Re: (ET) Education...

["steves" <ssawtelle fcc net>]

Know where you're coming from. I'm an EE and this stuff is confusing.
'Course I managed to not take the motors class (why would I ever need
that?). Also, remember some of the guys on this list do EV stuff either for
a living or should be- so don't be surprised to get left behind sometimes -
I know am.

Some of the manuals have a good section on reading the schematics and
understanding relay operation. Try the general info file in GE service
manual son the elec-trak.org site. The manuals also break the various major
circuits down into smaller drawings which are easier to follow. However you
are right in that it can be hard to relate the schematic to a physical
device.

Some help (excuse me if this is too obvious or too confusing):

- FU is a fuse.
- The field refers to a magnetic field. Generally we mean the field 
winding.
A motor runs by interaction of two magnetic fields. One is created in the
armature which are the windings on the shaft of the motor. The other
magnetic field comes from actual magnets (as on the mower motors), or the
field winding. In either case that is the stationary part of the field and
is in the actual motor housing. Most (all?) ETs vary speed mostly by adding
series resistance to the armature winding - which lowers the current (and
magnetic field is proportional to current). But (and I still am trying to
get my mind around this) you can also increase the speed by making the 
field
current less - this is called field weakening. I understand it when I read
about it, but not well enough to describe it well. A Google search may
provide better descriptions.
- The schematics do a decent job of showing how the wires are actually 
run..
If you see two lines coming in to one end of a fuse on the drawing. then
there should be two wires joined at that fuse on the ET.
- The wires are numbered on the schematic and at each end of the wire
(usually), but sometimes they are hard to read and/or to get to.
- On the schematic, the relays are not depicted very well as physical
devices. The coil part ( a circle) is usually drawn apart from the contacts
(two straight lines), because one goes with the control circuits and the
other with power circuits.They usually have a common label (PTO, etc).
- The manuals do have drawings that show the physical location of the 
relays
in the ET, but of course it's easy without the jumble of wires and 
different
panels, etc. I find it hard tracing through circuits. The light circuit in
my E20 evidently shorted out before I got it and it's near impossible
tracing the wiring out.
- Lastly, the total circuit is made up of several sub-circuits. The PTO
circuit is pretty independent of the lift circuit and motor circuit, etc.
Try to focus in on the circuit you are troubleshooting. Say the armature
circuit on the E15. It's a small part of the schematic and encompasses 3
relays: The 'L' relay ( power to the armature circuit), And the 1A and 2A
relays which bypass the resistors. They are controlled by coils with like
names. If you trace thru the control card (hey- semiconductors - I know
that!) -it basically has solid-state switches that power the relay coils
based on other inputs and some time delays.

- Another reason we need an ET meet - some hands on training would be good
for all of us!

- SteveS