Single to 3 phase vfd

[Alan CharlestonParticipant @alancharleston78882]

Hi,

I'm in the process of restoring an old Boxford AUD lathe. It came without a motor so I've been running it with an old 1/4 HP washing machine motor until I had the lathe running to a point where I was confident I didn't have a piece of scrap metal. I'm there now and I'm ready to splash out a bit of money on a proper motor. I'm planning on using a 750W (1 HP) 3 phase motor with a single phase to 3 phase variable frequency drive. I've got a quote for the bits locally (New Zealand). The motor is OK at $277 but the going price here for the VFD seems to be $550 – $600.

I can get something such as this

https://www.aliexpress.com/item/CE-220V-0-75KW-750W-Frequency-Converter-Single-Phase-Input-3-Phase-Output-Frequency-Inverter-For/32840280647.html?ws_ab_test=searchweb0_0,searchweb201602_1_10152_10065_10151_10344_10068_10345_10342_10547_10325_10343_10546_10340_10341_10548_10541_10562_10084_10083_10307_5680011_10175_10060_10155_10154_10056_10055_10539_10537_10312_10059_10313_10314_10534_10533_100031_10103_10073_10102_10557_10142_10107,searchweb201603_25,ppcSwitch_5&btsid=d7db39d6-79fe-4b42-97b8-b8bc600abdd9&algo_expid=15d9db68-cf5a-4ac7-9ee7-9b9014bd65fd-1&algo_pvid=15d9db68-cf5a-4ac7-9ee7-9b9014bd65fd&rmStoreLevelAB=0

from aliexpress for about $130.

Has anyone had any experience with this item or a recommendation for a suitable device from Aliexpress?

Regards,

Alan

[Alan CharlestonParticipant @alancharleston78882]

[John HaineParticipant @johnhaine32865]

I'm not sure about that one Alan but people seem to get good results from HuanYang vfds, which are also available from Aliexpress.

[Micky TParticipant @mickyt]

I have just recently fitted a 1.5hp 3 pahse motor to my Boxford AUD on a HuanYang vfd with no problems. The vfd has been in service for about a year as it was previously fitted to my Grayson Lathe and has performed very well. even setting it up was fairly easy once I had got my head around the chinglish manual.

Mick

P.S I even made my own pendant to operate the vfd remotely 

Edited By Micky T on 15/11/2017 08:31:43

[john fletcher 1Participant @johnfletcher1]

Hello Alan, I've 3 friends who have fitted HuanYang inverters and have no complaints what so ever. I programmed the inverts for them and made a simple program list so if you do buy one I could send you a copy. Please don't get the idea I'm an expert, just some one who got there in the end. Generally speaking it is easy to change the motor into Delta. Some one posted an excellent series of pictures on here about changing over from Star to Delta. John

[Ian S CParticipant @iansc]

The two places I would inquire at are Scott Machinery, or R.R. Fisher, they are just firms I have had contact with, I'v had quite a bit of stuff from Fishers', and their prices seem reasonable. Scotts' will sell you a complete lathe either new or reconditioned.

Ian S C

[Alan CharlestonParticipant @alancharleston78882]

Hi,

Thanks for the replies. The HuanYang vfds are a bit more expensive than the one I was looking at but still cheaper than the local quote. I'm a bit worried about the "Chinglish" manuals as raised by Mick so I may look at getting the HuanYang vfd so I can take advantage of John's offer to help with the programming.

John, what was the model number of the inverter your friends installed. The problem with sites like Aliexpress is that the choices are confusingly large. Buying from China is always a gamble but if your mates are happy this reduces the uncertainty a bit.

Thanks for the tip a bout local suppliers Ian. I'll give Fishers a ring tomorrow as well.

