Renovating a Hardinge HLV-H

[BillTodd]

Here's the first draft of the new control circuit. I have avoided as much 'electronics' as possible (even to the point of using a relay as an inverter) to keep it as a set of simple black boxes.

It works as follows:

By default it powers on to the low speed setting with the Speed Select Relay's nc output engaging the 2ML contactor connecting the low speed windings to the VFD.

If the Speed Change Lever is moved left to the Slow position. A RUN signal is supplied to the VFD via the Speed Select relay and R1/C1 (more on these later). The VFD's 0Hz contact will close, switching the output of the Inverter relay to open. The VFD will ramp up the motor to full speed 480rpm (50Hz) in a few seconds.

Now If the Speed Change Lever is moved right to the Fast position. The Speed Select relay's no output is open so the RUN signal drops to OFF and the VFD ramps down to 0Hz (Stopped). When it reaches 0Hz the VFD's output contacts open forcing the Inverter relay's output to 24v. The 24v 0hz signal is used to change and latch the Speed Select relay to High speed. As the relay changes speed, R2 is taken to 24v, charging C2 in about a hundred milliseconds (to give time for the contactors to settle) and generating a new RUN signal to the VFD. (R4 discharges C1 via R1 ready for the next speed change)


If the Speed Change lever is then switched back to the Slow position, when the 24v 0Hz signal is generated, it is applied to R3 which disables the Speed Select relay's coil so switching it back to Slow.

If the Speed Change lever is centred (STOP) then the RUN signal is removed and the brake is applied. The previously selected speed is retained by the Speed Select relay.