The Stovebolt Site Forums The Shop Area The Tool Chest Rotary phase converter

I recently bought an older series 1 Bridgeport mill from a friend of mine. I need to get a phase converter, I plan on going rotary NOT static. I'm not sure what horsepower to go with. My mill is 1hp, and I plan on possibly expanding to a lathe and maybe a bigger welder in the future. Would a 3hp rotary phase converter be adequate? Am I correct in thinking that a 3hp converter is capable of running up to 6hp worth of equipment?

Keith,

Do you have your mind made up on the rotary converter deal? Here are my thoughts. I have a a Bridgeport clone that I ran off of a static converter and it worked flawlessly. I have a 5 HP Unisaw running off of a static unit and it works flawlessly.

I have built rotary units with capacitors, a magnetic starter and idler motor. I am sure you have researched all this online. Phase-A-Matic is a pioneer in the field of static and rotary converts and I have included a link to them.

Having blown all this smoke I will say this. Switch mental gears and think 'AC Inverter". The price is pretty compararble and the benefits are bountiful. You get tons of options, the most used on a Bridgeport or lathe being infinite variable speed, clear up to 400 HZ. You get acceleration and deceleration ramps and braking too. Instant reversing which is 'way cool' when using the mill as a tapping machine.

On a lathe, you don't have to change gears to go from 200 RPM clear up to 2000 RPM, and as soon as you hit the OFF switch, the headstock comes to a stop in nanoseconds if you have it setup that way.

Each machine tool would have its own inverter and they have built in motor protection. The motor will see a modified three phase so you don't have to derate like you would with a phase converter.

E-bay sells lots of these inverters (Drives Warehouse). I have found Hitachi to be one of the most reasonable and easy to program. There are tons of used ones too. Most will take single phase input even though they don't advertise as such. Any single phase input will result in a three phase output.

Look at the prices and decide. If you are set on a phase converter, I would weigh the static against the rotary. There aren't going to be many times when you are running two machines at once. I'm not sure on this, but a welder, being a transformer may not be the perfect candidate for any type of third leg 'fake' generation. The motor windings are what help to create the image of a third leg and this isn't the case with a transformer.

http://www.phase-a-matic.com/PDF/RPL-2009-C.pdf

Stuart

Stuart, I'm glad you replied. I always read your advise and respect your knowledge.

I hadn't thought of a variable speed drive. The thing that scared me away from the static ph conv. was the fact that I want to be able to reverse quickly, and I wasn't sure that I would be happy with the static converters' ability to do this.

I'm assuming that there is no need to go overkill with a drive, since a separate drive is required for each machine tool.

Here is one that I found on e-bay. Does this look similar to what you mentioned. Is this a good price?

Keith,

The one you linked on e-bay is a typical unit at a great price. It has all the regular options, more than you would ever want, and I'll bet it's cheaper than even a static converter. You can mount the drive on the wall and stick a small aluminum or plastic enclosure right on the mill with FWD and REV momentary pushbuttons and a nice speed pot. I think they are the neatest thing since canned milk.

Stuart

I've made a few rotary converters, and bought a ready made one.

I also just did some more research on converters, and decided that the VFD might be good for a single motor. But if you have more than one tool you need more VFD's. You also have to have the VFD hard wired to the motor, and the length of that wire needs to be short. Switches have to be on the VFD side, not the motor side.

I'd recommend a rotary converter for your application, even a homemade one would be great. Size it at least the same as the largest motor you would run, then go bigger if you would ever have more than double that HP on at once.

I've got a 15HP rotary converter running my lathe right now, and will run my whole shop on it when I move in a few months.

When I'm ready to upgrade I'll get one of these "digital" converters. All I read about them is great, and from talking to the folks they seem very helpful and professional. A friend of mine also has one and is very pleased with it. http://www.phaseperfect.com/

Grigg

Grigg,

You are correct, the frequency drive is hard wired to the motor, but I can't think of any thing that wouldn't be hard wired to the motor. There is no length limitation on motor or control wiring until you get into a tremendous distance between drive and motor then you stick in a line reactor.

I'm not sure what you mean about switches on the drive side and not the motor. The drive IS the switch! I'm a big fan of freq drives and have installed many of them.

Non technically speaking, the drive is the ON-OFF switch, the REVERSE switch and motor protection all rolled into one dinky little enclosure. These are a few of the things this little box can do that a phase converter (static or rotary) could never do:

Accelerate or decelerate to a ramp of your choice.

Dynamically brake the motor as fast as you want.

Jog the motor forward or reverse.

Protect the motor from over current.

Instant reversing with accel/decel ramps.

And last but not least, variable speed from 0 HZ clear up to 400 HZ all with the turn of a simple potentiometer.

