Hardinge KL-1

[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

[pauly45]

Everything seems to be fine with the main motor. No nasty noises.
The VFD indicates about 2A when running.

Now to re-do the wiring.

I wanted to use as many of the original switches and contactors as possible, but knew that most of the wiring would have to go.

The control box wiring looked like this when purchased:



I'll keep the original high/low speed switch, main power switch, and as many of the contactors that I need.
Wiring from the terminal blocks at the bottom will stay, and I'll just wire the new control into them

So, here is some of the top half removed. The new transformer mounted, together with two of the VFD's.
The top grey one is the FR-D740 for the main motor, the white one to the right is for the speed change motor.

[pauly45]

Well, the wiring is pretty much finished now.

There's a little tidying that's needed, but here is the control panel.
The original 'green' power on, and forward/reverse switches do the same job as before.
Theres a red indicator for the 240V_ac being available.
The small LED next to the forward/reverse switch is off when the main motor VFD is at 0Hz.
Theres a key switch to really make sure it can't be turned on accidentally.

I've put two fans in the front to get blow some air circulation in through the VFD's, and when I can get to the rear, I'll put two more in to suck air out of the cabinet.


And the cabinet wiring.



I think it functions quite well. I like the fact that I don't have to fiddle around with the vfd controls to work it, and overall, the lathe feels just like it would if powered from 3 phase.
The original lathe forward/reverse, high/low speed, faster/slower and pump on/auto switches all work the vfd's
The only thing I have yet to sort out is the brake.

A small niggle is that it is possible to have the high and low speed contactors trying to be on at the same time if I move the lever from high to low before the vfd has reached 0Hz.
It's not a big problem as they are interlocked so they cannot actually be on at the same time, but they buzz a bit if I don't wait until the motor has stopped.
Something to figure out later I think !

As soon as I can figure out how to save the circuit diagrams in sufficient detail, I will post them up.

[pauly45]

In the last photo of the previous post, in the bottom left is the inductor that's between the 240V_ac to 415V_ac transformer and the main motor vfd.

Based on the modelling, it's wound to be approximately 11mH.

The laminations are from a microwave oven transformer!
These transformers are great since they are an E-I configuration, welded together.
The weld can be carefully ground away to open up the laminations and get the original windings off. And the new ones on.

It is now gapped slightly, and held together with the clamps.

Unfortunately, it makes no noticable difference! Which I guess is good.
Only if I was to measure the current should I see a reduction in the peaks, otherwise I have to assume it is doing what the modelling says it should do...

[pauly45]

I've also decided upon some paint for the bits of the lathe I have cleaned up.

Trials of various paints seems to show this stands up well to the cutting fluid I have.

The paint is P383 Hi-Gloss one pack Polyurethane, manufactured by NEXA Autocolor.
I've gone for "Gun Metal Grey", code 2758.
Costs £26 per litre.

It's brushable, but can be sprayed if needed. although it brushes very nicely.

I'll let you know how it stands up to use!!

The collet closer is the first non-electrical bit I cleaned up and painted with the polyurethane.
From these grubby bits:


To this:

[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.

[pauly45]

I don't know how clear these are going to be as there is a lot of detail on them, but here goes.
These are the circuit diagrams for the lathe.
They are split into 'Power', 'Main Motor and Speed Change', and 'Coolant Pump and Carriage Feed'