VFD settings

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hobgobbln
Posts: 177
Joined: Tue Apr 13, 2010 7:31 pm
Location: Palmer, Ma

VFD settings

Post by hobgobbln » Tue Dec 02, 2014 11:07 pm

Last week I swapped out the motor on my lathe for a 3 phase and a TECO VFD. Now I am trying to get it tuned up but I've never used a VFD before. The number of settings and terrible documentation is making it tough.

Running Mach3 off the parallel port, into a Gecko G540. I've also got an index pulse card up and running so I know the actual RPM it's spinning.

After some hair pulling, I can start and stop the motor and vary its speed (funny story for another day). Problem is the requested spindle speed and the actual spindle speed are way off. I setup the pulley for 0 to 1000 RPM for testing. I charted the requested speed, the actual speed, the frequency the VFD was using and the 0 to 10v voltage coming into the VFD. I'm getting a spike in the lower rpm and the rest are higher than they should be. For the sake of testing I changed the pulley speeds to 0 to 3300 rpm, measured everything again and got the same spike. I don't see any way of altering Mach3 to fix it.

Would messing with the VFD bias or gain help to bring things closer to being linear? Any other settings/thoughts/suggestions? It's driving me nuts.

Thanks,
Griz
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vfd_curve.JPG

hobgobbln
Posts: 177
Joined: Tue Apr 13, 2010 7:31 pm
Location: Palmer, Ma

Re: VFD settings

Post by hobgobbln » Tue Dec 02, 2014 11:10 pm

I just noticed the scale on the bottom of the chart says 1-10%. It's actually 10-100%. Seems my graphing needs some work too :lol:

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mfletch
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Re: VFD settings

Post by mfletch » Wed Dec 03, 2014 1:14 pm

What frequency is the VFD set on what Hertz if your normal Hertz is 50 and the VFD it showing 60 the motor will run faster

Im not sure where your located but here in the UK were set at 50Hertz so when the VFD is on 50 the motor should be running at its max speed

hobgobbln
Posts: 177
Joined: Tue Apr 13, 2010 7:31 pm
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Re: VFD settings

Post by hobgobbln » Wed Dec 03, 2014 7:27 pm

The VFD is set to a max frequency of 80hz at the moment. I originally left it at the stock 60hz and had the same issue with linearity.

Even if I can't get rid of the bump in the graph I would like to figure out how to adjust it so the majority of it is as close as possible. It seems pretty linear after the 40% mark. Can anybody explain what effect changes to the gain or bias has or if there is a different setting I should look for?

Griz

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Dave_C
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Re: VFD settings

Post by Dave_C » Thu Dec 04, 2014 10:01 am

Griz,

I'm running a similar setup with my 2hp 3 phase motor with Mach 3. I had the same issue when I first fired it up and it took me quite a bit of time to figure out the issue.

1st, I set the drive to run the motor at 100% when it was at 60 Hz as my motor isn't rated to over speed!

Then I had to rework my "gear" chart in Mach 3 so the minimum and maximum speeds lined up with the minimum and maximum speeds of that gear. IE: when running in gear #2 of the chart I can hit 1,000 RPM at 60Hz and with the drive set to a minimum speed of 15% (9 Hz) I should get 150 RPM . So my max setting is 1,000 and my minimum is 150.

Using a 0-10 VDC output to the drive, I get a pretty good curve but it still does not track the requested speed exactly and I'm told that it will not and can not track exactly.

If you change over to a PID controlled setup, and you know how to tune the PID, you can get it to track. With a lathe, it just isn't worth the trouble to make it track exactly to the requested speed.

There is a lot of discussion on the Artsoft "Mach 3" forum and even there they don't all agree on how to do it or what it does or should do.

Now as far as setting gain and Bias, yes, I had to do that so that Mach 3 running at minimum speed could not take the drive below 15%. You can set a minimum output speed in Mach 3 setup as well but I found the Bias way to work better. My Drive manual actually had the example of how to do it and I've worked with drives for over 30 years so I understood most of it. (things get changed every day)

Good Luck,

Dave C.
I learn something new every day! Problem is I forget two.

hobgobbln
Posts: 177
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Location: Palmer, Ma

Re: VFD settings

Post by hobgobbln » Sat Dec 06, 2014 7:34 am

Thanks Dave. That gives me a general idea that I can work with.

Griz

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Dave_C
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Re: VFD settings

Post by Dave_C » Sat Dec 06, 2014 5:34 pm

Griz,

I got to thinking about the speed not tracking issue! One of the things I discovered while doing my setup was that no mater what speed I was in, the actual full speed was higher.

For example: I have 9 gear ranges on my lathe. #2 says 1,000 RPM but when I run the drive at full speed I see I get something close to 1,100 or there about.

So what I did was to put the lathe in each gear, set the drive to 100% speed and then write down the actual spindle speed that my optical encoder was reading for each gear. Then to come up with the minimum speed I multiplied the max speed times my 15% which is what I set my drive to for lowest speed. Some use 10% but that is pretty low for most motors. I like 15%.

Try that and see if you are closer to your requested speed as Mach 3 will ratio the requested speed for whatever gear range you are in based on what you put in this pulley table.

Hope that helps,

Dave C.
I learn something new every day! Problem is I forget two.

hobgobbln
Posts: 177
Joined: Tue Apr 13, 2010 7:31 pm
Location: Palmer, Ma

Re: VFD settings

Post by hobgobbln » Sat Dec 06, 2014 8:57 pm

I noticed the same thing when I swapped out my motor.

My highest speed is supposed to be 2400 rpm. Once I added my index pulse I noticed the true rpm was 2490 with my stock motor. After swapping out the motor for the 3 phase and VFD, 100%@60 Hz was giving me 2595. The weirdest part.......the stock motor was a 1725 rpm but the replacement is a 1700 rpm.

It looks like the bias setting is the best solution. I did find a diagram in the manual that sort of shows the effect of the bias settings and the effect of the gain setting which is confusing which is why I skipped over it to begin with. I'll mess with it and see how it goes. I just really wish people took the time to make the documentation clearer. We all need to start learning from scratch sometime.

Griz

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Dave_C
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Re: VFD settings

Post by Dave_C » Sat Dec 06, 2014 9:15 pm

Griz,

The Bias and Gain settings may be a little confusing but generally the Gain setting is used when you want the "Knob" on the drive to give speeds in both forward and reverse. You set the gain to 200% and at 0% you are in full reverse, at 100% you are stopped and at 200% you are full forward. I don't see that used in CNC setups unless you control the spindle by hand.

The Bias works differently and your manual should give some examples so that when Mach 3 is at 0 volts output you will be at your minimum speed. Then at 10 volts you will be at 100%.

I checked my spindle speeds a few minutes ago and I'm within 10 RPM of my requested speed so I'm happy!

I can look up my Bias setting if you need help coming up with the proper setting. Just let me know...

Dave C.
I learn something new every day! Problem is I forget two.

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