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Thread: Lathe power disconnect options

  1. #16
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    Quote Originally Posted by William C Rogers View Post
    I have the Laguna 18-36 lathe and the emergency stop switch is fixed in the headstock. I unplug the lathe every night and was thinking about putting some type of disconnect at the tailstock end to serve both to disconnect the power and use as an emergency stop at that end. What opinions do you have or what option are viable? Right now I would have to walk 25' to the breaker box to avoid crossing the line of fire.

    i was even thinking of getting a 120/240 relay and one of the outdoor remote systems to do this.
    Bill I am not the VFD expert, however on the Canadian forum there are a few, and the use and addition of or changing of VFD to machines are discussed often enough.

    So to show that these experts have no problem with shutting down and starting up of the VFD I’ll add this and if you want there is more on this and other threads on the forum.

    You can see that this person has used the VFD for years and shut it down and start it up with no problem.

    VFD question.jpg

    Here is the first answer to the question of a spray gun activated trigger for the VFD to start and stop, there aare several more answers.

    First answer.jpg
    Last edited by Leo Van Der Loo; 02-07-2018 at 11:53 PM.


    Have fun and take care

  2. #17
    Looking at the wiring diagram and pictures of the head stock on line you have 3 switches a 1 pot one switch is for fwd and rev another is main on/off switch and the last is emergency stop switch and the speed pot. when you are using the lathe and want to stop it to look at the turning you should use the speed control to stop it. when you are going to turn the unit off when you are done you should use the main on/off not the emergency and then unplug it. the emergency stop kills power to the motor an part of the vfd not all of it the emergency stop should be us for what it named for when something is going wrong and you need to stop quickly.
    Last edited by Keith Buxton; 02-08-2018 at 1:04 AM.

  3. #18
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    I did talk to Laguna CS yesterday about power disconnect. They said it was no problem to unplug the lathe at the end of the day. I also asked them if in an emergency condition if the VFD would be damaged if the power was cut while the lathe is running and again said it would not damage the VFD. So right now I can use the breaker to kill power to the lathe in an emergergency situation without crossing the line of fire. However the breaker is about 15 feet from the lathe. Using a relay is beneficial if you are constantly turning on and off through the relay. I still plan to disconnect the power cord, so a relay is not beneficial. Eventually I will put a simple kill switch at the end of the lathe. It will be in the on mode and only used should there be a reason to kill the power in an emergency. Hopefully it will never see the off position except for initial testing. As far as wiring into the existing emergency stop, it is more than I want to try to figure out.
    When working I had more money than time. In retirement I have more time than money. Love the time, miss the money.

  4. #19
    With most modern VFD controls the normal operation of start and stop are momentary push button switches, these switches usually are wired to programable "inputs" to the VFD to send pulse instruction to the vfd.
    The E-Stop button is usually a "maintained" switch which means the signal is maintained off and must be manually pulled or twisted to turn it back on, usually wired to programable "input".
    Depending on the VFD initial programming the "braking" function of the vfd under normal stop/start may be different than the E-stop "braking" function. E-stop likely will apply more braking action to stop the rotation quicker, based on the factory setting from the manufacturer of the lathe. Or it may simply just remove the run command and the work piece would just coast to stop.
    In both cases the power to the computer /programable board and the DC buss is still applied. This means the computer portion, the cooling fan, and the DC portion of the inverter are still energized and ready to respond to operator action.
    The cooling fan is important to keep running as the heat sinks used in the VFD can get very hot while running and need time to cool down, the fan is likely temperature controlled(mine is, I can hear it running, and it stops several minutes after a period of down time), lathe is still ready to run, just the internal VFD fan has stopped,
    Switching off the main power switch or unplugging the cord will remove the incoming power totally resulting loss of cooling to these heat sinks and could result in damage to the electronic speed control components of the drive.
    I suspect that the comments related to VFDs not liking "power off" switches in the main power line may be due to overheating of components because fan power was shut off.
    Adding a remote stop start push button is a great convenience and safety feature, my magnetic remote switch box lets me place it where it is most convenient for me, out of the line of fire.

