Another phase converter post (single to three phase 220V for 7.5hp CNC)

Hey guys,

So... we made rotary phase converters in school, balanced them with capacitors, all that jazz. I even made one for my dad's bridgeport. All said and done, I'd heard of the magical VFD that would work way better for converting single phase to three phase for use with a mill. Never thought I'd need one.

From sifting through other threads, I realized a VFD is NOT what I need because the signal isn't clean enough for CNC controls.

I have a Robodrill, which needs 220V three phase with peak power at 7.5hp. I have 220V single phase at the box.

Can someone give me the rundown of what I need to get power to this machine? A VFD apparently isn't going to solve my problems, and supposedly they don't make phase converters bigger than 5hp. Do I just need to make a rotary phase converter then balance the phase angle between legs?

Thanks guys. I know there's a million threads out there on weirdos like me getting cnc machines into their garages. I'm having a hard time locating just the right one. Feel free to point and laugh.

They... meaning just about everybody who makes them, make rotary phase converters bigger then 5 hp. Way bigger.

13engines said:

They... meaning just about everybody who makes them, make rotary phase converters bigger then 5 hp. Way bigger.

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I should have been specific: static phase converters.

thunderskunk said:

I should have been specific: static phase converters.

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Technically, a static converter is just start capacitors that start the motor, then drop out once at operating RPM. The motor then runs on 2 legs of the AC.

That being said, I don't see how that would work, as it seems like one leg would have to run the motor and CNC controls.

Just build a rotary phase converter with a large motor.

Here's a couple links to the Phase-a-Matic website. They make static converters for up to 75 hp.

http://www.phase-a-matic.com/PDF/SB.pdf

The PAM 900 is rated for 4 to 8 hp and the PAM 1200 is rated for 8 to 12 hp. The PAM 900 costs $230.00.
http://www.phase-a-matic.com/PDF/PS.pdf

The 1200 is a special build,. You'll have to call them for a quote.


North America phase converters also makes static converters up to 10 hp.
Static Phase Converter | Electronic Phase Converter


The HL 10 is rated for 4 to 10 hp and costs $192.00

I have several static converters in my shop. I have had a Phase a Matic on a mill for going on 20 years. I have an American Rotary on on a power hack saw, another on a lathe, and a North America on a drill grinder. All of mine are in the 1/3hp to 5 hp range. American Rotary and North American are now owned by Gentec. American Rotary no longer makes static converters. They did make static converters to at least 10 hp, and many are still available through retailers. To me they were the best for the money. They are considerably less expensive than Phase a Matic, and more heavily constructed than the North America models.

I also have a 15 hp American Rotary, rotary style converter waiting to be installed. It was scheduled to be done as part of a power upgrade for the shop last year. The new power panel has been installed, but the rotary converter remains on the shelf. I use all the machines nearly every day so I hate to put one or more out of business for the time it would take to install the rotary converter. All the machines are running fine on the static converters, so I'll leave well enough alone until time allows.

A quick suggestion if low cost is a major priority and you go the route of making your own rotary phase converter: Make friends with an HVAC contractor and get permission to scrounge their scrap pile. I have a neighbor who fits that description, and I found nearly all of the parts I needed to set up a nice contactor-controlled unit for zero cost - he was happy to get rid of anything I took - capacitors, both run and start, contactors of every variety, transformers to get 24v control signals, etc. I already had an old 3-phase motor on hand and plenty of suitable wire and wire nuts, and I built an enclosure for the motor (with ventilation, of course) and for the electronics out of scrap plywood on hand. All I actually had to buy were a couple of buttons (for start and stop) and a NEMA L14-30R receptacle; total cost was about $15.

I'm surprised it didn't come up here, but I just stumbled across the "Phase Perfect" converter. Seems to be very specific to running CNC machines on single phase power, which is exactly what I'm looking for, but MAN those suckers are expensive.

awake said:

A quick suggestion if low cost is a major priority and you go the route of making your own rotary phase converter: Make friends with an HVAC contractor and get permission to scrounge their scrap pile. I have a neighbor who fits that description, and I found nearly all of the parts I needed to set up a nice contactor-controlled unit for zero cost - he was happy to get rid of anything I took - capacitors, both run and start, contactors of every variety, transformers to get 24v control signals, etc. I already had an old 3-phase motor on hand and plenty of suitable wire and wire nuts, and I built an enclosure for the motor (with ventilation, of course) and for the electronics out of scrap plywood on hand. All I actually had to buy were a couple of buttons (for start and stop) and a NEMA L14-30R receptacle; total cost was about $15.

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I'd love to just build an RPC, as you're totally right. I've got family in the electrical trade, so sourcing both motors and panels for balancing legs isn't an issue.

My hesitation is the mountain of comments on several threads in PM about someone who either ran their machines on RPCs, switched to Phase Perfect and won't look back, or folks who got a Phase Perfect and have no regrets.

I bought a new Robo Mate back in 07 for my home shop. I built a 10HP rotary with a premade panel from Ebay. I ran this combination along with adding a Hardinge conquest42 to the mix for several hundred trouble free hours. I sold that Mate and a while later bought my current mill. A Mori MV40. Using this same converter it ran for quite some time but I would have glitches here and there that I would finally attribute to that "weak" third leg. So I built a bigger 15hp rotary. The "glitches" didnt go away and in fact it evolved into a worse issue where the older Fanuc AC spindle drive would blow one of the input fuses. It turns out those vintage drives do not like unbalanced/low supply voltage.
I bit the bullet and bought A phase perfect PT330D. It has probably been 80 hours of operation and I have not had a repeat of any of those issues.

Even when I was in the worst time of that fuse blowing episode, the old 10 and new 15hp rotaries worked fine for my Conquest(not at the same time). I ran a job on there turning 3.75dia 316 slugs for around 40hours total with no issue. When I was done with the lathe work I turned on the mill and blew a fuse during setup.
I think the newer drives are more tolerant of the imbalance.

GENERALDISARRAY said:

I bought a new Robo Mate back in 07 for my home shop. I built a 10HP rotary with a premade panel from Ebay. I ran this combination along with adding a Hardinge conquest42 to the mix for several hundred trouble free hours.

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projectnut said:

I have an American Rotary on on a power hack saw, another on a lathe, and a North America on a drill grinder.

I also have a 15 hp American Rotary, rotary style converter waiting to be installed.

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I think this is the route I'm going to take. I've been thoroughly warned that Phase Perfect is the best route, but I just can't afford it. While I also can't afford to replace a blown spindle, I'm only using one machine on this converter, and it sounds like you guys made it work, at least for a bit.

At the moment I'm leaning towards using American Rotary's 15HP panel with an idler dragged out of a plant shut-down. $400 versus $3600 means I don't need to take out a separate loan just to get my spindle turning. Maybe I'll be able to buy stuff like, y'know, tool holders, haha.

I run a Fadal 3016 in my garage off of a 15hp RPC and don't have any problems. I will probably move to a Phase Perfect at some point, just for space savings and some other reasons, but mill runs just fine.