VFD braking?

[VicParticipant @vic]

[VicParticipant @vic]

I know nothing about VFD's so please speak slowly when replying!

I bought a wood turning Lathe (sorry) which has a three phase motor and a VFD with an additional digital readout and start/stop/reverse/speed control. So far so good and all works well. When you stop the Lathe though it takes quite some time for the spindle to actually come to a stop, are there any settings on the VFD that can be changed to apply a braking effect to stop the spindle quicker?

I've had a quick look at the manual of which one half is Chinese and the English half may as well also be Chinese!

I'm not hopeful but it doesn't hurt to ask! It's a Delta VFD-S if that makes any difference.

[RobCParticipant @robc77385]

One way to do it is to connect a 'braking resistor' to the drive which, when the VFD is configured to know it is there, will help it slow down faster. The manual will (usually) have a list of suitable sized resistors in it somewhere, along with the settings you need to change.

The braking resistors are typically low resistance, high wattage, ceramic units (mine took a 100ohm 300W resistor).

[Involute CurveParticipant @involutecurve]

Some also have a free wheel setting, which often slow down quicker with this setup.

[John CParticipant @johnc47954]

Vic, my inverter has a 'ramp up/down' setting which determines how fast the spindle gets up to speed, and slows down. It's not braking as such, just the time taken to go from selected speed to zero. Yours would appear to be on page 5-3 of the manual, called decel time (1-10 and 1-12) The default appears to be 1 sec, so it may have been altered. Chapter 4.4 shows how to alter the parameters. Without the unit in front of me, I can't help you on changing the settings, but if you work through the guide 4.4 you should be able to get to Group 1 (Basic parameter), then item 10 (decel) and set the value to 10 (=1second)

There is a section on braking resistors, but you may find that decel solves your problem. If all else fails, you could try a factory reset to get accel and decel to be 1 sec

Rgds,

John

[Neil WyattModerator @neilwyatt]

I have mine set to ramp up/down on the start & stop switches, but to cut power completely on the e-stop.

If you have a jaguar CUB or other IMO inverter this may help:

http://www.model-engineer.co.uk/news/article/3-phase-conversion-and-other-alternative-methods-of-powering-a-mini-lathe/18752

Neil

[KWILParticipant @kwil]

Vic, just think of us who 50+ years ago were turning wood, no fancy VFD drives then!!

Apart from being able to set the speed carefully (and low) when roughing, I cannot see the need for a VFD. Perhaps Jason has a view?

[VicParticipant @vic]

Posted by KWIL on 19/09/2015 12:33:51:

Vic, just think of us who 50+ years ago were turning wood, no fancy VFD drives then!!

Apart from being able to set the speed carefully (and low) when roughing, I cannot see the need for a VFD. Perhaps Jason has a view?

It's just the way it came:

**LINK**

The variable speed (and reverse) is proving to be very useful but I liked the many of the others specs as well.

[VicParticipant @vic]

Thanks all so far for your input, I'll delve further into the manual.

[David JuppParticipant @davidjupp51506]

Some VFDs also offer DC injection braking to give more rapid stopping.

[Mike PooleParticipant @mikepoole82104]

Hi Vic,

Just to try and enlighten you on what your vfd is doing for you and help you to get the best from it. The supply is AC and is rectified to give a high voltage DC supply from which 3 phases can be created at any frequency you need for the speed you demand. The problem with trying to slow down quickly is the output stage of the inverter acts as an input back to the DC supply which will push the voltage higher, if the drive detects this it will try and dump this to an external resistor if fitted but if not fitted it will shut the drive down to protect itself. It looks as though your drive has a parameter 1-15 that can be set to slow the drive as rapidly as possible depending on the load, it may be worth trying this out as if you choose a fixed slowdown ramp it will have to be for the worst case scenario which will be the heaviest or fastest job you do. The great thing about VFDs is that they can be made to slow faster than a simple motor drive which unless a mechanical brake is fitted will always coast to a stop. With a resistor fitted to absorb the energy from the machine some quite savage rates of braking can be achieved. If the nose of the lathe takes screw on faceplates and chucks this may try to unscrew the faceplate when braking (just a possibility)

Mike

[egaParticipant @ega]

Vic:

You don't say what woodturning lathe you have but on my Graduate I have always followed the advice of the late Peter Child and slowed the lathe by pressure on the LH faceplate when turning between centres. I accept this doesn't answer your question directly and, like you, am no expert on VFDs. I don't have one on my machine but feel it would be very useful as changing the belt is tiresome.

Michael Poole:

I found your explanation to Vic helpful. Are you by any chance also conversant with the TECO Minicon VFDs? I have never got round to fitting the braking resistor which the supplier provided mainly because despite diligent reading of the manual I was not clear as to where it should be fitted.

My VFD runs my metal lathe where consistent, rapid braking would be a great help with screwcutting.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Michael Poole on 19/09/2015 14:37:52:If the nose of the lathe takes screw on faceplates and chucks this may try to unscrew the faceplate when braking (just a possibility)

That lathe does have a threaded spindle so active braking might not be a good idea.

