Tablesaw On/Off Switch with VFD

[fRED mCnEILL]

For those of you who use a VFD on their tablesaw I would be interested in knowing how you turn you saw on/off.
I personally have a rotary phase converter and have a magnetic switch on the saw outfitted with a "paddle" that lets me shut the saw off with my knee or foot. However I understand you can't use a switch in between the VFD and the saw.

On tools like drill presses, lathes etc an emergency shutoff may not be as critical as a tablesaw so am wondering how others do it.

Thanks

Fred

[Van Huskey]

Most if not all VFDs will have low voltage muti-function pins that allow for you to use a standard on-off switch or a forward/off/reverse switch. They for example can also be wired through a microswitch for a foot brake on a bandsaw and I have my jointer wired through the brake as well so I push the brake for my jointer and it cuts power to the motor which it was also designed to do without a VFD. VFDs are extremely flexible.

[Rich Riddle]

I never place a switch between the vfd and the motor; however, you can wire the switch to the low voltage side of the vfd. You are then using the same switch on the machine but cutting power/initiating power at the vfd itself.

[fRED mCnEILL]

Anyone else?

[Van Huskey]

Anyone else?


Not sure you are going to get much else unless you are interested in specific setups or part numbers for specific switches.

There are basically three ways to turn a machine off using a VFD.

1. use a high voltage switch to cut power to the VFD which is not ideal and you lose any braking you have set up in the VFD

2. use the switch on the VFD itself fine for some machines but as you mention you do not have a "quick slap" switch

3. use the low voltage circuit on the VFD to add an auxiliary switch that suits you where you want it which is anticipated and provided for by the VFD's design. This also allows you to use the braking potential of the VFD to stop the machine faster than it would ordinarily. If you use braking you do have to be careful not to use too much braking on something like a table saw since it can loosen the arbor nut so it is not as much safety on a TS just more a couple of extra seconds you save before you can move the wood.

[Mike Hermann]

Your power cord supplying single phase power (often 230V) goes straight to the VFD, and the VFD is wired straight to the 3 phase motor (making sure your motor is also wired for 230V). The VFD will often have teeny little start/stop buttons on them that will operate whatever equipment you have wired in, but reaching and finding those buttons is tough especially if you're in a bind. There are a number of terminals on a VFD that allow you to wire in a number of external controls, commonly a start/stop switch and a potentiometer to control motor speed.

The start/stop has to be something like a paddle switch, toggle switch, heck even a light switch, anything that will make a circuit. It only needs to be something that can carry a low voltage signal. Magnetic switches/starters will not work here though. I just use a fairly standard red-and-yellow paddle switch because they are easy to operate, and on my table saws, I can just bump them with my thigh to turn them off. The wire to these switches can be light gauge (I use lamp cord from a spool I acquired), but can be whatever you have on hand as long as it fits in the VFD terminals. Remember though: nothing, and I mean nothing, goes between the VFD and the motor.

I'm not an expert, but I have three VFD's on different machines, and this is what I learned. Each one has been easy to set up, and I'm able to customize the settings on each machine based on my needs. I can program in a soft start, add a little bit of braking when I shut a machine off, and vary speed if needed. On my lathe, I added a potentiometer to control speed and a FWD/REV switch so that I can sand my turnings in both directions. As Mr. Husky says above, VFD's are flexible.

--Mike

[Matt Day]

Fred,
Try asking over at OWWM, there is a lot of VFD usage there since many old industrial machines are 3 phase.
I'd be interested too since I need to decide what I'll do with my Unisaw. On the PM65 I restored I put in a mushroom push button (see below) on it and it worked good. On this one I may try a bigger paddle style (likely Shop made) that I can use my knee on. We'll see.
https://www.amazon.com/gp/aw/d/B008LT2VH2/ref=mp_s_a_1_4?ie=UTF8&qid=1484352320&sr=8-4&pi=AC_SX236_SY340_QL65&keywords=mushroom+switch&dpPl=1&dpID=413S4KLuw4L&ref=plSrch

[mreza Salav]

Van gave you the easy solution. Here is how I've setup my bandsaw:

http://www.sawmillcreek.org/showthread.php?189669-Running-my-3-phase-bandsaw-using-a-VFD&highlight=

The switch is an off-the-shelf one and can be placed anywhere you like or you can install a bigger paddle switch if you like.
It is wired to the control lines of the VFD and it is wired such that in case of a power failure your saw won't run (if the switch is left in "On" position) until you turn it off and then on again.