Regards,

Alan

[Alan CharlestonParticipant @alancharleston78882]

Hi,

My VF drive has arrived from China. I ended up getting a WK 9000 from NFLiXin. I've bought a couple of meters of 3 core, neutral screened cable (really expensive at $25/meter) to connect the vfd to the motor, which is earthed via the screen to minimise rf interference. I've never used this wire before, and I'm not sure how to make the connection to the screen. Is a short section of the screen twisted and put into a connector close to the wire and then a piece of insulated wire to the motor earth terminal, or is a section of the screen long enough to get to the motor earth terminal twisted and insulated with some heat shrink?

If anyone has a picture of this, I would be keen to see it.

Regards,

Alan

[David JuppParticipant @davidjupp51506]

The screen is not really intended as the Earth – that should be a separate core.

Easiest way to connect the screen is to use proper 'EMC' glands to suit the diameter of the cable used.

[john fletcher 1Participant @johnfletcher1]

Back to Alan, the Huanyang inverters which several of my friends have is 2.2 KW model, didn't see a part number. I altered the maximum current to what ever size of motor they needed. One has a Harrison I think 130, with a 3HP motor, another a much smaller lathe so lowered the maximum current as per the motor name plate. Once you get the hang of pressing which button and pressing one twice its OK. I've kept a list of notes for future use. If you send me a PM with your email address I'll send you a copy. The first one we bought was £90.40 it came from Leicester and was here in 3 days. One other came from some where in Germany and it was here in less than a week, strange old World. I've had a look inside and they look very good, I have 3 inverters of other makes of so called top quality, all second hand and can't see much difference. John

[David JuppParticipant @davidjupp51506]

Posted by David Jupp on 06/12/2017 07:24:40:

The screen is not really intended as the Earth – that should be a separate core.

Easiest way to connect the screen is to use proper 'EMC' glands to suit the diameter of the cable used.

That assumes the terminal box on the motor is metal – not one of those horrid plastic terminal boxes.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Alan Charleston on 06/12/2017 05:10:53:

… I've bought a couple of meters of 3 core, neutral screened cable (really expensive at $25/meter) to connect the vfd to the motor, which is earthed via the screen to minimise rf interference. I've never used this wire before, and I'm not sure how to make the connection to the screen. Is a short section of the screen twisted and put into a connector close to the wire and then a piece of insulated wire to the motor earth terminal, or is a section of the screen long enough to get to the motor earth terminal twisted and insulated with some heat shrink?

If anyone has a picture of this, I would be keen to see it.

Regards,

Alan

Hi Alan,

Assuming you have metal boxes you need a Brass Cable Gland like this:

They usually come in pairs, one for each end of the cable. Buy the correct diameter to fit the hole in the cabinet and – if fitted – the motor end terminal box. Some equipments come with threaded cable access holes: these threads are standardised should fit a gland of the right diameter.

The earth shield is clamped, usually between two washers, by the gland directly to the metal of the cabinet. You may need to remove paint to get a good connection. There's a variant where the gland comes with internal metal fingers that are squeezed onto the screen when the gland is tightened, but same principle.

The shield is provided to reduce EMC and should be earthed as close to the entry point of the cable as possible. The longer any tail between entry and earth the more EMC effectiveness is reduced. There's controversy about whether or not a shielded cable should be earthed at both ends. If you only earth one end, it should earthed on the VFD side, not the motor.

It's a bad idea to use an EMC shield as a safety earth. Instead you need 4 core shielded cable for a three-phase motor. The fourth core is used to provide the safety earth. It is connected to an existing safety earth terminal not to the cabinet. Unlike the EMC shield which has to be kept short, the earth wire may be as long as it needs to be to reach an earth terminal inside the control box.

Don't be tempted to run a separate safety earth wire to avoid having to buy some 4-core shielded. Doing that bypasses the shielding on the 3 cores feeding the motor rendering the EMC protection ineffective. Depending on what you have an extra wire may be awkward to fit as well.

Dave

[Alan CharlestonParticipant @alancharleston78882]

Hi All,

Thanks for the comments. For some reason I thought the screen was used as the earth lead so I bought a 3 core cable which of course was a total waste of money. Given that I made such a basic error I decided that perhaps it's not such a good idea to fiddle about with mains wiring. I've taken the motor and controller back to the motor supplier who will wire them up for me for not much more than it would have cost me for the (correct) cable and fittings.

