What's new
What's new

Why can't I use an A/C contactor?

leonpiper69

Plastic
Joined
May 8, 2013
Location
Levittown PA
So I am going through the manual for my new VFD and it says DO NOT connect and A/C contactor to the output of the VFD....... why?

I intended on just running the output of the VFD to a receptacle and just plugging my lathe into the receptacle and using all the controls on the lathe.

Really hoping I don't have to cut all the controls out of the lathe and direct wire the motor.
 
Because the VFD should never be open-circuited. All switching needs to be on the input side. You don't need to cut out the controls. Just bypass them and run the VFD straight to motor with reversing, etc. handled by VFD controls.
 
I can't give you exact reason for not putting a contactor or disconnect betwixt drive and load but most manufacturers indicate it can cause catastrophe.

This does not mean you can't use all the stock lathe controls. The output of the drive will be connected to the motor and all your controls will be wired to the logic buss of the drive. ON will signal the drive to run..OFF will turn it off. If you have a apron mounted handle for FWD/REV, this is easily wired into the buss to command those directions. A existing NC switch on a foot brake can be wired into the logic circuit to kill the motor when you stomp the brake.

Read the manual and you'll see how all this is possible using existing factory controls and switches. The logic wiring is the key and it's pretty simple.

Stuart
 
Because the VFD should never be open-circuited. All switching needs to be on the input side. You don't need to cut out the controls. Just bypass them and run the VFD straight to motor with reversing, etc. handled by VFD controls.

bypass = cutout. Why would I want to use cumbersome controls on a little box when I can control all of it right on the lathe. Except making it absolutely crawl (which would be rare) I can do everything right on the lathe.
 
I can't give you exact reason for not putting a contactor or disconnect betwixt drive and load but most manufacturers indicate it can cause catastrophe.

This does not mean you can't use all the stock lathe controls. The output of the drive will be connected to the motor and all your controls will be wired to the logic buss of the drive. ON will signal the drive to run..OFF will turn it off. If you have a apron mounted handle for FWD/REV, this is easily wired into the buss to command those directions. A existing NC switch on a foot brake can be wired into the logic circuit to kill the motor when you stomp the brake.

Read the manual and you'll see how all this is possible using existing factory controls and switches. The logic wiring is the key and it's pretty simple.

Stuart

I hadn't thought of wiring the controls to the logic bus. I was just wanting to keep it as simple as possible. Really the only thing I would need to wire in then after directly wiring the motor would be forward revers and stop and just not use the push buttons on the lathe. The completely adjustable speed control I will still be able to control manually. Just was not wanting to have to do it. More work with limited time to play with it. Really only can work on it when the kids are sleeping at night and I have ot be up early since the 5 yr old has this kindergarten camp thing from 0900-1130.
 
Don't know your machine. On my lathe, every factory switch was used in conjunction with the logic of the drive. If you look at the schematic for your drives logic circuit, you'll see that all commands are either switched open or closed. This is easy as your lathe controls are also switches that are open or closed.

Get the kids a babysitter, some popcorn and a Disney movie and sneak out into the shop, study the manual and you'll see it's really more simple than it appears.

The variable speed issue is solved with a small pot in a plastic hobby box mounted near the headstock. All the rest can be wired to existing controls.

Good luck.. a 5 year old can be a handful, but they're precious for sure.:)

Stuart
 
Don't know your machine. On my lathe, every factory switch was used in conjunction with the logic of the drive. If you look at the schematic for your drives logic circuit, you'll see that all commands are either switched open or closed. This is easy as your lathe controls are also switches that are open or closed.

Get the kids a babysitter, some popcorn and a Disney movie and sneak out into the shop, study the manual and you'll see it's really more simple than it appears.

The variable speed issue is solved with a small pot in a plastic hobby box mounted near the headstock. All the rest can be wired to existing controls.

Good luck.. a 5 year old can be a handful, but they're precious for sure.:)

Stuart

Wish that was an option. We don't really know anyone out here. wife is currently deployed. This is the closest we have lived to home and closest family is still a 5 hour drive one way. The boy is 5 and loves to help but I don't want him helping wire three phase let alone anything electrical or any machinery. I let him hit the on button on the mill sometimes but that's it. And he always has safety glasses on in the workshop.

