Electronics

Guest

Can someone help me????? My physics teacher asks me to identify what
internal resistance is and also he wants me to identify the effect it
has on a motor! Can someone help me with that information? I'm a little
lost on it! I tried finding information but no one was very helpful! I
hope you can help me! If you can please email me at
blactrak@hotmail.com! I appreciate all the help you can give me.

Boris Mohar · Guest

On 19 Jan 2005 16:17:47 -0800, blaktrac@hotmail.com wrote:

Boris Mohar · Guest

On 19 Jan 2005 16:17:47 -0800, blaktrac@hotmail.com wrote:

CJT · Guest

blaktrac@hotmail.com wrote:

Steve · Guest

Imagine a "perfect" battery, i.e.-one that will supply its output
voltage at *any* current. Of course this type of battery doesn't
exist becuase there is always going to be some internal resistance due
to the resistance of internal metal connections, the electrolyte
interface, etc.

The practical model for a battery (or any other source, AC or DC)
is an ideal source with a series resistor.

The way you would be able to measure the internal resistance of
a source is to measure the no-load voltage, then place a load
resistance that will cause the output voltage to be *half* of the
open voltage. The load resistor will be the same as the internal
resistance.

If I recall correctly, the rule of thumb for the starting current
for a motor is about 5 times the running current. If this assumption
is correct, you need to make certain that the source you are
using to drive the motor will supply enough starting current
to get the motor to run. The internal resistance of your
source will be the limiting factor.

Steve

<blaktrac@hotmail.com> wrote in message
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DaveM · Guest

Doing your homework for you...
Internal resistance is exactly what the term implies.. the resistance of
what's inside the motor. In the case of most motors (not counting the
brushless DC types), it will be the resistance of the wire in the motor
windings. Its effect will be as you would expect a resistance to exhibit..
as current passes through the wire, it will dissipate power, manifest in the
form of heat. I'm sure your instructor has broached the term "heat rise" in
the context of motors??
The heat generated by the IIR product in the wire contributes (but not
completely) to the heat rise of a motor under load.
Your next assignment from this newsgroup is to explain the other major
factor causing the heat rise of a motor.

--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!
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