Variable frequency drives (again, sorry!)

[Deadeye]

I've done some googling, watched some videos and read these threads:
union-graduate-1-5hp-motor-upgrade-project-t111486.html
union-graduate-t66355-15.html
union-graduate-conversion-advice-t120640.html
variable-speed-lathe-conversion-t100482.html
union-graduate-worth-switching-from-1-to-3-phase-motor-t115395.html
variable-speed-lathe-conversion-t100482.html

I'm about to acquire a 3 phase lathe and want to fit a VFD.
Keith's kindly bent himself around the corners to find that the motor is 0.75HP 220/415V Brook Gryphon.

Some specific questions:
1. Is it better (pros/cons/cost) to (from deomestic supply) use a 240V 1PH -> 220V 3PH VFD or to use a 240V 1PH -> 415V 3PH VFD? I had assumed the former, rewired to delta, but wanted to check!
2. I'm not *planning* on more 3PH machines, what rating VFD should I get? Is 0.5kW (i.e. the motor rating) too low? Is 1kW too high?
3. I assume I want IP55+ so I don't have to worry about dust?
4. Prices for like specs seem to vary a lot. From Chinese direct imports at £75 (I'm too scared of not having an English manual for those). Drawn from comments on other threads, I'm considering these; thoughts?:
https://inverterdrive.com/group/AC-Inve ... -070SC-EC/
https://inverterdrive.com/group/AC-Inve ... 0070-1F1X/
https://acim.nidec.com/drives/control-t ... ose-drives
5. How difficult is this for a reasonably intelligent electrical numpty?
6. Does that answer change if I want to reinstate the microswitches and foot stop?

One of the problems with searching out previous threads is often the links to products go dead unfortunately. So apologies if this has been done before, and thanks sincerely for the advice.

 

[porker]

1) The former will be cheaper for the VFD and you will have more choice.

2) The VFD outputs will usually need to be wired direct to the motor so will effectively be dedicated to that machine. The rating should be at least the motor rating but there is no real point going way over.

3) I guess so. The better IP protection the better but also depends where / how it is mounted

4) I guess you pay your money. I used Direct Drives years ago and I had no problems and great support

5) As per answer 2) the switchgear needs to be the input to the VFD and the outputs direct to the motor phases. The motor needs the links changing to delta from star. Plenty on internet but depends on how used to electrics you are. (I trained as an electronics engieer so it wasn't difficult but there are plenty of other things I don't know - like how to use a wood lathe!!). You will be the best judge of that but its not rocket science.

6) Other safety switches etc should be reconfigured to either the VFD inputs or the power to the VFD itself - depends on the VFD and the machine.

HTH
Matt

 

[Deadeye]

Hi Matt

Many thanks for that.

I think I'm ok with re-wiring the motor to delta. It was more the seemingly endless options (and whole new vocabulary) of the VFD settings.

Any thoughts on sizing?

Thanks again

J

 

[Sideways]

Just throwing this into the mix, but as soon as you put an electronic variable speed drive on a lathe, you're going to want to dial it down using the VFD instead of always swapping the belts.
When you reduce the speed of the motor, you also reduce it's power output.
If I was doing any conversion like this, I'd fit a substantially more powerful motor than the original so that I could run it a slower sppeds without overloading it. The drive has to be bigger to suit too. I'd be looking at 1.5x to 2x more power than the original. That way I could leave the belt on the middle pulley most of the time, control speed with the VFD and just shift the belt when I needed max torque or max speed
If you're already committed to the motor, you'll have to keep moving the belt to make any major changes to speed or risk overloading and stalling it.
A decent VFD will tolerate overloads of maybe 150% of full load current for 30-60 seconds provided it then drops back inside spec for a while so the drive can recover, but lathe work can be quite stop / start (which is demanding) so a drive with the capacity to run a motor one size up will give you a little more insurance if you use it a lot.

Google and download yourself a userguide for an Invertek ODE3 drive. These are known for a pretty straightforward menu / programming scheme.
If you can understand it, it will give you a good picture of how to wire and how to configure a mainstream european quality VFD. They're not very complicated devices, but they're not trivial either if you have no previous experience.

 

[porker]

I've run two motors on a Bridgeport at slightly more than the nominal motor ratings (2hp main motor and I think 0.5hp table motor from memory) and the drive were rated at or close to the equivalent hp). They both soft start so I don't think they need overrating but it's a hobby machine and doesn't get driven hard).

