DC motor relationship
Hi everyone,
For a DC Motor, what is the relationship between the characteristic below?
(In consider of "Increase" and "Decrease")
a = (Input Voltage)
b = (Input Current)
c = (Input Power)
d = (Velocity)
e = (Torque)
Just realiase that
Increase input voltage, velocity increase
increase load torque, input current increase
Incrase velocity, Torque decrease
how about power?
Current increases while speed deceases with torque linearly with torque up to the stall current, stall torque and zero speed.
Speed increases with voltage- now here's the thing to understand:
Double the voltage, and the no-load speed will double. Got it?
NOw if you had the same load but at two different voltages the difference in speeds will be the DIFFERENCE IN THE NO LOAD SPEEDS. So if the difference in no-load speed for two voltages was 1000RPM, if you apply the same load at those two voltages, the difference in speed will be 1000RPM (but they will obviously run slower because of the load, but the difference between the two voltages is 1000RPM). So increasing voltage will proportionally increase the speed, but the loaded speed is only increased by a FIXED NUMBER OF RPM. This fixed RPM increase under all loads is the difference in no-load speed between the two voltages.
Remember the first thing I said about:
"Current increases while speed deceases with torque linearly with torque up to the stall current, stall torque and zero speed."
Since you increased the RPM by a fixed amount, you also eseentially increased your stall-torque since you now need more torque before the motor will be zero speed. Of course, to get this extra torque you also need more current, so your stall current increases.
Understand? Increasing the voltage will increase your motor's loaded RPM by a fixed amount- a FIXED AMOUNT. THis fixed amount is calculated by the difference in no-load speeds between the two voltages, and no-load speed is proportional to voltage. THis was the point that took me forever to get it.
FOr the motor curves, when you increase the voltage, essentially the line on the motor curves:
1. voltage vs speed
2. and torque vs current
get extended further. THe slope doesn't change, the maximum point on the graph changes.
Power increases both with speed and torque. It maxes out at about 50% stall torque and 50% no-load speed and then starts to decrease again. Zero torque but infinite speed is no power. Zero speed but infinite torque is also no power. Of all of these, power is the *easiest* one to understand.
http://www.motortech.com/BULL_E-1.htm
Last edited by dknguyen; 30th April 2008 at 04:55 PM.
Tanaka Sensei (avatar) says: Please spell it "ridiculous" correctly! Not "rediculous". ^^
From wat i understand is
if let said for two voltage v1 and v2
If with Load 1 apply to both V1 and V2 will get the following result
V1 = 2 Volt => n1 = 4000rpm
V2 = 3 Volt => n2 = 5000rpm
diffirent in speed is 1000rpm ( is this the difference in no load speed as u mention above?)
If now with second load Load 2
V1 = 2 Volt =>n3 = 2000rpm
V2 = 3 Volt =>n4 = 3000rpm
in here, the diffirent in speed in still 1000rpm but will the speed goes slower due to different load
the difference in no load speed will always maintain 1000rpm
is this what you mean?
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