Thread: Another VFD & 3 phase question

> Can just about go anywhere near the mill/lathe on the wall. I standard power lead would have been handy though! Can't wait to have a play!

Simon, some hints:

- you want the cable from VFD to motor as short as possible
- if you have some, use shielded power cable for this (you can also slide a standard cable through a braided copper hose). It reduces rf interference to other peoples TV or radio nearby
- there must be no switch or fuse between motor and VFD, you must bypass all existing switchgear. But you may re-use your existing switchgear to operate the low voltage inputs to the VFD
- read the manual. For a machine tool, it is best (safer) to wire up the VFD controls such that accidental cable breakage prevents the motor from starting (3 wire method, both the signals for "run" and "forward" must be active for the motor to run, one active signal alone will not start the motor).
- wall mount is fine, but if your VFD has open cooling slots you must protect it from flying chips and dust. Some VFD's come already in a protection enclosure. But most VFD's are bought as bare units. They are intended to be installed inside an enclosure. A steel enclosure with a sealed hinged door is best, as sold by electrical suppliers. If a small metal chip thrown from your mill or lathe is allowed to enter through a slit in the VFD housing, you are likely to have a bang and smoke and a total write off of the VFD.
- you can add a fan with a filter mesh to get fresh cooling air into your enclosure. If you choose not to separately vent your enclosure, you must choose the enclosure large enough to allow for passive convection cooling. The VFD installation manual (sometimes also the user manual) will tell you how much space your VFD needs between itself and the adjoining cabinet walls. Usually you must derate the power of your VFD something like 10% for every 10 degree C that you allow the temperature inside the enclosure to rise above 30C. The VFD manual will tell exactly. In Australia, on a hot day, the enclosure can be 40C befor you even swith the VFD on. All modern VFD's will derate themselves if temperature rises, most do this by first reducing the chopper frequency and then by reducing output power. Also note that life span of a VFD is almost halved for every 10 degrees C you increase its operating temperature above some 30C. One of the most common reasons for VFD failure is drying out of the large DC-bus capacitors, due to either long storage without being connected to power - or to being operated in too hot an environment.

Chris

Hi guys, Paul and Chris,

Thanks Chris, what you have mentioned is pretty much covered in the user manual although you have to read about 50 pages of crap to extract it! I will probably mount it on the wall and provide it with the required protection from swarf. The leads to the motor should not be any longer than about 1M max. I was hoping to use the same unit to power both the mill and lathe (if I was to go down that path) but looking at the user defined and motor specific parameters, I'm not convinced that this would be an acceptable option. Unless I used identical motors for both. In any case, $140 for a 2.2Kw or less for a 1.5Kw it's hardly a big investment.

The motor I am using to play with ATM is a 3 phase variable frequency/speed motor with a maximum RPM (according to the name plate) of 4000 rpm. It is a 2 HP motor so I have set the max current at the appropriate level of 6 amps but have no idea how many poles it has or what it's specific V/F curve should be. In any case it happily does 5000 RPM at about 130Hz and seems it would continue to increase in speed linearly if the frequency was further increased but I dare not!

I have adjusted the V/F curve for the high torque output as in the book and have even increased the minimum and intermediate voltages on the curve which seems to have increased the torque at low frequencies. I'm not sure how much you can deviate from this without affecting the operating temperature of the motor though. The motor is rated at continuous for all speed ranges so it may be OK but not sure.

I have had a play with the carrier frequency too. I found the higher the frequency the less noise came from the motor and at setting 15 (20Khz) it was all but gone, although I dare say the neighbours may not be happy with the RF noise. The book makes mention that the higher the carrier frequency selected, the higher the heat buildup in the unit so once again a compromise has to be found, especially (as Chris mentioned) on hot days.

Now that I have had a play with 3 phase and VFD's and DC motors and their speed controllers, I can now appreciate the high torque generated a almost 0 rpm of DC motors compared with VFD driven induction motors.

I have not had the opportunity to make or attach a remote console for the operation of the VFD, I'm still just playing with it on the bench with the motor and using the (somewhat frustrating) front panel for all functions.

One other feature which may be of interest to others looking to purchase one of these: My VFD does not have a panel mounted POT BUT, it does have the decal on the front where one would normally go. It also states in the manual that if a remotely operated POT is to be used then an internal jumper needs to be moved which disables the POT on the front panel (if one were fitted) this answers the question as to what is to be done if you have a POT on the panel BUT you wanted to connect one remotely. No problem it seems.

Having fun!

Cheers

Simon

Originally Posted by simonl

One other feature which may be of interest to others looking to purchase one of these: My VFD does not have a panel mounted POT BUT, it does have the decal on the front where one would normally go. It also states in the manual that if a remotely operated POT is to be used then an internal jumper needs to be moved which disables the POT on the front panel (if one were fitted) this answers the question as to what is to be done if you have a POT on the panel BUT you wanted to connect one remotely. No problem it seems.

Hi Simon,

I did a bit of a blurb on fitting the missing pot ( although I think it was Joe that did it first) , in any event I use the exact same pot on a product, so have plenty available if you want one. I could drop one in the mail, just PM me your mailing address.