[Rich Riddle]

Matt,

You will get the same three answers on OWWM that Van outlined. I spent New Year's day at Bruce Norton's house in Tennessee discussing this. He's the guru (and an engineer) in OWWM for VFD applications. You can do it a few other ways that aren't recommended but you chance damaging equipment. The wiring of a VFD is fairly straight forward....the programming isn't as simple.

[fRED mCnEILL]

Thanks for the replies.

What is OWWM?

Regards

Fred

[Matt Mattingley]

Old Wood Working Machinery.com . But if you have any more concerns, I will try to answer as many as possible.

[fRED mCnEILL]

Thanks Matt.
I think I have enough info for now. What I thought might be a deal breaker for a VFD( i.e. on/off switch) turns out to be quite simple once you understand all the capabilities of a VFD.
I will keep you in mind if/when I have trouble with the install.

Regards

Fred.

[Terry Therneau]

There are two ways to wire start/stop on a VFD. The simple one is just like a light switch. For instance I have a VFD on my dust collector(a craigslist find with a 5HP 3phase motor), and I have multiple on/off switches in the shop that are wired exactly the same way you wire multiple switches for a light bulb. I can turn it on or off from anywhere. Except of course that the wire is a leftover spool of telephone wire that I happened to have. I have another on a table saw using a large mushroom switch such as Matt showed, in a spot that's easy to slap without looking.

The second way uses a pair of momentary push buttons, one normally closed and the other normally open: the usual "start/stop" pair you see on lots of machines. This setup is a bit safer in that if power were to go out (or a breaker trip), the saw won't start back on when the power is restored. Those switches are a bit more expensive since they usually come from the industrial side of the electric catalog rather than a big box store. I also have this style.

Every VFD I've seen allows either style, you just need to read the manual and set it up. For something like a saw or shaper my main criterion is a BIG stop button.

Terry T.

[Matt Mattingley]

Some better VFD's have eight inputs or more.
you can set:
input #1 to be the stop
input #2 to be forward running
input #3 to be reverse running
input #4-8... pick whatever you want that fills your needs.
And about 100 different commands including different speeds, breaking speed's, Potentiometers, command switch overs, counters, jog options, ... The list is pretty unlimited.

As Terry stated there is Basic two wire control, Basic three wire control (these are momentary pushbuttons) and then you can get into basic four wire control which has reverse. Some of the better VFD's are not just phase conversion. They are in miniaturized switching station/computer.

[Tom Trees]

Anyone else? Hi Fred Delighted this threads up here as I'm looking for a similar solution http://www.sawmillcreek.org/images/smilies/smile.gif Here's what I've done for my bandsaw ... I sometimes get fatigued all of a sudden sometimes , so I wired up two stops (3 wire control ) using a N/O start switch and 2 N/C stop switches in series . These buttons need to be twisted to activate the saw once pressed . Although if i trip the saw out ....It happened once or twice using the pot, when I was fettling/testing my BS tires, I had to press the stop button on the VFD to get it going again (Huanyang drive) It did not start again on its own ... Now onto the tablesaw I don't think these stop switches are exactly what I'm looking for with this application as there not large enough for my liking ... I was considering making some kind of paddle type device that Kelly Mehler uses masteringyourtablesaw 1 but I think I like a horizontal type paddle better like Carl Holmgren's on youtube He uses a toggle type switch in which you have to lift the horizontal beam up to activate the saw and hit it down to stop it . I might use this in conjunction with an awkard twist isolator switch, for any eejits If I ever had a party of folks come over ... although I think I will just remove the fuses instead if that ever happens . I could just make some kind of a hidden hook for the paddle aswell ...this might prove to be a better solution Awaiting some piccys if anyone has a better solution . Thanks Tom

[Rod Sheridan]

For those of you who use a VFD on their tablesaw I would be interested in knowing how you turn you saw on/off.
I personally have a rotary phase converter and have a magnetic switch on the saw outfitted with a "paddle" that lets me shut the saw off with my knee or foot. However I understand you can't use a switch in between the VFD and the saw.