I just don't trust people I don't know to watch my kids.

the variable speed I can still do manually, no need to wire anything and still have full control as it's mechanical and not electrically controlled. All I will need to worry about is forward, stop and reverse. It's actually the nicest lathe I have at home and I just picked it up. A 13" sheldon (although I will be surprised if I don't get banned because it's not a specific brand or something) w/ a 56" bed. My other 3 lathes don't compare. but I really want to get it up and running so I can get rid of another or two that I no longer need.

Tonight I will dive in and start hardwiring.
 
If you just use the VFD as a 3 phase source, it can work. Usually is best when the VFD is much bigger than the load, and can stand the inrush as the motor starts. We have members who do that.

The contactor coils do not particularly like low frequencies if you do vary speed, though, they may chatter, drop out, and otherwise cause trouble with the controls. That's with AC coils, obviously, but also DC coils with rectifiers and filter caps. And, with a "matched-size" VFD, how do you start it?

You can start the VFD, and have it accel to a frequency and voltage that the contactor coils will accept, and then you can start the motor, but you are already at a point where the motor inrush exceeds the VFD capability, so it will not work after all.

If the VFD is large, sufficient to start the largest motor, with the others already running, then you have much better chances. That is essentially what the "Phase Perfect" is... It is a high current partial VFD, (just the 3rd wire) which is intended to operate any combo of motors etc up to its max HP rating. And with the Phase Perfect, you DO use the regular machine controls.

But, with a VFD employed that way, you need a large one. For a 1 HP motor, at least a 5HP VFD would be needed. And it is probably best to find one where the manual does not scream and squall about switches as much as the very paranoiac ones do. Maybe the authors of the paranoiac manuals know dirty secrets about their VFDs.

I would suggest some form of filter after a VFD that you want to use that way.... A load-side inductor, followed by a radio interference filter. Keeps down interference, and reduces other spike voltage issues as well.
 
bypass = cutout. Why would I want to use cumbersome controls on a little box when I can control all of it right on the lathe. Except making it absolutely crawl (which would be rare) I can do everything right on the lathe.

You can pave your driveway with greased marbles and expect to do everything "right on the car" as you have always done as well.

I'm not sure which one is ultimately the more expensive rejection of conventional wisdom. But neither has a high probability of a favourable outcome.

Whilst "conventional Wisdom" does have higher probability of a favourable outcome than "UNconventional Foolishness", it is your VFD to abuse as you please.

We tried.
 
How much did your VFD cost?

If it's less than a hundred dollars, I'd go right ahead and disregard the
manufacturer's instructions and wire it up any way you want to.
 
bypass = cutout. Why would I want to use cumbersome controls on a little box when I can control all of it right on the lathe. Except making it absolutely crawl (which would be rare) I can do everything right on the lathe.
That's why rotary converters are used, they work just about the same as direct power from the electric company. VFDs when a certain change in the machine as designed is wanted or when someone wants to cheap out but then the cost is figuring how to use it.
Dan
 
A VFD wired to be controlled by the lathes standard functions (just ad the VS dial ;-) is a joy toi use and worth the effort.

Spindle direction, spindle braking and even a jog function (My Mazak has a button on the bed behind the power feed shafts.)

I run a 25 HP unit bought used (ebay) for very small money)

No contactors on the output, nothing ever get's unplugged except the mains when a lightening event is in the area.

Well worth the effort. I've got two done this way.

RPC put such a draw on the mains when starting. (Brown out)
That is not an issue with a VFD, and the reason I changed over.
 
If you just use the VFD as a 3 phase source, it can work. Usually is best when the VFD is much bigger than the load, and can stand the inrush as the motor starts. We have members who do that.

The contactor coils do not particularly like low frequencies if you do vary speed, though, they may chatter, drop out, and otherwise cause trouble with the controls. That's with AC coils, obviously, but also DC coils with rectifiers and filter caps. And, with a "matched-size" VFD, how do you start it?

You can start the VFD, and have it accel to a frequency and voltage that the contactor coils will accept, and then you can start the motor, but you are already at a point where the motor inrush exceeds the VFD capability, so it will not work after all.

If the VFD is large, sufficient to start the largest motor, with the others already running, then you have much better chances. That is essentially what the "Phase Perfect" is... It is a high current partial VFD, (just the 3rd wire) which is intended to operate any combo of motors etc up to its max HP rating. And with the Phase Perfect, you DO use the regular machine controls.

But, with a VFD employed that way, you need a large one. For a 1 HP motor, at least a 5HP VFD would be needed. And it is probably best to find one where the manual does not scream and squall about switches as much as the very paranoiac ones do. Maybe the authors of the paranoiac manuals know dirty secrets about their VFDs.