Russell.

[VicParticipant @vic]

The chuck is threaded onto a M33x3.5 spindle but has grub screws to prevent it coming off unintentionally.

[Mike PooleParticipant @mikepoole82104]

Hi ega, I do not have first hand experience of the teco mincon drive but I had a little browse of a manual on line and as David mentions above it would appear they use the DC injection braking system, this might explain your difficulty in finding what to do with the braking resistor as this type of braking would not use a resistor. There are a few parameters to set to give the braking effect required for your application. DC injection can give a very powerful effect and is sometimes used as safety brake on things like drilling machines where an almost instant stop can be achieved. Used as an emergency stop for operator protection puts quite a high mechanical stress on the machine but a much milder effect can also be used.

Mike

[egaParticipant @ega]

Michael Poole:

Many thanks for your rapid reply. I shall have another look at the manual in the light of your comments.

[Gary WoodingParticipant @garywooding25363]

I had a quick look at the online manual for the Delta VFD-S unit. Page 5-3 shows that the default setting for parameter 1-10 (the deceleration time) is 10 secs. which is quite a long time when you just want to stop the motor. Changing this parameter to to a lower value (2, say) should improve your perception of the slowdown time. If the time you choose is too low then the VFD will "trip out" with an overload error and you will have to reset it before you can continue. Fitting a braking resister will allow you to choose a lower value without tripping out, but you must choose a resister that matches your VFD power rating. My guess is that a 2 sec decel time will probably work OK.

[John CParticipant @johnc47954]

Gary, I think that the decel units are 0.1 sec – so the default is 1 sec.

John

[KWILParticipant @kwil]

Page 5.3 in the online manual states quite clearly Factory Default for Acceleration and Deceleration is 10.0 seconds, yes Ten secs

[John CParticipant @johnc47954]

And page 5.24 in the online manual states quite clearly Deceleration Time units 0.1 yes nought point one secs. With a default of 10 units, giving 1 second. Just so the OP doesn't get confused. A ten sec default accel and decel time would be quite long.

[VicParticipant @vic]

Thanks for the clarification folks. I only had a quick look but missed the 0.1 seconds per unit bit. As a result changing it from 1 second to 0.1 second isn't going to make a noticeable difference is it?!

[Gary WoodingParticipant @garywooding25363]

The Decel time on page 5-3 shows the range is from d0.1 to d600 Sec, with a factory setting of d10.0. So I think page 5-24 really means that the unit of resolution is 0.1 sec. Otherwise the d0.1 lowest value of Decal shown on page 5-3 would mean 0.01 secs. which is absurd.

 

(The edits were to get the hilites correct – my screen doesn't show them at the time of creating the post – everything is shown in bold)

Edited By Gary Wooding on 20/09/2015 10:21:33

Edited By Gary Wooding on 20/09/2015 10:22:21

Edited By Gary Wooding on 20/09/2015 10:26:41

[Les Jones 1Participant @lesjones1]

I think KWILL's interpretation is the correct one.

Les.

[Neil WyattModerator @neilwyatt]

Posted by Gary Wooding on 20/09/2015 08:45:41:

I had a quick look at the online manual for the Delta VFD-S unit. Page 5-3 shows that the default setting for parameter 1-10 (the deceleration time) is 10 secs. which is quite a long time when you just want to stop the motor. Changing this parameter to to a lower value (2, say) should improve your perception of the slowdown time. If the time you choose is too low then the VFD will "trip out" with an overload error and you will have to reset it before you can continue. Fitting a braking resister will allow you to choose a lower value without tripping out, but you must choose a resister that matches your VFD power rating. My guess is that a 2 sec decel time will probably work OK.

Gary's comment above is exactly my understanding of the situation. Experiment with using the 'coast' setting as well and see which gives the best results.

If you don't use an external resistor braking torque will be limited to 100% (or a smaller fraction, perhaps as low as 30%) of running torque – this suggests that the minimum stopping time can be no shorter than the fastest spin up time, unless you add a resisitor.

[MuzzerParticipant @muzzer]

If you look in the manual at Section 5.3, Group 8 (special parameters), there are settings for DC brake (aka DC injection). This doesn't require the braking resistor to be fitted and can give a useful improvement on decel times. You end up dumping the kinetic energy into the rotor but that really won't be an issue for an application like this with so little inertia. After all, the rotor "winding" of an induction motor sees a fair bit of current / dissipation under normal load anyway – it's how they work.

Have a go at playing with the settings. You won't damage anything if you've set the name plate parameters already and it can give quite a useful improvement. This setting is an additional function on top of the normal decel.

The limitation on decel is the DC bus voltage rising if the regen energy exceeds the losses in the system. Without a braking resistor circuit, the VFD can only inhibit its operation to protect itself if you try to decel too quickly.

Murray

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