On tools like drill presses, lathes etc an emergency shutoff may not be as critical as a tablesaw so am wondering how others do it.

Thanks

Fred

I don't have one on the table saw however I would use the standard saw stop/start pushbuttons like I do for the band saw, band mill and lathe.

I also like to have a disconnect switch on the machine so I don't have to unplug it when changing tooling............Rod.

[fRED mCnEILL]

My understanding is that the VFD should be hardwired to the saw and any emergency type switch should use the terminals provided because just turning off the power between the VFD and saw could do damage. Does this only apply when the saw is running?

[Dan Friedrichs]

My understanding is that the VFD should be hardwired to the saw and any emergency type switch should use the terminals provided because just turning off the power between the VFD and saw could do damage. Does this only apply when the saw is running?

I think Rod is saying to put a disconnect between the supply and the VFD, in this case, to facilitate blade changes, etc.

Technically, you could put a switch between the VFD and the motor to use as a safety disconnect - only to be opened when the motor is stopped - but that's an awful idea, since somebody is likely to accidentally open the switch while the saw is running, someday. Much better to put the disconnect between the VFD and the supply.

[Eric Keller]

depending on the vfd, the manual may give a way to switch off the output of the vfd to the motor, but you're not going to like how much that will cost you. At least a couple of contactors. Been a while since I have seen a circuit for that.

The low voltage side is the way to go. Most vfds allow you to add external braking resistors, might be worth it on a tablesaw

[Van Huskey]

Most vfds allow you to add external braking resistors, might be worth it on a tablesaw

You have to be really careful with the deceleration rate dialed in on a TS, too much and it will loosen the arbor nut. It is are great on some machines like big disc sanders and bandsaws for example.

[Matt Mattingley]

You have to be really careful with the deceleration rate dialed in on a TS, too much and it will loosen the arbor nut. It is are great on some machines like big disc sanders and bandsaws for example.
I think tablesaws are the best for high breaking rates! What can be better than hitting your stop paddle and having your tablesaw come to a stop in two seconds( or less )? I would call this safe! Actually in Europe, it is code to have stationary equipment come to a stop in less than 10 seconds.

Now all arbours don't allow this. On most consumer grade saws you will spin the armour nut off with blade bouncing uncontrollably! Better quality saws have arbour nut/outer flange inertia stopping. This is not new, this is old technology. Tablesaws in the 50s and 60s started preventing this with shear pin for blade plates. I think most want to get a good deal on an Asian saw. So you might be right.

[Van Huskey]

I think tablesaws are the best for high breaking rates! What can be better than hitting your stop paddle and having your tablesaw come to a stop in two seconds( or less )? I would call this safe! Actually in Europe, it is code to have stationary equipment come to a stop in less than 10 seconds.

Now all arbours don't allow this. On most consumer grade saws you will spin the armour nut off with blade bouncing uncontrollably! Better quality saws have arbour nut/outer flange inertia stopping. This is not new, this is old technology. Tablesaws in the 50s and 60s started preventing this with shear pin for blade plates. I think most want to get a good deal on an Asian saw. So you might be right.

You are never going to get any real safety benefit from resistive or DC injection braking on woodworking machines, it could help if you find yourself in a precarious position AND can hit the stop button. Tablesaws have so little momentum they spin down fairly quickly, nothing like a big bandsaw that might take 3-5 minutes or a big disc sander that can take 10 or more minutes to stop. The vast majority of American and Asian saws in hobby shops and even in small cabinet shops don't have any arbor locking mechanisms.

If you want added safety in a table saw buy a Sawstop or a slider you really aren't going to add much safety with any form of braking except Sawstop (or Bosch) type braking. VFD braking as it applies to woodworking is mainly the convenience factor as long as you use the rule of waiting until the tooling stops to move your cut pieces etc.

