Re: (ET) Debugging ET 12S (was Power Disconnect for an E12M)

[Allan <allanhv worldnet att net>]

>
>         Could it be that some of these tractors came with different type 
> motors?
> Or more likely am I out in left field with this.
>

I don't know about the E12 in particular, but many of the tractors were 
sold with
variations.  If your E12 has a tag (under the hood on my tractors), it 
should
designate the full part number.  It should include something like E12AA, 
E12BA, etc.

> On the E12 series, I believe the motors have permanent magnet
> fields.  There are NO field wires!  On my E12S, there are 6 wires to
> the motor.  The 2 heavy leads are the armature power leads.  The
> four lighter wires are for a centrifugal switch interlock cutout, and a
> thermal switch cutout.  These act in the same manner as the brake
> switch cutout and seat switch cutout.  These wires do not carry
> significant power, just solenoid control power.  This is why the
> motor will turn the same way if the "field" leads are reversed, or
> disconnnected.

You should be able to measure the resistance of the field.  If the 
connector is
really to a switch, it will either measure open or short.  If it is to a 
field, it
should measure on the order of 16 ohms.

Assuming your motor does have a field, it sounds to me like you correctly 
diagnosed
the problem.  I've had similar experience with an E20 motor.

Let me see if I can explain why the motor went in reverse with no field 
excitation.
Per earlier discussions in this group, some motors include an additional 
field
winding (for motor speed stabilization) which is wired in series with the 
armature.
If you power the armature with no load on the motor and don't power the 
field, this
extra winding, which is powered by the same lugs which power the armature, 
can
produce enough field magnetism to spin the motor.  Further, if you reverse 
the
armature power, this extra field winding must also reverse (since they are 
wired
together), so the motor does not reverse direction.

I found that on the E20 the motor will spin when the shift is in neutral, 
but it
draws a whole lot of current and has very little torque.  This is because 
the
"extra" field is very weak.  Caution: it is probably easy to burn out the 
motor
running it without the field connected.  Consider the extreme case of no 
field (and
no "extra" field), the motor will not spin at all making the armature of 
the motor
almost a dead short to the 36V.  Something will burn up.

> > My friend Craig has found a double pole double throw relay in
> > the Hosfelt catalog that appears to have adequate specs  10amp at 
> > 30volts
> > but for the ridiculously low price of $1.49!  I wonder if it is 
> > advisable
> > to use it?

If it is only to switch the field, the current should be pretty low.  16 
Ohms at 36V
would be 2.25A.  You could measure the field resistance to make sure.  
Don't forget
that you will want the field to be off when the motor is not running, or 
the battery
will run down.  Really, your best bet would be to call Bill Gunn, as others
previously suggested.

Good luck!

Allan