 

[Deadeye]

Thanks chaps

I'd prefer not to buy a whole new motor. I've seen "rule of thumb" advice to get a VFD at 2x the motor rating - around 1kW.

The advantage of the current motor is that it fits and it works!

 

[Terry - Somerset]

I understand that at slower speeds the motor power will fall. As a hobby turner I am not sure this really matters as slower speeds are typically reserved for doing finer work and sanding where power is not an issue.

It may also mean that at slow speeds I need to reduce the depth of cut and take a little longer to get to a finished shape.

A professional may slow the speed due to (say) an out of balance blank but would want to cut out material quickly and need the extra power.

Am I sort of right or am I missing something fundamental?

 

[TFrench]

I probably sound like a broken record, but as I always recommend when the question comes up, invertek are great. If I were you, I'd go for this one:
Invertek
More power than you need, but that means if you do decide you need a bigger motor you're not doing it all again. It's also dust proof, which means you dont have to build a ventilated enclosure to keep it in. Believe me, its worth the extra money! Speaking in my capacity as an electrical numpty, invertek are very easy to wire up and program. They supply a diagram which makes sense, which is more than I can say for any of the other brands I've tried. I think you should be able to wire the microswitches in series with the momentary stop switch and it will all work. I never bothered rewiring them on my graduate though. Feel free to ask any other questions about it - I've fitted a few now and I'll always go invertek given the choice.

 

[Deadeye]

Thanks for the reccomendation - really helpful.
I think it was your reccomendation that I included in my list above. Almost the same price but different model number and I can't see a difference in specification. Are they the same? I don't want to get my code letters wrong!

Also how do you actually use yours - do you adjust speed at the VFD or do you have a dial wired round onto the lathe face?

Thanks again!

J

 

[TFrench]

I can't see any difference! Sorry, I just picked the first ip66 one I saw on the website. Maybe worth giving them a ring to ask what the difference is. Nice thing with a 1.5kw one is that it draws under 13a so it can be run off a normal plug. On my lathe I've fitted the controls to the old switch panel. Start, stop and the black one is a potentiometer for speed control. The other picture is my pantograph, for that one I made a small panel so the controls were easily reachable (ignore the falling out grommet, that's the last job I need to finish on it!)
It's worth noting that both your control cables and the motor power cables need to be screened - I've used SY cable. You can get it from any electrical wholesaler. The connections on the inverter make it easy to do, so don't be intimidated by it.

Sent from my SM-G973F using Tapatalk

 

[selectortone]

I understand that at slower speeds the motor power will fall. As a hobby turner I am not sure this really matters as slower speeds are typically reserved for doing finer work and sanding where power is not an issue.

You also need slow speed when turning irregular-shaped blanks down to round. Depending on the size of the blank this can require considerable torque.

 

[woodfarmer]

Do not under estimate the level of aggravation caused by too little power at low speeds. I have a 1628 with a 2hp motor, when starting new bowls (on the slow pulleys) other than small bowls I have to concentrate mostly on not stalling the motor which is crazy easy to do. Once they are not so much out of balance I can wind the speed up and start cutting. It can help if you mount a heavy backplate to store some momentum.
At some stage in the future I hope to buy a smaller metal working lathe and I am determined to get a gear head one. Today I have been fly cutting a steel plate on the Holbrook, which will chomp its way through it at a steady 28rpm. (2 hp Brook motor) 1500 rpm in 28 out by gearing that is over 50 times the torque of the original motor. You need the torque for some slow jobs such as threading .

 

[Deadeye]

Thanks to everyone one here - really helpful (and especially the photos, thank you TFrench).

I've done a lot more reading today (recovering from surgery allows time for that!).

I'm gravitating towards:
- 1.5kW (i.e. 3 times the motor rating) 230v 1ph->230v 3ph drive
- Unfiltered (I don't want the EMC to trip my breaker)
- VxF (I couldn't see a compelling argument for vector control)

A couple of questions:
- Am I making a mistake on VxF? Is the additional control of vector worth it (it would have to be sensorless)
- Whilst IP55+ would be nice, it adds a lot of cost, and I can get a polycarbonate cabinet quite cheaply for IP20. Is this foolish?
- Where's good to buy a short length of shielded 4 core cable?