The thread on the mod is here..
https://www.woodworkforums.com/f65/hu...ml#post1437556

Regards
Ray

Originally Posted by RayG

Hi Simon,

I did a bit of a blurb on fitting the missing pot ( although I think it was Joe that did it first) , in any event I use the exact same pot on a product, so have plenty available if you want one. I could drop one in the mail, just PM me your mailing address.

The thread on the mod is here..
https://www.woodworkforums.com/f65/hu...ml#post1437556

Regards
Ray

That's great. Thanks for the offer Ray. PM sent.

Simon

I have asked this in another forum and have not gotten a good answer. the copper braided hose that you mention is that on the input power leads or for the output to the motor. in the instalation diagram it calls out a line reactor what purpose does this serve?

Originally Posted by oreos40

I have asked this in another forum and have not gotten a good answer. the copper braided hose that you mention is that on the input power leads or for the output to the motor. in the instalation diagram it calls out a line reactor what purpose does this serve?

I think the braided hose should go on the 3 phase output cables to the motor so shield any RF from the carrier frequency.

As for the AC reactor, others may know more but the instructions say to use one for PF improvement if the output capacity is greater than 1000 KVA. Not something I will ever need to worry about!

I'm still trying to work out how to adjust the ramp up and ramp down times. There are several references to 4 different ramp up and down times but I'm not sure how this works yet. I'll nut it out eventually.

Simon

Originally Posted by oreos40

I have asked this in another forum and have not gotten a good answer. the copper braided hose that you mention is that on the input power leads or for the output to the motor. in the instalation diagram it calls out a line reactor what purpose does this serve?

Simon's already answered the shielded cable part of the question...

The line reactor is for harmonic supression, there are usually two types used, the straight forward low pass filter type used for RF supression, the other type of filtering commonly used is dv/dt filtering for reducing voltage spikes, particularily where long cable runs are involved. (voltage spikes can breakdown motor insulation)

For home workshop usage, with cable runs fairly short ( usually less than 10m ) dv/dt filtering is not such a big deal, and with the sort of power levels home workshop vfd's are running, the RF levels aren't normally much of a problem.

If you are worried about RF interference, just get a TV or FM radio into the workshop and see if you can notice any interference.

Regards
Ray

Hi oreos40, and welcome to the forum.
At least now you have your question answered.

I see you are fairly new to the forum, so I thought I would let you know that I (and a lot of others here)consider Ray to be our electrical/electronic expert on the forum. He also has more than a handful of these VFD's himself, so is familiar with them and will definitely steer you in the right direction.

Just to show some stuff Ray works on, have a look here
https://www.woodworkforums.com/f65/po...ml#post1529000

Dave

Thanks for the info. and the answers. I have the components for the Vfd setup. I have a choice between DC or 3 ph VFD. the DC will go on the existing Lathe and the VFD will most likely go on the "monster" planned for the future. Thanks again!

I just won this in ebay auction. The guys says he has 2 more if im interested. I may get a few bucks off if i buy another one or two. Anyone interested? Easily wired for delta as they have the configuration for both.

http://item.mobileweb.ebay.com.au/vi...id=32581056191

Pm me.

Simon

Hi all,

OK I have had time for a little more of a play with my new toy. I am somewhat disappointed with the low end torque produced but I was expecting such based on discussions on this forum. My question is, How do I know if it's a limitation of the motor/VFD or whether I just have not capitalised on the system by having incorrect parameters set.

Namely all the variables that set the V/F curve. Can I increase the lower frequency voltages? How do I know if I have PD10 or PD009 set too high? will the motor heat up at low frequency? It's can't over current as I have that set with PD42.

Also PD145, 146,147. How do I max these to give maximum SAFE operation?

Cheers,

Simon

> I am somewhat disappointed with the low end torque produced but I was expecting such based on discussions on this forum.

Simon, sounds like what you have is a V/Hz only VFD. With those and an off the shelf 3ph motor you can expect no more than a 1:4 speed ratio. Than is from 25Hz to 100Hz, or more exactly 25-60Hz at near constant torque, and 60-100Hz at near constant power (where constant torque is the characteristic of a DC motor, and constant power is much like the characteristic of a diesel engine). All you can do with such VFD's is to optimize the low speed voltage boost parameter - you can increase this until your motor starts to run rough at about 15Hz. It will increase your available low speed torque, but nowhere near what you have at 25Hz.
If you really need to cover a wider speed range, you could:

- use a more modern VFD of the "sensorless flux vector" type, commonly just called a vector drive. Those can cover a speed ratio of about 6:1 to 8:1 with an off the shelf motor, meaning about 6 or 12Hz to 100Hz.
- or use a motor designed to run at much higher frequencies (like a water cooled router spindle motor used in cnc mills). With such a motor capable of 400Hz a 1:20 constant power speed range is possible.
- or oversize your drive. Say if you need 1HP at a 1:4 speed ratio, you buy a 1HP v/hz VFD and 1HP motor. But if you need 1HP at a 1:8 speed ratio, you can buy a 2HP v/hz VFD and 2HP motor. And so forth. The disadvantages are that you increasingly end up with a larger and heavier motor with larger inertia, and it costs more. But this is how they get large lathe to cover a wide speed range without using a gearbox to preselect a speed range.
- or use a DC drive. DC motors are constant torque from standstill up to extreme rpm's (until the rotor explodes from centrifugal forces). Brushless DC drives are in many respects like a VFD, same technology, but cover a vastly larger speed range. They also cost several times more than a VFD drive.

