Electrical question about VFD.....

[odie]

In my Minarik manual, it says that damage to the unit is possible if you return to zero rpm by using the potentiometer, and not use the brake. It doesn't say what kind of damage is possible, and that information is what I'm asking for.

Because I have unscrewed a turning, or two from the spindle by solely using the brake, I'm in the habit of first reducing the rpm by using the potentiometer, waiting a second or two, and then hitting the brake. Once in awhile I forget to use the brake, and this is the condition the Minarik manual warns about. So far, I've never seen any problems, but I'm wondering just what kind of damage to the unit is possible.....?


thanks.....

-----odie-----

 

[Don Wattenhofer]

Look in the manual for that drive see if there is a deceleration setting then all it will take is to increase the deceleration time then remark that label to "run - Stop".
That company was big into DC motor speed controllers, but they may have sold VFD's so look at the motor nameplate you may have a DC motor and if it is then there probably will not be a decel setting. If in doubt take a picture of the connection diagram in the manual and post it here.

 

[odie]

Look in the manual for that drive see if there is a deceleration setting then all it will take is to increase the deceleration time then remark that label to "run - Stop".
That company was big into DC motor speed controllers, but they may have sold VFD's so look at the motor nameplate you may have a DC motor and if it is then there probably will not be a decel setting. If in doubt take a picture of the connection diagram in the manual and post it here.

Yes, for sure.....it is a DC motor.

Thanks Don.....

-----odie-----

Still interested to know just what damage is possible, if the potentiometer, and not the brake is used.....?????

 

[Bill Boehme]

Don is right, it's not a VFD, it is simply a variable voltage driver for the DC motor. The issue about possible damage would be caused by turning the speed control to zero rapidly. In that scenario, there is a lot of kinetic energy in the motor's magnetic field and now the motor becomes a generator dumping that energy back into the controller and possibly causing voltages or currents that exceed the maximum rating of some of the controller's components. I assume that the brake is dumping that energy into a power resistor where it is safely dissipated as heat.

My suggestion would be to very slowly turn the speed control pot to zero. That should be sufficient to prevent any kind of damage. I imagine that your current practice is OK since you have been doing it for many years and haven't broken anything.

 

[James Seyfried]

I have a VFD question too. Last month the VFD on my Powermatic 3520B was acting a little flaky. Possibly caused by me blowing off wood chips by the controller? I had to reset it several times from it's reset button. I had typically used the red stop button but with concerns that it wouldn't turn back on I started turning speed control pot down. Whatever was going on seems to have cleared up, (that's what makes me think I caused the problem) but it has me wondering if it is easier on the VFD to turn it down or to use the stop button. Or maybe it doesn't make much difference. Anyone have some thoughts, experience, or opinions on which is better for longevity? Maybe this has been asked before, I did search the forum an answer though.

 

[Dean Center]

An electrical engineer and fellow turner friend said to use the stop button. While there is some suggestion leaving the lathe on with zero speed can cause VFD damage, this was not his reasoning. His thought was that wearing out the red button is a cheaper fix than wearing out the potentiometer. I suspect you'll get more sophisticated responses from the very knowledgeable folks on the forum, but this was a persuasive answer for the Cheapskate Turners Association.

 

[Don Wattenhofer]

An electrical engineer and fellow turner friend said to use the stop button. While there is some suggestion leaving the lathe on with zero speed can cause VFD damage, this was not his reasoning. His thought was that wearing out the red button is a cheaper fix than wearing out the potentiometer. I suspect you'll get more sophisticated responses from the very knowledgeable folks on the forum, but this was a persuasive answer for the Cheapskate Turners Association.

This thread was mistakenly called as being about problems with VFD's however his motor is DC therefore his controller is not a VFD so if you have questions about VFD's (Variable Frequency Drive that only work with 3 phase AC induction motors) you could start a new thread.

 

[Dave Landers]

I have a VFD question too. Last month the VFD on my Powermatic 3520B was acting a little flaky. Possibly caused by me blowing off wood chips by the controller? I had to reset it several times from it's reset button. I had typically used the red stop button but with concerns that it wouldn't turn back on I started turning speed control pot down.

Two things come to mind. First is that the switches PM uses are on the cheap side, especially given where they're mounted in the headstock with no dust control. The start/stop switch has a tendency to stick in the stop position. The big red button pulls a tiny little piece of plastic that then relies on a spring to engage the micro-switch. I have to lube mine (dry graphite) every few months (and mine is mounted in a dust-resistant box).

If you had to reset the VFD due to a VFD fault (something unusual on the display) then that's different - I've only had to do that when I bog down the motor excessively. But the act of walking around to hitting the reset could also have just happened to give the on/off switch time to start working.

 

[Bill Boehme]

I have a VFD question too. Last month the VFD on my Powermatic 3520B was acting a little flaky.

"Flaky behavior" (a highly technical term) is usually the result of "flaky parts" used in the headstock. The switches and potentiometer used by Powermatic are not the best so the likely cause of flakiness is noisy switch contacts or worn wiper path on carbon film potentiometer. You can get better quality parts for less $$ if you don't buy them from Powermatic. A much better potentiometer uses conductive plastic rather than carbon film. look for switches that have environmentally sealed contacts.