BTW I don't want any machines with high breaking rates... sorry couldn't resist. :p

[Matt Mattingley]

So do you consider a TS stoping in 2s better than 45s??? Or it doesn't matter???? My 30" disk sander takes 14 minutes to stop. I hit the stop button and walk away. Maybe if it was in a Federal penitentiary, for safety, it might want it to stop like a SS.

OH,... By the way... I did buy it out of the old Kingston Pen and it was in their wood working shop for inmates. No stopping with 14 min spinning... I haven't found any bone, blood or skin yet. I guess I can say, even our less brilliant in society are not idiots. A SS is for the schools and those without a fearfull respect.

[Erik Manchester]

By the way... I did buy it out of the old Kingston Pen and it was in their wood working shop for inmates. No stopping with 14 min spinning... I haven't found any bone, blood or skin yet. I guess I can say, even our less brilliant in society are not idiots. A SS is for the schools and those without a fearfull respect.

LOL, Matt, I think that most inmates of the Kingston Pen were there because they preferred to spill others blood as opposed to their own.

Your JTA would certainly trim the fingernails of the careless in short order.

[Malcolm McLeod]

For those of you who use a VFD on their tablesaw I would be interested in knowing how you turn you saw on/off.
I personally have a rotary phase converter and have a magnetic switch on the saw outfitted with a "paddle" that lets me shut the saw off with my knee or foot. However I understand you can't use a switch in between the VFD and the saw.

On tools like drill presses, lathes etc an emergency shutoff may not be as critical as a tablesaw so am wondering how others do it.

Thanks

Fred

Already lots of good advice on how to execute the Start/Stop function, and I'm also reassured by the uniform recommendation not to insert a switch between the VFD and the motor.

If anyone is interested in 'why' no interposing switch, I can provide a case-in-point: I was called to a site where an industrial user had a production line with multiple stations that each used a single VFD multiplexed to 5 different small motors (1/4 to 2Hp). Each motor would be selected by rotary switch, then the VFD 'jogged' in Fwd or Rev to make adjustments. The selector switch would disconnect one motor (turn off it's starter), and connect another (turn on it's starter). Each starter connected the respective motor to the station's VFD. They had ongoing issues with the VFDs faulting (line would run for 5-6 hrs out of 24).

The problem was traced to the motor starters. The operator was changing the selector switch while the VFD was still in it's accelerating or decelerating phase. The starters would switch immediately. A fault is generated on the VFD when a motor load is suddenly connected to the VFD output bus that is in the middle of it's accel/decel ramp. We installed PLC code to prevent motor starters from switching while the VFD was 'active'. The next day they ran 22 of 24 hours.:D

The above system is probably well beyond what the average Creeker will use in their shop, but the lesson is still applicable - don't put any switch between motor<>VFD. The above were premium quality VFDs and were 'just' faulting. The imports may very well be damaged by such.

[Malcolm McLeod]

You are never going to get any real safety benefit from resistive or DC injection braking on woodworking machines, it could help if you find yourself in a precarious position AND can hit the stop button. Tablesaws have so little momentum they spin down fairly quickly, nothing like a big bandsaw that might take 3-5 minutes or a big disc sander that can take 10 or more minutes to stop. The vast majority of American and Asian saws in hobby shops and even in small cabinet shops don't have any arbor locking mechanisms.

If you want added safety in a table saw buy a Sawstop or a slider you really aren't going to add much safety with any form of braking except Sawstop (or Bosch) type braking. VFD braking as it applies to woodworking is mainly the convenience factor as long as you use the rule of waiting until the tooling stops to move your cut pieces etc.

BTW I don't want any machines with high breaking rates... sorry couldn't resist. :p

You are dead on that VFD's certainly aren't safety devices, but the braking function can be ....reassuring? Maybe?

If you do choose to use the braking function, make sure you follow the instructions for external 'braking resistors'. When a motor is spooling down it becomes a generator. In the typical On/Off switch-operated TS or BS, the generated voltage has no where to go, so no current flow, so no braking (simplistically). If a VFD is connected and configured for braking, it can apply a resistance to dissipate this power (as heat).