At this stage I'm a bit annoyed with myself for being too ambitious by going for a 3 phase motor and vfd rather than a single phase motor with a reversing switch but I suppose if it works I may appreciate it.

Regards,

Alan

[SillyOldDufferModerator @sillyoldduffer]

Don't be discouraged Alan, you got very close. It will be worth it in the end – a 3-phase motor and VFD is definitely better than a single-phase motor.

If it's any consolation, even though I know all about not using screens as an earth, I absent-mindedly ordered 3-core screened for my lathe. I realised the mistake as soon as I looked at the cable closely. Too late – I'd already stripped the old wiring out…

As you say "I was a bit annoyed with myself"!

Dave

[ChrisHParticipant @chrish]

+1 on "don't be discouraged" Alan, once you experience the variable speed control a vfd gives you'll wonder why they aren't fitted as standard and how you ever lived without it.

One word of warning – hope it's not teaching granny to suck eggs – but watch the motor temp on low frequencies, if the motor goes too slowly it doesn't get enough cooling air, the motor fan is going too slowly to shift the air, and the motor can overheat. If you find that happening rig up a stand-alone fan to blow air over the motor, an old computer fan seems to work well (and could well be free!), but I don't go that slow for that long a time for it to have ever been a problem for me, so don't have a fan, but I do check the motor when I do.  That's usually only when screw cutting do I go that slow because I'm a bit of a scaredy cat not wanting to louse things up. But the beauty of the vfd is that I can go that slow, say 35 rpm, when I need to!

I also fixed up a rpm indicator using a package of led display, preassembled circuit board, proximity sensor and magnet got off E-Bay for about £6.50 inc delivery from Hong Kong to the UK – how did they do that for the money AND make a profit I asked myself – put the display and pcb in a little plastic box, made up a mount for the proximity sensor and magnet on the end of the head shaft and gave it a 12v dc supply and that's well worth it too – with a vfd and a variator on the lathe belt drive I didn't have a clue what revs I'd dialled in for the lathe before! See other threads on here for that – they feature the package and how to wire it up.

Chris

Edited By ChrisH on 07/12/2017 11:27:10

[Alan CharlestonParticipant @alancharleston78882]

Hi All,

Sorry for the delay in letting all those who helped know how I got on.

The controller I settled on was a Series 9000 Vector Frequency Controller

After paying the motor supplier to install the cable between the controller and the motor, I installed the motor in the cabinet under the lathe (a real PIA) and was in the process of mounting the controller when the cable came out of the gland. I got in touch with the motor supplier and after we had passed through the “Well I've done hundreds of these and nobody's complained before!” phase it transpired that they had used glands designed for armoured cable rather than screened cable. So, (mutter, mutter) back under the lathe again to get the motor out and back to the supplier. The proper glands gave much more secure connections.

After the motor was reinstalled and the controller mounted, I started using the system and came across a couple of problems which centred on the motor deceleration time. The motor supplier had set this at 6 seconds which he said was standard for lathes as too short a time could result in the controller being burnt out.

The first problem I encountered was during threading. My usual practice is to cut a 3mm wide groove with a depth equal to the root diameter of the thread at the end of the thread. The tool is then run into the groove, the motor stopped, the tool withdrawn and then returned to the start point by running the motor in reverse. The half nuts remain engaged throughout. The delay between switching off the motor and the tool actually stopping, made it difficult to get it to stop in the groove. The lathe has an 8TPI lead screw and a Norton gearbox to cut imperial threads and a range of metric threads can be cut employing change gears. I didn't have a thread dial indicator with the lathe however I managed to make one which meant I could disengage the half nuts at the end of each cut which stopped the tool dead. So that was one problem sorted.

The second problem with the delay between pressing the STOP button and the lathe actually stopping is safety. If I get into trouble and press STOP, there will be a period of continued operation. It will be worse than a lathe continuing to rotate due to momentum as I suspect the ramp down period will be under power and will overcome the force produced as I am wound into the work.

