Random Shut Down of Laguna Revo 18/36

[Joe Frank Porter]

What awesome responses!!!

I've since turned some of my more common 12/13" drier bowls without the same problem occurring. If, however, I take some of these same 13" bowls and change the belt to the higher RPM range and max out the speed, they will sometimes do the same thing. This tells me that the VFD DELTA S1 is really just doing its job, as David and Bill explained above.

Since i harvest my own Walnut, Cherry, Hickory and Oak from my neighborhood when builders clear lots, I rough turn a lot of heavy wet hardwood. I probably have more occasions for my VFD to do correctly what it does than the average turner. I did email Laguna Customer service the info I posted for the thread. No reply yet.

A side note: Builders cannot just clear trees in the county I live in, Beaufort County SC. If a tree is more than 8" in Diameter as shown on the initial lot survey, you have to have a reason to take it out, such as necessary for placement of the house. If Its a special tree like a Live Oak, You have to mitigate. My neighborhood is covered with Live Oaks, here on the Coast.

Thanks to you all,
Joe Porter

[William C Rogers]

Can't offer anything on a fix, but I never turn off my 1836 to inspect work. I simply set the speed to zero. I do not use the panic switch at all and prior to unplugging it each day I turn the machine off with the on/off switch.

Thanks for posting. I am going to start using this method in stead of the off on switch.

[tom lucas]

Didn't someone in another thread post that they were able to re-program their VFD to stop this from occurring? I think it was a Grizzly lathe. Perhaps Laguna has a similar fix.

Having to turn the speed down slowly before stopping, thereby losing one's speed set point, is less than ideal. To me it's a design flaw with the VFD. The VFD should be equipped to deal with backcharging EMF levels caused by any speed the lathe is design to operate without requiring a reset.

Now the chuck coming unscrewed, that's scary.

[Bill Boehme]

Since you mentioned that the belt is in the high speed range it is obvious that is most of the problem. A far better solution is to not have the belt in the high speed range for large heavy pieces. The low speed range will give you much more torque and the speed will still be more than adequate. I have a 3 step pulley on my Robust AB and the belt stays in the low speed range probably more than 99% of the time.

[Joe Frank Porter]

I do turn in the low speed range 90% of the time and I went to the high speed range only to test the conclusions we were discussing. Sorry to confuse the issue.

[David C. Roseman]

I'm not a sparky or an EE, but I'll offer my further thoughts on this.

I'll disagree with Tom that there is a design flaw in the VFD on the Revo 18/36. That inverter is the Delta S1 (the VHD-S series), manufactured by Delta Electronics, Inc. (not to be confused with Delta Power Equipment Corp). The S1 is an industry workhorse that's been used for many years in industrial automation applications on all types of equipment. Two other examples in wood lathes that use it are the Powermatic/Jet 3520B and Jet 1640EVS models, both highly regarded and fine company for the Revo 18/36. For PM's 3520C, PM uses the Delta E series VFD. Tom mentioned Grizzly in his post. For Grizzly's big G0800, Grizzly uses the Delta EL series, and for its G0733 and G0766 it uses the Delta M series, which is a slightly later series than the S series.

In all these and many other brands of VFDs, there is already internal dynamic braking capability built into them. When the equipment they are installed on is switched off, or the speed control turned down quickly, the motor rotation that continues due to inertia (mechanical energy) is partially converted back into electrical energy to create reverse current braking and help to slow the rotation. The excess energy is converted into heat inside the VFD. If the regenerated voltage exceeds the set max at the DC buss, the VFD will shut down power to avoid damage from further regeneration. It will throw an over-voltage fault code until the lathe is shut off for a few moments and then turned back on. As noted earlier, when the lathe is switched off with a very heavy workpiece turning at speed, this can happen.

There are three ways I know to reduce the likelihood of this if it is happening, all within the design of the VFD.

1. Easiest fix: Simply turn the speed control down slowly to stop the lathe. It's only necessary when spinning heavy workpieces anyway. Unless you're a production turner regularly spinning very heavy blanks, the additional few seconds needed for this doesn't strike me as a big deal. Also, not that hard to remember the rpm you were turning at when you stopped to check your work, especially with the digital rpm readouts on the newer lathes.

2. Second approach: Adjust the VFD's "deceleration" parameter setting so that the motor speed ramps down less quickly when switched off. This is the least satisfactory approach, IMO. If turning the speed control down slowly makes you impatient, extending the deceleration time will too. If will extend the stopping time even on smaller, lightweight workpieces. Moreover, I suspect that even if you were to change the setting to maximum deceleration time, it still might not be enough to allow you to switch the lathe off suddenly with some monster workpieces.

