3 phase motor connections

Hi Peter Did your lathe come with any switch gear. As I remember it 3 phase motor usually had a ‘Memota’ (a trade name) switch. You pressed the green button and the rest was automatic.

I have acquired a Taylor Hobson engraver with a 1/4 hp AC motor. The motor plate says 220/380/440 V. The motor has a bakelite terminal block marked C B A N. One wire of the 3 phase supply goes to each of the C B A terminals; N has no external connection. Can I convert this motor to run on a 220v static inverter? Or, will any damage occur to either motor or inverter if I use the connections as is? Loss of torque is no problem.

Thanks in advance,

John

Edited By John Corden on 07/07/2014 18:54:40

John,

Given that it's marked for 220v, I'm pretty sure it will run O.K. on the inverter

Those terminal connections are [presumably] Phases A, B & C, and Neutral.

... As described, it is wired in Delta.

MichaelG.

These small motors usually run quiet happily in delta configuration using the very simple single run capacitor with extra start boost capcitor in parallel static converter configuration.

For many years I ran the 2/3 rd HP motor on a Pollard Corona drill in this manner with the start capacitor simply linked via the machine start button terminal. Holding the button down for a one-two count being sufficient time for the start cap boost to get things up'n running after the contactor had thrown in. Pollards provided their own start button parts and innards for his machine with very over-engineered contacts.

Clive

Ok, thanks for the replies. I will give it a try!

Rgds,

John

Hi Michael,
(With reference to John Corden's motor.) I do not think from the above there is enough evidence to show that is wired in delta. To be sure it is wired in delta there must be two wires coming from inside the motor connected to each of the terminals A, B, C. These connections might be on the underside of the connector block. It should also be confirmed that there are no wires from inside the motor connected to the N terminal. The easiest way to confirm this is to check that there is no continuity between the N terminal and any of the other three terminals.

Les.

Les,

Thanks for the Sanity-Check ... I was beginning to worry about that.

>>> John: Please note. <<<

MichaelG.

Noted, Thanks!

Sounds to me as though John's motor is wired for 380/440 volts, as there is only one wire on each of the A,B,C terminals. There will probably be 3 wires connected to the N terminal, these are the other end of the windings connected to the A,B,C.  These may be underneath the paxolin baseplate so not readily visible.

To run from an inverter these 3 wires need to disconnected from N and reconnected to A,B,C but in a specific order.

There should be a diagram on the inside of the terminal cover to show which order! This probably refers to wires by colour, which will have faded over the years.

Otherwise checking with a meter will be needed to find which of the 3 'N' wires corresponds to the 'A,B,C' wires.

Then seek more advice as to how to connect them. Don't want to overload with info that might not be needed!

Phil

Edited By Robbo on 08/07/2014 22:14:12

Thanks all for the suggestions. I took the paxolin terminal block off and there were just 3 wires disappearing into the body of the motor - nothing connected to N at all. I checked the resistance between each of the other terminals and it was about 80 ohms. So if the motor was wired in star, that would be the resistance of two windings in series, if it was in delta it would be the parallel resistance of one winding and two windings - which I think is 1.5. I didn't think either way would hurt the inverter...(famous last words)..so wired it up and it runs perfectly! I haven't check the speed yet - it has 2880 on the motor plate, but it works fine and runs fast enough to force air through the motor to cool it.

Thanks agin,

John