motor question

There's a guy who regularly advertises in homeworkshop.org.uk, Gavin Oseman, in Malvern ISTR, 2 to 3 phase converters to run off 220V

In mesh mode, you wire each winding ends to form a triangle with no neutral, if you see what I mean?

Greetings Peter, Get the inverter. One advantage of an inverter is the ability to change speed while turning. This can be especially helpful if the tool is chattering. The speed can be dialed in to stop the chatter. It also help in facing cuts. The speed can be increased as the tool approaches center, or decreased if facing away from the center. This tends to keep the surface speed closer to constant which can lead to better surface finishes and longer tool life. Another advantage, if the inverter can handle it, is instant reverse, which is great for power tapping. I do a lot of power tapping. There is a slight disadvantage with the inverter and it is a wiring problem. You must turn on the motor with the inverter switch and reverse the motor with the inverter. A good solution is to use the lathe switch gear to do this. Disconnect the switch gear from the lathe and connect it to the inverter. And it is probably easier to change the wiring than it is to change the motor timewise. Eric

I recall a technique known as the Miller System - I first heard it in and electrical eng module at Uni but some I knew who had the same problem mentioned it perhaps 20 years back.

I'd have to look it up to be sure but, as far as I recall, you install 2 caps (similar to used as 'starter' caps).

L1 - L

L2 - N

C1 links L to L3 C2 links N to L3

(caps in series across the supply, L3 to centre point. )

I've never had cause to try it in anger, I think we did a practical looking at the phase etc at Uni but that was about 40 years back.

I also recall mention of using a 'slave' motor as some way to generate the required shift but I've no idea how that is configured.

Just remember you have a threaded nose lathe. The spindle will reverse, the chuck might not. Not saying don't, just be ready for the time the chuck doesn't reverse.

The capacitor trick to run a 3phase motor ion simpngoe phase is the basis o f the many converters sold. Most have an auto transformer to convert the 23

0v to 380v so that you can run the 3 phase motor in star mode and duel spee d motors. An inverter won?t run a duel speed motor witored in star . If you want to try the capacitor converter, it?s best to run a p ilot motor of twice the hp of the machine motor and chose the cap sizes acc ordingly. Then, when you connect the machine motor to the pilot you stand a better chance if having near balanced phases.

In most modern 3 phase motors, there are 6 terminals labelled U1, U2, V1, V

2, W1 and W2 connected by links. For star, the links are usually connected in a line, thus joining U2, to V2 to W2. For delta (aka Mesh) the links a re placed in parallel so that U2 connects to V1, V2 connects to W1 and W2 connects to U1.

If you run a pilot motor on a converter, or using your own selected capacit ors, the set-up is called a rotary converter and you then connect your mach ine motor U, V and W to the pilot U, V and W respectively.

There is a lot of info on how to find the value of caps and diagrams. Pers onally, I find the inverter route the best.

Where I live getting three phase power was excessively expensive, even for a commercial shop. I would have had to pay $15,000.00 just for the wire back in 1997. And I wouldn't have owned the wire. So I use a big rotary phase converter to power my shop. But most of my machines have inverter drives connected to the rotary converter. Variable speed is really important to a commercial shop. Even if I had three phase coming into the shop most machines would still have inverter drives on them. Inverter drives are also known as VFDs. One lathe has a 15 HP spindle and it "instantly" reverses when spinning at

5000 RPM. It slows and reverses very fast. It does this by dumping the rotational energy back into the incoming power line. A mill I have with a 10 HP spindle also reverses very fast, which is good for power tapping, which is the only way I tap on that machine. But it dumps the rotational energy into heating coils, just like you would find on a stove top. Eric

On 21/02/18 16:12, houstonceng wrote: [..]

Ah, mesh == delta. I was wondering about that.

This motor has only three output wires, plain white, unlabelled. It says

220V mesh or 380V star on the plate. I think it was connected to 380V 3-phase before, but I'm not sure.

If I get a 220V inverter, how do I wire it up?

Thanks,

-- Peter Fairbrother

Wire it delta for 220V operation. I've ordered a number of bits from these guys

and found the service good. The inverter package I bought used an ABB inverter and it came with a comprehensive programming manual and was easily programmed from the front panel as I suspect most are these days. I suspect the days of having to use a proprietary external programming unit are gone fortunately and the inverter prices seem to have come way down.

When you say it has three wires coming out, are these actual wires out of t he terminal box on the motor, or the number of wires inside the terminal bo x. Irrespective of the way the motor is configured, Star or Delta, there a re normally only three wires connecting the wind8ngs and, there should be, an earth wire as well.

Peter

After the motor has been connected in Delta, you have three wires out of th e Inverter (aka VFD) each one of 2hich connect to one pint on the Delta giv ing 230v per phase. The 240 live and neutral supply is connected to the in verter, usually to thermoplastic marked L1and L2. The Control wirescome fr om either a separate panel containing a start button, stop button, speed se lecting potentiometer, reversing switch and, in some cases, a jog/Run switc h, although the latter is not really necessary. When I fitted a VFD to my lathe, I used the carriage mounted start, stop, reverse lever switch and on ly needed a pot to be added, but decided to add an additional emergency sto p switch operating the power contractor. Hitting this, takes all power from the lathe.

Andy