It also requires knowing how to go into the VFD to make parameter changes, not to be taken lightly. The Delta inverters, like others, have multiple user-programmable parameters that the equipment manufacturer can customize for the intended application. There is a keyboard on the VFD for this, but programming can also be done with proprietary software and an interface using the VFD's telecommunication port. One of the parameter settings can lock the keyboard so that a special code must be entered to make changes. Powermatic/Jet, Grizzly, and I suspect Laguna and other brands, lock the keyboard to prevent inadvertent or ill-advised changes from end-user tinkering. They are not likely to give the codes out to a hobby woodturner for this reason. So going in through the telecommunications port is the easier route.

3. Third approach: Add an external braking resistor. The Delta VFDs and other quality inverters are specifically designed for the addition of an external braking resistor to supplement the built-in dynamic braking if the intended application warrants. Delta offers them through authorized distributors for around $50, and generic braking resistors with the same spec values are available online for around $30, last I checked. To do this still requires going into the VFD to make several necessary parameter changes, so although it's not difficult, it's not for everyone.

The addition of an external braking resistor allows the VFD to handle higher regeneration voltage and dissipate heat better. This in turn allows the VHD's deceleration parameter to be set to a faster rate of deceleration. But there's a downside to this if deceleration is too quick. Bill Boehm describes this vividly in his post, and I've had a similar experience. I've added an external braking resistor to the Delta M series VFDs on both my Grizzly G0733 and G0766. I hadn't experienced any over-voltage shutdowns, but I wanted to experiment with different deceleration and acceleration settings out of curiosity. Several years ago, after I added the resistor and adjusted the deceleration rate on the G0733's inverter, I spun a heavy bowl blank up to about 800 rpm, then quickly dialed the speed control to zero. The Oneway Stronghold chuck and blank instantly spooled off the end of the spindle. They were stopped from liftoff only by the tool rest that was fortuitously positioned near the face of the blank! Needless to say, my curiosity was satisfied, and I readjusted the deceleration parameter to slow things down.

[Roger Chandler]

David, what a wonderful technical answer. You and I both know that a lot of issues stem from the operator trying to do things the lathe electronics were not programmed to do. Operator induced errors can be VERY dangerous. Thank you again for helping our Laguna friends understand what many of our Grizzly owners already have learned. Your VFD technnical explanations are as good or better than any I’ve ever read. Thank you, my friend!

[David C. Roseman]

Roger, thank you for your kind words!

[Mick Fagan]

David, I too would like to add my thanks for a very detailed and informative answer to possible variations and/or issues with lathes running this VFD.

I have been keenly following this thread since its inception as I have my first lathe with a VFD, which is the Revo 2436 which runs the same VFD. Recently I placed a rather heavy wet blank on and turned it and learnt quite a lot about the braking effect of a VFD on a lathe and heavy stuff. My blank was approximately 53kg (115lb) and the very first thing I noticed was that all of my previous turning on this lathe with much smaller work pieces the braking worked effortlessly, albeit longer to initially slow down with heavier pieces, but it always worked.

This certainly didn't happen with the bigger blank, it just free wheeled and free wheeled. Which wasn't an issue as I guessed the heavy blank was too much for the braking system; appears my guess was correct. At least it meant I became aquainted with the hand wheel and how to use it. I have been accustomed to hand wheels which resemble automobile wheels, as opposed to the Laguna wheel which is more of a two stepped pole emanating out of the head stock.

Having being heavily accustomed to the larger Vicmarc type wheel and grabbing it to slow down, this wheel took some getting used to using the different shape. I now prefer this wheel to the Vicmarc type. One just needs to remember not to get too close to the indexing apparatus.

I have been using my lathe and have always just pressed the stop switch, checked my work, given it a hand roll to start it turning, then switched it back on, whereupon it returns to the revolutions I was previously working. Now it is early days as I have only had this lathe since last November, but I don't think there will be any issues.

Speaking of switching off and on, I have found the rear extra remote switch unit fantastic. In fact, apart from the initial fiddling with the new toy turning, I have almost exclusively used the cabled remote switch box for all working of the lathe. It suits my turning perfectly as I turn to my right to place my tool onto a stand alone tool tray with my right hand, while I reach up and use my left hand to press the off button. With normal weighted work the machine stops in approximately 3-5 seconds, meaning that by the time I have turned back to the lathe to check my work, things have stopped.

Once again, many, many thanks for that information.

Mick.

[tom lucas]

David,
Thanks for your information. You clearly have looked into this and understand the details of how these VFD's behave. I admittedly have not. The current limiting resistor solution clearly has some drawbacks related to the chuck spinning off.

