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

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

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

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

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

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.