PM 3520B VFD powered when plugged in?

[Alan Heffernan]

My Powermatic 3520B is lit up when it is plugged in. The digital rpm indicator is shining away. This makes me think the VFD is powered and ready to go as well? I must admit that I haven't located the wiring diagram yet and thought I would ask here.
The concern was raised from a buddy of mine who has had some VFDs toasted in a power blip during a storm. He highly recommended that I disconnect the machine when it is not in use. He believes VFDs are quite sensitive to voltage spikes.

I am thinking of mounting a master switch/disconnect vs. unplugging it all the time. I did this for a PM drill press that shines all the time and it is much more convenient to throw a switch vs. unplugging it and then plugging it in when needed.

Two questions:
1. Is the VFD hot when the machine is plugged in?
2. Do you unplug/disconnect yours when it is not in use?

Thanks for the help,
Alan

[John Conklin]

I've always heard that they are susceptible to power spikes too and unplug mine when not in use. Better safe than buying a new one, I figure.

[John K Jordan]

Yes, it is always on. Yes, I have a disconnect switch in a box stuck to the end of the lathe with magnets.

i don't like to disconnect anything repeatedly by pulling the plug since it will eventually wear the plug and socket. If you do, a light coating of dielectric grease on the prongs will lubricate and prolong life.

The VFD on one of my Jet 1642 lathes died, maybe from a power surge, I don't know. I have it switched now too.

The big red Stop button on the front of these lathes does NOT switch off the VFD but only switches low voltage control lines, 10 volts. Doc Green has articles on the 3520 electronics on his web site which applies to VFDs in general.

Edit: look under the PM electrical for explanation and a circuit diagram. His other articles also have a wealth of information.
http://www.docgreenwoodturner.com/articles.html

JKJ

[Alan Heffernan]

Yes, it is always on. Yes, I have a disconnect switch in a box stuck to the end of the lathe with magnets.

i don't like to disconnect anything repeatedly by pulling the plug since it will eventually wear the plug and socket. If you do, a light coating of dielectric grease on the prongs will lubricate and prolong life.

The VFD on one of my Jet 1642 lathes died, maybe from a power surge, I don't know. I have it switched now too.

The big red Stop button on the front of these lathes does NOT switch off the VFD but only switches low voltage control lines, 10 volts. Doc Green has articles on the 3520 electronics on his web site which applies to VFDs in general.

Edit: look under the PM electrical for explanation and a circuit diagram. His other articles also have a wealth of information.
http://www.docgreenwoodturner.com/articles.html

JKJ

Amen to the constant unplugging.

Thanks for the link to the electrical schematic.

[David Gilbert]

I purchased a seven year old 3520b and I believe that it had been continuously plugged in for all seven of those years. The VFD controller worked fine except that some of the display elements had burnt out which makes reading the numbers difficult if not impossible. This hasn't caused any problems except when I wanted to lower the lathe's low speed from 52 to 26 so I can sand my warped bowls. Moving through the different registers to enter the password and then entering the four new values was tedious but successfully completed. Having the lower speed is essential and used all the time. It hasn't caused any problems with the lathe.

Not to forget the original topic of this thread, I unplug my lathe when thunder storms are predicted or when I will be away from the lathe for several days. By the way at Arrowmont, all their lathes are left plugged in 24/7/365 and Tennessee has a lot more thunder and lightning than we do in western New York.

Cheers,
David

[John K Jordan]

Not to forget the original topic of this thread, I unplug my lathe when thunder storms are predicted or when I will be away from the lathe for several days. By the way at Arrowmont, all their lathes are left plugged in 24/7/365 and Tennessee has a lot more thunder and lightning than we do in western New York.


Most places leave them plugged in. What we don't know is if their main power is protected against surges. Many commercial places are.

You can add a service entrance "whole house" surge protector at the electrical panel or even outside which will protect from many damaging surges. I bought one at a local electrical supply house and the clerk told me the local city electrical department will install them for free for anyone who asks. You can install it yourself if you can work safely inside the panel. Mine has a light that indicates its health.

I'm certainly not endorsing this one but here is an example. I suspect we would all be better off putting one on our house and on our shop power:
https://www.amazon.com/Panamax-Whole-Home-Service-Entrance-Protector/dp/B00271MIV4

JKJ

[Doug Rasmussen]

I'm not doubting the situation is as described, power on anytime it's plugged in.

What I find hard to believe is a company like Powermatic would do this. I wonder what an OSHA inspector would say about this if it was in a commercial shop

[David Delo]

I have a Delta Surge Capacitor Model CA-302R at the panel to protect the house & shop but I still unplug the lathe. Just a procedure habit along with turning the rpm dial to zero and cleaning up after each use. YMMV.