  5. #20
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    Quote Originally Posted by Bert Delisle View Post
    With most modern VFD controls the normal operation of start and stop are momentary push button switches, these switches usually are wired to programable "inputs" to the VFD to send pulse instruction to the vfd.
    The E-Stop button is usually a "maintained" switch which means the signal is maintained off and must be manually pulled or twisted to turn it back on, usually wired to programable "input".
    Depending on the VFD initial programming the "braking" function of the vfd under normal stop/start may be different than the E-stop "braking" function. E-stop likely will apply more braking action to stop the rotation quicker, based on the factory setting from the manufacturer of the lathe. Or it may simply just remove the run command and the work piece would just coast to stop.
    In both cases the power to the computer /programable board and the DC buss is still applied. This means the computer portion, the cooling fan, and the DC portion of the inverter are still energized and ready to respond to operator action.
    The cooling fan is important to keep running as the heat sinks used in the VFD can get very hot while running and need time to cool down, the fan is likely temperature controlled(mine is, I can hear it running, and it stops several minutes after a period of down time), lathe is still ready to run, just the internal VFD fan has stopped,
    Switching off the main power switch or unplugging the cord will remove the incoming power totally resulting loss of cooling to these heat sinks and could result in damage to the electronic speed control components of the drive.
    I suspect that the comments related to VFDs not liking "power off" switches in the main power line may be due to overheating of components because fan power was shut off.
    Adding a remote stop start push button is a great convenience and safety feature, my magnetic remote switch box lets me place it where it is most convenient for me, out of the line of fire.
    Bert, thanks for the detail. I do have a better understanding regarding power relating to VFDs. Since I disconnect power when I am done for the day, it is important to leave the VFD power on for a few minutes for cooling rather than disconnecting immediately after shutting down. I understand that it is not good to disrupt power when the lathe is running. The emergency stop switch compensates for that by leaving power to the VFD and cooling fan. Although not ideal since that I don't have the capability to wire a remote emergency stop, would be to put a power disconnect at the end of the lathe. If used it would put the VFD at some risk due to cooling, but with power removed no additional heat would be generated. I would only use this option in an emergency situation and hopefully never.
    When working I had more money than time. In retirement I have more time than money. Love the time, miss the money.

  6. #21
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    William, Get a friend to wire the second emergency stop switch in series with the first. Now either switch will shut it down in the fashion Bert describes for emergency off mode. Easily accomplished.

  7. #22
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    it would have some disadvantages for sure if needed to be moved often. but most heavy equipment is hard wired and a manual throw disconnect is used between the provided power source and the pigtail from the machine . But a big zap of lightning could still make that jump in the switch. but if hit that hard there would be other issues as well, seen it quite a few times when live in FL. worked in utilities.

  8. #23
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    Quote Originally Posted by david privett View Post
    it would have some disadvantages for sure if needed to be moved often. but most heavy equipment is hard wired and a manual throw disconnect is used between the provided power source and the pigtail from the machine . But a big zap of lightning could still make that jump in the switch. but if hit that hard there would be other issues as well, seen it quite a few times when live in FL. worked in utilities.
    I still plan to unplug the lathe as I always do. The switch would only be used in an emergency condition. Strange thing yesterday as I had a 13" spalred maple bowl 2nd turning and dry 11% MC. I had turned it to about 1/2" thickness and stopped the lathe to check. I was turning the inside and there was some tearout so I figured I would put some sanding sealer and sharpen my gouges. As I was putting the sanding sealer on all of a sudden "SNAP" and it cracked from the rim to the base just sitting there. I didn't see any indication of a flaw. I can only speculate if turning I would have seen a big chunk come off and I would have been on the tail stock end and need to shut the lathe down.

    Glenn, I don't have any friends that I know of capable to wire the emergency stop.
    When working I had more money than time. In retirement I have more time than money. Love the time, miss the money.

  9. #24
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    Since no one else knows for sure, I'm safe to add my 2 cents.
    First.You should unplug your VFD after every use. I don't care how long you've been lucky. I lost my PM 3520 due to a lighting surge.
    Second. Circuit breakers are not switches. Don't use them to shut stuff off. Plus, that won't protect you from a surge.
    Third. There is a thing called a sand resistor which absorbs energy created by the motor during braking. The sand in it absorbs heat. As Roger says, it's in the circuitry of the VFD. The sand resistor is a protector for the motor and VFD. I think if you disconnect the power as you propose, you'll bypass this safety feature which protects your equipment. In spin down, the motor becomes a generator.

    If I'm wrong about this, I apologize in advance.
    RP

  10. #25
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    Quote Originally Posted by Robert Edington View Post
    ...You should unplug your VFD after every use. I don't care how long you've been lucky. I lost my PM 3520 due to a lighting surge.
    Visiting my son this week end - he said when a thunderstorm threatened he started unplugging everything in the house. He had just unplugged the last "device" when lightning hit. The only thing it fried was the ice maker on his fridge which he didn't think to unplug. A neighbor lost multiple TVs, iPads, audio equipment, computers - basically almost everything plugged in.

