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ronseto
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Technical Fields - Technical Writing - New Member Engineering Fields - Marine Engineering - New Member

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Location: Vancleave, Ms about 30 miles inland from Biloxi and the coast
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3 Phase Converters

04/10/2014 4:00 PM

I'm looking to add a 3 ph machine to my workshop. There are at least four ways to convert from single ph to 3 ph that I know of. They are:

1. Variable Frequency Drive (VFD); reversing and speed control being a plus feature.

2. Static Solid State; 1/3 power loss

3.Rotary Phase Converter; Some loss of power.

4. Motor/Generator Set (MG Set); No loss of power, but very expensive.

If you were going to convert, which method would be the most reliable and cost effective?

I've had some experience with MG sets on ships, but they were used for frequency conversion. I'm not sure if they make them for phase conversion.

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 Mr.Ron from South Ms.
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SolarEagle
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#1

Re: 3 Phase converters

04/10/2014 4:15 PM

What sort of load are we talking about? What type of machines, average usage??

http://www.grainger.com/category/phase-converters/power-supplies/electrical/ecatalog/N-8dt

http://www.finewoodworking.com/workshop/qa/three-phase-machines-in-shop.aspx

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ronseto
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#2
In reply to #1

Re: 3 Phase converters

04/10/2014 4:51 PM

5 hp electric motor, non-compressor duty. Typical use would be for a saw, jointer, planer, sander.

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ignator
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Location: Iowa, USA
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#3
In reply to #2

Re: 3 Phase converters

04/10/2014 6:50 PM

ronseto, I recommend a VFD, although your use does not require speed control of a spindle as in a lathe, milling machine. I have a 3ph 14inch table saw that has a 7.5HP motor, and have a 10HP VFD powering this.

Looks like your powering wood working equipment.

The one benefit you can use is the built in brake of a VFD.

Checkout prices at dealerselectric, they have full pdf manuals online for TECO.

I did start out using a RPC, but I found the noise in the shop of the idle motor to be annoying (and this was a manual start/stop before using the machine it was powering).

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tcmtech
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#4

Re: 3 Phase converters

04/10/2014 8:10 PM

Here you go. All you need to know about how make your own direct drive converters.

3 phase converter schematic TCM Tech System.

Hundreds built by countless people and in use now!

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Wal
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Location: Phnom Penh
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#5
In reply to #4

Re: 3 Phase converters

04/11/2014 12:04 AM

That was pretty neat!

The required tuning by trial though, limits this method to DIY/hobby/education situations.

If you needed to convert single to polyphase in a commercial arena then it probably would be more bother and risk than it is worth. (still nice to know in the event of desperation though!)

Your caveat regarding adequate capacity of the incoming single phase supply to start the motor is worthy of careful consideration.

A VFD is pretty much a plug and play arrangement and high starting currents can be suppressed if the VFD is set up for softstarting as well.

So, in my opinion, the VFD is the way Ron wants to go.

A motor generator would be my next choice. These are still widely used especially where noise filtering is an issue. Flywheels are excellent harmonic filters.

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dhayanandhan
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#6

Re: 3 Phase converters

04/11/2014 2:57 AM

Dear Mr.ronseto,

since you have clarified the Load as 5 H.P., (I presume it as constnt speed duty) I would suggest Solid State Converter system, since now a days High Efficiency systems are available.

DHAYANANDHAN.S
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sawmilleng
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#7

Re: 3 Phase converters

04/11/2014 3:18 AM
Re: 3 Phase converters
I have played with 3 phase conversion over the years and have built systems similar to what TCMTech has put forth as well as using VFD systems.

I have found that my needs are best served with a VFD system, and although it has its warts the variable speed feature has been very useful for my uses. (My home shop has a mix of woodworking and metalworking tools.) The one most valuable use for a VFD has been on a drill press, where variable speed is very handy.

The VFD system may not be as useful if you want to be able to generate 3 phase power and treat it like a second utility around the shop, where you stop and start any number of machines on the same power supply. A VFD does not like to be up and running and have someone close a contactor to slam a big motor on line--it is designed to bring the motor up to speed when the VFD is started.

I set up my shop VFD with a PLC control. Since I had only 1 VFD and a half dozen machines that wanted 3 phase to operate on, I set up the PLC to control contactors that directed power to a certain machine. So if I was at the drill press, I punched the "start" button at the drill press which immediately closed the contactor that directed power to the press and also started the VFD. It also connected the potentiometer at the drill press to the VFD so I could dial the speed to whatever I wanted.

Of course, this is a one-man shop and I can only run one machine at a time. So when the drill press is running no other machine can be powered. As a matter of fact, I set the PLC up so that when a machine was running, ALL the pushbuttons on any other machine in the shop became "stop" buttons. I had teenage boys who used my shop and I wanted a bit of a safety feature. If they got into trouble with a machine, the idea was you could punch any button in the shop to stop their machine, kind of like a global E-stop.

Another detail that the OP needs to keep in mind: Unless the VFD is designed to be a phase-converting VFD, you need to remember that it is designed to have 3 phase power coming INTO the VFD. If you are putting only single phase power into the VFD, the current rating of the VFD is the limiting factor. Putting current into only one phase of a VFD will give you only 58% of the nameplate rating of the VFD. So a 10 hp rated VFD will only give you 5.8hp on a single phase input.

Hope this helps,

Jon
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ronseto
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#8
In reply to #7

Re: 3 Phase converters

04/11/2014 4:17 PM

You have answered all my concerns and then some. Looks like the VFD sgl to 3 ph is the way for me to go.

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dhayanandhan (1); ignator (1); ronseto (2); sawmilleng (1); SolarEagle (1); tcmtech (1); Wal (1)

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