I would suggest some form of filter after a VFD that you want to use that way.... A load-side inductor, followed by a radio interference filter. Keeps down interference, and reduces other spike voltage issues as well.

Just gonna bite the bullet and hard wire it. Three hp VFD 3 HP motor so.... but that explains why the first one was just clicking, not enough frequency to close the contactor.
 
How much did your VFD cost?

If it's less than a hundred dollars, I'd go right ahead and disregard the
manufacturer's instructions and wire it up any way you want to.

If it was less than a hundred bucks I wouldn't be allowed to post about it ;)

It's a 3hp Teco I just bought brand new direct.
 
A VFD wired to be controlled by the lathes standard functions (just ad the VS dial ;-) is a joy toi use and worth the effort.

Spindle direction, spindle braking and even a jog function (My Mazak has a button on the bed behind the power feed shafts.)

I run a 25 HP unit bought used (ebay) for very small money)

No contactors on the output, nothing ever get's unplugged except the mains when a lightening event is in the area.

Well worth the effort. I've got two done this way.

RPC put such a draw on the mains when starting. (Brown out)
That is not an issue with a VFD, and the reason I changed over.

The Teco has the variable speed dial, but I would rather use the variable speed on the lathe. Don't have to reach as far that way as I won't be mounting the VFD to the lathe but on the wall right behind it.
 
The boy is in bed but the 2 yr old is still up. So while she watched pepa pig (I had the baby gate on the door to the garage and the living room is about 14 ft from that door) I managed to get it up on some dollies so I can at least have better access to the wiring.

Once she goes to bed I will work on gutting the contactor panel and extra fuse box (though I may wire in the fuse box later on) and at least test wire it up and make sure it functions properly before mounting everything and even starting on moving other lathes around.

I will end up wiring the forward reverse and stop into the logic bus but speed control will just be controlled on the machine even though the VFD has speed control.
 
The Teco has the variable speed dial, but I would rather use the variable speed on the lathe. Don't have to reach as far that way as I won't be mounting the VFD to the lathe but on the wall right behind it.

put a 10K pot ON THE LATHE! That's why I wrote (ad"d" the VS dial) Sorry for my typo and cryptic way of stating things.

The VFD on the big lathe is on the wall behind thew machine, along with the braking resistor module, and the vfd that supplies the suds pump. The smaller lathe has the VFD in the tail end cabinet.. I never touch either of the units unless I want to reprogram some feature (accel/decell or braking time /mode etc.
When running collet work, with higher spindle speeds, the lighter weight on the spindle allows faster ramp times to speed and then stop. That can save time on repeat work when optimized.

OH! I use the gear boxes in the headstock for all they have to offer. Always trying to keep the drive motor "happy" and quiet at around 60 hz. There are some sweet spots!
I use the VS function of the VFD to hit the highs and lows. Fine tuning a chip is a pleasure. "Turn 'em blue. then back a few" can go for depth of cut, feed or sfpm.

Last week I was coiling 1/4 dia wire in 12" diameter rounds. With a suitable mandrel in the chuck, and the headstock gears set to the lowest spindle speed (39 rpm at 60 hz), by dialling back the potentiometer for the VFD to output about 5hz, I had a rotation rate of about 5 RPM and could accomplish the task of guiding the wire by hand. It took all of 10 minutes to wind up four coils of 6 feet of wire each. ;-)
 
put a 10K pot ON THE LATHE! That's why I wrote (ad"d" the VS dial) Sorry for my typo and cryptic way of stating things.

Ah ha. That would be easy too. But my lathe has a cool handle to just increase and decrease speed on the fly infinitely variable. So I kind of want to use it. That is half the fun of having a walking stick I think.

I just need to figure out wiring up the three switches. The Teco manual doesn't give a lot of info. I am sure I will figure it out I just need to do some reading and then start checking some wiring. Looks like S1-S5 are all normally closed switches for fwd/stop rev/stop preset spd 1 preset spd 2 and reset. but none for starting. I have a nice box on the front of mine with three giant buttons FWD, RVS & STOP. I would just like to use them :(
 
In case it helps anyone else in the future the printed manual that comes with the Teco L510 is missing have of the actual manual. I found the manual online and there is a way to at least program it to use the start and stop buttons (potentially but I need to check my factory sheldon buttons to verify if those will work). But I still don't see a way to use the reverse button..............yet.
 








 
Back
Top