“I'd rather regret the things that I have done than the things that I have not.”
― Lucille Ball

Monday, June 9, 2014

AC Drive for my bench drill press

The drill machine as is.
When we emigrated to the Philippines we also moved our household goods and personal effects. One such item was the bench drill press of my late father.

I didn't realize that the electric motor was a 3-phase motor, and I was sure that it would be difficult/expensive to get 3-phase connection to our property in the Philippines. The solution I had in mind was to use our generator - also included in our household - as this one has three phase output.

However, when I tried this out some years ago, it turned out that the generator had not enough power to drive the motor when a large drill was used. So I was planning to replace the motor by a single phase equivalent AC motor, if available.

A couple of weeks ago I did some research on the Internet for a 3-phase solution before buying another motor and found two different solutions on Youtube.

The first one was to feed one coil of a delta configured 3-phase motor with the mains and adding a large capacitor from one of the two connections to the remaining point of the delta, see the sketch.

I tried it out and it worked. You need a capacitor of 8uF per HP of motor power. I didn't try it with heavy load, but it seems to work, although there is some power loss.

The capacitor feeds the top with a current that is out of phase compared to the mains and hence makes it a 3-phase solution.
I am not sure if this trick works with a star configured motor. The one in my drill machine is a 2-speed motor, for low speed it is configured as a Delta for high speed as a Star, or sometimes called a Y.

The other solution is much more sophisticated. It's an AC Drive , it has a 1-phase input and a 3-phase output with variable frequency. Hence this device is also called a Variable Frequency Drive or VFD. I decided to go for the second option and ordered 2 AC Drives in the US from AutomationDirect.com. The second one is for a Lathe that I want to build. More about it in another post.


The advantage of the AC Drive that I ordered, a GS2 model, is that you can remove the front panel and operate the drive remotely. It has a small potentiometer which is used to vary the speed, and the display shows you the frequency fed to the motor, or if you like the speed of the drill press in RPM. In the latter case you have to set some parameters in the drive.

There are ten groups of parameters which you can use to configure the drive and match it (fine tuning) with the motor to be driven. However you can just connect it to the motor and it will work.

So when the units arrived I just had to bold it onto the drill machine, which I had prepared already and connect the wires. I had removed the 2-speed switch and configured the motor for high speed (Y) and in stead of the switch mounted a bracket to the machine for the drive. I also added a lamp to illuminate the work peace on the drilling table.

See below some pictures.

The lamp and bracket are already mounted to the machine

GS2 bolted onto the bracket, wires connected, ready for operation
In operation, drilling for my Lathe


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