Midi-Maestro and Maxi Maestro Drive
20
Example 2
Max required speed = 3000
RPM
Vref = 5V
Ke = 10 (10V at 1000
RPM)
Vdt =
3000 5 10
10,000
15V
××××
==
Measure the tachogenerator output voltage with a
digital multimeter, and adjust the maximum
speed for the multimeter to show the calculated
value. Calibration should be optimized using a
speed indicator.
Adjusting the nominal current
When the nominal current rating of the motor is less
than the nominal current of the Drive, it is possible to
reduce the maximum value of current produced by the
Drive by fitting a
RIN resistor.
1. Use the following equation to calculate the value
of the
RIN resistor:
RIN =
(10,000 I )
I-2I
NOM
PEAK NOM
××
Where:
I
NOM
= nominal desired current value
I
PEAK
= Drive peak current value
Note
I
PEAK
is a threshold level which is 2 × I
NOM
output
current of the Drive.
When the required nominal current is reduced, the
resulting I
PEAK
current may be more than 2 × I
NOM
before the I
2
t protection reduces the peak current to
the nominal value.
In this case, the peak current is supplied for less than
2 seconds. Added protection is required to stop the
I
PEAK
value increasing to more than 2 × I
NOM
. See
Adjusting peak current.
When I
NOM
is the theoretical nominal current, and the
denominator equals zero,
RIN should be open circuit.
Example 3
To calculate a value for
RIN for the Model 200 × 25/50
with a 15A nominal current.
(())
(())
RIN =
10,000 15
50 - 2 15
××
××
== 7500, ΩΩ
Where:
15 is the requested nominal current
50 is the theoretical peak current of the Drive
The following table may be used for finding an
approximate value of I
NOM
.
RIN Maxi-Maestro
200 ×× 25/50
kΩΩ
I
NOM
25
56.0 23
57.0 21
15.0 19
10.0 17
7.5 15
5.6 13
3.9 11
2.7 9
Adjusting tacho loss protection
RRT resistor
1. Set Switch 3 at
ON to enable tacho loss protection.
2. Use the following equation to calculate the correct
value for the
RRT resistor:
RRT Vm Ke==××××−−××[( . ) ]0 0424 1 183000
Where:
Vm = Maximum speed in
RPM ÷1000
Ke = Motor voltage constant (voltage at 1000
RPM
— in general V × 1000÷RPM)
Example 4
Max speed =
3000 RPM
Vm = 3
Motor voltage constant (at 1000
RPM) Ke = 15
RRT ==××××−−××==[( . ) ]0 0424 3 15 1 183000 166164ΩΩ
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