# Questions tagged [resistance]

A measure of how much a conductor opposes current flowing through it. It can also refer to a part of a circuit, which has a non-negligible resistance value.

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### Multimeter Negative Resistance

I have a Fluke 87V multimeter and sometimes when I measure some resistors (in power supply PCBs I saw it) it shows me negative value of resistance. Why this? It is some flaw of the multimeter or it ...
1 vote
205 views

### How can I measure the resistance of non-linear devices using a digital multimeter?

Is the value of resistance that appears when we measure the resistance using a DMM at the terminals of any electronic device the total equivalent resistance of that device which is also called load ...
48 views

### Cascoding circuit output resistance issue

I was studying a cascoding circuit that was built as a constant current source. I am having a few confusions in this circuit: I read that we need to increase the output resistance of the current ...
1 vote
29 views

### How to set resistance measurements of particle layers in a resistivity cell, using an electrometer?

I am new to the use of electrometers as I come from the totally different environment of analogue experiments in fluids. Although I am familiar with the electrical measurements concepts, I am ...
37 views

### Why is the output resistance of a CMOS inverter determined by the NMOS when the output is high but by the PMOS when the output is low?

For the output pulled high, my professor's slides give this diagram: and the equation $$r_{DSN} = \frac{1}{k_n'\left( \frac{W}{L} \right )_n \left(V_{DD} - V_{tn}\right)}$$ and for the output ...
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### Multimeter range

I've been using a small multimeter meter and the problem is that anytime I want to measure amperage that exceeds 200 mA, I have to switch the red probe the 10 A port. Unfortunately, I can't get the ...
27 views

### Percentage difference of winding measurements

I am trying to learn more about the proper winding measurement of power transformers. In this regard I am following this tutorial https://www.youtube.com/watch?v=3HIEIoa4NKA&list=LL&index=2. ...
98 views

### Relay contact resistance spec off?

This Finder relay series specifies Power lost to the environment without contact current W 0.4 with rated current W 1.4 And a rated current of: Rated current/Maximum peak current A 10/15 If I ...
1 vote
63 views

### Detailed calculations for DIY SSR (solid state relay) circuit

I just want to understand the calculations for a DIY SSR project. I do know the components required but I don't know how to calculate resistance values for this circuit. Also, what is the output of ...
40 views

### Megger terminals clarification

I saw that some meggers inject the test voltage / current from the - (minus) terminal while do this from the + (plus) terminals (don't know why, it probably depends on the manufacturer?) Currently I ...
1 vote
91 views

### Spark gap breakdown voltage vs gap area

I've been trying to design a 1 MV hydrogen gas spark gap. I found the resistance of such to be in the range of 7 Ω/cm, not suitable for a target 40 kA current. Can I make the spark gap shorter without ...
131 views

### Getting four times the power by arranging four resistors

If I'm given four resistors of value R and power rating P (each resistor dissipates up to P), what are ways I can arrange these resistors so that my circuit has a power of 4P and resistance of R? One ...
89 views

### In circuit debugging using continuity test on DMM give un-predictable results

I did a continuity test, between a ground point of my PCI card (audio) and a resistance (47Ω SMD). No beeping sound on both ends of the resistance. After I de-soldered the resistance from the board, I ...
44 views

### Can I measure pinholes in a dielectric layer using LCR meter?

I have a thin dielectric film (~1 um) and I want to measure the quality of the film in terms of not allowing leakage current through pinholes. Can I use an LCR meter for this purpose? If yes, how? If ...
52 views

### Darlington Amplifier circuit (TIP 120) [duplicate]

I'm trying to wire a darlington TIP120 just to see if I can get the 1000 hfe dc gain at 100mA like it said on the data sheet. I made the circuit like it appeared in the data sheet, but wasn't ...
39 views

### Total Resistance, Source Current, Voltage & Current Across Resistor

I am doing some practice questions. However, there doesn't appear to be any answers online. Therefore, I am checking if I am correct here. Could you please let me know if my analysis and calculations ...
2k views

