Hardinge KL-1

[m_c]

Rotary converter effiency depends on how well they're built.

I built an ammeter into mine, and when sitting with no load the needle is barely above zero. The noise of the idler motor does annoy me, although that's probably more to do with it sitting on top of a bit plywood with minimal vibration damping!

I am however considering upgrading to a digital convertor, as the latest purchase is going to be far too much hassle to convert to single phase, and may be pushing the power limits of the current rotary.

[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.

[EddyCurrent]

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.

I've never heard of this done before. Devices inside the drive use a particular phase for synchronisation, that's why they specify which terminal to use if you are on single phase input, also a 3phase rectifier relies on phases being 'out of phase' for the return current but 2 of yours would be 'in phase'.
I hear what you are saying about the original motor but to be honest a modern 240v 3 phase motor is going to be just as good, the 240v drive will be cheaper and you won't need a transformer.

[bikepete]

"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."

Not sure if it's mine you saw but if so thanks! Mine's written up at

HLV conversion to VFD - circuit and pics

Six years on it's still working fine. If I were to do it again I'd probably somehow add an interlock to the speed change as various people suggested just to be on the safe side and also an external speed pot. But neither is likely to rise to the top of the projects list for a while.

[EddyCurrent]

"I've also seen another 'mycnc' contributors hardinge powered this way, and it's impressive.

But nowhere did I see two of the VFD inputs commoned up as suggested, also LowEnergyParticle seemed to make most sense. Other than being 'romantic' about the old machine I don't see the logic (no pun intended) in not making use of it's digits inputs for control and preset speeds.

[pauly45]

It's been suggested to me by a VFD expert at work that this method of using a step up transformer to power the VFD will result in the current in the secondary of the transformer having too high a peak current, and over time damaging the capacitors within the VFD.

He has done a circuit simulation based on some inductance measurements of the transformer I did which were:

0 to 240V shorted, Inductance and resistance measured across 0 to 415v
50Hz 1.107mH 1.59Ω
100Hz 1.094mH 1.59Ω
300Hz 1.090mH 1.612Ω
1kHz 1.0877mH 1.798Ω

0 to 415V shorted, Inductance and resistance measured across 0 to 240v
50Hz 365.2µH 0.571Ω
100Hz 365.1µH 0.572Ω
300Hz 365.1µH 0.578Ω
1kHz 364.3µH 0.641Ω

The set-up:



And these were the results:



The secondary current can be seen as the narrow/tall "sine" wave, peaking at 13.599A.
This is based on a 1.1kW power, and the transformer inductance measurments above.

It's been recommended that I add some extra inductance in the secondary of the transformer, and before the VFD input to smooth out the peaky "AC" and lower the peak current. This should stop me knocking out the capacitors in the VFD over time. I'll get to that inductor.


Meanwhile, I had got hold of some VFD's while I had been waiting for the lathe, so have ended up with:

For the main motor - a Mitsubishi FR-D740-036-EC. 1.5kW.
For the speed change and coolant pump - two Mitsubishi FR-S520S-0.2K-EC. 0.2kW

[pauly45]

So, the first job was to run up the motor to see if the lathe had any serious issues.

I lashed up a setup using a different motor to check it all out first before moving it over to the hardinge.

A simple setup - the transformer, VFD and a couple of switches to control forward and backwards.
Wired into the lathes original high-low speed switch so I could test forward and backards in both speeds.

[EddyCurrent]

Interesting analysis, similar thing applies if motor cables are very long, not a problem in your case.
Power Drive Services - Electric Motor Specialists - Three Phase Line Chokes

[Ulsterman]

Single phase to three phase conversion (3 phase converters)
What about going this way ----single to three phase convertor and leave the machine as is !

[pauly45]

Hi 'Ulsterman'
There are certainly many ways to achieve the same outcome, and this would be one of them.
It would probably have meant that I could have left all the wiring as is - but where is the fun in that !!

I also didn't want a second motor whirring away constantly, and as I'd need at least the 2.2kW, at £566+VAT+postage - pushing £700 for one of these, this is far more than what I've spent on some second hand VFD's and some wire!!
The 2.2kW version is also a 15A input, so couldn't run off a 13A plug top.