Super Mini Mill 2 Phase Converter - Donkey?

[TravisR100]

I've got a SMM2 on the way with the standard 10K spindle. Any suggestions on RPC sizing? Brands? Models? I had originally intended to go with a Phase Perfect but budget is making evaluate all options.

[Matt@RFR]

I'm running a VF-2ss off of an American Rotary phase converter. When the machine was installed, the tech commented on how good the incoming power from the phase converter was. I'd contact them for size recommendation, they are great to deal with.

[TravisR100]

I contacted deselectric.com which some members here mentioned. Larry there is telling me that I need a minimum a 30hp converter and shoud use a 40hp. This seems like complete overkill for a super mini mill 2. No? He says if I don't use the larger size I'll never hit top speed and will have a problem on instant reversals such as when tapping.

[Geof]

Originally Posted by TravisR100 I contacted deselectric.com which some members here mentioned. Larry there is telling me that I need a minimum a 30hp converter and shoud use a 40hp. This seems like complete overkill for a super mini mill 2. No? He says if I don't use the larger size I'll never hit top speed and will have a problem on instant reversals such as when tapping.

He could be (partially) correct, I think the reason is that when the converter is delivering close to its rated maximum the phases get out of balance and the machine is sensitive to that. I think it is the control electonics draw power across two legs of the incoming supply via a transformer so the machine needs these legs to be good.

However, you will be able to hit top speed, the problem shows up during spindle acceleration to 10000 rpm especially if you have the machine moving the table into position while the spindle runs up. Then you have the spindle motor and two servos drawing full power for a second or two.

It is less likely that you would have problems tapping because you are not gpoing to tap at 10000 rpm and the draw is much less accelerating to around 2000 rpm. But even then there is a work-around; there is a Parameter for maximum spindle load during acceleration which is set at 195(%) out of the factory. You can drop this as low as you like and all it does is take slightly longer to reach top speed. I run my Super and a TL-2 both at the same time from a 14.7 kva diesel generator and all I had to do was drop the Parameter to 100(%). The spindle on the mill takes about an extra 1/2 to 1 second to reach 10000 rpm and the lathe chuck takes about 1 to 1-1/2 seconds longer

[DEAN]

What about the power requirements for both Digital and RPC. Doesn't it require a lot of power to fire up and run and 40HP motor?

[Geof]

It does need a lot of power to fire up a 40 hp motor but the SuperMiniMill 2 has a 15hp motor. Also firing up a spindle motor is not quite the same as starting a regular three phase motor on line supply. The spindle motor is ramped up by the controller which limits the power applied to the motor and this means the power being drawn from the supply is also limited; to something like 40 amps for a SuperMiniMill. This id different to a regular three phase motor which may briefly draw hundreds of amps when it is firing up.

[TravisR100]

So this kind of brings me back to my original question, for a Super Mini Mill 2, which rotary phase converter would you suggest? What HP rotary phase converter would you suggest? The mini mill will be the only thing running on this phase converter.

[lkenney]

the rule of thumb that I use is that your rotary phase convertor should be twice the normal hp rating for your spindle motor. If your motor is rated at 15 HP then a 30 HP will do you well. But I suspect that your motor is really a 10 hp with a 30 minute overload rating at 15hp. Therefore a 20HP is what you need. You should get one that is balanced for CNC with a switch box. I use phase convertors from Many, LA. I will get the name for you in the morning when I get to the shop. I am running two of thes convertors and have had no problem with them in the past three years.

Lowell

[TravisR100]

lkenney, thanks. This was sort of my assumption as well. Really a 10hp motor so a 20hp phase converter would do fine. The deselectric.com guy suggested i needed at least 30hp if not 40hp. I just wasn't sure if the rule was double the nameplate hp of the machine or double the peak hp of the machine when sizing a converter.

[lkenney]

I am surprised that deselectric was giving you the advice to over size your PC. they have always been very straight forward with me. It is their PC that I use.

Lowell

[TravisR100]

That's why I posted here. Wasn't sure if they were just trying to make more money on a larger RPC or if I really needed something that big. Still not sure what to buy. Would like to hear from anyone else who might have an opinion.

[lkenney]

The one thing I learned the hard way was to run only one CNC machine on a RPC. I blew the FANUC control on our lathe by trying to run both on a 30HP convertor. After i went to a RPC on each machine we have not had any trouble but the year that I tried to run on one was VERY expensive. I know shops that do get by with this but I would not recommend it to anyone after what we went through. It just the way that works for me.

Lowell