Thanks again

J

 

[TFrench]

While a polycarb cabinet is cheap, you then have to ventilate it well enough for drive to get the correct cooling - the manual will tell you how much clearance you need around the drive. On the first 2 I did I used a steel enclosure and cut 4x2" holes in the sides and covered them with ultra fine stainless mesh. It definitely worked - I never got dust in there but given the time and effort it took I certainly won't bother again now I've found these ones!
You can get screened cable from any electrical factors or ebay. You'll need 4 core 1.5 SY for the motor connection and I think I used 7 core 0.75 SY for my control circuit on the pantograph.
Unfiltered is fine, I had problems with a bosch one tripping the breaker till I removed the EMC screw.

And I don't understand VxF :lol:

 

[Sideways]

City Electrical Factors (CEF) have improved a lot in recent years and most branches sell common sizes of SY cable by the metre for a fair price. They also have some decent plastic enclosures if you decide on drive that is not dust proof.
Control wiring can be wired in SY but if you look on ebay for CY cable, this is better. Improved screening, more flexible, lighter weight for low voltage control voltages.
Don't mess about. Any decent european brand VFD will offer vector control. It's just the most up to date system of monitoring and adapting the output to the motor moment to moment. The invertek ODE 2 and ODE3 ranges all have it as standard.

 

[Deadeye]

Thanks Sideways.

Cable like this? https://www.ebay.co.uk/itm/CY-CABLE-0-5 ... QGRgL-9q0g

I assume I want about 5m of 4 core. But 1mm? 1.5mm? 2.5mm??

Am I right that only the wiring from the drive to the motor needs to be CY? I can use ordinary twin and earth to the drive (from a 13A plug) and standard wires to the potentiometer and switching?

 

[Sideways]

That's the stuff.
CY is for a remote control box.
SY is for drive to motor.
The single phase mains supply into the drive can be solid core fixed wiring if the drive is boxed and fixed to a wall, or if the drive's attached to the machine I would feed it via SY cable with blue CE connectors (just because it's robust) or a tough rubber flex like HO7RNF if an ordinary 13A plug is enough.

0.5mm is enough for the CY control wiring because it carries no current to speak of, but I prefer 0.75 or 1mm just because the conductors are a bit more robust and take less damage when the terminals are screwed down on it.
When I do a remote control box for an invertek I typically need 3 or 4 conductors for start/stop (3 is enough if you use 2 push buttons, 4 if you use switches to get fwd and reverse) and 3 more for a speed control potentiometer so I tend to standardise on 7 core, just occasionally 9.
For the motor, 1.5mm SY, 3 core + earth is usually plenty. 2.5mm if you have something like a 3kW motor.
Lastly. Buy a decent pot(entiometer). You don't want a 10 turn one. Vishay is a quality brand. Bourns another. An all in one pot with a built in control knob allows them to be pretty dust proof.

 

[Deadeye]

Thanks Sideways! That's fantastic info!

Woooo- I get to go shopping!

I will take photos and try to write up the whole process (assuming success!) so the info is in one place for future newbies.

Thanks everyone. Excited now.

 

[graduate_owner]

Just my 2p worth.
Firstly, if you turn down the speed of the motor, you also slow down the cooling fan and so risk motor overheating. Might be worth fitting an additional motor with cooling fan which runs at permanent full speed, if space permits.
Secondly, you might just decide to invest in another 3 phase machine, using the same invrter. I have done this - my inverter runs 4 machines, but as has been said, the inverter output must be directly connected to the motor. I accomplished this by connecting the inverter output to several 3 phase sockets in parallel, each one bring isolated as necessary by a 3 phase isolator. Each machine then can be permanently connected, and select via the appropriate isolator. The remote on/off switch has magnets on the base of the box so I just take it to the machine in use and it sticks to any iron parts of the machine.
Finally, the enclosure. My first inverter died and I am sure it was because of dust and moisture ingress. My replacement is in a large metal enclosure made from old desktop computer cases. Large enough to allow air to circulate within the enclosure. The mains input is through a thermostat which is set to cut out if the temperature should rise unacceptably - hasn't done so yet. The inverter is a 3 hp invertek, and the maximum motor currently innuse is 1 hp which may be why the temperature doesn't rise? Anyway I don't change any settings on the inverter for different motors, just select and off to go. There are multiple parameters which can be set but I just didn't bother.

K

 

[Sideways]

Invertek drives have an automatic mode that allows them to learn the characteristics of the attached motor, but there are limits to it. The drive will switch the motor off in case of overload but the level & duration of that overload depends on the drive knowing the motor rating and the load type (pump / fan / general industrial). I keep one big 4kW drive on the wall for motor testing etc, and use a very similar system with an isolator interlocked socket in the motor lead. I keep a cribsheet handy and can quickly reprogram the drive for whatever motor I hook up.