But that said, stop for a moment and ask yourself: WHY do you want a wider speed range in the first place? You say this VFD is for a lathe. Ok, what are the reasons that make variable speed desirable on a home/hobby type lathe?
- ease to change surface speed on the fly when facing (no need to stop and change gear and restart)
your simple v/hz VFD does that with ease
- when the lathe chatters, you can quickly change rpm up or down to avoid the speed that causes resonances that lead to chatter
your simple v/hz VFD does that with ease
- you can slow down much slower than the lathes slowest gear, think of thread cutting or winding springs or wires
your simple v/hz VFD lets you do this down to about 1/4 of the lowest spindle speed you had without variable speed, a vector type VFD would let you do this from standstill
- you can get twice the maximum spindle rpm for turning very small diameters or for polishing or for turning plastics....
your simple v/hz VFD does that with ease
- controlled acceration and decelleration is easy on the driveline components
your simple v/hz VFD does that with ease (you may have to program a longer ramp time if you use a large 4-jaw chuck with a heavy workpiece to avoid the VFD tripping)
- you get a brake, the spinde comes quickly to a stop as opposed to coasting to a halt, say for taking a control measurement or when hitting the emergency stop
your simple v/hz VFD does that with ease
- safe "plug reversing"
your simple v/hz VFD does that with ease

Think about it, about the only thing your your simple v/hz VFD cannot do for you, is to do away with your lathes gearbox. You need to keep it, be it a geared headstock or a belt change system, to preselect a speed range. You will need to select a gear MUCH LESS OFTEN than without variable speed, but you still need the "mechanical advantage" of a gear box. Now think about, how much money would it be worth to you to get rid of the need to preselect a speed range. You see, nearly all of us have come to the same conclusion - it is just not worth it in a home shop. Better buy tools for the saved money. It is a very common misconception to think variable speed must mean direct drive to spindle and no more speed changes. Give it a try, install it to your lathe - I am sure you will be happy with your new VFD drive. I always say, this is the best modification one can do to a manual lathe!!! Chris

Hi Chris,

Once again you produce a well thought out, balanced and informative post! Yes you are quite correct. When I first thought of the idea of a VFD and variable speed control, I had in mind both a mill and lathe operating from a motor coupled by belt directly to the spindle, by-passing both of the noisy (more the mill) gearboxes and do away with ANY gear changes. I now know that I had unreasonable expectations but as you say I will still have the luxury of complete freedom of spindle speed from top to bottom with perhaps 1 gear change.

It's actually my mill that I want to convert first. The gearbox is noisy at best but sometimes the gear lever "wanders" and then tries to jump into the next gear causing an all mighty gut wrenching grinding of gears until you hit the stop button. Also, from a conversion point of view, the mill will present the simplest machine to convert. It will also give me the opportunity to get rid of the dodgy control box on the side of the gear head that is held by 2 flimsy screws and replace it with an ABS control box that will also contain the RPM module and have a swing away hinge as I always seem to gouge my forehead on it when I take a closer look in between cuts!

Back to gear changes, I should be able to keep one of the levers in "2" position and just toggle between H and L lever settings. L2 gives a ratio of about 10:1 meaning it may give a speed range of approx. 70 - 300 rpm. H2 gives a ratio of 2:1 so perhaps 350 - 1500 rpm representing probably 95% of my milling speed needs.

The motor I intend using for the lathe is a little more flexible being a variable frequency motor. It seems happy to rev from about 800 rpm up to (and beyond) 5000 rpm at about 160 hz. I have not tested what it's maximum frequency rang is but it continues to ramp well beyond it's max rated rpm of about 5000 rpm with frequencies of 200+ hz. I have set the max freq on the VFD as 150 Hz but I may need to re-adjust this for the induction motor I'm picking up for the mill which is a standard 4 pole, 1440 rpm motor.

The DC motor option for the lathe still teases me with interest!

Cheers,

Simon

Originally Posted by simonl

Once again you produce a well thought out, balanced and informative post!

Yes, a very lucid, informative and interesting post. D.C. motors and drives would be great if only they were comparable in price to A.C. motors and dives of the same power. The unfortunate reality is that they are vastly more expensive unless you get really lucky on eBay or similar. That may still be an option Simon, but you would need to know just what you were getting, and just what you needed to make it work. Easier for Chris than for you and me, so it is probably get lucky with a vector drive with some compromises or a standard V/Hz drive with even more compromises; "you pays your money and makes your choice."
Regards,
Rob.