Picking up on NDIYs instruction manual and ease of installation points a simple report covering :-

1) what are you using it on

2) make, model and date of purchase

3) cost

4) how easy the instruction manual was to follow

5) how easy was it to connect and mount the device (some have very little room for the wires and tucked away fixing holes that is almost impossible to get a screwdriver straight onto the screw head)

6) did it work straight out of the box

7) if not, how easy was it to get the parameters right

8) optional advanced user comments on doing more than just basic run the machine set-up

9) if you had problems how helpful was the supplier

8) likes, dislikes and "the little issue that drove / drives you nuts"

9) bottom line are you happy wih how well it works and would you buy another

10) comments such as why you chose that one et al

would probably be helpful in making the appropriate choice.

Probably best organised as a topic folder with threads for each inverter model covered so folk could chime in with assistance on anything tricky. Needs to be strongly moderated of course.

Maybe supplier rating too.

The combination of technological advances and low cost of Far East imports means that most normal folk have no feel for the price / performance ratio of these boxes. As we generally need to make every £ do the work of 5 (or even 10) its awfully tempting to try and buy a little too far down market. When you do that all the trimmings that make life easy are the first to go.

For the size of device we are likely to use the price differential between inexpensive but not "too cheap to trust" import "no name" VFD boxes from "never heard of them" suppliers and a branded one from folk like Inverter Drive Supermarket is in the weekly shop or two territory. So it's getting hard to justify buying unbranded from a box shifter. Better to save up for a bit longer than risk being frustrated by making an inappropriate choice.

With a well chosen modern device installation isn't a problem.

The last two I installed were an Eaton DE1 and a Schneider-Altivar-ATV12.

The Eaton is designed to be a near direct replacement for a standard contactor and was pretty much as easy to install. Ideal for running my car lift. Just press the start button and it goes. Small enough to fit in the main box too. Just add switches (and a potentiometer if you want more than a fixed speed or two). But it doesn't have a display so you need a calibrated dial if using speed control.

The Schneider was effectively just as easy. No need for switches this time if you run it off the front panel but but it did need running down a simple set up choice menu including one to do its vector setting thing. The easy set-up manual on the Eaton was sufficient, the Schneider manual is good and easy to follow but Inverter Drive Supermarket have their own uber-easy "just follow the steps" version. Hafta say the IDS set-up manual was actually too easy for a guy like me with some experience. Started thinking about things instead of just doing it and had to start over!

Clive

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A very useful internet resource I've found for VFD info. is the Inverter Drive Supermarket website. They sell a fairly wide range of VFD brands, and for some of these they publish a downloadable Quick Start Guide, as well as the manufacturer's manual. The QSGs are written, I think, by IDS themselves and give very clear details of how to wire and programme for various remote control configurations, eg 2-wire, 3-wire, speed pot.

I don't think they cover the low-cost ebay offering though.

SoD makes excellent points about the difficulty of providing good, simple, advice on technical issues through a forum.

Especially because of the "multiple guru" problem where several folk with decent expertise say pretty much the same thing in different ways.

Ideally its best to not only stick with one guru but also to choose one who explains things in a way that suits the way you think. I'm sure everyone has had the experience of having something clearly and correctly explained to you but for some reason not being able to properly follow it until another person uses just the right form of words to break the logjam. Whereup everything falls into place and you feel really stupid for not getting it first time round.

However with the current, and future, state of the art sorting tricky technical questions after a VFD has been bought is probably not a good way to help folk. Far better to ensure they choose an appropriate one in the first place.

For the non-demanding applications that we will generally be concerned with there is a goodly choice of VFD boxes that really are easy to set up with straight forward step by step instructions that any methodical person can follow. As easy set up pretty much boils down do how well and carefully the control software has been written there is, unsurprisingly, no significant price premium for being easy.

As I suggested previously some sort of guide, in standardised style, from practical experience should enable a prospective user to see where a particular VFD sits on the easy set-up / installation techie level spectrum. Hence the purchaser can choose a drive they can handle. Even if problems are encountered the forum will mostly be dealing with only a subset of the VFD market concentrated around ones that are intended to be easy.

Clive

Newton Tesla sell a package of inverter and control panel pre wired and set up for a range of popular lathes. I've bought 3 inverters off him, always had good after sales.

The manuals tend to be very hard going, mine are better than the ones for Chinese DRO, but not by much!