### If capacitors are frequency-dependent resistors, then what are inductors?

I was reading The Art of Electronics 3rd Edition, there it was saying "You can think of capacitors as frequency-dependent resistors." So in terms of this description, what could inductors be?...
1 vote
47 views

### Resistance measurement: Agilent 34401A vs. Fluke 179

I was attempting to measure isolation resistance between the output of an isolated DC/DC converter to machine chassis. I was somewhat surprised to see a large difference in measurement between a 6 1/2 ...
29 views

### Coil resistance and input current in stepper motor H-bridge

Vcc: type: charger Current: 2.5 A Voltage: 12 V Stepper motor: Model: JK42HS40-1704 Coil resistance: 1.65 Ω Coil current: 1.7 A When choosing resistor R1.1 and R1....
67 views

### How can I maximize the power consumed in this resistor?

simulate this circuit – Schematic created using CircuitLab I have gotten really stuck on this question. The question is: Determine R3 so that maximum power is consumed in R3. What is that ...
123 views

### Resistance value randomly changing

I am facing a weird issue where value of resistance (0402 package SMD) is changing randomly. I have a fully functioning board design and have multiple boards where this issue is happening on same ...
75 views

### Series resistor vs PCB track impedance

I want to understand the below question: There are digital interface for example, MII/RMII lines. It requires a PCB characteristic impedance of 50 Ω. Also, better EMC flexibility, it is said to place ...
200 views

### What is I1, I2, I3 and I4?

simulate this circuit – Schematic created using CircuitLab I have really gotten stuck on this question where I need to calculate I1, I2, I3 and I4. The numbers for the circuit is: V(a)=2 V, V(b)=...
1k views

### What is the difference between 1206 and 0612 (reversed) SMD resistors?

I wanted to know what is the difference and if a 1206 resistor can be chosen as second source of a 0612 if the other specifications are the same
72 views

### 50's style Ford Auto Gauges

I'm looking for resistance wire to re-wrap vintage auto gauges that have been burnt open. These gauges work by wrap wire around a metal bar that when heated it bends which moves the needle. The ...
35 views

### Resistance measurement to voltage trigger [closed]

I am looking for a circuit that will take a resistance change that comes from detecting the presence of a dilute salt solution and converting it to a 5 volt trigger signal. The resistance changes from ...
77 views

### Limitation of the Thevenin's equivalent circuit

simulate this circuit – Schematic created using CircuitLab Thevenin's theorem independently derived in 1853 by the German scientist Hermann von Helmholtz and in 1883 by Léon Charles Thévenin (...
141 views

### Is there a systematic way to choose parallel resistors?

I'm designing a circuit, and I need a particular resistance. However, I don't have a resistor with that value. Therefore, I want to combine two resistors in parallel. In principle, with the parallel ...
194 views

### How should I test my USB cables?

Some time ago, I purchased the FNB58 USB multimeter from FNIRSI with the intention of testing some of my USB cables. Ideally, I wanted to throw away those that are redundant and/or those that pose a ...
29 views

### Combining cable resistance and law of resistances in parallel circuits

For a parallel circuit it is true that $1/R = 1/R_{1} + 1/R_{2}$ Consider two equal cable switched parallel to each other. Their individual resistance is $R = phi * l * A$, where phi is constant. ...
119 views

### Can an 18.7 Ω resistance between Vcc and GND cause an increase in current?

This is an ECU PCB and the measurement of resistance between Vcc and GND for the TC1762 Tricore MCU in the PCB is 18.7 Ω. I have a reference board, the resistance there is 400 Ω between Vcc and GND ...
1 vote
95 views

### Measuring power in AC

I have a heater running at 240VAC. I'm trying to measure the power by datalogging the voltage and current then multiply both inorder to get the power reading. I know that this method works well with ...
1 vote
107 views

