- Joined
- Jul 2, 2014
- Messages
- 7,594
Thanks, Mark. I will look into the drive reactor. I made a workholding jig and used the grinder today to hone 4 sides (8 cutting edges) of a Sandvik carbide scraper blank, and it worked just fine. Looks like I need finer diamond than 600 to get the finish I really want. I will possibly make a cast iron or aluminum lap and charge the lap with diamond grit. There is well more than adequate power for what I am doing at 5 Hz, and the machine and motor seem to behave themselves well. Mark, you exactly addressed the potential issues I am interested in. Thanks!The insulation of the motor is at risk in an older motor but I do not see that the low speed presents any greater issue than would be seen at higher frequencies, the most significant factor is the carrier frequency. The pulse voltage is the same but the the pulse width would be smaller. Ideally you would want to stay around 2-3 Khz carrier frequency. The other consideration to tame the voltage spikes to an older motor is to use a drive reactor, these are placed between the VFD and the drive. They should to be sized for the maximum motor amperage and the operating voltage of the motor. Be careful and look up the specifications as many sold are for higher voltage motors. I would look at TCI KDR drive or output reactors. Probably recommend the KDRA28HC1 below even though it is rated for a 3Hp motor, a high Z will have a higher impedance to smooth spikes. I do not see a problem running the motor a low frequency but the Hp is greatly reduced, also at low speeds the motor over current may trip even with a low load. I had this issue when using VFDs for axis drives at below 10Hz.
https://transcoil.com/products/kdr-output-load-reactor/
High Z
KDRA25H, KDRA26H KDRA27H C1 denotes enclosure
https://www.ebay.com/itm/new-TCI-KD...amps-10-6-3ph-3-phase-protection/112477816224
Low Z
KDRA26L, KDRA27L or KDRA27L
https://www.ebay.com/itm/TCI-TRANS-COIL-KDRA26L-Surplus-New-not-in-factory-packaging/391875171464
https://www.ebay.com/itm/TCI-TRANS-COIL-KDRA28LC1-Surplus-New-In-factory-packaging/391750911526