Another vote for Inverter Drive Supermarket. When I was converting my Chipmaster a few years back. Colin Gibson was very patient in answering my very basic questions and ensuring that I got the right spec product and associated components. This I was very grateful for and somewhat surprising for a commercial organisation who were only going to get a single order from me. On the back of this, the VFD (Emerson Commander) was installed, configured and worked first time. I will say that I did read the manual end to end before starting the install.

Just looked on Inverter Drive Supermarket and Schneider 0.75kw is under £100 that's a lot cheaper than I was expecting, must have a look at Newton Teslar as well.

I have a large Boxford CNC lathe. The spindle is driven by a massive DC motor.

The motor is showing its age, and I am looking at upgrade options.

One option is to replace it with an AC motor and VFD – but I have no experience with VFDs.

I have 3 phase power available, so would only need the drive for speed control.

My question please – what range of viable motor speeds can I expect through a VFD please? What are your experiences?

For the technical I would probably use a 4 pole 2hp motor.

Many thanks

John

Thanks Old Mart.

So I looked at some suitable drives on the inverter drive supermarket (that's a great resource by the way – thanks).

A suitable Parker drive says it varies down to 0.5hz which would in theory be about 70 rpm. Is it right to assume the motor power would be pretty well degraded at that level?. I guess there would be other issues such as heat.

Has anyone run a motor at 200 rpm ish from a VFD? , and if so how was it.

Thanks

John

Tricky to give a simple answer, because much depends on the motor, the VFD and what it's used for.

Motor torque is degraded at low frequencies (and high ones), but the effect may not matter much. Modern VFD's apply techniques to increase torque at low frequencies, for example by altering the waveform to pass more amps – they aren't limited to sine-waves like the mains. However, the motor is likely to get hot, worse when it's only cooled by an impeller, and run very slow for a long time.

My Chinese lathe addresses the problem with a moderately clever VFD and a two-speed belt drive. It covers 30 rpm to 2500rpm in two ranges, which allows the motor to spin at a reasonable lick even at 30rpm. From memeory the belts are 12:1, so 30rpm at the spindle has the motor doing 360rpm. The motor is fitted with a separate fan that runs continually at high-speed and I've never managed to get the motor warm! I'm genteel hobby lathe work, with plenty of gaps between cuts, not a busy professional workshop working at top speed. Which describes you best?

Depends on the motor too. Provided the insulation can take it, the heat cause by slow speeds may not matter. Pre-war electric insulation may produce dreaded magic smoke at 80°C, later motors are good for 130°c or more, maybe as high as 220°C in this century. Heavily built motors dispose of heat faster than flimsy ones, taking longer to overheat. Fitting a giant motor to over-drive a machine tool is daft in my opinion, but could be sensible if the purpose is controlling heat at low tick over. Far better to fit a belt or gears to a suitably powerful motor though.

Dave

I have a large Boxford CNC lathe. The spindle is driven by a massive DC motor.

Post a picture of the rating plate of the existing DC motor, as it is difficult to make recomendations when you don't know the specification that you are trying to duplicate.

On many occasions at my last employment (CNC machine tool rebuild & retrofit) we ended up keeping DC spindle motors rather than replacing them with a new AC solution, as it was just not possible to duplicate the original motor characteristics with a new AC one.

AC motors usually have a much wider speed range than DC, but the down side is that they usual had a much higher base speed (the point at which the motor goes from constant torque to constant power). In some cases the base speed of the AC motor was twice that of the DC original & would have required an expensive reduction gearbox between the new motor and the machine. So although getting the DC motor professionally refurbished & driving it with a modern microprocessor thyristor drive was expensive, it was cheaper overall & retained the original machine performance.

This was on larger machinery than usually gets into model engineering workshops, but still something to bear in mind.

Is your machine a Boxford ACL ?

Nigel B.

Hi John,

A long time since I last saw an ACL – I wired the first one (prototype), some time in 1982, I think. Norwin drives & an ANC control on that one IIRC

An SEM motor will probably be a permenant magnet servo motor of the MT series – "weighs a ton" suggests maybe an MT40 or MT52 (these had double armature brushes, the MT40s were singles). There should be a rating plate on the motor with the model number, speed & torque rating. WIth that info, should be easy enough to work out a suitable replacement.

Nigel B.