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

Sunday, May 17, 2015

Calibrating my Drill Press VFD (GS2)

VFD and RPM gauge give the same reading, calibration completed!
If you followed my posts on machining projects, you may remember this post, where I explained what I did to replace the pulley/belt variable speed mechanism by a Variable Frequency Drive (VFD) converter.

The model of my VFD is a GS2-21P0 (1 HP) from Automation Direct in the US.

In another  post  I shared with my readers my experience with ordering a "revolution per second (RPM) speed sensor and LCD display" or tacho-gauge in China, to measure the RPM's of a rotating shaft or spindle.

Hall sensor and tiny magnet on the chuck spindle pulley
I used this device to check the parameter - called k-factor, see below - that you have to enter in the VFD to let it display the drill chuck speed of the drill press, rather than the rotating speed of the driving motor shaft. This is of course what you want to know when drilling a hole.

So I attached the display temporarily to the drill press, as well as the magnetic Hall sensor close to the pulley on the spindle of the chuck and glued a tiny magnet on the pulley.

From the motor specs and the speed translation table on the drill press you can already calculate what the speed rate is between motor shaft and chuck spindle to calculate the k-factor.

Belt on position 3
Original speed settings table
The motor itself is a German AEG 3-phase motor from just after the war. It is a 50 Hz and 2-speed motor, which is done by switching from a 3-phase Delta configuration to a Star (or Y). See this post for Delta and Star configurations.

I had configured the motor as a Star after removing the Hi/Low speed switch. This results in the highest speed (1360 compared to 670 RPM). The belt is on position 3, see picture on the right.

So the drill press is configured as II-3 - see picture below - which gives a chuck spindle speed of 710 RPM when the motor is running at its maximum speed.

Hence the k-factor to be programmed in parameter P8.01 - see below manual page 4-5 - is defined as:
display value / output frequency or:
710 RPM / 50 Hz = 14.2
The problem was that - as turned out later when I contacted the customer service department of Automation Direct - for whatever reason on my VFD the decimal point is not displayed.

GS2 manual
The value range of P8.01 - see manual on the right - is defined as from 0.01 - 160.0, however on my display I get a range of 1 - 160.

By trial and error and comparing with my RPM display unit described above, I found already that a value of 155 for the k-factor gave the correct RPM value in the display of the VFD.

Given the fact that the decimal point is not working this would probably mean that 155 should be read as 15.5. And this is close to what I calculated before as 14.2.

So I am confident now that the RPM value displayed by the VFD is really the speed of the chuck spindle.

I want to add that I am very pleased with the speed and quality of the support desk of Automation Direct.

I am considering to replace the Hi/Low speed switch again, but this is another project.


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