VFDs have small internal resistors that can stop relatively light loads (different VFD sizes have different internal resistors, so can stop different loads). Braking capacity is dependent on both time and load. You can brake a (relatively) big load over a long time, or a light load in a short time. If you try to stop a big load in a short time, the internal resistors can be overheated and damaged.
I've not tested this, but as an example you could probably stop a TS in 2-3 seconds with VFD braking (internal resistors). I would think a similar Hp 14" BS, should be set for no less than 12-15 seconds on a similar VFD.

Most VFDs offer external braking resistor packages. I'd think they are well worth the investment if you need or want a VFD to stop a 24" BS (or a disk sander with a 14 minute over run!!).

[Dan Friedrichs]

If you try to stop a big load in a short time, the internal resistors can be overheated and damaged.

I'm not certain this applies to EVERY VFD, but I would suspect that the vast majority of VFDs have protection to avoid damaging themselves - either an over-voltage limit or an over-temp limit. In the event that you set the decel time too fast, it will try to generate more power than the internal resistance can handle, and simply trigger an over-voltage fault and stop trying to brake the motor (instead, it will just allow it to coast down).


Most VFDs offer external braking resistor packages. I'd think they are well worth the investment if you need or want a VFD to stop a 24" BS (or a disk sander with a 14 minute over run!!).

The ones sold by the VFD manufacturers are way overpriced, though. These are simply power resistors that you can buy very cheaply - just size the value of resistance and wattage per the manual:
http://www.mouser.com/Search/ProductDetail.aspx?R=HS100_100R_Jvirtualkey1126000 0virtualkey284-HS100100R5%25

[Matt Mattingley]

Not all VFD's have internal break resistors or if they do they are usually pretty small. Not all VFD's have the internal hardware that external break resistors can be added. If high inertia stopping is required, this needs to be a prerequisite when selecting a VFD. I'll be testing this break resistor in the near future on an 18" Direct drive table saw. It is 1000 W 30R. VFD's cannot displace the heat generated (by themselves) in heavy inertia stopping. A external break resistor needs to be added. This thing weighs more than the VFD.

351973

[Dan Friedrichs]

Good points, Matt. And that's a sexy resistor ("phrases I thought I'd never say for $100, please, Alex...")

[Tom Trees]

The above system is probably well beyond what the average Creeker will use in their shop, but the lesson is still applicable - don't put any switch between motor<>VFD. The above were premium quality VFDs and were 'just' faulting. The imports may very well be damaged by such.
I was thinking of eventually running two tablesaws with a single cheap VFD using a rotary switch,
I've obviously heard that switching it, will destroy the inverter while the machine is powered on, but I'm not in any kind of environment
where I would have to do this quickly, so can wait for the machines to fully stop (and some more) before switching .

I just wasn't sure if I would be able to, with the cheap drives ,as one machine is 3HP and the other has only 2HP .
I wasn't sure if I'd have to do a parameter change, or if it's possible to have another rotary switch for changing the allocated settings
for machine 1 and machine 2 ...
So I would have a nearby panel with two rotary switches, and only twist these rotary switches , when the VFD is powered off ?
Or does the VFD need to be powered on, to recognize the rotary switching with the interface/mobus/low voltage controls ?
Can someone clarify this please,
as I have been wanting to know this for a while .
Thanks kind folks
Tom

[Malcolm McLeod]

I was thinking of eventually running two tablesaws with a single cheap VFD using a rotary switch,
I've obviously heard that switching it, will destroy the inverter while the machine is powered on, but I'm not in any kind of environment
where I would have to do this quickly, so can wait for the machines to fully stop (and some more) before switching .

I just wasn't sure if I would be able to, with the cheap drives ,as one machine is 3HP and the other has only 2HP .
I wasn't sure if I'd have to do a parameter change, or if it's possible to have another rotary switch for changing the allocated settings
for machine 1 and machine 2 ...
So I would have a panel nearby with two rotary switches, and only then switch over, when the VFD is powered off ?
Or does the VFD need to be powered on, to recognize the rotary switching with the interface/mobus/low voltage controls ?
Can someone clarify this please,
as I have been wanting to know this for a while .
Thanks kind folks
Tom

The industrial system I referenced used a PLC to manage the switching (multiplexing) to the various motors. The PLC talked to the VFDs and would not allow motor starters to switch the VFD's load from one motor to another, unless the VFD was stopped (the output buss was at 0volts & 0hz). I could have accomplished the same thing by training the operators to open the control enclosure, verify that the VFD in question has in fact stopped, and only then switching to another motor. (People being people, I changed the program.):rolleyes:

Assuming you can successfully manage the 'logic' part of this (don't switch the saws while VFD is active), then you CAN do what you describe. I'm also going to assume you'll run these at rated speed - - just using the VFD to get 1ph --> 3ph power conversion.