Phase converters work well but they are very dumb, need a magnetic contactor or drum switch and require additional motor protection.

I too have both types of controls. The dumb one is on the table saw, the smart ones are on the drill press, lathe and mill.

Stuart

Stuart, I'm not saying the VFD's are bad, they do look like a good idea in some cases. But to run a whole shop from one is not an option like it is with a single converter.

I understand how you "switch" with the VFD, in reality you "control" all aspects of the motor start, stop, and reverse with the VFD.
But if you had a forward/reverse drum switch on your Bridgeport you couldn't use it between the VFD and the motor, that's all I was trying to say.

Or take my B&S #2 milling machine for example it has 4 different motors, a VF drive as a converter would be impractical, as I would need 4. Even then the spindle motor is switched by the clutch and brake lever on the column, I'd have to do something different there, might not need to use it at all?

Just saying there are a number of options to get three phase power, (or an approximation of it) depending on the use some ways are better than others.

Grigg

Grigg,

I understand...I get carried away with little electronic gadgets, sorry.

Just to add a bit to your post...yes, a drum switch can be used between a frequency drive and a shop tool. My lathe and my drill press are both controlled with a drum switch. With an inverter, you have a programming choice for control options. Momentary, three wire, maintained, two wire etc.

I know several folks that do have a rotary stuck in the corner of the shop, and first thing in the morning they turn it on and then are free to start whatever machine tool they use during the day...not all at once though.

Stuart

Can a switch be used in the wires between the drive and the motor?
Or can it be used to control the drive (drive and motor hard wired with no switch in line)?

I'm thinking No and Yes respectively.

Grigg

Grigg,

The drive has motor leads and control wiring, just the same as any starter or contactor. Motor leads run from drive directly to the j-box on the motor. Any control circuit would run from a drum switch or pushbutton station to the drive. The drive has a buss with line connection, motor connection and control wiring connection.


Stuart

Stuart&Grigg, this is a good discussion from 2 very knowledgeable people here on the 'Bolt. I'm leaning more toward the VFD since my Bridgeport is older and not variable speed. Stuart, if I understand VFDs correctly, in my situation I could just put the mill in the highest gear and use the drive as my variable speed?

Keith,

Sort of...what you want to do put the mill in the lowest gear, meaning the small groove on the motor sheave and the large groove in the spindle sheave. This gives you the most torque, and because the VFD has the ability to run up to at least 200 HZ, you can get tons of top end..more than you would ever need.

When I say this, I don't mean to put the mill in "back gear" which is of course its lowest range. The low ratio I speak of is achieved with the sheaves and drive belt. Does this make sense.

Stuart

Gotcha! Thanks.

As one who installs VFDs and programs them and also has worked some with rotary converters and has days operating generation and distribution.

1. If you need 3 phase from single phase for multiple tooling then rotary converter may be best option - especially if you want hard wired ie conduit etc and do not want to fool around with plug and unplug. Make sure converter has more capacity than all loads you intend to run simultaneous. Add a little extra capacitiy if you have hard starter ie air compressor.
2. you can run multiple motors off one vfd but ideally they should all be the same size.
3. NEVER BREAK the output of a running VFD. Turn them off with either the panel control or a hard wired stop.
4. If it has the capacity you could use one VFD to run multiple tools but you are back to plug and unplug or complicated switching. Do #1.
5. On machine tooling I would select speed and feed using gearbox and then fine tune speed with VFD
6. IF you run motor at very low speed ie 10Hz or less have additional cooling fan. Motor fan is running too slow to cool motor and you will burn it out.

dan Bentler

I found an old 35 hp 3 phase grain bin motor for cheap and a bunch of capsitors for free and wired up a rotary. But, I don't need variable speed (well I could use it on the lathe). I run a 7 hp table saw, 5 hp dust collector, and 5 hp lathe. All is conduit hardwired. Like my setup.

I also read somewhere that if you have multiple tools in your shop run off of one rotary phase converter, i.e.: lathe, mill, table saw, etc and have one large item like a welder for instance, you can turn all the other tools on and they will all work together as rotary converters to power the large tool. Please note, they have to be free-idling though to act as additional converter capacity.

BUT, all that said, I WOULD NOT recommend buying a 3 phase welder unless you already had the phase conversion capacity in place already, as it's cheaper to just get a good single phase machine... Unless you have one of those new digital rotary converters, your power balance will never be quite right when you're running a welder (do to the constantly fluctuating load current) and poor arc stability is the result..... This is all things I've learned when thinking of buying a 3 phase welder..... Also, from my research, the average 300 amp 3 phase welder is going to need a 25hp phase converter! :O

Just something for you guys to think about....

Personally, when the day comes that I get a mill, lathe, etc, they will all be run off of VFD's...... Quiet, no waste power when machinery is turned off, etc........