Explain phase converters to me, please

I have a 3 phase motor in my vintage French dough mixer, and I just found out that although I have a 3 phase transformer on the pole, the electric company won't reconnect it, since they're upgrading everything system-wide and a new transformer will cost me about $12k. So, all that means is I'm getting a phase converter to run my mixer, and my electrician has recommended a rotary phase converter. From what little I've read (and understood) about these things, I'm simultaneously frightened and intrigued.

Can somebody explain to me how these beasts work like I'm a five year old? Because that's about my level of understanding electricity.

IIRC, you are driving a 3 phase generator with a single or split phase(stander dryer outlet) motor.

Far as I know, Tesla invented 3 phase after inventing single phase. 3 phase power has 3 wires and there's voltage between each of the wires. Your 2 wire electricity (not counting the ground) off your power pole has voltage between each of the wires, but there's only 2 wires, so there's only a single energy set (single phase.) A phase converter "adds" in the 3rd wire (leg) and makes the 2 wire power "work" like it came in on 3 wires. It is not as efficient as a true 3 phase system, but you can use your 3 phase motors on the single phase power you are supplied with.

Pretty much what Kenny said.

In slightly more complicated terms, the three phase generator has (you guessed it) three terminals. Single phase is fed in through two of these terminals. Generally this isn't enough to actually start the generator spinning, so you need a magnetic starter to get the ball rolling. Once the generator is spinning, it is making power at all three terminals, each 120 degrees out of phase with each other (three phase power). Since the single phase is hooked up to two of these terminals and not to the other, there is a potential (particularly when applying a load to the 3 phase power) to unbalance the generator, which unbalances the power, which can damage your 3-phase appliance, so you have some kind of idler motor (the single phase Kenny talked about) to help stabilize the power output when you start making bread dough.

That's my understanding of it, anyhow. Take that with a grain of salt.

I have heard you can rewire a 3 phase motor to run on split phase power, at a lower output, naturally. Popular with the Bridgeport crowd, IDK how much reserve power you have in a French mixer.

How many horsepower is the motor? You could replace it with a single phase if it's not huge. I'm not sure what constitutes as huge. ( ...)

RossD wrote: How many horsepower is the motor? You could replace it with a single phase if it's not huge. I'm not sure what constitutes as huge. ( ...)

That's what I would try first. How "French" is the mixer? In Europe they run on 50 Hz vs. the 60 Hz we use.

Old-school phase converters are as Kenny mentioned: a 3-phase generator powered by a single phase motor. The output will need to match the HP rating of your motor, bearing in mind the 1-phase drive motor will draw more current. Will it run on a dryer receptacle? Dunno... What HP is the mixer motor? In the end, KW is KW, regardless of voltage or the number of phases. More phases spreads the load out more, hence why large motors are usually 3 phase.

Another option: google "single phase to three phase vfd" and you should get something like one of these: http://www.wolfautomation.com/products/23778/general-purpose-ac-micro-drive-nema-1br-single-or-3-phasebr-delta-vfd-s?gclid=CMqi8rn1vrcCFdSj4Aod_3YAMg This would likely require a bit of rewiring at the mixer but would give you the added benefit of easily adjustable speed control, although you need to be careful as if you lower it too much you can overheat the motor due to lack of cooling from its internal fan.

I'm not surprised the power company is reluctant to give you three phase for one motor. Plus, besides the cost of the transformer, you would also have to either install a new panel to distribute the 3 phase power or replace your existing single phase panel.

I believe the motor is 7.5/10hp. I have the specs somewhere...

The motor's Italian, for the record. Best of both worlds! At least it's not English...

FWIW, you can get a 10HP single phase motor for about $600 to $1000 in two different ways:

• Buy a good brand like Baldor on sale, used or a refurb
• Buy a HF compressor and throw the compressor away :)

Really? A 10 HP dough mixer? What are you running, a bakery?

Single phase motors that big are pretty rare. I know there are 7.5hp and 10hp motors out there, but after 35 years in the business I've never seen one. What voltage is this thing? European motors are often designed to run at voltages we don't have in the US.

Yeah, what Stuart said. I recently had to design a power feed for a European piece of process equipment. I ended up going with a buck-boost transformer to get the facility 208v-3p up to a voltage the unit would reliably run on. While a 480v option was available, the upcharge was more and would have added to the delivery time.

It's hard to say if the motor frame would be easy to find and I agree 7.5 hp is on the upper limit of what you'd want to run on a 230 or 240 volt single phase circuit (a two pole breaker in your panel).

Head over to:

Where this is all they talk about, really...

And read.

I have 2 3-phase machines in my shop. A 5hp vertical mill, and a 5hp lathe. I run them both of a 5hp Phase-a-matic rotary phase converter. It's on a 30A 240V breaker, and is run from a mag starter. Once running it synthesizes the 3rd leg of the triad. Voila' - 3 phase power and a soothing hum.

Phase-a-matic

picture a waterwheel on its side. You are going to dive it pressurized water from a hose. Pressure = voltage

If you only have one hose, you stand at one point and aim the hose. It will take a lot of water to get it moving (current) and keep it moving.

If you have two friends who have hoses, then you can put them at equal distances to squirt their hoses at the wheel. This is more efficient than you squirting the single hose.

Now, if your friends water supply gets taken away, you can cheat by tapping in to your hose and still have the three propulsion points. But you will have less power unless you increase the current.