why is an additional resistance needed to limit the current when starting a DC motor?
397994
http://www.4qd.co.uk/faq/bmnc3.html   should answer that
167026
Read this article and the other links inside.\n\nhttp://en.wikipedia.org/wiki/Dc_motor
114097
casey's last sentence is wrong:\nthe more resistance the slower the flow rate \npressure is determined by voltage\n\njdub says:\n"for example...the higher the voltage, the greater the resistance, and the higher the current, the lower the resistance...etc.."\nshould say_ that a a higher voltage will need a greater resistance to oppose flow in order to keep the current the same, or if you want to raise current you would either raise voltage across given resistance, or lower the resistance at a given voltage.\n\nbrmick says:\nthat air is a better conductor than concrete,\nThis largely depends on the frequency of the source, gases are not generally considered conductive, while concrete which is largely water is a moderate conductor especially if wet or wetted.\nDO this take two light bulbs and wire one of each lamps leads to the other then tie it to its intended source (series) using the remaining leads. check the voltage across the source and between the lamps. Assuming you have two equal size lamps you have {nearly-ignoring impedance} doubled the resistance. and so the current and wattage are cut.
1124807
In a situation where you remove the resistor and join the two ends\nyour fan will rotate at full speed without any regulation.\nThe resistor does the job of regulating the current to the fan and thus controls its speed.\nA bad resistor heats up, utilising power, thus wasting energy.
832719
Not really here to give you the lesson you should have had!\nBut, in short:\nA resistor LIMITS the current passing through, as Ohms law, V = R x I (Volts = Resistance x Current)\nA capacitor keeps an electric charge (like a battery), but does NOT let the current passing through.  When C is empty, and a voltage is put across, a current flows through C until the cap is charged with the same voltage as the voltage across.  Once this is reached, the cap does not let any current through.
424406
I would get a 500 watt inverter to have some safety, you figure with volts times amps but if it uses a motor the starting current can be 5 times the running amps.
1047481
A motor requires about 6 times as much current to start as it does to run, so a static-capacitor phase converter must have some means of switching a large group of capacitors in and out during motor starting.\n  \nA typical unit uses a potential-type motor starting relay  to regulate the larger start capacitor, while a smaller (in value) capacitor provides continuous power to run the motor. As the motor speed increases, the potential relay removes the start capacitor from the circuit, and the motor operates.
919217
Like everything else, it depends.  The concern is that at the maximum current you will draw, there is sufficient voltage at the point of use.  Voltage drop depends on the amount of current, and the resistance of the circuit.  \n\nYou can determine the minimum voltage requirements for whatever you are driving.  Knowing the resistance per foot of various sizes of wire, you could determine the size wire needed.\n\nNow it becomes a matter of economics.  Is larger wire less expensive than a transformer--or two if you are going to maintain the original equipment operating voltage.
1065990
In Electronics Physics:\nthe use of an oscillator feedback loop as a power supply. Add a bridge rectifier to the output and feed the DC current Resistance limited back to the oscillator amplifier setup. Like using an auditorium feedback signal to drive the DC system.
1029495
It is impossible to tell from the information given.  YOu need to know the power factor and efficiency too.  \n\nAt full load of a motor that big it is likely to be 95% efficiency and have power factor of probably 0.8.  \n\nIF (!!) that is true, then the current is (75 hp * 746 W/hp)/(480  V *sqrt(3))/0.95/0.8 Amps (rms)\n\nNotice I've considered a wye-connected motor too - that's where the sqrt(3) comes from.  I also get 90 A (like the previous guy)!
412964
use the delta when you are starting a large motor since it can be hooked to energize only part of the windings of the motor at a time this allows for less amperage to be used to get the thing turning
912980
it depends on the load and the nature of the large appliance\nthe flush example was great but it does not describe dthe momenteraly effect ( it was nice though).\n\nwhen you deal with inductive loads there is something that is called start up current.  it can be 2 to 6 times the nominal current under normal operation. that means that if a device needs 2 amperes of current when it is originally powered the consumption may reach till 10A. then the current returns to normal copnditions. \nall due to inductive and self inductive effects where the device opposes to the change and so on till an equilibrium is reached.\n\nthe demand of the current during start up is great and that is way momentarely  the lghts dim.
40073
An automobile has a DC (direct current) battery and therefore uses a DC starter.  Current flows in only one direction just as in a flashlight with batteries.\n\nMany snowblowers can be plugged into an AC (alternating current) outlet in the garage and use AC starters.  Current flows in opposite directions through the starter completing 60 cycles every second.  The voltage rises from zero to a peak drops to zero and continues to a negative peak before returning back to zero once each cycle.  The graph of voltage with respect to time forms a sinusoid.
688358
When the infinite resistance setting is selected the circuit sees this as the maximum allowable resistance to current flow which would be an open circuit - when selected, there is no connection being made through any resistor network inside the decade resistance box. Internally it is an open circuit.
399258
just put a limiting resistor. 60mA and 12V. Limiting resistor =R=(V-Vled)/I. assuming the extreme, 0V for Vled. R=12/6e-2=200ohm. that way the current will never exceed 60mA.
209090
It's 8 Amps, the current has to be the same through both of them because it's a series circuit
95862
it gets hot, which in turn causes more resistance, and it gets even hotter, which causes more resistance.  if there are enough amps, the metal will melt.