Rockwell Automation 20A PowerFlex 70EC/700VC - Manual (Page 98)

94 Shear Pin
Shear Pin As a default, the drive will fold back when the output current exceeds the current
limit level. However, the shear pin feature can be used to instantly fault the drive
when output current exceeds a programmed amount. Additionally, the drive can be
programmed to ignore this condition during acceleration and deceleration which
often requires current that would otherwise cause a shear pin fault. Also, the
condition can be completely ignored for a programmable amount of time. There are
situations where a fast acceleration of the motor will cause the drive to output
current to the motor near or at the current limit value for shear pin and fault the
drive while in acceleration. To avoid this condition set bit 11 in parameter 238 to
“1”. Using bit 11 in parameter 238 without bit 4 being “1” has no effect. In addition
a shear pin time needs to be set in parameter 189. This will allow current limit for
[shear pin time] before faulting the drive.
A unique fault (Shear Pin, F63) will be generated if the function is activated and the
condition occurs.
Configuration
•
P238 [Fault Config 1], bit 4 (Shear Pin) = “1” - this enables the shear pin fault).
•
P238 [Fault Config 1], bit 11 (ShearPNo Acc) = “1” - this enables the ignore
feature during accelerations.
•
P189 [Shear Pin Time] = desired amount of time to ignore the shear pin
condition before a fault occurs (e.g. 0.5 sec).
•
P147 [Current Lmt Sel] = “Cur Lim Val” - specifies the source of the current
limit level. Can also com from analog inputs.
•
P148 [Current Lmt Val] = desired value for current limit and shear pin fault (e.g.
15 amps).
Application Example
By programming the Shear Pin feature, the drive will fault, stopping the excess torque before
mechanical damage occurs.
Skip Frequency Figure 15 Skip Frequency
70EC 700VC 700H
✔ ✔
70EC 700VC 700H
✔ ✔
Frequency
Time
(A) (A)
(B) (B)
Skip Frequency
Command
Frequency
Drive Output
Frequency
Skip + 1/2 Band
Skip – 1/2 Band
35 Hz
30 Hz
25 Hz