The STOP button on the controller is a fairly small target to hit if you're in a hurry and I would like to install a larger STOP button. I presume this can be achieved by utilising a pair of the analogue input terminals and a switch but I can't make head or tail of the Manual. Can anyone help me with some advice regarding this?

After all this negativity, there are some aspects of the VFD that I like.

The ramp up time gives a very gentle start which is particularly good if the work has some weight.

I can do threading at 100rpm without having to engage the backgear.

When parting off, it is useful to be able to change the speed to get away from a resonant frequency if chattering becomes a problem.

The VFD reduces the number of pulley changes required which, given that they involve kneeling on the ground and fumbling around in the cabinet under the lathe is much appreciated.

On balance, given the hassles I had getting the VFD up and running and the safety concerns, I'm not sure if I would install a VFD and a 3 phase motor rather than a single phase motor and a reversing switch if I had the time over again. I suspect not.

This is the second time I have written this. The first time I made the mistake of trying to create an album of pictures to go with the words. When I returned to the post it had – of course – disappeared. I'm not making the same mistake again.

Regards,

Alan C.

[Michael BriggsParticipant @michaelbriggs82422]

Alan, I have yet to come across a vfd that does not protect itself if the deceleration is too fast. A controlled ramp down is another useful feature of vfd control rather than a motor free wheeling to a standstill. I usually set mine to stop as quickly as possible without tripping the drive.

As far as minimum frequency is concerned I would not hesitate to run at 10 hz, I doubt you will find the motor gets warm unless on a machine that runs continuously for long periods, certainly not the case for my lathe. Michael

[John HaineParticipant @johnhaine32865]

Looking at the data on your VFD I see that it has vector control, which is very desirable. It means that it adjusts the drive applied to the motor to keep an estimate of the rotor current constant even down to low speed, possibly even stopped (though that normally needs a rotor position sensor). This should limit the stator current at low speed to minimise heating, and as Michael says you should be able to run the motor down to very low speed, maybe only a few hertz, with little reduction in torque. Applying some cooling to the motor using an old computer fan or two should sort out any heat problems.

On the question of cabling. I've pointed out before that you need to connect the braided shield to the unit earths at both ends for RFI. There is some confusion with earth loops here. When tracking down hum in audio systems, where the hum frequency is very low, usually it is best to avoid having multiple earth paths between for example a turntable and preamp. At RF though the idea is to keep all the interference currents inside the shield, which includes the braid on the cable. If you only earth at one end, then at the other end the RFI currents on the inside of the braid have nowhere to go but the outside, where they can then radiate, nullifying the point of the shielding! In radio systems we would never dream of not connecting the outer of a coaxial cable to ground at each end (unless we want to make an antenna) – the principle is the same.

This also means that both ends of the shield are at ground potential, so if you add a safety ground wire, for preference run along the outside of the cable and taped closely to it, it is not going to radiate RF because there are no RF voltages at its end to drive current into it. So 3-core shielded cable plus a separate safety ground should be fine as long as the shield is properly connected at each end and the safety ground firmly bonded close to the same points. 4-core shielded best, 3-core shielded plus a separate ground OK.

I have to admit that the VFD on my mill uses unshielded cable and doesn't have a filter – shame on me! I haven't had any complaints about RFI including from the domestic authorities.

It's a conventional non-vector VFD and I often run it at 5 Hz or lower for short periods for tapping, as well as at slightly higher speed for milling or drilling if I can't be bothered to shift the belt and the job is short.

[MuzzerParticipant @muzzer]

Very provocative John!

As I'm sure you know, there is conflicting advice from the various manufacturers about whether it's best to ground one end or both. This has been done to death here on several occasions.

In practice, neither is right or wrong and it may be necessary to use one or the other, depending on your installation. Yes, I've done this in a professional environment, so I'm speaking from experience. As you point out, it often doesn't matter in a domestic environment if you are prepared to risk getting chinned by an irate neighbour or spouse.

Murray

[Author]

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