Re: [CAD_CAM_EDM_DRO] Re: capacitor

mariss92705 wrote:

> Les, Jon,
>
> I don't mean to belabor the point but once I have my teeth into
> something I have to take to its conclusion. That means I have to make
> sure I understand the underlying principle or have others show me
> where I am mistaken.
>
> I am making two assumptions:
>
> (1) "Energy return" during deceleration is not a given.
> (2) There is no difference between acceleration and deceleration.

There is a big difference. Energy flows the other way during
deceleration. In other words, when a motor is accelerating a load,
the current and voltage relationship is much like a resistor. When
decelerating a load, the current flow is the other way, and the motor
has the characteristic of a NEGATIVE resistor, ie. a power source.
If the deceleration is severe, then the armature resistance may indeed
absorb all energy, and the circuit looks resistive again, but for larger
motors with heavy loads being gradually decelerated, this is not
usually true. I will make some measurements on my system to
prove this over the weekend.

>
> Both points are tied together in this thought experiment:
>
> Say you are in a car that is rolling backwards at 20 MPH and the
> transmission is in "drive". You apply torque (press the gas) to the
> drive wheels at a constant rate. The car decelerates, stops, then
> accelerates until you are going 20 MPH in the forward direction. Oh
> yeah, and your eyes are closed as well (don't try this at home folks,
> this is a trained professional driver).
>
> The questions are:
>
> (1) If "energy return" is a given, why are you pressing the gas pedal
> during deceleration?

Most transmissions will NOT let you do this! certainly, with a manual
transmission, unless you burn the clutch severely, the engine will be
spinning backwards, and acting as a weak brake, but producing no
power. If you could do this with an automatic, it would burn a great deal
of power in the torque converter. The torque converter or clutch would
be forced to burn ALL the energy of the moving car, plus the energy
applied by the engine at RPM x torque.

>
> (2) Can you tell when deceleration ends and acceleration begins?
> Remember, your eyes are closed (no peeking).

In the car, it is hard - without instruments. The servo amp could tell,
but in general it doesn't care much, either. Shortly before speed drops
to zero, the voltage across the armature terminals will pass through
zero, and the motor will change from negative resistance to positive.
The armature resistance causes this to happen just before the armature
actually reverses direction.

Jon