Soft Start For Electric Motor

John,

Inverters are sized in kW eg 1.5, 2.0 ,2.5 each time you jump up a size the cost increases. Your lathe was made for industrial use 5 days a week most home users find that they can downsize a bit save cost.

A VFD used correctly is a superior solution to a rotary or static converter - if it wasn't then Mitsubishi, Hitachi, Huyundai, Scheider, ABB etc, would be making static and rotary converters - they are not.

I have had VFD on my M250 for a year, how many times have I use the VFD to change spindle speed ? - not once.

Why ? Its like riding a bicycle with gears. The gears allow you to go faster whilst maintaining the same pedal rpm, you could go faster or slower by changing your pedal rpm but there comes a point where changing gear is more efficient. So I use the lathes gearbox to change spindle rpm because that is the most efficient way of working. You can use the VFD instead but there is a point at which changing gear is more efficient and as Jo ? said you will lose torque at low rpm (and risk overheating the motor too) Probably not the most techically correct explanation but it works for me.

Ignore claims that a VFD solution is less efficient - the losses in the VFD are not worth considering

It's easy to get confused by the names. 'Phase Converter' is a different animal from a 'VFD (Variable Frequency Drive)' or from an 'inverter' depending on who is using the term ans what they think it means. Check carefully before you buy what the thing actually does.

I'd go with the 'check wiring first' advice. Try relocating your workshop to the kitchen and using the oven feed. You can alwyas live on takeaways.

Edited By jason udall on 15/05/2014 13:29:05

I would not want to be without my variable speed now. Its ideal when cutting threads using a die on the lathe, I can turn down a bit of hex to the required size at say 1000rpm then just back out the tool, bring up the tailstock, turn the speed down to 50rpm at the same time then run the thread down the part before running in reverse to back the die off at a faster speed then back upto 1000rpm to tidy the end with a file. Far easier than stopping the lathe, fitting a spindle crank, winding that to cut thread and then back it out.

Likewise when drilling a hole in stages, start with a small drill at full speed then just keep changing bits as you work up through the sizes to a big blacksmiths drill no need to keep stopping and moving gear levers or worse change belts.

Same with the mill its nice to slow it down for countersinking, running an out of balance boring head or using the dial type centering gauge without the needle being a blur. I would have thought a VFD on your Sixis with its 1000rpm slowest speed belt was ideal if you want to use it with anything else than small milling cutters.

Used sensibly with the lathe belts/gears set for the main work in hand and the VFD to drop it down on occasion makes things very nice to use.

I think most stories of low torque are from the imported machines that use DC motors on variable speed rather then VFDs on AC motors

J

Edited By JasonB on 15/05/2014 13:35:59

Static converters start by creating two phases, the running of the motor creates the third phase. A rotary converter has a motor already fitted and that has already created the third phase. Both deliver full power when running.

Jason: May I suggest you stop your motor before going directly from forward to reverse, if you want the motor to last. If you use a coventry die head to cut your threads you can, if you must, go in full speed and no backing out is necessary with all its risks of swarf getting trapped and damaging the threads.

Jo

Motor does stop as you have to go Fwd-0-Rev Though its quicker to press stop then select rev and start as the Back EMF braking stops the chuck faster than letting it run free down to a stop in zero before selcting reverse.

Never found swarf damage to be a problem whether backing out under power or by hand before I had the variable.

Edited By JasonB on 15/05/2014 14:59:13

Ditto what Jason said.

Not using the variable speed function of a VFD is a massive loss of utility in my book. I still use the gearbox of course, but being able to alter the RPM on the fly is brilliant for helping in all sorts of ways, one of which is tuning out chatter, especially when using boring tools.

Martin.