I'd put 2 starters in a electrical enclosure with the VFD and use a single 3-position switch on the door to select the respective saws: "3Hp - OFF - 2Hp". Two contact blocks on the switch would have XOO (on-off-off) (:: 3Hp saw starter ON in left position), and OOX logic (:: 2Hp saw starter ON in right position).

You can put a pilot light, fed from the VFD terminal strip, to indicate the VFD is running and/or stopped, and so inform you it's safe to switch. This would allow you to leave the VFD itself powered all the time, should you choose to do so.

That leaves the logic to change the VFD settings to appropriate values for the respective saws (most important would be the current limits for each). It can, I believe, be done on some VFDs, but I would have to know more about the specific make/model to offer more. You could add a third contact block on the selector switch to feed this signal to the VFD.

Or, you could operate the 3Hp on same settings as the 2Hp??

Edit: This scheme begs the question of how you start/stop each saw - - at the respective saws. The STOP function is relatively easy: use a STOP PB at each saw with maintained, normally closed contacts. Both switches would be wired in series. For START, you could wire a pair of switches in parallel - - but it means you could start the selected saw from the switch on the other saw...not a good thing. To prevent this means the START circuit has to run thru the selector switch as well, and that gets pretty complicated to design remotely ....on a woodworking forum. And, I suspect somewhere in here, it's cheaper to just get a second VFD!

[Dan Friedrichs]

Tom, I recently bought a cheap VFD on ebay that has parameter settings for 2 different motors. I'm not immediately sure how you specify which motor is being used, but it definitely allows programming of 2 motors and switching between them.

That said, it was only $100 for a 2HP VFD, so I'd probably just buy a separate one....

[Matt Mattingley]

The problem here is, there is a 3 hp in a 2 hp Motors that do not have the same characteristics. They can be run in the V/H mode with the 2 hp motor having overload fusing.

These can be run together if desired. The drive needs to be sized accordingly. You can start both motors using the same drive.
If you're going to hard start using a contactor the VFD has to be rated for the smallest motor + 450%.

So if the 2 hp is already online and you want to add a 3 hp, the VFD needs to be rated for 5 hp +450% of 3 hp. Average amps per horsepower is 3A. So to accomplish a hard start on the largest motor you would need
6 A output + 3hp X(3A x450%)= A 15 hp VFD. They are about $1000.

This is a phase perfect technology. They are pretty much running a 20 hp VFD. This creates three-phase with allowable hard starts up to 10 hp. Pretty neat kit if you want to spend that kind of money. Phase perfect cannot variable speed a selected machine. They are only a very well-balanced phase converter.

I run in my shop numerous VFD's and an 20 RPC and a 5 hp RPC. My RPCs are only used to run my machines that are in the 550 to 600 V range. I do have one plug for 240 V three-phase off the RPC. I am comparing apples to oranges here. A RPC or phrase perfect will convert and whole shop. A VFD is usually just one machine. Most of my southern friends don't need a Rotary phase converter (RPC). Last year I built my own portable for testing machines. It converts single phase to three phase 240 V/600v. These are not toys!
http://youtu.be/gs-wPZOLc2A

[Tom Trees]

Assuming you can successfully manage the 'logic' part of this (don't switch the saws while VFD is active), then you CAN do what you describe. I'm also going to assume you'll run these at rated speed - - just using the VFD to get 1ph --> 3ph power conversion.


I'd put 2 starters in a electrical enclosure with the VFD and use a single 3-position switch on the door to select the respective saws: "3Hp - OFF - 2Hp". Two contact blocks on the switch would have XOO (on-off-off) (:: 3Hp saw starter ON in left position), and OOX logic (:: 2Hp saw starter ON in right position).

