Re: (ET) how does the late model I5 speed control work?

[The CZ Unit <cz alembic crystel com>]

Ok, I went out and floored it on my E20. Good wiring, newer disconnect, 
all power wires were cleaned and assembled, BB600 cells, fully charged.

It goes right to full power, full field. You can hear the motor whine, 
it does not go into field weakening until the tractor is well underway 
and stable. Battery volts are in the middle of the meter, so it's not 
low powering out at the battery. All contactors engaged.

Now the E20 has two differences from the E15: First the motor pulley is 
smaller so you get more power with less speed. Which can be made up for 
by the additional speeds. Second, the motor does have a compensation 
coil on the field that is *in series* with the armature. Thus under high 
power draws in forward it helps to strengthen the field and reduce the 
potential amp draw at the armature. I don't know/don't think the E15 has 
this.

That might be the whine, the secondary field is limiting armature 
current. The drawback to this is that in reverse the tractor will pull 
way *MORE* current since the field is reversed and is acting against the 
natural field circuit. Ergo progressive field weakening. However since 
the high speeds are locked out in reverse this is only weird when going 
backwards up a hill in D2.

Anyway, the E15 motor is much more jerky, I guess this is the lack of 
compensating field and larger pulley. Which would explain why they put 
that whole speed reduction thing in. The E12 has a similar motor so they 
put in the centri clutch.

Chris