Emco Mentor Mill conversion

[m_c]

You only effectively need 1 capacitor to run a three phase motor from a single phase, however you normally need to use a few connected in parallel to acheive the required capacitance.

Search for 'static phase convertor' if you want to know more, however you need to check the generated voltages while running to ensure the 'false' phases aren't too high/low, and the voltages will also vary depending on load.

[GEOFFREY]

Ross, as m_c said ,you do usually only need one capacitor, connected across one leg of the delta triangle, but to get the correct capacitance you may need a couple in parallel. It is sometimes necessary to have an additional capacitor to increase the capacitance for initial starting, especially if starting under some load. this extra capacitor can be operated with a spring loaded switch, held on until the motor reaches speed (only a second or so) or as I do now using a timer circuit. G.

[Swarfing]

If you really want to go down that route then have a read of this. It helped me get my cross feed motor going on my BP. I could not swap that out because of the frame of the motor.

phaseconverter

[GEOFFREY]

Exactly! G.

[Ross77]

Thanks guys, I think I'll pass on the capacitor route then. Worth mentioning though as it might help someone else.

Out of interest what is the verdict on DC motor vs AC + vfd or is that a question for another thread
?

[Swarfing]

It's not quite true you only need one cap? i had to use a few to get the balance right on all the phases. Takes a bit of messing but worked well in the end and saved me using a VFD for the job. Ross it is horses for courses, for me i prefer to use AC and VFD because it is easier. Brushless DC would be second choice but expensive (large servo would be even better). How deep are your pockets?

[GEOFFREY]

Swarfing, once the correct value cap has been established, apart from the "start" cap you are still only putting "C" across one leg of the delta (or am I missing something?). To give the correct "C" value you may well decide to use a combination of caps to achieve that value, but a single item of the correct value can usually be found. If Ross already has an inverter then obviously that is the best way ahead for him. I only make this point because I would not like to be thought of as misleading anybody. G.

[Ross77]

It's not quite true you only need one cap? i had to use a few to get the balance right on all the phases. Takes a bit of messing but worked well in the end and saved me using a VFD for the job. Ross it is horses for courses, for me i prefer to use AC and VFD because it is easier. Brushless DC would be second choice but expensive (large servo would be even better). How deep are your pockets?

Cheers, I always thought that ac with vfd was more reliable but restrictive on high rpm also I had heard that torque at low speed can be an issue.

I was more looking at cheap treadmill motors, mainly because I picked one one up on ebay for £1. Not had chance to break it down yet but the specs say 1.75hp continuous and 3hp peak. geared down to 3000 rpm for the mill as it has roller bearings then that would be about 3hp continuous. geared up 1:2 on another spindle it should still achieve 1hp at 12000rpm