You can put a pilot light, fed from the VFD terminal strip, to indicate the VFD is running and/or stopped, and so inform you it's safe to switch. This would allow you to leave the VFD itself powered all the time, should you choose to do so.

That leaves the logic to change the VFD settings to appropriate values for the respective saws (most important would be the current limits for each). It can, I believe, be done on some VFDs, but I would have to know more about the specific make/model to offer more. You could add a third contact block on the selector switch to feed this signal to the VFD.

Or, you could operate the 3Hp on same settings as the 2Hp??

Edit: This scheme begs the question of how you start/stop each saw - - at the respective saws. The STOP function is relatively easy: use a STOP PB at each saw with maintained, normally closed contacts. Both switches would be wired in series. For START, you could wire a pair of switches in parallel - - but it means you could start the selected saw from the switch on the other saw...not a good thing. To prevent this means the START circuit has to run thru the selector switch as well, and that gets pretty complicated to design remotely ....on a woodworking forum. And, I suspect somewhere in here, it's cheaper to just get a second VFD!

Thanks Malcom
Judging from what you've said ...
It does not sound possible, to have a rotary switch to change over, from machine 1 to machine 2 by using the low voltage panel ...
Even if the VFD was plugged out/power off no illumination on screen and then,only then, ... use the second rotary switch that would be inbetween
the motor and the VFD to change over motor to the other .
As you said, it seems that the only parameter difference between machines, would be the motor HP rating (for just using the VFD for phase conversion purposes)
I did not think it would be necessary to have a really cool light to tell me which machine is ready to be initiated, as I thought a rotary switch with an arrow
or similar would be enough. (thanks for the suggestion though)
I have not used a tablesaw yet so can't say for sure that 2HP would not be enough ..I'm patient though (not to mention very cautious about using a TS)
and the scheme you mentioned could be made feasible ...As I was thinking of making a latch on the start button/bar system I previously mentioned
anyway , ( something like Carl Holmgrens switch design, but with a hidden latch )
Since I am the only one who is in the workshop, the possibility of starting one TS with the other TS switch is not a concern .

Dan
I am interested in knowing what VFD you got, which has the option of having the ability to change between machines .
I'm struggling to save up for the one VFD so having two is not an option ...
I originally got this second TS for cheap,to use for the motor to make a cyclone with , as I thought it was 3HP and a farm style tablesaw in the advert pics .
As It turns out it is an OK machine, just needing a lot of work ,and I couldn't bare not souping this baby up .
Some might like it here because it's another Italian beast in the shop .

Matt
I think I confused things somewhere, by not stating that I would be only using one machine at a time .
Thanks though for your comments ,I'm sure their is some lurking folks gleaning from your expertise !

So if it all comes to it, and I can't figure it out ...
I know with a cheap 100 quid unit, that I can stick a rotary switch between the motors and the VFD and change
the max voltage parameter ...
I imagine you could get used to it
I might ask some folks on youtube, with the same VFD I have allready, can it be done ...
It might take some time to get a reply though and I worry that this thread might have lost momentum, so to speak .
Can't mention any Italian machine on this forum without some piccys though !
That's the rules :cool:
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Magic tablesaw (Possibly Funken too, from the only other pic I've seen on the web )
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Thanks again folks .
Tom

[jack forsberg]

Not all VFD's have internal break resistors or if they do they are usually pretty small. Not all VFD's have the internal hardware that external break resistors can be added. If high inertia stopping is required, this needs to be a prerequisite when selecting a VFD. I'll be testing this break resistor in the near future on an 18" Direct drive table saw. It is 1000 W 30R. VFD's cannot displace the heat generated (by themselves) in heavy inertia stopping. A external break resistor needs to be added. This thing weighs more than the VFD.

