Hardinge KL-1

[pauly45]

I hear what you are saying about changing the motor, but the motor in the Hardinge lathe is a highly balanced motor, with two sets of windings for a low and high speed so there is just no sense in removing it and changing it for an inferior motor. Plus, the cost to convert using a transformer and VFD's isn't really that large.

Yes, I may be going over the top with 3 VFD's, but this is a project and a challenge.
I've also seen another 'mycnc' contributors hardinge powered this way, and it's impressive. It also makes sense to me as it retains all the original lathe controls.


Some calculations for the transformer :

The motor is 1.5hp which is 1.1kW (1hp = 0.746kW)
Assuming a 90% efficiency of the VFD then 1.1kW/0.9 = 1.22kW required.
Approximately, Transformer kVA = 1.22kW/0.7 = 1.74kVA.

However, this rating would be for heavy, continuous operation, which I'm just not going to do, so I have gone for a 1.5kVA Autowound Transformer. This will keep costs and physical size of the transformer down to an acceptable level.
An isolation transformer will be bigger and more expensive, and I've been told it's just not necessary.

This will step me up from 240V to 415V, then this will connect into two of the connections of a 3 phase input VFD.
I'll common up two of the inputs to share the loading on one AC cycle a bit more across the VFD rectifier diodes.