    JKJ

  11. #26
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    Quote Originally Posted by Robert Edington View Post
    Since no one else knows for sure, I'm safe to add my 2 cents.
    First.You should unplug your VFD after every use. I don't care how long you've been lucky. I lost my PM 3520 due to a lighting surge.
    Second. Circuit breakers are not switches. Don't use them to shut stuff off. Plus, that won't protect you from a surge.
    Third. There is a thing called a sand resistor which absorbs energy created by the motor during braking. The sand in it absorbs heat. As Roger says, it's in the circuitry of the VFD. The sand resistor is a protector for the motor and VFD. I think if you disconnect the power as you propose, you'll bypass this safety feature which protects your equipment. In spin down, the motor becomes a generator.

    If I'm wrong about this, I apologize in advance.
    RP
    If the way I propose it would just be a quick off then on that would reset the latched power on switch to off, so if the electronics sense heat it should bring the protection back on. In all reality I doubt this would ever be used, but realize the possibilities. I would think there have been instances where there is a brief power interruption when a VFD device is in operation.
    When working I had more money than time. In retirement I have more time than money. Love the time, miss the money.

  12. #27
    I am unclear how if the VFD is unplugged before the fan has completely cooled is a problem. If the machine were going to be turned on in the next 5-10 minutes, then the fan would assist in accelerating the cooling between uses and during use. However, if the machine will be shut for the day, and the fan is interrupted mid-cooldown, then wouldn't the lack of power to it mean it's going to cool just fine in - what - an hour?

    I might think the problem is the abrupt cutting of power to any electronics. However, I notice that when I unplug the lathe, the VFD remains powered for another 20 seconds, and the LED annouces a different mode, before finally clicking off.

    I am not knowledgeable on this, so please lmk where I am being naive.

  13. #28
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    Quote Originally Posted by William C Rogers View Post
    If the way I propose it would just be a quick off then on that would reset the latched power on switch to off, so if the electronics sense heat it should bring the protection back on. In all reality I doubt this would ever be used, but realize the possibilities. I would think there have been instances where there is a brief power interruption when a VFD device is in operation.
    William, this actually highlights one of the biggest risks of a do-it-yourself double pole-double throw (DPDT) switch wired into the input 220v AC power side of the VFD between the 220v wall receptacle and the lathe. It sounds like that's what you have in mind, rather than wiring a switch into the low voltage circuitry of the lathe's existing switch. If the input power is cut off, but then cut back on as you describe, without waiting at least two minutes, you risk damaging the VFD. Here is an excerpt from an article by Thomas Robbins, a machine systems Applications Engineer, titled "Feed the Right Power to Your VFD." The whole article can be viewed and downloaded at http://www.machinedesign.com/motorsd...fd-right-power

    Excerpt:

    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.

    The problem that Robbins describes is in addition to the two that others have already mentioned: Interrupting all power to the lathe (1) defeats the VFD's cool-down cycle, and (2) defeats any built-in dynamic braking feature, thus causing the lathe to go into free-wheel.

    In an emergency, stopping the lathe is the important thing. If you can't reach the lathe's built-in E-stop switch safely, then of course pulling the plug, flipping the circuit breaker, or using a do-it-yourself 220v DPDT switch is better than nothing. But we should be aware of the unintended consequences. BTW, if we happen to be turning at the time of a power failure, the loss of the cool-down cycle and the dynamic braking feature occurs then, as well. And if the power comes back right away, the risk of damage that Robbins describes exists. But occasional power failures are pretty much unavoidable. Even if an automatic back-up generator system is in place the risk exists absent a very sophisticated setup, as the cut-over to standby power will likely involve delay and voltage swings. Robbins discusses that in the full article.

    I'm not a sparky, but bottom line for me is that a remote switch intended for use as a "start/stop" switch, rather than simply to shut off all power in an emergency same as pulling the plug, should only be wired into the lathe's existing low-voltage start/stop circuit.

    Evidently none of this came up in your conversation with the Laguna customer service person. Perhaps he/she was only thinking in terms of an occasional shut-down of 220v input power while the lathe is operating, so didn't see a risk of damage to the VFD as a practical matter. And of course pulling the plug after the lathe has been shut down properly is not a problem at all.
    Last edited by David C. Roseman; 02-12-2018 at 12:07 PM. Reason: typos

  14. #29
    Wonderful information, explaining the technical aspects of all this David! Thank You so much for reliable information that helps us protect our hard earned investments in our machines.
    Remember, in a moments time, everything can change!

    Vision - not just seeing what is, but seeing what can be!




  15. #30
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    David, I also appreciate your in depth explanation. So I have decided not to install any remote. Although very unlikely, if the situation arose I will use my headstock emergency switch. I will figure out a way to engage it without putting myself in harms way. I have never had a situation where I needed a remote emergency stop and suspect this is a rare occurrence.
    When working I had more money than time. In retirement I have more time than money. Love the time, miss the money.

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