Manual

P26 MOTOR OVERLOAD

The SM-Plus

™

is UL approved for solid state motor overload protection, and therefore does not require

a separate thermal overload relay for single motor applications.

The drive contains an adjustable thermal overload circuit that protects the motor from excessive

overcurrent. This circuit allows the drive to deliver up to 150% current for one minute. If the

overload circuit “times out”, the drive will trip into an OVERLOAD fault (displayed as “PF”).

MOTOR OVERLOAD should be set to the ratio (in percent) of the motor current rating to the drive

current rating in order to properly protect the motor. See the example below.

Example: A 3 HP, 480 Vac drive with a 4.8 Amp rating is operating a 2 HP motor with a

current rating of 3.4 Amps. Dividing the motor current rating by the drive current rating yields 71% (3.4

/ 4.8 = 0.71 = 71%), so this parameter should be set to 71%.

P27 BASE FREQUENCY

The BASE FREQUENCY determines the V/Hz ratio by setting the output frequency at which the drive

will output full voltage to the motor. In most cases, the BASE FREQUENCY should be set to match the

motor’s rated frequency.

Example: A 460 Vac, 60 Hz motor requires a V/Hz ratio of 7.67 (460 V / 60 Hz = 7.67 V/Hz) to

produce full torque. Setting the BASE FREQUENCY to 60 Hz causes the drive to output full voltage

(460 Vac) at 60 Hz, which yields the required 7.67 V/Hz. Output voltage is proportional to output

frequency, so the 7.67 V/Hz ratio is maintained from 0 - 60 Hz, allowing the motor to produce full

torque from 2 Hz (below 2 Hz there is less torque due to slip) up to 60 Hz.

NOTE: If this parameter is changed while the drive is running, the new value will not take effect until

the drive is stopped.

P28 FIXED BOOST

FIXED BOOST increases starting torque by increasing the output voltage when operating below half of

the base frequency, which increases the V/Hz ratio (see diagram below). For better out-of-the-box

performance, SM-Plus

™

drives are shipped with a setting that is different from the factory default, as

seen in the table below. If a factory reset is performed, FIXED BOOST will default to 1.0%.

FACTORY FACTORY

HP SETTING HP SETTING

0.25 -1 5.3 % 7.5 2.7 %

1.5 4.4 % 10 2.4 %

2 4.4 % 15 2.2 %

3 3.6 % 20 2.0 %

5 3.0 % 25 1.8 %