[Malcolm McLeod]

I'm not doubting the situation is as described, power on anytime it's plugged in.

What I find hard to believe is a company like Powermatic would do this. I wonder what an OSHA inspector would say about this if it was in a commercial shop

I am not an OSHA inspector, but a VFD with power applied (plugged into un-switched outlet) is basically the same thing as a motor starter with power applied, or a circuit breaker with power applied. The input is hot all the time. The output side of the device is only hot when the appropriate actions tell it to be so.

You can either build a switched outlet and plug the tool into it, or hard-wire the tool to a switch. But that said, I've seen industrial VFDs that have been under power for years with no issues.

[Doug W Swanson]

I have my 3520 plugged into a switched outlet for this very reason. Makes things easier in the long run....

[Josh Bowman]

I have protected main, but that's not enough for me, since I've had my share of surges. So I put single throw triple pole switches on both my lathes. Results are the same as unplugging it. You can see the disconnect I put on on the headstock leg of my PM3520.

[Larry Copas]

I copied my answer from another thread that asked a similar question.

It seems on most lathes equipped with a VFD the switch on the lathe only stops the rotation and does nothing to open the power leads. I know on my General after hitting the stop button I hear the fan in the VFD continue to run for about 10 seconds.

To actually open the power leads I installed a simple fused disconnect. Since I knew I would forget to shut it down at the end of a session I installed a green LED to attract my attention. I got four of the LED's on eBay for $5 with free shipping. BTW my lathe is 230V so I bought 230V LED's to kiss.

340372

[Alan Heffernan]

Thanks to all for the feedback.

I decided to put in a master switch. Here's what I will mount on the wall near the lathe. Simple solution - rated for 2 hp and 220v. The 3520B has a pilot light showing when power is on, the lathe speed indicator lights up.

I ordered this switch through my "Prime" supplier and it should be in hand late tomorrow. I already have the mounting box along with the conduit and fittings.

340382

[Wes Thom]

I've always heard that they are susceptible to power spikes too and unplug mine when not in use. Better safe than buying a new one, I figure.
If that one item needs protection, then everything needs that protection. What most needs protection if a surge exists? Smoke detectors. Do you also unplug a refrigerator, furnace, air conditioner, all phones, clocks, all computers, and every LED and CFL bulb? Effective protection means nobody even knew a surge (ie direct lightning strike) existed.

A millimeters gap in a switch or fuse will do what to something that is not 'blocked' by three miles of sky. Protection never worked by 'blocking' a surge. Protection was always about the path taken by a surge - as demonstrated by Franklin in 1752.

Lightning seeks earth ground. A best connection to earth was wood in a church steeple. Steeple destroyed. Franklin simply connected that electricity to earth on a path that was not destructive - a properly earthed lightning rod. Then hundreds of thousands of joules dissipated harmlessly in earth - not destructively in a steeple.

Lightning seeks earth ground. A best connection to earth was a strike to utility wires far down the street incoming to every household appliance. Appliance destroyed. Even 100 years ago, that electricity was connected to earth on a path that was not destructive - a properly earthed 'whole house' type protector. Then hundreds of thousands of joules dissipated harmlessly in earth. Then superior protection already inside every appliance and machine is not overwhelmed.

This is critical. That connection to earth must be low impedance (ie less than 10 foot). And to a 'single point earth ground'. Because a protector (like a lightning rod) is only as effective as its earth ground.

That is your 'secondary' protection layer. Each protection layer is defined only by earth ground. Also inspect your 'primary' protection layer. Pictures (not text) after the expression "open vertical grounds" apply. Many have woefully compromised protection especially due to copper thieves.

Nothing 'blocks' destructive surges. Protection must exist every second of every year. Gaps in switches or fuses are easily blown through by a surge. Protection is defined by how that current connects to earth. A low impedance (ie wire has no sharp bends) connection is critical. A protector is only as effective as its earth ground. And not just any earth ground. Water pipes are even insufficient. Single point earth ground. Effective protection is mostly about an earth ground - not by protectors and not by human intervention.

Another destructive path to earth is via a concrete floor beneath a machine. Concrete is an electrical conductor. Just another reason why a surge must be earthed BEFORE entering a building. By lightning rods or a 'whole house' solution.

[Alan Heffernan]

If that one item needs protection, then everything needs that protection. What most needs protection if a surge exists? Smoke detectors. Do you also unplug a refrigerator, furnace, air conditioner, all phones, clocks, all computers, and every LED and CFL bulb? Effective protection means nobody even knew a surge (ie direct lightning strike) existed.

