Thread: VFD switching on a Hercus 260

Originally Posted by cba_melbourne

>...........I need to get my head around this 2-wire vs 3-wire control issue...........


It is actually 3 or 4 wires (not 2 or 3 wires as I mentioned). But let me explain what I mean:

3-wire start-stop control

Imagine a VFD that is programmed to run forward, if you apply 24V to input 1. And it runs in reverse if you apply 24V to input 2. And it stops, if both inputs 1 and 2 are open. That is a total of 3 wires (+24V, run FWD, and run REV). If this control cable suffers a short circuit between +24 and any of the other two wires, the motor starts on its own with potentially dire consequences. If say the FWD wire breaks, you may have the operator leaving the main switch in FWD position and walk away, and when someone moves the broken wire it may make contact and the motor starts unexpectedly, with potentially bad consequences.


4-wire start-stop control

Imagine a VFD that is programmed to run only forward, if 24V is applied to BOTH input 1 (run FWD) AND input 3 (enable VFD). And it only runs backwards, if 24V is applied to BOTH input 2 (run REV) AND input 3 (enable VFD). Now a simple short between any two wires is not going to start the motor. And a broken fwd, rev or enable wire is going to cause the VFD to trip, so you need to turn it off and on again to restart (the software for 4-wire control regards any fwd or rev signal without enable signal as a potentially broken cable and locks the VFD. It also regards any FWD or REV signal with enable signal both active during power-on of the VFD as a broken wire and locks the VFD).

Wire shorts usually happen when the control cable gets squashed. Wire breakage happens where control cables are continuously bent, or where cables are not properly finished/protected at the connector ends. Both problems are initially often only intermittant. The 4 wire method uses one extra input, it is still not 100% foolproof, but definitely safer than the 3 wire method. Me personally, I find this reason enough - but I concede that many low cost VFD have limited input lines, and the 4 wire method may mean to sacrifice another feature....

Chris

PS: I would personally not recommend to connect the chuck hood to an E-Stop, IF you are the sole user of this lathe. If other people use it too, then yes.

Stop in 3 wire is "should be" normally closed, so that an open circuit should stop the motor, and start FWD/START REV are normally open, with starts interlocked with stop.

Ok....not sure what that was all about....

This discussion has bought up some flaws in my system. I use a double pole double throw rotary switch. Rotate one way for forwards, other for reverse. The first pole signals the FWD and REV logic, the second pole signals the ON logic. If-the FWD wire was to break, i would have no forwards but still reverse. If the ON wire was to break i'd get nothing. But if the REV wire was to break i would get FWD with the switch in either position. This is because with no FWD or REV signal the huanyangs will run FWD with just the ON signal.

As to the whole chuck coming off thing, my point is not to just set the VFD to 2 sec ramp down and try it. Start with a high number and work your way down. Same if you wish to use DC braking, start with the lowest voltage possible and go from there. With luck the worst you will do is overload the VFD, but if you are unlucky you may be playing a very scary round of classic catches.

Cheers,
Ew

Originally Posted by Pete F

The first VFD I fitted I used CAT5 data cable in fact.

My installation manual calls for thin gauge twisted pairs for control wiring, so I am planning to use Cat5 too.

Chris,
Thanks, that leaves me one logic input spare for e-stop.

Hi jack620,
I attach a quick diagram of what other members have beensaying to give you an idea of the control circuit that is being discussed. Ihave put the Emergency Stops into the VSD at Input 3 and in the program youwould need to make it an overriding command on Input 1 & 2 which are theForward & Reverse commands. This way you can set the amount of ramp up& down times for the three inputs and is in keeping with what other membersare saying about bringing the Lathe to a controlled stop in the threesituations.
I would like to add that I would not wire the control this wayas I would use other methods to perform the Emergency Stop.
You need to read the Altavar’s Manual closely as the Inputs1 to 4 are programmable and you need to set what type of Reset you want.
The diagram is just simplistic and does not take intoaccount if you have other controls e.g. Light, Water etc.
If you are not good at control circuits, sizing the CircuitBreaker etc I suggest you get an Industrial Electrician and you may need tospeak to a Schneider Drives Technical person about the program parameters ifyou are unsure, they are usually helpful on the phone.

Regards,
Keith_W.

