Emco Mentor Mill conversion

[Ross77]

Ok had another look tonight and the plate says 440 star, so might be in luck, bought some smaller gear pullers and got the motor apart without damaging it. Only 3 wires + earth go in to the motor there looks to be more wires joined and pushed down into the casing. not brave enough to dig them out yet, think I had better find a diagram for which wires are which coil.

if it was possible to convert to 240v what size inverter would I need? rated 0.25kW@ 440v so 0.125kW@ 240v? I have an inverter that I bought for the lathe but Its 1.5kW so might fry the small motor.

thanks for the 240>440 info but I think that if the motor cant be rewired to run on 240 then I will do the DC motor swap which looks a bit easier now I know I can use the existing top plate.
Cheers

[m_c]

If it is star, then the first thing you need to do is find the star point. *runs of to find image*

A quick google gave me the lower of the two images on this page - Star Delta Start Up Principles
(ignore the writing/figures, as it's explaining something you really don't need to worry about!)

as you should be able to see, the lefthand is Star configuration. What you need to do, is split the star point, then reconnect the coils in Delta (right hand image), and apply the power inputs to the delta points.
The motor will still be 0.25kw, however it will now require almost twice as much current, which should be around 1-1.2A of the top of my head. You can use a bigger inverter, however you'll need to alter the current limit settings to ensure it limits the amount of current should the motor get overloaded for any reason.

[Ross77]

I have also never used a proprietry inverter due to cost considerations, but have sacrificed some torque and used capacitors to give "quasi" 3ph. Whilst this may be frowned upon I have found this to be a good solution on motors up to 3HP

As long as its safe and it works for what ever application its in then I dont think it matters, I read that some of the Emco lathes and mills are configured like this from the manufacture.

Thanks Mc, worth a try.

[Ross77]

sorry for the short reply, had to go out sooner than I thought. thanks for getting star - delta spec I was hoping to get the wire colours for each coil but the best I can find from emco is brown, blue, black, to the motor. looks like I'm going to have to find them buy trial and error, or testing. as a starting point Ill draw up the existing arrangement and get back back to you if that's ok?

Thanks again for your help. if there is a way to get this working on 240v then I'm keen to sort it out so I can test the machine before I make to many plans.........looks like some gorilla has been pounding on the draw bar with a hammer to release the collet holder and bent the top part of the spindle. arrgg

[GEOFFREY]

Stick with it it Ross. I am fairly sure you will be able to run that motor on single phase with with your inverter (or capacitors!).
When you check out the wiring you should be able to find the star point fairly easily, and once the wires are separated can then just do a simple ohms check to identify the three windings. Reconfigure as delta and you will be away. Good luck. G.

[m_c]

I'd highly doubt the coil wiring will have any sort of identification. They're usually just the enammeled copper wiring with a bit extra insulation slid over the top.

[Ross77]

I think I have it sorted now! the motor was wired in star and has 6 coils which are interconnected in pairs. Before I cut the star connection I tested the input wires and got 100 ohms across each phase, which in star con fig is 2 coils (4 actually). When I cut the star connection and retested each coil I got continuity from the buzzer and 50 ohms reading.

The question is can I run it using a capacitor in delta configuration to test? or will it only run from the inverter and risk damaging that if I got the rewire wrong? Lastly can I use a cap from another 240v motor or is the capacitance value dependant on the motor?

Thanks again