My view is that this design is "flawed", or more accurately: just "cheaped out". I am an electrical engineer and know the "tripping" can be avoided. It would be pretty simple to put in a TRUE dynamic current sense/limiting circuit whereby you can brake quickly for small objects (low currents) and more progressively for larger ones (high currents). Of course there would still be a trade off between stopping too fast causing the chuck to unspin and taking too long to stop. TRUE dynamic braking system would allow for current control, braking just enough to stay below the trip point. It would not rely on a simple, "dumb" resistor limiter. That would be the simplest solution, likely using pulse width modulation (think anti-lock brakes), requiring just a few dollars in extra parts. In a more sophisticated solution, a torque/moment sensor could be added along with current sensing. This sensor would measure the energy on the spindle and adjust braking accordingly. Having a-priori knowledge of what is happening on the spindle, it would minimize the chance that the chuck comes unscrewed. TRUE Dynamic braking would likely be all that is needed, though. With enough thought and better knowledge of how the VFDs work, I'm sure there are a number of designs that could achieve better results than the simple current limiting resistor.

[David C. Roseman]

Mick, you are more than welcome. Glad the info was useful. Sounds like you're really enjoying the Revo 24/36, and giving it a good workout with 53kg blanks. Yikes! I'm guessing you're either 6'6" tall and 240lbs, or use an engine hoist or chain fall to mount workpieces that size.

I've only heard good reports about the Revo 18/36 and Revo 24/36. Laguna seems to have hit a sweet spot with both. I think Nanjing Harvey Machinery Co, LTD builds them to spec for Laguna at their factory in Jiangsu, as they do the G0799 and G0800 for Grizzly, and the big Powermatics. Plus their own line of big lathes. Impressive machines coming out of China these days.

[David C. Roseman]

David,
Thanks for your information. You clearly have looked into this and understand the details of how these VFD's behave. I admittedly have not. The current limiting resistor solution clearly has some drawbacks related to the chuck spinning off.

My view is that this design is "flawed", or more accurately: just "cheaped out". I am an electrical engineer and know the "tripping" can be avoided. It would be pretty simple to put in a TRUE dynamic current sense/limiting circuit whereby you can brake quickly for small objects (low currents) and more progressively for larger ones (high currents). Of course there would still be a trade off between stopping too fast causing the chuck to unspin and taking too long to stop. TRUE dynamic braking system would allow for current control, braking just enough to stay below the trip point. It would not rely on a simple, "dumb" resistor limiter. That would be the simplest solution, likely using pulse width modulation (think anti-lock brakes), requiring just a few dollars in extra parts. In a more sophisticated solution, a torque/moment sensor could be added along with current sensing. This sensor would measure the energy on the spindle and adjust braking accordingly. Having a-priori knowledge of what is happening on the spindle, it would minimize the chance that the chuck comes unscrewed. TRUE Dynamic braking would likely be all that is needed, though. With enough thought and better knowledge of how the VFDs work, I'm sure there are a number of designs that could achieve better results than the simple current limiting resistor.

Tom, thanks for your comments. No doubt there are price points that would justify more sophistication in what the machinery vendors spec for their choices of VFDs. Just looking at the large line of inverters offered by Delta Electronics, Delta may already have higher priced models with more sophisticated dynamic braking. And they're just one of several quality inverter manufacturers. The issue, I guess, is cost vs. a combination of perceived benefit and marketability. There's also, as you note, the trade off of creating such effective braking that it can actually become a hazard unless there is enough sophistication in the system to monitor and modulate that as well.

BTW, I recall that you recently added a Grizzly G0766 to your shop. If you are interested in eventually adding an external braking resistor (and the potential for scary fast stops ), send me a PM with your email address. I'll be happy to send you a tutorial I wrote up three years ago on doing it. It also covers making other parameter adjustments on the Delta VFD-M series inverters.

[Brice Rogers]

I had an instant recall of this thread yesterday when I quickly turned down my G0766. I had a medium sized platter (perhaps 14") mounted on a 5-1/2" chuck (heavy), a set of Cole-jaws and a set of eight (home made) Cole-jaw extensions. So, there was some mass there. But not as much as some other people regularly turn. The chuck started to unscrew. Yikes !!Perhaps I could have used a grub screw in the chuck or could have tightened the chuck more than I did, but I was surprised that this happened.

So, I doubt that I will add a resistor to allow me to stop more quickly. It already stops pretty quickly. Quick enough for me.

I almost always use the speed control to ramp down the lathe. It'll wear out the potentiometer a bit more quickly, but it isn't a hard job to change the pot.

[Russell Nugent]

The manual for my nova Saturn says that if I'm going to use the variable brake assist then I must use a chuck with a locking grub screw.

[tom lucas]

Yeah, Dave you are right. It's cost vs performance. And in this case some bit of safety to consider too. Thanks for the offer on the tutorial. I'll shelve that offer for now, as I've had my VM120 chuck spin loose once already and it has no grub screw capability. While I can work on these machines and fiddle with them as needed, I much prefer to have the machine work for me rather than me work on the machine. I do enough of that in my day job. I prefer it to work more like a toaster: no thought - just toast .

The G0766 stops plenty fast enough. Though I don't want to use the pot every time, I'll just have to see. Maybe dampen the braking by placing my hand on the work piece. Right now I'm too busy with yard work and other projects with little time to turn. Hopefully I'll have time to get back to it in May.