[Newbie] Troubleshooting a KBVF24D VF drive

[Screen Guy]

Have a puzzling "no go" on my KBVF24D variable frequency drive. After overloading my lathe motor, everything stopped. Looking at the LEDs, the diagnostic seems to indicate short circuit. I isolated the lathe motor and my other machine and still, short circuit signal. Tried removing the auto/manual jumper and bridging it with a momentary contact switch as the manual indicates for reset and still no joy. I'm real charry of the capacitors in this thing. Is anyone familiar with this drive and can recommend a safe trouble shooting procedure? Any idea how long the capacitors might hold a charge in case I must ship it back for repairs? Thanks for any suggestions.

 

[cathead]

Get out the volt-ohm meter and do a little testing for volts across the capacitors. Some units have a bleeder resistor across the
capacitor to drain off any voltage, some however do not. You could test your power transistors using ohms scale to determine
if the transistors may have shorted. Also, a resistor across the caps to deplete them if you feel the need, some folks
just short them out but probably is not the recommended thing to do. A charged electrolytic with no bleeder resistor can hold a
charge for days. If you are going to work on it, discharge the caps first.

 

[Screen Guy]

Sounds like I may be in over my head here. Thanks for the advice Cathead. May consult an electrician.

 

[Bob Korves]

I isolated the lathe motor and my other machine and still, short circuit signal.

Did you have more than one motor hooked up to the VFD? From your first post, it sounds like it.

 

[Screen Guy]

not at the same time. One is isolated by a switch, the other by a 4 prong plug, so as a mortal, I can only run one machine at a time.

 

[Bob Korves]

not at the same time. One is isolated by a switch, the other by a 4 prong plug, so as a mortal, I can only run one machine at a time.

Be careful. You can have problems, sometimes big problems, when running more than one motor off of a single VFD. It is a best practice to have hard wiring from the single VFD to the single motor. There may be exceptions, but should be approached with care and understanding.

 

[mksj]

Did you follow the instructions for the current overload reset? The VFD capacitors should be discharged in about 5 minutes after the VFD is turned off, almost all have some means to drain the charge from the DC supply caps. If the direction below are followed and you still see a short, you might try it with no motor connected. If it still shows a short then something probably failed in the VFD, there does not seem to be any other reset or fusable device on the board. I would also call KB Electronics, they have very good tech. support.

11.3 Restarting the Drive After an I2 t Fault Has Cleared – The drive can be restarted after an I2 tthe Fault has cleared by any of the following methods.
Note: If an I2t Fault occurs, the motor may be overloaded. Check the motor current with an AC RMS responding ammeter. Also, the CL setting may be set too low. See Section 13.7, on page 42.

1 Disconnect and reconnect the AC power (approximately 15 seconds). The “ST” LED must change from quick flashing red to flashing red/yellow.
2 Set the Main Speed Potentiometer to zero (fully counterclockwise). Note: In order to be able to reset the drive by setting the Main Speed Potentiometer to zero, it is necessary to have the MIN Trimpot set to zero (fully counterclockwise).
3 Open and close the Enable switch or contact. See Section 9.8, on page 35.

 

[Screen Guy]

I'll try the potentiometer reset next and let you know the results. Thanks for the info on the capacitors. I agree, I see no other fuse or reset on the board or in the manual other than what you reference.