VFD, rotary phase converter or motor swap to single phase?

[projectnut]

A TV lawyer might say “asked and answered.” I tell you, my 3HP lathe is on a static phase converter, which also works the Bridgeport mill, the Kalamazoo 9”x16” horizontal saw and the Jet vertical bandsaw. I cut metal a lot, and have NEVER encountered a lack of power in any operation, nor even heard the slightest audible change in power. Anything near any power limit is preceded with an incredible amount of blue hot flying chips that are too uncomfortable for me to press on harder. The tools seem to me to limit usable power before the phase converter does.

I think this loss of power point is highly overrated, at least for my reasonably aggressive use of the equipment.

I would agree. I have a static converter on my 2 hp Sheldon 13" lathe. It has a speed range from 60 to 2,200 rpm. I often cut mild steel with HSS tooling at a depth of .125" and have on occasions gone as deep as .187" when I'm in a hurry. I've never had the motor even slow down let alone stall. I have had the belts slip if I really get carried away.

I have on occasion cut 6061 aluminum at a depth of .250 just to see if it was possible. The lathe doesn't complain, but it seems like it's beyond the practical limit. It seems safer and more practical to limit it to .125" or less

 

[BEI]

Something I forgot to mention is the power consumption of an RPC. You have a motor larger than the machine you are operating running continuously, plus the draw of the machine itself. I have a 7.5 hp RPC (for sale), which I used it for about a month. I objected to the continuous whine, mama objected to the electric bill.

How is your rpc configured, for outdoor running or in the shop? Does it’s control box sit on top like some American Phase machines or does it require wall mounting? Who makes it and what are you wanting for it?

 

[BEI]

A TV lawyer might say “asked and answered.” I tell you, my 3HP lathe is on a static phase converter, which also works the Bridgeport mill, the Kalamazoo 9”x16” horizontal saw and the Jet vertical bandsaw. I cut metal a lot, and have NEVER encountered a lack of power in any operation, nor even heard the slightest audible change in power. Anything near any power limit is preceded with an incredible amount of blue hot flying chips that are too uncomfortable for me to press on harder. The tools seem to me to limit usable power before the phase converter does.

I think this loss of power point is highly overrated, at least for my reasonably aggressive use of the equipment.

Didn’t mean to offend. Perhaps I should have asked first if you made heavy cuts on steel before I asked. Wasn’t meaning to dismiss your input. Can you tell me which brand of static converter is the most reliable and long lasting? Thank you for your help.

 

[Winegrower]

Didn’t mean to offend.

Ha ha, is that even possible??

Can you tell me which brand of static converter is the most reliable and long lasting?

Really, I can only say that I have bought 5 Phase-A-Matics (while helping friends), and all worked fine and still do. These were the better priced of the units I considered.
There's not that much to go wrong.

 

[BEI]

The budget way of building an RPC is to buy a RPC panel, and then get a used three phase motor, perhaps from Ebay, to use as an idler.

This sounds like a doable and less costly option. It raises a few questions though. First, can I use a 3hp motor as the idler (the same hp as the lathe) or must it be larger? Second, is the idler motor speed important? Does it need to be same speed as the lathe? And, since I don’t know what an inverter type motor is, I wonder if I can or cannot use such a motor? I took a look on eBay and there appears to be a few at reasonable cost available but what is needed?

 

[Dabbler]

Your idler motor must be at least 30% larger in HP than your starting motor for normal applications. For a lathe it is recommended that it be at least 50% higher, because of the high current draw associated with starting the gearbox and chuck. My 7.5HP lathe is fed by a 15HP rotary converter.

[edit] You do not *need* an inverter duty motor.

as I posted in an earlier post, use a 5HP rotary converter or higher.

 

[rabler]

As @Dabbler said you need to oversize the rotary phase converter. You’ll want a 5HP converter, (or larger) which means it uses a 5hp motor as an idler. As long as it is a 3phase 220V motor, rpm doesn’t matter, and whether or not it is inverter rated isf also not important. Lower rpm motors may be quieter/less of a background noise source.

 

[Dabbler]

I honestly don't understand the problem with rotary converters and noise. Having worked in woodworking shops over a 50 year span, they are much quieter than any cyclone dust collector, table saw or even bandsaw...

The guy I bought the converter from had it in an outdoor 'doghouse' - not the best place for capacitors to live for 40 years (we get -40 degrees here most winters).

 

[BEI]

Thank all of you for your advise. Given what I’ve read from you, I’ve decided to go with a static converter with the option to make it an rpc if desired. The VFD option is not completely off the table but that can always be done somewhere down the road if I find myself wanting the control options a VFD offers. The North American static converter should be here by the end of the week. Again, thank you.