Hi Keith,
thanks for going to the trouble. I started on the wiring this morning and I am doing exactly as you suggest with the addition of the original Hercus start button being connected to LI4. I will also include the original stop button in the series loop with the foot and headstock cover switches.

That way the original controls function exactly as they always did. I just need to check out how to program the inputs to make this work. LI4 will need to be able to accept a momentary input.

Chris

Originally Posted by Ueee

Now why didn't I thinknk of that.........

You clearly stated earlier in the thread that having a chuck come loose would not be a problem.

No. He said that it had not been a problem ON HIS LATHE.

Said lathe having same spindle nose etc as the one under discussion and fitted with working VFD.

I have nothing to add as my lathes have either DIN or camlock spindle noses. Well, except for the Smith-Drum but adding a VFD to that one would be akin to applying lipstick to a pig.

PDW

Originally Posted by Pete F

You get what you pay for.

Like Stuart, my e-stop and regular stop are the same. On the 260 it's a 2 second stop cycle, I can't recall what the other lathe is, I probably would have made them the same. I can't imagine a VFD being able to stop a lathe so suddenly it would unscrew a chuck, especially not without some pretty serious braking resistors. That energy needs to go somewhere.

No mention of Pete's lathe only.

This is now just a pointless waste of space on Chris's thread. Clearly the chuck will never unscrew from a hercus under vfd ramp down and braking. Since I don't own a hercus clearly I have no idea what I am talking about.

Here is a basic drawing for a 3 wire control. I'm not sure if it is totally applicable to the VFD and the existing controls.
I could not see a circuit of the existing controls in the posts, did I miss it?

-Josh

The Altivar 12 has a nice extra feature called "decelleration ramp adaptation".
In addition to normal time based ramp as fond on just any basic VFD, it has two more options that may be selcted instead:

- It can automatically increase decelleration time when stopping high inertia load, to prevent DC bus overload. This means you always have the shortest possible stopping time, even when changing workpiece weight, without need to set manually a longer ramp time. This function is only available without an external brake resistor module.

- Motor braking without the use of an external brake resistor. It makes use of motor losses to dissipate some of the regeneration energy.

Both functions are new to me (my VFD's are all older models). Once you got it all setup and you had time to play around a bit, I would like to hear what you think about these two modes. Chris

Thanks gents. The VFD is installed and "working". I have initially just configured it for 2-wire control via the rotary selector. It works in FWD, but not REV. I have checked and there is 24V on the logic input 2 when I select REV. I need to look at the settings for input 2.

I have set max freq to 75Hz. That seems fast enough to me.

Accel and decel are set to 2 seconds for now.

Chris

Hi Chris,

Do you have an parameter like "reverse rotation select"?

Hard to help without the manual.

Stuart

Found a manual. Assuming its the right one. You do have reverse inhibition but the default is no. Page 60 if I have the right manual.

So no help there

Stuart

Stuart,
thanks for looking into it for me. There is a parameter called Reverse Direction (rrS) which selects the logic input assigned to the reverse command (page 66). Default is Inactive. It wasn't easy to find, nor is it intuitively named.

The VFD is now fully functional. All controls operate exactly as they did before. Well almost- selecting the FWD/REV knob to centre with the motor running doesn't stop the motor. I have to hit the red stop button. I can live with that. I may move the speed control pot to a more convenient position if I get sick of leaning down to adjust the speed.

I've also included a picture of my foot operated e-stop. A standard palm-operated stop switch mounted from behind the cabinet with a hinged wooden kick-plate.

Thanks to everyone who offered advice.

Chris

Originally Posted by jack620

Stuart,
thanks for looking into it for me. There is a parameter called Reverse Direction (rrS) which selects the logic input assigned to the reverse command (page 66). Default is Inactive. It wasn't easy to find, nor is it intuitively named.

The VFD is now fully functional. All controls operate exactly as they did before. Well almost- selecting the FWD/REV knob to centre with the motor running doesn't stop the motor. I have to hit the red stop button. I can live with that. I may move the speed control pot to a more convenient position if I get sick of leaning down to adjust the speed.

I've also included a picture of my foot operated e-stop. A standard palm-operated stop switch mounted from behind the cabinet with a hinged wooden kick-plate.

Thanks to everyone who offered advice.

Chris

Chris
So how did you end up wiring it up?