Re: [DML] Marc Goldstone/Automatic transmission computer

["Walter" <Whalt@xxxx>]

>Is anyone familiar with the theory of reverse EMF occurring on the computer
>governor?

Sure. Here goes another one of my hair brained technical explanations: The
closest thing one can readily relate this to is the a/c compressors on old
GM cars since the protective device (a diode) is mounted right on the
electrical connection to the compressor where it is visible when you open
the good.

Electric clutches and solenoids are basically coils of wire. When
electrical current flows through this wire, it becomes a magnet. Electrical
energy and magnetic energy mutually create each other at the speed of light.
When electrical energy flows through the coil, it produces a magnetic field
around the coil. When the electrical energy is disconnected, the magnetic
field collapses around the coil and in the process induces an electric
potential across the coil that can have an extremely high electrical
pressure (voltage) or EMF, electromotive force -- it is called by many
names. This spike can damage other systems connected to the car. In order
stop this from happening, all you need to do is install a diode (protective
device) across the coil.

A diode is a device that has two electrical connections like a battery.
It's purpose in electronics is to allow electrical current to flow through
it in one direction more easily than the other. What makes a diode so adept
at protecting a car's electronics from reverse EMF is it's property to
conduct current in predominantly one direction. The nature of reverse EMF
is that it is, well, reversed. If you push a current though a coil and then
take the current away, then the reverse EMF is sort of like pushing on a
spring and having it snap back. Since a diode works as a one way valve to
current, it will appear invisible to the original current (the force pushing
on the spring) that runs the coil and then appear to be a short circuit to
any reverse EMF (the damaging rebound from the spring) that the coil
develops as it is turned off.

In the DeLorean, diodes like these are used on the a/c compressor clutch
(which uses an electromagnet to engage and is basically a type of solenoid).
The door lock module also uses one to absorb the reverse EMF produced from
the door lock solenoids. On the original module, this diode was underrated
along with other components in the module and is prone to premature failure.
Concerning the transmission computer governor, the engineer who designed it
didn't know what he was doing. He forgot to include shunting diodes in the
circuit to protect the computer from the reverse EMF produced by the shift
solenoids. When rebuilding the computer, it is a good idea to add these
protective devices to the circuit.

This is a quick explanation of WHY it is done. If I tried to explain it
better, it would take too long. If you want to know HOW it is done, there
are explanations in the DML archives. If rebuilding the computer is beyond
your abilities, you can mail it off to various people on the DML who can
upgrade it for you.

Walt Tampa, FL