### JFET or MOSFET for controlling the speed of a compressor (via resistance modulation)

I've recently purchased a 12v compressor with a control unit attached (QDZH35G - usually meant for refrigerators or A/C units, but this is for a DIY project). The speed of the compressor can be ...
330 views

### Its possible to link a group of 1/4 W resistors as an alternative to a resistor with a high power rating (1.25 W)?

I have 10 resistors. Each one is 10 Ω. Is it possible to reach 3.3 Ω with a power rating of 1.25 or 1.5 W? I tried to get 3.3 Ω by linking in parallel (3 resistors), but the power rating is not high ...
351 views

### Why is the resistance in a double-cone conductor higher at the positive terminal?

I am trying to understand the current flow in a simple constricted conductor that looks like this: And I have built a simple model that is based on charge conservation. When I simulate this in steady ...
1 vote
85 views

### Balancing resistance circuit with two voltage sources

Hello, first I'm not sure if the title describes well enough the problem. I have the following circuit. Left side is a part of a voltage regulator. Point A has a fixed potential of 1.2V (a feedback ...
185 views

### Transistor functionality confusion [closed]

Overview I'm reading a book about the basics of electronics and I've gotten to the section on transistors and it's brought up some confusion for me. I first understood Transistors to be basically ...
45 views

### Powering a grid of peltier tiles using a power supply

I'm trying to supply power to an 8x8 grid of peltier tiles from a power supply that provides 3-15 volts, with a max current of 40 amps (the power supply doesn't allow me to limit the current). I want ...
79 views

### How to calculate resistance in LED project with the goal of extending battery life

I'm converting a kerosene lantern to battery-powered LEDs, loosely based on an Instructables project. It uses 4AA batteries (6 volts) and 2 LEDs wired parallel, and 470-ohm resistors. The yellow ...
1 vote
90 views

### Does wrapping kiln resistance wire back on itself reduce the temperature of that stretch of wire?

When replacing the resistance wire in an electric kiln, most manufacturers recommend wrapping the resistance wire back on itself at the ends where it connects to the electrics. Although I haven't ...
157 views

### How does current affect voltage?

I'm currently trying to relearn all electronic principles from the ground up and I'm reading this book about it as well. I understand that in the water analogy voltage could be like water level/...
96 views

### Voltage fluctuations in TIP122

I have used the following circuit diagram for power supply using a transformer,simple bridge rectifier and filter capacitor at the back of it to get 12V dcI have used the TIP122 as shown: Idealy the ... 249 views

### Proof of formula for resistors in series? [closed]

FACT: When resistors $R_1$ and $R_2$ are connected in series, they can be replaced by an "equivalent" resistor $R_1+R_2$ (in the following I am using $R$ and subscripts to denote ...
4k views

### Why are kiloohm resistors more used in op-amp circuits?

In operational amplifiers working in the negative feedback configuration, the voltage gain depends on the "ratio" of resistances. In most textbooks I have seen that both feedback and input ...
406 views

### CAN-Bus: Wire Impedance vs Terminal Resistor

I'm seeing several pre-fabricated "CAN-Bus" cables with (2) DB9, 120 ohm terminal resistor connections, while the cable's impedance is 100 ohms. A. What is the purpose for this mismatch? B. ...
1 vote
163 views

### Which circuit or device can I use to lower my electronics power usage

Resistance device uses 1.0 kW on standalone usage load measurement. I tried using diodes in series to half the power rate to 500 W, Wondering whether to use a 220V to 110 V step down or reduced the ...
1 vote
268 views

### Typical resistance of an SMD solder joint

Do you have an idea of the typical resistance between a PCB track and a SMD resistor pad? That is, the resistance of the solder on, for example, a 0402 resistor. The idea behind my question is that I'...
64 views

### Thevenin's resistance with a dependant source

I have this circuit for which we must find the Thevenin resistance in considering the load is $R_L$. For this case I calculated $E_{th}=-\beta i_b R_4$ by shorting the load resistor $R_L$ so the ...