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You know one thing not mentioned here is ithat the majority of VFD's in the world are actually being fed three phase power and as such in a lot of cases don't need an external break resister to dump the high DC bus voltage . This is your typical fault if the deacceleration is too fast for the internal break sector . As others have suggested the motor is the generator and regenerative braking can dump power back into the three phase mains makes the VFD more energy efficient . The reason for breaking machines faster than they would normally coast down in terms of safety is to do with rundown accidents . Many a finger is lopped at run down . Blades run silent and rundown accidents caused by reaching in to grab a piece of scrap And not realizing the blade is still spining . It's well-documented in Europe in accident reports being dramatically reduced by having machine stopped in less than 10 seconds .

[Matt Mattingley]

You know one thing not mentioned here is ithat the majority of VFD's in the world are actually being fed three phase power and as such in a lot of cases don't need an external break resister to dump the high DC bus voltage . This is your typical fault if the deacceleration is too fast for the internal break sector . As others have suggested the motor is the generator and regenerative braking can dump power back into the three phase mains makes the VFD more energy efficient . The reason for breaking machines faster than they would normally coast down in terms of safety is to do with rundown accidents . Many a finger is lopped at run down . Blades run silent and rundown accidents caused by reaching in to grab a piece of scrap And not realizing the blade is still spining . It's well-documented in Europe in accident reports being dramatically reduced by having machine stopped in less than 10 seconds .

Jack, even some three-phase equipment that is being fed three-phase using a VFD from three phase utility line, for hirer inertia stops, Break resistors are still needed. But, they are about a 1/20th the size, for reasons you just stated. For example this 5 hp motor is getting 1000 Watt break resistor. This same break resistor could be used on a three phase VFD that (with three phase utility) is 100 hp. A VFD can create reactive current in breaking state. Single phase shops electrical is not really set up with utility to be back feeding this kind of energy. Most of the time the energy that is back fed is usually consumed in the industrial plant and never makes it back on to the Power grid. I guess you can say it is kind of a on-site generator.
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[Matt Mattingley]

http://www.sawmillcreek.org/member.php?130924-Tom-Trees
You can actually use the same VFD running two different machines that are different horsepower. You need to put adequate fusing (after the VFD) for the smaller machine (and you can use a simple forward reverse contactor rewired and use the onboard relay in the VFD to switch at 0 V/hz). But you need to buy the VFD for the larger machine motor.

[Todd Willhoit]

You know one thing not mentioned here is ithat the majority of VFD's in the world are actually being fed three phase power and as such in a lot of cases don't need an external break resister to dump the high DC bus voltage . This is your typical fault if the deacceleration is too fast for the internal break sector . As others have suggested the motor is the generator and regenerative braking can dump power back into the three phase mains makes the VFD more energy efficient.

What you are describing is the exception rather than the rule. Very few VFDs have an active front end which permits regeneration back to the line. Aside from vehicles, for the vast majority of applications it 1) is not necessary, and 2) does not fit the price point.

If someone is going to use a braking resistor, please make sure it is kept free of dust. Resistors make nice fire starters. I know of one case in which the line voltage was elevated over night due to reduced loading on an upstream transformer. The increased line voltage caused a high DC bus voltage. The algorithm activated the braking circuit to dissipate the bus voltage. Since the line held the voltage high, the resistor was active for an extended period. Wood dust on the element ignited causing a large fire.

[Malcolm McLeod]

Another common sense reminder (like keeping them dust free): If you plan to use external brake resistors, make sure they are mounted appropriately. Don't put them where you can hit 'em with a bare leg, lean back on them, let a child touch them, etc....

It's easy to forget that VFDs and their accessories were developed for industrial environments, with UL/NEMA/NFPA/OSHA/MSHA codes typically requiring they be placed in a control enclosure or dedicated motor control center. As these devices migrate into our home shops, make sure you don't take their design roots for granted. Please.

I'd hate to think my advice got someone a spot on a GEICO commercial.

[jack forsberg]

Probably a good idea to keep the breaker resistor out of the VFD enclosure . Generally they don't get Warm Unless repeated breaking Over short periods of time . Should all be listed in your manual as to proper breaking intervals. It's also not the best thing for the motor to rapid stop. Some programs will lock the rotor with full torque at zero RPM . So the application should be reviewed as often a larger drive is required . Matt let me know how that big five horse power break unit works out and if you need one for your 3 hp