The reason this lathe was set up with a VFD and 3 ph motor was because when I bought it off ebay it had been dropped off a forklift damaging the cross feed screw and gear cover , this meant it was used as a spare parts machine so it came with no motor or controller .

The VFD cost the same as a replacement driver board and the motor was similar .

Back then brushless motors were not around – well not on mini lathes anyhow , it was bought as a stuff around with it project in mind .

Reading the original conversion article, despite the abundance of safety warnings the system does not comply with basic electrical safety, machine safety or emissions requirements.

Most importantly the "E" stop should break the input supply to the drive. This could be direct or via a no-volt release contactor wired to the LV stop. The latter is best as if there is no drive failure the drive will bring the machine to a stop faster than just cutting the power. You have to cut the power as well to cover for a drive control failure. A E stop on just a control input is not good enough.

To comply with low voltage regulations (and common sense safety) this type of drive must be fitted inside a protective enclosure. The control panel wiring should use screened cable.

To comply with emissions regulations the particular drive shown needs an external input filter. (the CUB inverters with an "E" suffix to the part number have a filter built in and come with an earthing plate) A good filter can cost as much as the drive. Technically you then have to get it tested for emissions before using it (yes even as a personal item). Testing may be a bit much, but a decent filter is essential.

Not trying to stop people doing "DIY" but we should at least try to do things correctly.

Robert G8RPI.

Hi,
As long as the VFD has not failed it will continue to be powered by the DC "Bridge" capacitor and if the e-stop control input is active at the same time as the mains input disconnected the drive will go into dynamic breaking to stop as soon as possible. The energy in the rotating parts is actually dumped into the capacitor keeping it carged until it stops. Drives with very high inertia loads that have to stop quickly in normal operation have to have a brake resistor to dissipate the energy so the capacitor does not over charge.

I thought the green wire was a screen but it's not mentioned and not in the circuit diagram.

The current version of the EMC Directive may be dated 2014 but the original was 1989 and the law requiring comliance in the UK came into force in 1996.

Robert G8RPI.

Edited By Robert Atkinson 2 on 17/12/2018 19:41:30

Hi Neil,

I'll try to find a reference but most are for manufacturers and importers. The obligation for conformity happens when a item is put on the market or is first put into use. The VFD's despite having CE marks are components and only comply with the directives if the manufacturers instructions are followed. Generally this means filters, enclosures and safety devices. Having tested many items using VFDs and electrically similar servo drives, I can say that they won't pass without significant work. There is no dispensation in the EMC directive for one-offs or personal use. The only dispensations are for electronic development kits for professional use in R&D facilities and for radio amateurs. Note that you have to be compliant, you don't HAVE to test. I feel a reasonable hobby approach is to use filters and enclosures (for electrical safety under the low voltage directive) as recommended by the manufacturer. While machinery and LCD "failures" only put you and others in your workshop at risk (maybe neighbours if it catches fire), EMC can affect many services even some distance away. These include "safety of life" systems such as emergency services radios and aircraft navigation systems.
If there is an issue, you should at least be able to show some diligence.

Robert G8RPI CEng MRAeS

EMC problems are usually pretty obvious on a Software Defined Radio. I happen to be trying to sort a serious EMC problem out at the moment. Here's some screenshots from SDRs at a quiet location in Weston-Super-Mare compared with what I get in a noisy village about 40 miles away.

First. This is Weston's view of about 30 seconds worth of the entire radio spectrum from 0-30MHz. No signal is black, then with increasing strength up through white, green, yellow and red. Genuine signals are narrow vertical lines, noise tends to be broad. Most of the light blue in this screenshot is a mixture of man-made and natural noise. There's quite a lot of noise, but this is fairly good.

In comparison here's what's received at my home:

Note the almost total absence of man-made signals! My SDR is almost deafened by man-made noise. The horizontal lines most obvious on the right are Ethernet signals, probably leaking from an IP over Powerline system nearby. Much of the white fog is VDSL (Broadband Internet) leaking from telephone lines, probably because neighbours have unbalanced their feeds by fitting extension cabling inside their homes. (This also reduces download speed.) The wavy wide green, yellow and orange vertical streaks are caused by switch-mode power supplies – cheap ones are rarely well filtered.

A major problem living in a village is that all the power-lines are strung between poles. Any radio muck that escapes past a filter can be radiated by miles of cabling acting as a good antenna.  Most homes these days have some leaky electronics – if my home is typical about 90% of devices are fine, and about 10% are rogue.

The fun really starts when I turn on my lathe. The extra noise generated by the VFD is very obvious at the bottom of the screen.

I feel guilty about my noisy lathe. I improved it slightly last year by fitting well-screened cable between motor and VFD, but I haven't tried any filters yet.  When playing lathes I'm not listening to shortwave radio.

Domestic radios aren't good at detecting EMC issues – they're rather deaf, and sharply tuned to loud local broadcasts. If interference can be heard on an ordinary radio you have a major problem.

If you have filters please use them. Also avoid counterfeit and very cheap switch-mode power supplies. And if something's not in use, unplug it!

If you happen to own an SDR, it's worth checking what you can hear against an internet accessible SDRs, Try sdr.hu and websdr.org

Dave

Edited By SillyOldDuffer on 18/12/2018 14:57:38

Here is the general arrangement of th belt tenshioner , nothing special just a sliding spring loaded block that locks into the grooves in the shaft . I still have to make a handle withthe mechanism to make pulling up the sliding block ( screwed to the end of the cap screw and is located in a slot in the main body ) . This arrangement also allows the motor to be locked forward so the belt is loose .

Edited By XD 351 on 21/12/2018 05:28:16

If all the above is true then there needs to be a dedicated thread for VFD interference issues because anyone wanting to use one on any lathe needs to be aware of this . There is no reason why you couldn't use the same set up shown with a dc treadmill motor . I am not trying to promote the virtues of a vfd set up , just show how i have done it and so that those who may be interested may gain some insight or ideas .

With my ultrasonic cleaner i fitted  a  commercially available unit because one of the driver boards had failed and destroyed the inductor so  the  new filter covered all the boards . 

When i was a kid i worked out  that a small dc motor running flat out would cause an interference stripe across the tele which drove my old lady mad especially when the daily soap opera was on – she never worked out what caused it otherwise I wouldn't be here .🤪 

Edited By XD 351 on 21/12/2018 10:02:24

Cooling is via 12v automotive fan mounted inside the cabinet and the air is ducted up to the fan shroud of the motor , it then exits through a vent on the end of the motor enclosure. The fan is pwm controlled so i can set the airflow and this also keeps the fan a bit quieter as it doesn't run flat out . The vfd is also mounted inside the cabinet and the fan also gives some airflow for that as well .