Final Adjustment
4-8 Manual # 42-02-7223
Determine the Armature Current Limit (System 12 SCR Drive)
Armature current limit (Configuration > Drive > Safety tab) is a percentage of SCR drive maxi-
mum output current rating and may range up to 276%. To determine the Armature current
limit setting, first find the Maximum Full Load Output Current rating on page -D1 of the job
prints. It is desirable to provide 250% of the full load current rating of the hoist motor during
acceleration or deceleration. (In high performance applications, up to 276% may be desirable.)
For example, if the drive maximum full load output current rating is 180 Amps DC and you wish
to limit full load amperage to 140 Amps DC, with a 250% acceleration capability, you must set
Armature current limit to 194% (140/180 x 250 = 194%).
• Make the calculation and set Armature current limit accordingly. (If setting is correct, you
should not see the SCR drive Current Limit indicator LED turn on during normal opera-
tion. It may light during emergency deceleration, especially during testing.)
In some cases, where the voltage limiting mechanism (as determined by Armature voltage
limit) is severely exercised, the Current Limit LED on the SCR drive may light. This may indi-
cate excessive voltage limiting as well as current limiting. Be aware that a low value for Arma-
ture current limit may result in oscillation at high speeds. Once stable operation is achieved, be
sure to increase Armature current limit to at least 200%.
Determine Motor Field Adjustments (System 12 SCR Drive)
Motor field adjustments may be handled in one of two ways:
• Begin by setting the Field standing voltage (Configuration > Motor Field > Control tab) to
known values and then program Field running voltage to 80% of forcing voltage. In this
case, the SCR drive will weaken the motor field as necessary to keep armature voltage from
exceeding the maximum allowed value. Later, when test weights are available, running
voltage should be adjusted so that, when the car is running at contract speed with a full
load in the up direction, actual armature voltage is equal to rated armature voltage from
the motor name plate. This works well when the motor field has moderate inductance.
• In cases where the motor field is highly inductive and cannot weaken as quickly as neces-
sary, armature voltage limiting circuits in the SCR drive will interfere with the current reg-
ulator, causing the Current Limit LED to light. This must be avoided because it will be
felt in the car. In these instances, you must program a value for high speed motor Field
running voltage (Configuration > Motor Field > Control tab) and program the value for
Field weakening begin and Field weakening end parameters so that significant motor field
weakening occurs before the car reaches maximum armature voltage. Field weakening
begin may be increased as long as there is no armature voltage or speed overshoot. Verify
armature voltage in both up and down directions. Cases where the motor field must
weaken to less than 65% of the forcing voltage are almost certain to require setting Field
running voltage and Field weakening parameters.
At this point, if the motor field is at least moderately warm, you should run the car on inspec-
tion and check to see that the desired Field forcing voltage (Configuration > Motor Field > Con-
trol tab) is the same as that which you measure between terminals MF1 and MF2. It is most
important to get the forcing voltage right using this calibration. It is possible that the measured
standing voltage may be different from the desired standing voltage value. This is OK. Adjust
Field standing voltage to the actual value as measured on terminals MF1 to MF2.
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