The VAC-III is one of Okuma’s most popular conventional spindle drive units. With 3 powerful models, the VAC-III comes in a 6kW, 11kW and 22kW capacity. The VAC-III boasts quick, clean control signal communication through its fiber optic connection to the NC.  This fiber optic connection allows for faster transmission of data and immunity from electromagnetic interference on the signals. Standard copper cables are used for encoder, resolver and winding select connections. Easy access fuse holders on the edge of the power board allow for the ability to quickly check for and replace blown fuses. With distinct, bright LEDs on the control board, the VAC-III provides easy to read LED indication for alarms and operation status.

A pair of large seven segment LEDs gives the user clear alarm and operation status readout in conjunction with the standard LED indicators. This alarm data is also transferred to the NC which displays the alarm name and alarm data on the main screen.


Some common errors and alarms for VAC-III drives include alarm 10 (motor cable overcurrent) or alarm 14 (input voltage drop).

In the event of an alarm 10 overcurrent, double check all motor cables and wiring. Check motor and cable insulation and look for any short-circuited, broken or grounded connections. A megger is needed to properly check motor and cable insulation. For detailed videos on how to use a megger to check for deteriorated or failed insulation, check out our videos online.

If alarm 14 is displayed, verify that the incoming power at the R, S, T terminals are within the allowable range of 170VAC to 242VAC. With the power off, double check all fuses to see if any have blown. Finally, make sure that the ‘between-board’ connectors are properly seated and making good connection.

An additional alarm, alarm 37, indicates a pulse generator feedback fault. This error shows that the VAC drive is not reading the output signal from the pulse generator. This issue may be caused by a failure on the drive’s control board or with a failing pulse generator unit.

For additional troubleshooting advice or for inquiry on repair or purchase of the VAC-III spindle drive, please give us a call at (847)-465-9060.

Tags : Okuma, Spindle Drives, VAC-III, Okuma Alarms & Failures