A millimeters gap in a switch or fuse will do what to something that is not 'blocked' by three miles of sky. Protection never worked by 'blocking' a surge. Protection was always about the path taken by a surge - as demonstrated by Franklin in 1752.

Lightning seeks earth ground. A best connection to earth was wood in a church steeple. Steeple destroyed. Franklin simply connected that electricity to earth on a path that was not destructive - a properly earthed lightning rod. Then hundreds of thousands of joules dissipated harmlessly in earth - not destructively in a steeple.

Lightning seeks earth ground. A best connection to earth was a strike to utility wires far down the street incoming to every household appliance. Appliance destroyed. Even 100 years ago, that electricity was connected to earth on a path that was not destructive - a properly earthed 'whole house' type protector. Then hundreds of thousands of joules dissipated harmlessly in earth. Then superior protection already inside every appliance and machine is not overwhelmed.

This is critical. That connection to earth must be low impedance (ie less than 10 foot). And to a 'single point earth ground'. Because a protector (like a lightning rod) is only as effective as its earth ground.

That is your 'secondary' protection layer. Each protection layer is defined only by earth ground. Also inspect your 'primary' protection layer. Pictures (not text) after the expression "open vertical grounds" apply. Many have woefully compromised protection especially due to copper thieves.

Nothing 'blocks' destructive surges. Protection must exist every second of every year. Gaps in switches or fuses are easily blown through by a surge. Protection is defined by how that current connects to earth. A low impedance (ie wire has no sharp bends) connection is critical. A protector is only as effective as its earth ground. And not just any earth ground. Water pipes are even insufficient. Single point earth ground. Effective protection is mostly about an earth ground - not by protectors and not by human intervention.

Another destructive path to earth is via a concrete floor beneath a machine. Concrete is an electrical conductor. Just another reason why a surge must be earthed BEFORE entering a building. By lightning rods or a 'whole house' solution.

Thanks for the history lesson and the dissertation on lightning.

Back to the question - if you have a PM3520B, do you unplug/disconnect yours when it is not in use?

[John K Jordan]

If that one item needs protection, then everything needs that protection.


This is true about destructive, high-energy surges from a local lightning strike. Nothing practical will stop it once it enters the building. I believe the surge protectors will protect from some of the smaller surges, those that will not jump the gap but might still damage an electronic device like a VFD.


Alan, As for unplugging lathes with a VFD including the PM3520, I forgot add to the count: the guy I bought my used 3520b from always disconnected it from the power lines when not in use.

JKJ

[Joe Kaufman]

In the event of an electrical storm, it is probably better to open the ground connection to the machine also, therefore unplug. A switch is cleaner electrically than plugging and unplugging the cord so long term operation, a switch also has merit.

[Michael Schneider]

Interesting article of the care and feeding of a VFD
http://machinedesign.com/motorsdrives/feed-your-vfd-right-power


It was interesting to read the section on not power cycling the VFD more that once every 2 minutes. I alway unplug, wait a couple of minutes for the capacitors to discharge, then plug back in.


"Do not cycle the input power more than once every two minutes. In fact, drive manuals specifically warn that switching a drive off and on without waiting two to three minutes is detrimental: Applying input power more quickly causes a buildup of voltage in the input pre-charge circuit, and eventually burns it out. Why? Here, the dc bus capacitors don't have enough time to discharge, and the input circuit needs time to stabilize. Otherwise, additional input can damage the charge relay circuit, or at the very least, blow the input fuses or circuit breaker.
In other words, the pre-charge circuit allows a certain time limit for the inrush limiter to send current through to charge the dc bus capacitors. The inrush limiter resistance changes with temperature. The hotter the limiter gets, the lower the resistance value. When that pre-charge time ends, the relay cuts off and the capacitors hold the charge. When the drive is powered down, this voltage bleeds off through resistors in the discharge circuit. Power reapplied too quickly meets an inrush limiter that hasn't had time to cool down to an acceptable resistance level, so the current will be higher, and consequently, could blow the fuses or possibly damage the pre-charge circuit."

[John K Jordan]

It was interesting to read the section on not power cycling the VFD more that once every 2 minutes. I alway unplug, wait a couple of minutes for the capacitors to discharge, then plug back in.


Michael, thanks for that info, it is interesting. It might explain why the VFD in one of my Jet 1642 lathes died. It got flaky when I lived in a city where the power was interrupted often and then finally died. I kept the Jet plugged in all the time. I remember many times over the years when the power went out then came back on in less than 2 minutes, sometimes, several times in a row. (Funny that we had way more trouble with power in the city than on the farm here out in the country!)

The potential for unintended power cycling is probably as good a reason to disconnect power as the threat of power surges.

JKJ