

What power supply do I need for my LED light strips?

My set up is this: Power supply > RGB LED WiFi controller > 1 to 3 cable splitter > 2M cable (x3) > 132.5cm 120leds/m 5050 RGB strip (x3) I contacted the eBay seller about what power supply I would ...
2
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1answer
87 views

Does it make sense to use differential ended inputs to measure current signals with shunt resistor?

If I use 500 meters 4-20mA current loop in an outdoor environment, does it matter whether I use single ended or differential ended data acquisition inputs? I know that for voltage signals ...
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0answers
974 views

Improved Howland Current Source not providing less than 1mA

I've learning a lot about op amps and constant current sources lately. I've implemented the above Improved Howland VCCS. Found it on page 6 of TI's "A Comprehensive Study of the Howland Current Pump": ...
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0answers
724 views

Spark minimum current

I know from the title may sounds wired. But it makes sense to me at least for my restricted knowledge of high voltages. I'm always working with low or house voltage as well as this question may refer ...
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0answers
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Datasheet for Keyes IR Transmitter (KY-005) wanted

Can someone help me find the datasheet for the Keyes IR Transmitter (KY-005)? I know how the pins work, I just need to figure out its voltage drop and how much current should go through it. Thanks! :...
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0answers
194 views

comparator input latches high?

I am using a a TI TLV3202 comparator (U2B) with a bridge circuit as shown in the schematic below. It is followed by a DG4157 analog switch. This is related to this question I had asked earlier. ...
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1answer
29 views

Calculating battery life considering the capacity drops depending on load current (2 x 4 AA-packs in parallel)

This is a very recurrent question, about calculating the battery life given certain circuit current usage. This example will be similiar to this one in terms of the battery used and the consideration ...
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0answers
77 views

How do I choose currents through my circuit?

Beginner here. I've recently "almost" finished a project in which I am using a relaxation oscillator to get a square wave output with a certain frequency. The circuit works as I wanted but ...
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0answers
51 views

What could be the reason for the difference in current and voltage for this transistor?

I am supposed to be doing an online engineering assignment and was in the midst of simulating some circuits in Multisim when I noticed something. The placement of the ammeter before and after the ...
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0answers
68 views

Multiple LED branches with a current regulator

I would like to drive a lot of LEDs with the same current, so I decided to use a current regulator. I am not sure which circuit is better for uniform current in all branches. Should I use two separate ...
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1answer
74 views

Resonance peak occuring in Bode plot of DC-DC Control Loop before the cross over frequency. Why?

Like, how does the resonance happen before the cross over frequency? Can someone explain the intuition behind it?
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0answers
74 views

Power bank's output current

I'm wondering what factor determines the maximum output current of a power bank. Is it limited by the internal battery's current or the output current of the voltage regulator? Also I'm not sure that ...
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0answers
74 views

Slew rate in a transmission line

Let's say I have a 3km long transmission line with a capacitance of C = 50pF/m, the resistance is 100Ohm. The inductance and the conductance per unit length are negligible. If I want to receive the ...
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2answers
184 views

Why is this "fading" as if the current draw is too high?

I am attempting to build a "dice game" based upon an Arduino Uno. There will be 5 dice represented by LEDs. To manage the number of LEDs (7 for each die + 1 for an indicator) I have elected -...
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1answer
61 views

Building intuition on the behavior of inductors and capacitors with both voltage and current

I understand that an inductor cannot change current instantaneously, however I am not sure how that relates to the voltage. In a high pass RL circuit, for example, I know that the inductor presents a ...
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0answers
42 views

Does a 12V cable of an ATX power supply have an overcurrent protection on its own when more current is drawn than the cable could withstand?

I want to use an old ATX power supply to power a project of mine. For that I'd like to utilize a single 12V cable from the 20 pin connector which is 18 awg and therefore can safely handle around 6 ...
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0answers
53 views

What is the effective value of the current of the voltage generator?

I need help with this task, if anyone had a similar problem it would help me. The task is: A voltage generator is connected to the primary of an ideal transformer, transformation ratio n rms values ​​...
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1answer
41 views

AL5810Q LED driver does not maintain a constant current

I am designing a controller for an LED matrix. The controller which must provide a constant 15mA where only ONE LED is turned on at a time. One of the features of this implementation is the high ...
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0answers
43 views

Automotive relay circuit

I have a relay in my car that is constantly fed power through a fuse to terminal 30 and terminal 86, the wiring diagram shows the ignition does not need to be on. When I check positions 30 and 86 with ...
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0answers
43 views

Primary Current in a Transformer

In the image attached above, the book uses I2 = V2/Z2. However, the question says "primary is excited by 200V". So, V2 should be 100V. Is the solution wrong then. Question for reference: ...
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How to determine the lowest bound of current sensor sensitivity?

I would like to build current logger using Arduino. I am having hard time finding out and understanding the lowest bounds of current sensor sensitivity. The following link states sensitivity this way &...
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49 views

Fourier transform of the electrical conductivity function

In this pdf https://studylib.net/doc/18704299/chapter-1 the author writes that the Fourier transform of the current density is: $$ \Delta j_{i}(\mathbf{k}, \omega) \equiv \frac{1}{(2 \pi)^{2}} \iiiint ...
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82 views

Differential Signal Measurement best practice

I have 4 differential signal pairs (LVDS Data lines and Clock) running between my Microcontroller and TFT. There are no test points over the lines. Can someone tell me what is the best practice and ...
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0answers
35 views

How to calculate the pressure and velocity of an ionised gas that is being impelled with magnetic pressure

Calculating the velocity and pressure of an ionised gas based on magnetic pressure and magnetic force. Questions: Based on magnetic pressure expressed on an ionised gas, how do I calculate the ...
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1answer
81 views

Why would a multimeter (ammeter) connected in series prevent the instrumented device from powering on?

I'm trying to measure the current used by a 3.5" hard drive in an external enclosure. I connected my multimeter in series with the positive 12V power supply, but in doing so, the hard drive ...

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