Jetter JM-105, User Manual, Page: 66 / 106

7 Description of Connections
66 Jetter AG
The following entirety of vectors limit constant current operation:
1. Independent of the speed, a certain voltage is needed for having the set current
overcome the resistance of the phase. :
Where:
Continuous rated current I in Ampere [A]
Resistance R per phase in Ohm [
]
2. Dependent on the speed, a certain voltage is needed for reversing the polarity of
the motor current. This voltage is calculated as follows:
Where:
Continuous rated current I in Ampere [A]
Inductivity L per phase in [Vs/A]
Angular velocity in [rad/s]
The angular velocity of a stepper motor is:
Where:
Pole pair number
= 50
Speed n in [RPM]
Angular velocity v in [°/s]
3. When the motor is rotating, the influence of the EMF (Electro-Motive Force) can
be realized as well. It is opposed to the operating voltage and decreases the
effective voltage during power build-up; power build-up, which is speeded up by
the EMF, though.
Theoretically, the motor can be driven to about the same speed which is needed for
the vector sum
to just compensate the phase voltage. Above this speed, the
motor cannot be driven any more.
Fig. 19: Addition of voltage in a synchronous machine
U
1
R I
⋅
=
Ω
U
2
ω
L I
⋅ ⋅
=
ω
ω
ω
2
π
f 2
π
Z
P
min
60s
----------
n 2
π
=
Z
P
RPM
360°
-------------
v
⋅ ⋅ ⋅ ⋅ ⋅ ⋅
= =
Z
P
U
S
U
EMF
R I
⋅
ω
L I
⋅ ⋅
U
S